WorldWideScience

Sample records for voluntary isometric contractions

  1. Twitch potentiation induced by stimulated and voluntary isometric contractions at various torque levels in human knee extensor muscles.

    Science.gov (United States)

    Miyamoto, Naokazu; Yanai, Toshimasa; Kawakami, Yasuo

    2011-03-01

    The purpose of this study was to compare the extent of twitch potentiation (TP) after stimulated or voluntary contractions at identical intensities for the human knee extensor muscles. Isometric knee extensions of 10 s were performed at 20%, 40%, and 60% of maximal voluntary contraction (MVC) torque level, through percutaneous electrical stimulation of the quadriceps at 80 Hz or voluntary contraction. Twitch responses were evoked by stimulating the femoral nerve percutaneously with supramaximal intensity. The extent of TP after the stimulated contraction was greater than that after the voluntary contraction at the 20% MVC torque level, whereas a stimulated contraction induced a smaller extent of TP than did a voluntary contraction at contraction intensities higher than 40% MVC. We suggest that this contraction intensity dependence of differences in TP after stimulated and voluntary isometric conditioning contractions is responsible for differences in the recruitment pattern of motor units during the conditioning contractions.

  2. Effects of vibratory stimulations on maximal voluntary isometric contraction from delayed onset muscle soreness.

    Science.gov (United States)

    Koh, Hyung-Woo; Cho, Sung-Hyoun; Kim, Cheol-Yong; Cho, Byung-Jun; Kim, Jin-Woo; Bo, Kak Hwang

    2013-09-01

    [Purpose] The aim of this study was to investigate the effect of vibratory stimulation on maximal voluntary isometric contraction (MVIC) from delayed onset muscle soreness (DOMS). [Subjects] Sixty healthy adults participated in this study. The exclusion criteria were orthopedic or neurologic disease. [Methods] The researchers induced DOMS in the musculus extensor carpi radialis longus of each participant. Subjects in the control group received no treatment. The ultrasound group received ultrasound treatment (intensity, 1.0 W/cm(2;) frequency 1 MHz; time, 10 minutes). The vibration group received vibration stimulation (frequency, 20 MHz; time, 10 minutes). Maximal voluntary isometric contraction (MVIC) was recorded at baseline, immediately after exercise, and 24, 48, and 72 hours after exercise. [Results] MVIC measurements showed statistically significant differences in the vibration group compared with the control group. [Conclusion] Vibratory stimulation had a positive effect on recovery of muscle function from DOMS.

  3. Comparison of maximum voluntary isometric contraction of the biceps on various posture and respiration conditions for normalization of electromyography data

    OpenAIRE

    Lee, Sang-Yeol; Jo, Marg-Eun

    2016-01-01

    [Purpose] Maximum voluntary isometric contraction can increase the reliability of electromyography data by controlling respiration; however, many studies that use normalization of electromyography data fail to account for this. This study aims to check changes in maximum voluntary isometric contraction based on changes in posture and respiration conditions. [Subjects and Methods] Twenty-two healthy volunteers were included in this study. Using 22 healthy subjects, MVIC of the biceps brachii m...

  4. Handgrip Maximal Voluntary Isometric Contraction Does Not Correlate with Thenar Motor Unit Number Estimation

    Directory of Open Access Journals (Sweden)

    Arun Aggarwal

    2012-01-01

    Full Text Available In slowly progressive conditions, such as motor neurone disease (MND, 50–80% of motor units may be lost before weakness becomes clinically apparent. Despite this, maximal voluntary isometric contraction (MVIC has been reported as a clinically useful, reliable, and reproducible measure for monitoring disease progression in MND. We performed a study on a group of asymptomatic subjects that showed a lack of correlation between isometric grip strength and thenar MUNE. Motor unit number estimation (MUNE estimates the number of functioning lower motor neurones innervating a muscle or a group of muscles. We used the statistical electrophysiological technique of MUNE to estimate the number of motor units in thenar group of muscles in 69 subjects: 19 asymptomatic Cu, Zn superoxide dismutase 1 (SOD 1 mutation carriers, 34 family controls, and 16 population controls. The Jamar hand dynamometer was used to measure isometric grip strength. This study suggests that MUNE is more sensitive for monitoring disease progression than maximal voluntary isometric contraction (MVIC, as MUNE correlates with the number of functional motor neurones. This supports the observation that patients with substantial chronic denervation can maintain normal muscle twitch tension until 50–80% of motor units are lost and weakness is detectable.

  5. Plyometric training improves voluntary activation and strength during isometric, concentric and eccentric contractions.

    Science.gov (United States)

    Behrens, Martin; Mau-Moeller, Anett; Mueller, Karoline; Heise, Sandra; Gube, Martin; Beuster, Nico; Herlyn, Philipp K E; Fischer, Dagmar-C; Bruhn, Sven

    2016-02-01

    This study investigated effects of plyometric training (6 weeks, 3 sessions/week) on maximum voluntary contraction (MVC) strength and neural activation of the knee extensors during isometric, concentric and eccentric contractions. Twenty-seven participants were randomly assigned to the intervention or control group. Maximum voluntary torques (MVT) during the different types of contraction were measured at 110° knee flexion (180°=full extension). The interpolated twitch technique was applied at the same knee joint angle during isometric, concentric and eccentric contractions to measure voluntary activation. In addition, normalized root mean square of the EMG signal at MVT was calculated. The twitch torque signal induced by electrical nerve stimulation at rest was used to evaluate training-related changes at the muscle level. In addition, jump height in countermovement jump was measured. After training, MVT increased by 20Nm (95% CI: 5-36Nm, P=0.012), 24Nm (95% CI: 9-40Nm, P=0.004) and 27Nm (95% CI: 7-48Nm, P=0.013) for isometric, concentric and eccentric MVCs compared to controls, respectively. The strength enhancements were associated with increases in voluntary activation during isometric, concentric and eccentric MVCs by 7.8% (95% CI: 1.8-13.9%, P=0.013), 7.0% (95% CI: 0.4-13.5%, P=0.039) and 8.6% (95% CI: 3.0-14.2%, P=0.005), respectively. Changes in the twitch torque signal of the resting muscle, induced by supramaximal electrical stimulation of the femoral nerve, were not observed, indicating no alterations at the muscle level, whereas jump height was increased. Given the fact that the training exercises consisted of eccentric muscle actions followed by concentric contractions, it is in particular relevant that the plyometric training increased MVC strength and neural activation of the quadriceps muscle regardless of the contraction mode. Copyright © 2015 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.

  6. Repeatability of maximal voluntary force and of surface EMG variables during voluntary isometric contraction of quadriceps muscles in healthy subjects.

    Science.gov (United States)

    Rainoldi, A; Bullock-Saxton, J E; Cavarretta, F; Hogan, N

    2001-12-01

    The repeatability of initial values and rate of change of EMG signal mean spectral frequency (MNF), average rectified values (ARV), muscle fiber conduction velocity (CV) and maximal voluntary contraction (MVC) was investigated in the vastus medialis obliquus (VMO) and vastus lateralis (VL) muscles of both legs of nine healthy male subjects during voluntary, isometric contractions sustained for 50 s at 50% MVC. The values of MVC were recorded for both legs three times on each day and for three subsequent days, while the EMG signals have been recorded twice a day for three subsequent days. The degree of repeatability was investigated using the Fisher test based upon the ANalysis Of VAriance (ANOVA), the Standard Error of the Mean (SEM) and the Intraclass Correlation Coefficient (ICC). Data collected showed a high level of repeatability of MVC measurement (normalized SEM from 1.1% to 6.4% of the mean). MNF and ARV initial values also showed a high level of repeatability (ICC>70% for all muscles and legs except right VMO). At 50% MVC level no relevant pattern of fatigue was observed for the VMO and VL muscles, suggesting that other portions of the quadriceps might have contributed to the generated effort. These observations seem to suggest that in the investigation of muscles belonging to a multi-muscular group at submaximal level, the more selective electrically elicited contractions should be preferred to voluntary contractions.

  7. Post-exercise depression following submaximal and maximal isometric voluntary contraction.

    Science.gov (United States)

    Cunningham, David A; Janini, Daniel; Wyant, Alexandria; Bonnett, Corin; Varnerin, Nicole; Sankarasubramanian, Vishwanath; Potter-Baker, Kelsey A; Roelle, Sarah; Wang, Xiaofeng; Siemionow, Vlodek; Yue, Guang H; Plow, Ela B

    2016-06-21

    It is well known that corticomotor excitability is altered during the post-exercise depression following fatigue within the primary motor cortex (M1). However, it is currently unknown whether corticomotor reorganization following muscle fatigue differs between magnitudes of force and whether corticomotor reorganization occurs measured with transcranial magnetic stimulation (TMS). Fifteen young healthy adults (age 23.8±1.4, 8 females) participated in a within-subjects, repeated measures design study, where they underwent three testing sessions separated by one-week each. Subjects performed separate sessions of each: low-force isometric contraction (30% maximal voluntary contraction [MVC]), high-force isometric contraction (95% MVC) of the first dorsal interosseous (FDI) muscle until self-perceived exhaustion, as well as one session of a 30-min rest as a control. We examined changes in corticomotor map area, excitability and location of the FDI representation in and around M1 using TMS. The main finding was that following low-force, but not high-force fatigue (HFF) corticomotor map area and excitability reduced [by 3cm(2) (t(14)=-2.94, p=0.01) and 56% respectively t(14)=-4.01, p<0.001)]. Additionally, the region of corticomotor excitability shifted posteriorly (6.4±2.5mm) (t(14)=-6.33, p=.019). Corticomotor output became less excitable particularly in regions adjoining M1. Overall, post-exercise depression is present in low-force, but not for HFF. Further, low-force fatigue (LFF) results in a posterior shift in corticomotor output. These changes may be indicative of increased sensory feedback from the somatosensory cortex during the recovery phase of fatigue.

  8. System identification of the mechanomyogram from single motor units during voluntary isometric contraction.

    Science.gov (United States)

    Uchiyama, Takanori; Hashimoto, Erika

    2011-09-01

    A mechanomyogram (MMG) from single motor units of the anconeus muscle in voluntary isometric contraction was recorded from seven subjects using a spike-triggered averaging technique. The MMG system, in which the input was an ideal impulse and the output was the MMG detected with an acceleration sensor, was identified as the fifth-order model by the subspace-based state-space model identification method. The transfer function of the MMG system was factorized to the second- and the first-order models. The second-order model was compared to the standard form of the second-order model, and its resonance frequency was calculated. The resonance frequencies of the second-order models were 166 ± 61 and 93 ± 27 Hz, which were within the range of the values estimated from mechanical impedance in the literature. The equivalent mechanical model of the MMG system of the single motor unit was proposed on the basis of the fifth-order model. The model might be useful to evaluate the visco-elastic properties of the anconeus muscle.

  9. A comparison of two gluteus maximus EMG maximum voluntary isometric contraction positions

    Directory of Open Access Journals (Sweden)

    Bret Contreras

    2015-09-01

    Full Text Available Background. The purpose of this study was to compare the peak electromyography (EMG of the most commonly-used position in the literature, the prone bent-leg (90° hip extension against manual resistance applied to the distal thigh (PRONE, to a novel position, the standing glute squeeze (SQUEEZE.Methods. Surface EMG electrodes were placed on the upper and lower gluteus maximus of thirteen recreationally active females (age = 28.9 years; height = 164 cm; body mass = 58.2 kg, before three maximum voluntary isometric contraction (MVIC trials for each position were obtained in a randomized, counterbalanced fashion.Results. No statistically significant (p < 0.05 differences were observed between PRONE (upper: 91.94%; lower: 94.52% and SQUEEZE (upper: 92.04%; lower: 85.12% for both the upper and lower gluteus maximus. Neither the PRONE nor SQUEEZE was more effective between all subjects.Conclusions. In agreement with other studies, no single testing position is ideal for every participant. Therefore, it is recommended that investigators employ multiple MVIC positions, when possible, to ensure accuracy. Future research should investigate a variety of gluteus maximus MVIC positions in heterogeneous samples.

  10. A comparison of two gluteus maximus EMG maximum voluntary isometric contraction positions.

    Science.gov (United States)

    Contreras, Bret; Vigotsky, Andrew D; Schoenfeld, Brad J; Beardsley, Chris; Cronin, John

    2015-01-01

    Background. The purpose of this study was to compare the peak electromyography (EMG) of the most commonly-used position in the literature, the prone bent-leg (90°) hip extension against manual resistance applied to the distal thigh (PRONE), to a novel position, the standing glute squeeze (SQUEEZE). Methods. Surface EMG electrodes were placed on the upper and lower gluteus maximus of thirteen recreationally active females (age = 28.9 years; height = 164 cm; body mass = 58.2 kg), before three maximum voluntary isometric contraction (MVIC) trials for each position were obtained in a randomized, counterbalanced fashion. Results. No statistically significant (p < 0.05) differences were observed between PRONE (upper: 91.94%; lower: 94.52%) and SQUEEZE (upper: 92.04%; lower: 85.12%) for both the upper and lower gluteus maximus. Neither the PRONE nor SQUEEZE was more effective between all subjects. Conclusions. In agreement with other studies, no single testing position is ideal for every participant. Therefore, it is recommended that investigators employ multiple MVIC positions, when possible, to ensure accuracy. Future research should investigate a variety of gluteus maximus MVIC positions in heterogeneous samples.

  11. Time to Maximal Voluntary Isometric Contraction (MVC) for Five Different Muscle Groups in College Adults.

    Science.gov (United States)

    Morris, A. F.; And Others

    1983-01-01

    College men and women were studied to ascertain the force-time components of a rapid voluntary muscle contraction for five muscle groups. Researchers found that the time required for full contraction differs: (1) in men and women; and (2) among the five muscle groups. (Authors/PP)

  12. Specific modulation of corticospinal and spinal excitabilities during maximal voluntary isometric, shortening and lengthening contractions in synergist muscles.

    Science.gov (United States)

    Duclay, Julien; Pasquet, Benjamin; Martin, Alain; Duchateau, Jacques

    2011-06-01

    This study was designed to investigate the cortical and spinal mechanisms involved in the modulations of neural activation during lengthening compared with isometric and shortening maximal voluntary contractions (MVCs). Two muscles susceptible to different neural adjustments at the spinal level, the soleus (SOL) and medial gastrocnemius (MG), were compared. Twelve healthy males participated in at least two experimental sessions designed to assess corticospinal and spinal excitabilities. We compared the modulation of motor evoked potentials (MEPs) in response to transcranial magnetic stimulation and Hoffmann reflexes (H-reflexes) during isometric and anisometric MVCs. The H-reflex and MEP responses, recorded during lengthening and shortening MVCs, were compared with those obtained during isometric MVCs. The results indicate that the maximal amplitude of both MEP and H-reflex in the SOL were smaller (P shortening MVCs but similar (P > 0.05) in MG for all three muscle contraction types. The silent period that follows maximal MEPs was reduced (P muscle. Collectively, the current results indicate that the relative contribution of both cortical and spinal mechanisms to the modulation of neural activation differs during lengthening MVCs and between two synergist muscles. The comparison of SOL and MG responses further suggests that the specific modulation of the corticospinal excitability during lengthening MVCs depends mainly on pre- and postsynaptic inhibitory mechanisms acting at the spinal level.

  13. Inhibitory interneuron circuits at cortical and spinal levels are associated with individual differences in corticomuscular coherence during isometric voluntary contraction

    Science.gov (United States)

    Matsuya, Ryosuke; Ushiyama, Junichi; Ushiba, Junichi

    2017-01-01

    Corticomuscular coherence (CMC) is an oscillatory synchronization of 15–35 Hz (β-band) between electroencephalogram (EEG) of the sensorimotor cortex and electromyogram of contracting muscles. Although we reported that the magnitude of CMC varies among individuals, the physiological mechanisms underlying this variation are still unclear. Here, we aimed to investigate the associations between CMC and intracortical inhibition (ICI) in the primary motor cortex (M1)/recurrent inhibition (RI) in the spinal cord, which probably affect oscillatory neural activities. Firstly, we quantified ICI from changes in motor-evoked potentials induced by paired-pulse transcranial magnetic stimulation in M1 during tonic isometric voluntary contraction of the first dorsal interosseous. ICI showed a significant, negative correlation with the strength of EEG β-oscillation, but not with the magnitude of CMC across individuals. Next, we quantified RI from changes in H-reflexes induced by paired-pulse electrical nerve stimulation to the posterior tibial nerve during isometric contraction of the soleus muscle. We observed a significant, positive correlation between RI and peak CMC across individuals. These results suggest that the local inhibitory interneuron networks in cortical and spinal levels are associated with the oscillatory activity in corticospinal loop. PMID:28290507

  14. Feasibility of an Isometric Maximal Voluntary Contraction Test in Hematological Cancer Patients during Thrombocytopenia

    Directory of Open Access Journals (Sweden)

    Philipp Zimmer

    2013-01-01

    Full Text Available Introduction. Resistance training is rarely offered to hemato-oncological patients in the daily clinical routine due to its potential harmful impact on the cardiovascular system and the long periods of thrombocytopenia experienced by these patients. Therefore, it is important to determine a valid assessment to define and control resistance training. In this study, the feasibility of a maximal voluntary contraction (MVC test was investigated in hemato-oncological patients. This inexpensive assessment may be a practicable alternative to the one repetition maximum test which is currently described as the gold standard. Methods. 29 hemato-oncological patients with platelet counts between 30000/μL and 70000/μL were recruited for this pilot study. Complications like petechial bleedings, muscle convulsion, and pain were assessed using the Brief Pain Inventory before and 48 hours after the MVC test, which was performed unidirectionally for the quadriceps muscle. Results. We did not detect any statistically significant test-related exacerbations or pain development. Discussion. MVC testing seems to be a feasible method to control a resistance training program in hemato-oncological patients. Further studies need to extend their methods and, for example, compare the MVC test with the one repetition maximum test.

  15. EMG, bite force, and elongation of the masseter muscle under isometric voluntary contractions and variations of vertical dimension.

    Science.gov (United States)

    Manns, A; Miralles, R; Palazzi, C

    1979-12-01

    The relation EMG activity, bite force, and muscular elongation was studied in eight subjects with complete natural dentition during isometric contractions of the masseter muscle, measured from 7 mm to almost maximum jaw opening. EMG was registered with superficial electrodes and bite force with a gnathodynamometer. In series 1, recordings of EMG activity maintaining bite force constant (10 and 20 kg) show that EMG is high when the bite opening is 7 mm, decreases from 15 to 20 mm, and then increases again as jaw opening approaches maximum opening. In series 2, recordings of bite force maintaining EMG constant show that bite force increases up to a certain range of jaw opening (around 15 to 20 mm) and then decreases as we approach maximum jaw opening. Results show that there is for each experimental subject a physiologically optimum muscular elongation of major efficiency where the masseter develops highest muscular force with least EMG activity.

  16. Neuromuscular fatigue following isometric contractions with similar torque time integral.

    Science.gov (United States)

    Rozand, V; Cattagni, T; Theurel, J; Martin, A; Lepers, R

    2015-01-01

    Torque time integral (TTI) is the combination of intensity and duration of a contraction. The aim of this study was to compare neuromuscular alterations following different isometric sub-maximal contractions of the knee extensor muscles but with similar TTI. Sixteen participants performed 3 sustained contractions at different intensities (25%, 50%, and 75% of Maximal Voluntary Contraction (MVC) torque) with different durations (68.5±33.4 s, 35.1±16.8 s and 24.8±12.9 s, respectively) but similar TTI value. MVC torque, maximal voluntary activation level (VAL), M-wave characteristics and potentiated doublet amplitude were assessed before and immediately after the sustained contractions. EMG activity of the vastus lateralis (VL) and -rectus femoris (RF) muscles was recorded during the sustained contractions. MVC torque reduction was similar in the 3 conditions after the exercise (-23.4±2.7%). VAL decreased significantly in a similar extent (-3.1±1.3%) after the 3 sustained contractions. Potentiated doublet amplitude was similarly reduced in the 3 conditions (-19.7±1.5%), but VL and RF M-wave amplitudes remained unchanged. EMG activity of VL and RF muscles increased in the same extent during the 3 contractions (VL: 54.5±40.4%; RF: 53.1±48.7%). These results suggest that central and peripheral alterations accounting for muscle fatigue are similar following isometric contractions with similar TTI. TTI should be considered in the exploration of muscle fatigue during sustained isometric contractions.

  17. Reliability of maximal voluntary isometric contraction testing in a multicenter study of patients with amyotrophic lateral sclerosis. Syntex/Synergen Neuroscience Joint Venture rhCNTF ALS Study Group.

    Science.gov (United States)

    Hoagland, R J; Mendoza, M; Armon, C; Barohn, R J; Bryan, W W; Goodpasture, J C; Miller, R G; Parry, G J; Petajan, J H; Ross, M A

    1997-06-01

    Maximal voluntary isometric contraction (MVIC) is becoming widely used for monitoring disease progression in amyotrophic lateral sclerosis (ALS). We evaluated the variability of MVIC in a large multicenter (29 sites) drug trial in ALS. Intra- and interrater variability were assessed twice during the 19-month study. Intrarater reliability increased from the first to the second test, approaching the reliability reported for a single experienced clinical evaluator, but interrater reliability did not. Multiple clinical evaluators in a single site increased the variability of MVIC measurements. Rigorous quality assurance standards and monitoring of clinical evaluators should be incorporated into the design of multicenter studies using MVIC, since low variability is necessary to detect a modest treatment effect.

  18. Feedforward consequences of isometric contractions: effort and ventilation.

    Science.gov (United States)

    Luu, Billy L; Smith, Janette L; Martin, Peter G; McBain, Rachel A; Taylor, Janet L; Butler, Jane E

    2016-08-01

    The onset of voluntary muscle contractions causes rapid increases in ventilation and is accompanied by a sensation of effort. Both the ventilatory response and perception of effort are proportional to contraction intensity, but these behaviors have been generalized from contractions of a single muscle group. Our aim was to determine how these relationships are affected by simultaneous contractions of multiple muscle groups. We examined the ventilatory response and perceived effort of contraction during separate and simultaneous isometric contractions of the contralateral elbow flexors and of an ipsilateral elbow flexor and knee extensor. Subjects made 10-sec contractions at 25, 50, and 100% of maximum during normocapnia and hypercapnia. For simultaneous contractions, both muscle groups were activated at the same intensities. Ventilation was measured continuously and subjects rated the effort required to produce each contraction. As expected, ventilation and perceived effort increased proportionally with contraction intensity during individual contractions. However, during simultaneous contractions, neither ventilation nor effort reflected the combined muscle output. Rather, the ventilatory response was similar to when contractions were performed separately, and effort ratings showed a small but significant increase for simultaneous contractions. Hypercapnia at rest doubled baseline ventilation, but did not affect the difference in perceived effort between separate and simultaneous contractions. The ventilatory response and the sense of effort at the onset of muscle activity are not related to the total output of the motor pathways, or the working muscles, but arise from cortical regions upstream from the motor cortex.

  19. Physiological response to submaximal isometric contractions of the paravertebral muscles

    Science.gov (United States)

    Jensen, B. R.; Jorgensen, K.; Hargens, A. R.; Nielsen, P. K.; Nicolaisen, T.

    1999-01-01

    STUDY DESIGN: Brief (30-second) isometric trunk extensions at 5%, 20%, 40%, 60%, and 80% of maximal voluntary contraction (MVC) and 3 minutes of prolonged trunk extension (20% MVC) in erect position were studied in nine healthy male subjects. OBJECTIVES: To investigate the intercorrelation between intramuscular pressure and tissue oxygenation of the paravertebral muscles during submaximal isometric contractions and further, to evaluate paravertebral electromyogram and intramuscular pressure as indicators of force development. SUMMARY OF BACKGROUND DATA: Local physiologic responses to muscle contraction are incompletely understood. METHODS: Relative oxygenation was monitored with noninvasive near-infrared spectroscopy, intramuscular pressure was measured with a transducer-tipped catheter, and surface electromyogram was monitored at three recording sites. RESULTS: The root mean square amplitudes of the paravertebral electromyogram (L4, left and right; T12, right) and intramuscular pressure measured in the lumbar multifidus muscle at L4 increased with greater force development in a curvilinear manner. A significant decrease in the oxygenation of the lumbar paravertebral muscle in response to muscle contraction was found at an initial contraction level of 20% MVC. This corresponded to a paravertebral intramuscular pressure of 30-40 mm Hg. However, during prolonged trunk extension, no further decrease in tissue oxygenation was found compared with the tissue oxygenation level at the end of the brief contractions, indicating that homeostatic adjustments (mean blood pressure and heart rate) over time were sufficient to maintain paravertebral muscle oxygen levels. CONCLUSION: At a threshold intramuscular pressure of 30-40 mm Hg during muscle contraction, oxygenation in the paravertebral muscles is significantly reduced. The effect of further increase in intramuscular pressure on tissue oxygenation over time may be compensated for by an increase in blood pressure and heart

  20. Force depression following muscle shortening in sub-maximal voluntary contractions of human adductor pollicis.

    Science.gov (United States)

    Rousanoglou, Elissavet N; Oskouei, Ali E; Herzog, Walter

    2007-01-01

    Mechanical properties of skeletal muscles are often studied for controlled, electrically induced, maximal, or supra-maximal contractions. However, many mechanical properties, such as the force-length relationship and force enhancement following active muscle stretching, are quite different for maximal and sub-maximal, or electrically induced and voluntary contractions. Force depression, the loss of force observed following active muscle shortening, has been observed and is well documented for electrically induced and maximal voluntary contractions. Since sub-maximal voluntary contractions are arguably the most important for everyday movement analysis and for biomechanical models of skeletal muscle function, it is important to study force depression properties under these conditions. Therefore, the purpose of this study was to examine force depression following sub-maximal, voluntary contractions. Sets of isometric reference and isometric-shortening-isometric test contractions at 30% of maximal voluntary effort were performed with the adductor pollicis muscle. All reference and test contractions were executed by controlling force or activation using a feedback system. Test contractions included adductor pollicis shortening over 10 degrees, 20 degrees, and 30 degrees of thumb adduction. Force depression was assessed by comparing the steady-state isometric forces (activation control) or average electromyograms (EMGs) (force control) following active muscle shortening with those obtained in the corresponding isometric reference contractions. Force was decreased by 20% and average EMG was increased by 18% in the shortening test contractions compared to the isometric reference contractions. Furthermore, force depression was increased with increasing shortening amplitudes, and the relative magnitudes of force depression were similar to those found in electrically stimulated and maximal contractions. We conclude from these results that force depression occurs in sub

  1. Differences between measured and resultant joint moments during isometric contractions at the ankle joint.

    Science.gov (United States)

    Arampatzis, Adamantios; Morey-Klapsing, Gaspar; Karamanidis, Kiros; DeMonte, Gianpiero; Stafilidis, Savvas; Brüggemann, Gert-Peter

    2005-04-01

    The purpose of this study was to examine two hypotheses: (a) during voluntary and electrically induced isometric contractions the moments measured at the dynamometer are different from the resultant moments in the same plane around the ankle joint and (b) at a given resultant moment during electrically induced isometric contractions the ankle angle while loading is different from the ankle angle while unloading. Twenty-seven long distance runners participated in the study. All subjects performed isometric maximal voluntary contractions (MVC) and contractions induced by electrostimulation at four different ankle-knee angle combinations on a Biodex-dynamometer. The kinematics of the leg were recorded using the vicon 624 system with eight cameras operating at 120 Hz. The main findings were: (a) the resultant moment at the ankle joint and the moment measured by the Biodex-dynamometer during isometric contractions are different, (b) during a plantar flexion effort the ankle angle changes significantly, whereas the knee angle shows only small and in most cases not significant changes, and (c) at identical resultant ankle joint moments the ankle angles are different between the loading and the unloading phases. The observed differences may lead to erroneous conclusions concerning the following: (a) diagnostic of muscle architecture, (b) estimation of the moment-ankle angle relationship and (c) estimation of the strain and hysteresis of tendons and aponeuroses.

  2. Forearm muscle oxygenation during sustained isometric contractions in rock climbers

    Directory of Open Access Journals (Sweden)

    Jan Kodejška

    2016-02-01

    Full Text Available Background. Bouldering and lead climbing are divergent disciplines of the sport of rock climbing. Bouldering moves are short and powerful, whilst sport climbing is longer and require a greater degree of endurance. Aim. The aim of this study was to compare forearm muscle oxygenation during sustained isometric contraction between lead climbers (LC and boulderers (BO. Methods. Eight BO and twelve LC completed maximal finger flexor strength test and sustained contractions to exhaustion at 60% of maximum voluntary contraction (MVC. Differences between BO and LC in maximal strength, time to exhaustion, force time integral (FTI, and tissue oxygenation (SmO2 were assessed by t-test for independent samples. Results. LC showed significantly lower level of average tissue oxygenation (BO 38.9% SmO2, s = 7.4; LC 28.7% SmO2, s = 7.1 and maximal tissue deoxygenation (BO 25.6% SmO2, s = 8.2; LC 13.5% SmO2, s = 8.5. LC demonstrated significantly lower finger flexor strength (519 N, s = 72 than BO (621 N, s = 142. LC sustained a longer time of contraction (not significantly (BO 52.2 s, s = 11.5; LC 60.6 s, s = 13 and achieved a similar value of FTI (BO 17421 Ns, s = 4291; LO 17476 Ns, s = 5036 in the endurance test. Conclusions. The results showed lower deoxygenation during sustained contraction in BO than LC despite similar FTI, indicating different local metabolic pathways in both groups.

  3. Forearm muscle oxygenation decreases with low levels of voluntary contraction

    Science.gov (United States)

    Murthy, G.; Kahan, N. J.; Hargens, A. R.; Rempel, D. M.

    1997-01-01

    The purpose of our investigation was to determine if the near infrared spectroscopy technique was sensitive to changes in tissue oxygenation at low levels of isometric contraction in the extensor carpi radialis brevis muscle. Nine subjects were seated with the right arm abducted to 45 degrees, elbow flexed to 85 degrees, forearm pronated 45 degrees, and wrist and forearm supported on an armrest throughout the protocol. Altered tissue oxygenation was measured noninvasively with near infrared spectroscopy. The near infrared spectroscopy probe was placed over the extensor carpi radialis brevis of the subject's right forearm and secured with an elastic wrap. After 1 minute of baseline measurements taken with the muscle relaxed, four different loads were applied just proximal to the metacarpophalangeal joint such that the subjects isometrically contracted the extensor carpi radialis brevis at 5, 10, 15, and 50% of the maximum voluntary contraction for 1 minute each. A 3-minute recovery period followed each level of contraction. At the end of the protocol, with the probe still in place, a value for ischemic tissue oxygenation was obtained for each subject. This value was considered the physiological zero and hence 0% tissue oxygenation. Mean tissue oxygenation (+/-SE) decreased from resting baseline (100% tissue oxygenation) to 89 +/- 4, 81 +/- 8, 78 +/- 8, and 47 +/- 8% at 5, 10, 15, and 50% of the maximum voluntary contraction, respectively. Tissue oxygenation levels at 10, 15, and 50% of the maximum voluntary contraction were significantly lower (p muscle contraction and that near infrared spectroscopy is a sensitive technique for detecting deoxygenation noninvasively at low levels of forearm muscle contraction. Our findings have important implications in occupational medicine because oxygen depletion induced by low levels of muscle contraction may be directly linked to muscle fatigue.

  4. Monitoring elbow isometric contraction by novel wearable fabric sensing device

    Science.gov (United States)

    Wang, Xi; Tao, Xiaoming; So, Raymond C. H.; Shu, Lin; Yang, Bao; Li, Ying

    2016-12-01

    Fabric-based wearable technology is highly desirable in sports, as it is light, flexible, soft, and comfortable with little interference to normal sport activities. It can provide accurate information on the in situ deformation of muscles in a continuous and wireless manner. During elbow flexion in isometric contraction, upper arm circumference increases with the contraction of elbow flexors, and it is possible to monitor the muscles’ contraction by limb circumferential strains. This paper presents a new wireless wearable anthropometric monitoring device made from fabric strain sensors for the human upper arm. The materials, structural design and calibration of the device are presented. Using an isokinetic testing system (Biodex3®) and the fabric monitoring device simultaneously, in situ measurements were carried out on elbow flexors in isometric contraction mode with ten subjects for a set of positions. Correlations between the measured values of limb circumferential strain and normalized torque were examined, and a linear relationship was found during isometric contraction. The average correlation coefficient between them is 0.938 ± 0.050. This wearable anthropometric device thus provides a useful index, the limb circumferential strain, for upper arm muscle contraction in isometric mode.

  5. Neuromuscular performance of maximal voluntary explosive concentric contractions is influenced by angular acceleration.

    Science.gov (United States)

    Hahn, D; Bakenecker, P; Zinke, F

    2016-12-28

    Torque production during maximal voluntary explosive contractions is considered to be a functionally more relevant neuromuscular measure than steady-state torque, but little is known about accelerated concentric contractions. This study investigated torque, muscle activity, and fascicle behavior during isometric and fast concentric contractions of quadriceps femoris. Ten participants performed maximal voluntary explosive isometric, isovelocity, and additional concentric knee extensions at angular accelerations ranging from 700 to 4000° s(-2) that resulted in an angular velocity of 300° s(-1) at 40° knee flexion. Concentric torque at 40° knee flexion was corrected for inertia, and the corresponding isometric torque was matched to the time when the target knee angle of 40° was reached during concentric contractions. Electromyography of quadriceps femoris and hamstrings and ultrasound of vastus lateralis were measured to determine muscle activity, fascicle length, and fascicle velocity (FV). The faster the acceleration, the more torque was produced during concentric contractions at 40° knee flexion, which was accompanied by a reduction in FV. In comparison with isometric conditions, concentric quadriceps muscle activity was increased and torque during accelerations ≥3000° s(-2) equaled the time-matched isometric torque. Our results provide novel evidence that acceleration influences torque production during maximal voluntary explosive concentric contractions. This is suggested to be due to series elasticity and reduced force depression.

  6. Age and Sex Effects on the Active Stiffness of Vastus Intermedius under Isometric Contraction

    Directory of Open Access Journals (Sweden)

    Cong-Zhi Wang

    2017-01-01

    Full Text Available Previously, a novel technique was proposed to quantify the relationship between the muscle stiffness and its nonfatigue contraction intensity. The method extended the measured range of isometric contraction to 100% maximum voluntary contraction (MVC using an ultrasonic shear wave measurement setup. Yet, it has not been revealed how this relationship could be affected by factors like age or sex. To clarify these questions, vastus intermedius (VI stiffness of 40 healthy subjects was assessed under 11 step levels of isometric contraction. The subjects were divided into four groups: young males, young females, elderly males, and elderly females (n=10 for each. In a relaxed state, no significant difference was observed between the male and female subjects (p=0.156 nor between the young and elderly subjects (p=0.221. However, when performing isometric contraction, the VI stiffness of males was found to be significantly higher than that of females at the same level (p<0.001, and that of the young was higher than the elderly (p<0.001. Meanwhile, for two knee joint angles used, the stiffness measured at a 90° knee joint angle was always significantly larger than that measured at 60° (p<0.001. Recognizing the active muscle stiffness of VI contributes to body stability, and these results may provide insight into the age and sex bias in musculoskeletal studies, such as those on fall risks.

  7. A Study on the Differences of Quadriceps Femoris Activities by Knee Alignment during Isometric Contraction.

    Science.gov (United States)

    Park, Seol; Ko, Yu-Min; Jang, Gwon-Uk; Hwang, Yoon-Tae; Park, Ji-Won

    2014-11-01

    [Purpose] This study attempted to identify how genu varum or valgum affects the electromyographic activities of the vastus medialis, vastus lateralis, and rectus femoris during knee isometric contraction. [Subjects] Fifty-two healthy young adults were enrolled in this study. They were enrolled and classified into three groups by knee alignment conditions: the genu varum, genu valgum, and control groups. [Methods] The electromyographic activity ratio of the vastus medialis to the vastus lateralis and rectus femoris were calculated using the percentage of maximum voluntary contraction. The participants contracted their quadriceps during isometric contraction at 30 and 60° of knee flexion. [Results] The genu varum group had more activity in the vastus medialis than in the vastus lateralis and rectus femoris, whereas the genu valgum group had more activity in the vastus lateralis and rectus femoris than in the vastus medialis. There was a significant difference in the muscle activity ratio between the vastus medialis and vastus lateralis by angle of knee flexion degree only in the genu valgum. There were no significant differences in any of the three groups in terms of the muscle activity ratio of the vastus medialis to the rectus femoris by angle of knee flexion. [Conclusion] The quadriceps femoris was used for different strategies according to knee alignment during isometric contraction at 30 and 60°. This study suggests that rehabilitation training programs used to strengthen the quadriceps should consider the knee alignment conditions of the target subjects.

  8. Voluntary activation level and muscle fiber recruitment of human quadriceps during lengthening contractions.

    Science.gov (United States)

    Beltman, J G M; Sargeant, A J; van Mechelen, W; de Haan, A

    2004-08-01

    Voluntary activation levels during lengthening, isometric, and shortening contractions (angular velocity 60 degrees/s) were investigated by using electrical stimulation of the femoral nerve (triplet, 300 Hz) superimposed on maximal efforts. Recruitment of fiber populations was investigated by using the phosphocreatine-to-creatine ratio (PCr/Cr) of single characterized muscle fibers obtained from needle biopsies at rest and immediately after a series of 10 lengthening, isometric, and shortening contractions (1 s on/1 s off). Maximal voluntary torque was significantly higher during lengthening (270 +/- 55 N.m) compared with shortening contractions (199 +/- 47 N.m, P < 0.05) but was not different from isometric contractions (252 +/- 47 N.m). Isometric torque was higher than torque during shortening (P < 0.05). Voluntary activation level during maximal attempted lengthening contractions (79 +/- 8%) was significantly lower compared with isometric (93 +/- 5%) and shortening contractions (92 +/- 3%, P < 0.05). Mean PCr/Cr values of all fibers from all subjects at rest were 2.5 +/- 0.6, 2.0 +/- 0.7, and 2.0 +/- 0.7, respectively, for type I, IIa, and IIax fibers. After 10 contractions, the mean PCr/Cr values for grouped fiber populations (regardless of fiber type) were all significantly different from rest (1.3 +/- 0.2, 0.7 +/- 0.3, and 0.8 +/- 0.6 for lengthening, isometric, and shortening contractions, respectively; P < 0.05). The cumulative distributions of individual fiber populations after either contraction mode were significantly different from rest (P < 0.05). Curves after lengthening contractions were less shifted compared with curves from isometric and shortening contractions (P < 0.05), with a smaller shift for the type IIax compared with type I fibers in the lengthening contractions. The results indicate a reduced voluntary drive during lengthening contractions. PCr/Cr values of single fibers indicated a hierarchical order of recruitment of all fiber

  9. Blood flow and muscle oxygenation during low, moderate, and maximal sustained isometric contractions.

    Science.gov (United States)

    McNeil, Chris J; Allen, Matti D; Olympico, Eric; Shoemaker, J Kevin; Rice, Charles L

    2015-09-01

    A reduction of blood flow to active muscle will precipitate fatigue, and sustained isometric contractions produce intramuscular and compartmental pressures that can limit flow. The present study explored how blood flow and muscle oxygenation respond to isometric contractions at low, moderate, and maximal intensities. Over two visits, 10 males (26 ± 2 yr; means ± SD) performed 1-min dorsiflexion contractions at 30, 60, and 100% of maximal voluntary contraction (MVC) torque. Doppler ultrasound of the anterior tibial artery was used to record arterial diameter and mean blood velocity and to calculate absolute blood flow. The tissue oxygenation index (TOI) of tibialis anterior was acquired with near-infrared spectroscopy (NIRS). There was a progressive increase in blood flow at 30% MVC (peak of 289 ± 139% resting value), no change from rest until an increase in the final 10 s of exercise at 60% MVC (peak of 197 ± 102% rest), and an initial decrease (59 ± 30% resting value) followed by a progressive increase at 100% MVC (peak of 355 ± 133% rest). Blood flow was greater at 30 and 100% than 60% MVC during the last 30 s of exercise. TOI was ∼63% at rest and, within 30 s of exercise, reached steady-state values of ∼42%, ∼22%, and ∼22% for 30, 60, and 100% MVC, respectively. Even maximal contraction of the dorsiflexors is unable to cause more than a transient decrease of flow in the anterior tibial artery. Unlike dynamic or intermittent isometric exercise, our results indicate blood flow is not linearly graded with intensity or directly coupled with oxygenation during sustained isometric contractions.

  10. Change in the ipsilateral motor cortex excitability is independent from a muscle contraction phase during unilateral repetitive isometric contractions.

    Directory of Open Access Journals (Sweden)

    Kazumasa Uehara

    Full Text Available The aim of this study was to investigate the difference in a muscle contraction phase dependence between ipsilateral (ipsi- and contralateral (contra-primary motor cortex (M1 excitability during repetitive isometric contractions of unilateral index finger abduction using a transcranial magnetic stimulation (TMS technique. Ten healthy right-handed subjects participated in this study. We instructed them to perform repetitive isometric contractions of the left index finger abduction following auditory cues at 1 Hz. The force outputs were set at 10, 30, and 50% of maximal voluntary contraction (MVC. Motor evoked potentials (MEP were obtained from the right and left first dorsal interosseous muscles (FDI. To examine the muscle contraction phase dependence, TMS of ipsi-M1 or contra-M1 was triggered at eight different intervals (0, 20, 40, 60, 80, 100, 300, or 500 ms after electromyogram (EMG onset when each interval had reached the setup triggering level. Furthermore, to demonstrate the relationships between the integrated EMG (iEMG in the active left FDI and the ipsi-M1 excitability, we assessed the correlation between the iEMG in the left FDI for the 100 ms preceding TMS onset and the MEP amplitude in the resting/active FDI for each force output condition. Although contra-M1 excitability was significantly changed after the EMG onset that depends on the muscle contraction phase, the modulation of ipsi-M1 excitability did not differ in response to any muscle contraction phase at the 10% of MVC condition. Also, we found that contra-M1 excitability was significantly correlated with iEMG in all force output conditions, but ipsi-M1 excitability was not at force output levels of below 30% of MVC. Consequently, the modulation of ipsi-M1 excitability was independent from the contraction phase of unilateral repetitive isometric contractions at least low force output.

  11. Reduced complexity of force and muscle activity during low level isometric contractions of the ankle in diabetic individuals

    DEFF Research Database (Denmark)

    Suda, E. Y.; Madeleine, Pascal; Hirata, Rogerio Pessoto;

    2017-01-01

    BACKGROUND: This study evaluated the structure and amount of variability of surface electromyography (sEMG) patterns and ankle force data during low-level isometric contractions in diabetic subjects with different degrees of neuropathy. METHODS: We assessed 10 control subjects and 38 diabetic...... patients, classified as absent, mild, moderate, or severe neuropathy, by a fuzzy system based on clinical variables. Multichannel sEMG (64-electrode matrix) of tibialis anterior and gastrocnemius medialis muscles were acquired during isometric contractions at 10%, 20%, and 30% of the maximum voluntary...... during low-level isometric contractions, reducing the system's capacity to adapt to challenging mechanical demands. The observed patterns of neuromuscular complexity were not associated with disease severity, with the majority of alterations recorded in moderate subject....

  12. In vivo human gastrocnemius architecture with changing joint angle at rest and during graded isometric contraction.

    Science.gov (United States)

    Narici, M V; Binzoni, T; Hiltbrand, E; Fasel, J; Terrier, F; Cerretelli, P

    1996-10-01

    1. Human gastrocnemius medialis architecture was analysed in vivo, by ultrasonography, as a function of joint angle at rest and during voluntary isometric contractions up to the maximum force (MCV). maximum force (MVC). 2. At rest, as ankle joint angle increased from 90 to 150 deg, pennation increased from 15.8 to 27.7 deg, fibre length decreased from 57.0 to 34.0 mm and the physiological cross-sectional area (PCSA) increased from 42.1 to 63.5 cm2. 3. From rest to MVC, at a fixed ankle joint angle of 110 deg, pennation angle increased from 15.5 to 33.6 deg and fibre length decreased from 50.8 to 32.9 mm, with no significant change in the distance between the aponeuroses. As a result of these changes the PCSA increased by 34.8%. 4. Measurements of pennation angle, fibre length and distance between the aponeuroses of the gastrocnemius medialis were also performed by ultrasound on a cadaver leg and found to be in good agreement with direct anatomical measurements. 5. It is concluded that human gastrocnemius medialis architecture is significantly affected both by changes of joint angle at rest and by isometric contraction intensity. The remarkable shortening observed during isometric contraction suggests that, at rest, the gastrocnemius muscle and tendon are considerably slack. The extrapolation of muscle architectural data obtained from cadavers to in vivo conditions should be made only for matching muscle lengths.

  13. Localized Electrical Impedance Myography of the Biceps Brachii Muscle during Different Levels of Isometric Contraction and Fatigue.

    Science.gov (United States)

    Li, Le; Shin, Henry; Li, Xiaoyan; Li, Sheng; Zhou, Ping

    2016-04-22

    This study assessed changes in electrical impedance myography (EIM) at different levels of isometric muscle contraction as well as during exhaustive exercise at 60% maximum voluntary contraction (MVC) until task failure. The EIM was performed on the biceps brachii muscle of 19 healthy subjects. The results showed that there was a significant difference between the muscle resistance (R) measured during the isometric contraction and when the muscle was completely relaxed. Post hoc analysis shows that the resistance increased at higher contractions (both 60% MVC and MVC), however, there were no significant changes in muscle reactance (X) during the isometric contractions. The resistance also changed during different stages of the fatigue task and there were significant decreases from the beginning of the contraction to task failure as well as between task failure and post fatigue rest. Although our results demonstrated an increase in resistance during isometric contraction, the changes were within 10% of the baseline value. These changes might be related to the modest alterations in muscle architecture during a contraction. The decrease in resistance seen with muscle fatigue may be explained by an accumulation of metabolites in the muscle tissue.

  14. Localized Electrical Impedance Myography of the Biceps Brachii Muscle during Different Levels of Isometric Contraction and Fatigue

    Directory of Open Access Journals (Sweden)

    Le Li

    2016-04-01

    Full Text Available This study assessed changes in electrical impedance myography (EIM at different levels of isometric muscle contraction as well as during exhaustive exercise at 60% maximum voluntary contraction (MVC until task failure. The EIM was performed on the biceps brachii muscle of 19 healthy subjects. The results showed that there was a significant difference between the muscle resistance (R measured during the isometric contraction and when the muscle was completely relaxed. Post hoc analysis shows that the resistance increased at higher contractions (both 60% MVC and MVC, however, there were no significant changes in muscle reactance (X during the isometric contractions. The resistance also changed during different stages of the fatigue task and there were significant decreases from the beginning of the contraction to task failure as well as between task failure and post fatigue rest. Although our results demonstrated an increase in resistance during isometric contraction, the changes were within 10% of the baseline value. These changes might be related to the modest alterations in muscle architecture during a contraction. The decrease in resistance seen with muscle fatigue may be explained by an accumulation of metabolites in the muscle tissue.

  15. The effect of local skin cooling before a sustained, submaximal isometric contraction on fatigue and isometric quadriceps femoris performance: A randomized controlled trial.

    Science.gov (United States)

    Hohenauer, Erich; Cescon, Corrado; Deliens, Tom; Clarys, Peter; Clijsen, Ron

    2017-04-01

    The central- and peripheral mechanisms by which heat strain limits physical performance are not fully elucidated. Nevertheless, pre-cooling is often used in an attempt to improve subsequent performance. This study compared the effects of pre-cooling vs. a pre-thermoneutral application on central- and peripheral fatigue during 60% of isometric maximum voluntary contraction (MVC) of the right quadriceps femoris muscle. Furthermore, the effects between a pre-cooling and a pre-thermoneutral application on isometric MVC of the right quadriceps femoris muscle and subjective ratings of perceived exertion (RPE) were investigated. In this randomized controlled trial, 18 healthy adults voluntarily participated. The participants received either a cold (experimental) application (+8°C) or a thermoneutral (control) application (+32°C) for 20min on their right thigh (one cuff). After the application, central (fractal dimension - FD) and peripheral (muscle fiber conduction velocity - CV) fatigue was estimated using sEMG parameters during 60% of isometric MVC. Surface EMG signals were detected from the vastus medialis and lateralis using bidimensional arrays. Immediately after the submaximal contraction, isometric MVC and RPE were assessed. Participants receiving the cold application were able to maintain a 60% isometric MVC significantly longer when compared to the thermoneutral group (mean time: 78 vs. 46s; p=0.04). The thermoneutral application had no significant impact on central fatigue (p>0.05) compared to the cold application (p=0.03). However, signs of peripheral fatigue were significantly higher in the cold group compared to the thermoneutral group (p=0.008). Pre-cooling had no effect on isometric MVC of the right quadriceps muscle and ratings of perceived exertion. Pre-cooling attenuated central fatigue and led to significantly longer submaximal contraction times compared to the pre-thermoneutral application. These findings support the use of pre-cooling procedures

  16. Impaired neuromuscular function during isometric, shortening, and lengthening contractions after exercise-induced damage to elbow flexor muscles.

    Science.gov (United States)

    Turner, Tanya S; Tucker, Kylie J; Rogasch, Nigel C; Semmler, John G

    2008-08-01

    The purpose of this study was to examine the effect of exercise-induced damage of the elbow flexor muscles on steady motor performance during isometric, shortening, and lengthening contractions. Ten healthy individuals (age 22+/-4 yr) performed four tasks with the elbow flexor muscles: a maximum voluntary contraction, a one repetition maximum (1 RM), an isometric task at three joint angles (short, intermediate, and long muscle lengths), and a constant-load task during slow (approximately 7 degrees/s) shortening and lengthening contractions. Task performance was quantified as the fluctuations in wrist acceleration (steadiness), and electromyography was obtained from the biceps and triceps brachii muscles at loads of 10, 20, and 40% of 1 RM. Tasks were performed before, immediately after, and 24 h after eccentric exercise that resulted in indicators of muscle damage. Maximum voluntary contraction force and 1-RM load declined by approximately 45% immediately after exercise and remained lower at 24 h ( approximately 30% decrease). Eccentric exercise resulted in reduced steadiness and increased biceps and triceps brachii electromyography for all tasks. For the isometric task, steadiness was impaired at the short compared with the long muscle length immediately after exercise (Pshortening compared with the lengthening contractions after exercise (P=0.01), and steadiness remained impaired for shortening contractions 24 h later (P=0.01). These findings suggest that there are profound effects for the performance of these types of fine motor tasks when recovering from a bout of eccentric exercise.

  17. Dystonic neck muscles show a shift in relative autospectral power during isometric contractions.

    Science.gov (United States)

    De Bruijn, E; Nijmeijer, S W R; Forbes, P A; Koelman, J H T M; Van Der Helm, F C T; Tijssen, M A J; Happee, R

    2017-07-17

    To identify effects of a deviant motor drive in the autospectral power of dystonic muscles during voluntary contraction in cervical dystonia patients. Submaximal (20%) isometric head-neck tasks were performed with the head fixed, measuring surface EMG of the sternocleidomastoid, splenius capitis and semispinalis capitis in CD patients and controls. Autospectral power of muscle activity, and head forces was analyzed using cumulative distribution functions (CDF). A downward shift between the theta/low alpha-band (3-10Hz) and the high alpha/beta-band (10-30Hz) was detected using the CDF10, defined as the cumulative power from 3 to 10Hz relative to power from 3 to 30Hz. CDF10 was increased in dystonic muscles compared to controls and patient muscles unaffected by dystonia, due to a 3-10Hz power increase and a 10-30Hz decrease. CDF10 also increased in patient head forces. Submaximal isometric contractions with the head fixed provided a well-defined test condition minimizing effects of reflexive feedback and tremor. We associate shifts in autospectral power with prokinetic sensorimotor control. Analysis of autospectral power in isometric tasks with the head fixed is a promising approach in research and diagnostics of cervical dystonia. Copyright © 2017 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.

  18. Fatigability and recovery of arm muscles with advanced age for dynamic and isometric contractions.

    Science.gov (United States)

    Yoon, Tejin; Schlinder-Delap, Bonnie; Hunter, Sandra K

    2013-02-01

    This study determined whether age-related mechanisms can increase fatigue of arm muscles during maximal velocity dynamic contractions, as it occurs in the lower limb. We compared elbow flexor fatigue of young (n=10, 20.8±2.7 years) and old men (n=16, 73.8±6.1 years) during and in recovery from a dynamic and an isometric postural fatiguing task. Each task was maintained until failure while supporting a load equivalent to 20% of maximal voluntary isometric contraction (MVIC) torque. Transcranial magnetic stimulation (TMS) was used to assess supraspinal fatigue (superimposed twitch, SIT) and muscle relaxation. Time to failure was longer for the old men than for the young men for the isometric task (9.5±3.1 vs. 17.2±7.0 min, P=0.01) but similar for the dynamic task (6.3±2.4 min vs. 6.0±2.0 min, P=0.73). Initial peak rate of relaxation was slower for the old men than for the young men, and was associated with a longer time to failure for both tasks (PMuscular mechanisms and greater relative muscle activity (EMG activity) explain the greater fatigue during the dynamic task for the old men compared with the young men in the elbow flexor muscles. Recovery of MVC torque however relies more on the recovery of supraspinal fatigue among the old men than among the young men.

  19. Firing rate modulation of human motor units in different muscles during isometric contraction with various forces.

    Science.gov (United States)

    Seki, K; Narusawa, M

    1996-05-06

    To examine the factors affecting the control of human motor units, rate coding strategies of the motor units were investigated in upper limb and intrinsic hand muscles during voluntary isometric contraction of steady force levels up to 80% of maximal voluntary contraction. Numerous spike trains from single motor units were recorded from the m. first dorsal interosseous (FDI) and the m. biceps brachii (BB) of eight human subjects by means of tungsten micro-electrodes, and the mean firing rate (MFR) was calculated for each subject and inter-individual comparisons made. The MFRs of the FDI were larger than that of the BB at the higher force level, and substantial differences were not found between these muscles at the lower force level. The slope of the linear regression line of MFRs vs. exerted forces for the FDI was more than twice that for the BB. Therefore, isometric force control of the FDI depends more on the rate coding strategy. The difference in rate coding between the FDI and BB motor units may be determined by factors other than muscle fiber composition, because both muscles are known to possess a similar composition of fiber types. Possible mechanisms underlying these characteristics of rate coding strategy are considered in this report.

  20. Differences in twitch potentiation between voluntary and stimulated quadriceps contractions of equal intensity.

    Science.gov (United States)

    Jubeau, M; Gondin, J; Martin, A; Van Hoecke, J; Maffiuletti, N A

    2010-02-01

    This study compared the extent of twitch and M-wave potentiation (POT) between voluntary and stimulated quadriceps contractions performed at the same intensity. Sixteen healthy men completed 10-s isometric knee extensions at 40% of the maximal voluntary contraction torque under electrical stimulation and voluntary conditions. Single stimuli were delivered to the femoral nerve to evoke twitches before (PRE) and from 3 to 600 s after the end of each conditioning contraction. Changes in twitch contractile properties and M-wave characteristics were compared between the conditions. The extent of twitch peak torque POT was smaller for the stimulated (122+/-20% of PRE) than for the voluntary condition (133+/-20% of PRE). The magnitude of POT for the maximal rate of twitch torque development was also smaller for the stimulated trial. Rectus femoris M-wave amplitude was potentiated by the voluntary but not by the stimulated contraction. It was concluded that stimulated contractions resulted in smaller twitch and M-wave POT than voluntary contractions, despite equivalent torque output and duration. The spatially and temporally fixed recruitment of motor units with electrical stimulation and therefore the lower number of activated motor units compared with voluntary actions of equal intensity could explain the present findings.

  1. [Effect of thyroidectomy on energetics of isometric muscle contraction in white rats].

    Science.gov (United States)

    Soboliev, V I; Moskalets', T V

    2007-01-01

    The effect of thyroidactomia on parameters of energetics of isometric contractions of front shin--bone muscle of white rats is studied in in situ experiments. It is shown that experimental atiriosis lengthen considerably the latent period of muscle contractions (+95%) considerably reduce (in 5.5 times) the speed of it contraction in first phase of contraction act and also considerably increase the time (+37%), which necessery for developing maximum strength of contraction. Thyroidactomia with general negative influence on ergothropic characteristics of isometric muscle contraction decrease considerably the expenditure of thermal energy on maximum strength of contraction unit (-17%) or on middle isometric tension unit (-9.3%).

  2. Identification of time-varying dynamics of the human triceps surae stretch reflex. I. Rapid isometric contraction.

    Science.gov (United States)

    Kirsch, R F; Kearney, R E; MacNeil, J B

    1993-01-01

    We have examined the time variations of stretch reflex dynamics throughout rapid voluntary changes in the isometric contraction level of the human triceps surae muscles. This was achieved by superimposing a small stochastic displacement upon many such changing contractions and then identifying the time-varying relationship between the perturbation and the evoked electromyograms (EMGs). An "ensemble" time-varying system identification technique was used to estimate these input-output dynamics as a set of impulse response functions, one for each time before, during, and after the change in contraction level, with a temporal resolution equal to the data acquisition rate. Three main findings resulted. First, stretch reflex gain (relating joint velocity to EMG) was significantly modulated during changes in voluntary contraction level, increasing as the subject contracted the muscles and decreasing as the subject relaxed. Second, stretch reflex dynamics did not change with contraction level, even when its gain varied substantially. Third, the time course of the gain changes closely followed the level of the EMG, even though the subjects used rather different activation and deactivation patterns. These results suggest that, for the behavior studied (i.e., rapid changes in isometric contraction level), stretch reflex gain and motoneuron pool activation level were controlled by a common descending command rather than being independently specified.

  3. Gravitational effects on human cardiovascular responses to isometric muscle contractions

    Science.gov (United States)

    Bonde-Petersen, Flemmig; Suzuki, Yoji; Sadamoto, Tomoko

    Isometric exercise induces profound cardiovascular adaptations increasing mean arterial pressure and heart rate. We investigated effects of simulated +Gz and -Gz respectively on the central and peripheral cardiovascular system. Sustained handgrip exercise was performed at 40% of maximum for 2 minutes in five subjects. This maneuver increased mean arterial pressure by 40-45 mm Hg both during head out water immersion which simulates weightlessness, as well as bedrest during -25, 0, and +25 degrees tilt from the horizontal. Lower body negative pressure (-60 mm Hg for 10 min) attenuated the response to handgrip exercise to 30 mm Hg. It also increased the heart rate minimally by about 20 beats per minute while the water immersion, as well as head up, head down and horizontal bedrest showed increments of about 50 beats per min. It was concluded that the response to isometric contraction is mediated through the high pressure baroreceptors, because similar responses were seen during stresses producing a wide variation in central venous pressure. During lower body negative pressure the increased sympathetic nervous activity itself increased resting heart rate and mean arterial pressure. The responses to static exercise were, therefore, weaker.

  4. Disturbance of contralateral unipedal postural control after stimulated and voluntary contractions of the ipsilateral limb.

    Science.gov (United States)

    Paillard, Thierry; Chaubet, Vincent; Maitre, Julien; Dumitrescu, Michel; Borel, Liliane

    2010-12-01

    One session of sustained unilateral voluntary muscular contractions increases central fatigue and induces a cross-over of fatigue of homologous contralateral muscles. It is not known, however, how this cross-transfer affects contralateral unipedal postural control. Moreover, contralateral neurophysiological effects differ between voluntary muscular contractions and electrically stimulated contractions. The aims of this study were thus to examine the effects of muscle fatigue on contralateral unipedal postural control and to compare the effects of stimulated and voluntary contractions. Fifteen subjects took part in the protocol. Fatigue of the ipsilateral quadriceps femoris was generated either by neuromuscular electrical stimulation (NMES) or by isometric voluntary muscular contraction (VOL). Postural control on the contralateral limb was measured before (PRE condition) and after the completion of the two fatiguing exercises (POST condition) using a force platform. We analyzed body sway area and the spectral power density given by the wavelet transform. In POST condition, postural control recorded in the unipedal stance on the contralateral limb was disturbed after NMES and VOL fatiguing exercises. In addition, postural control was similarly disturbed for both exercises. These results suggest that cross-over fatigue is able to disturb postural control after both stimulated and voluntary contractions.

  5. Structural features of cross-bridges in isometrically contracting skeletal muscle.

    OpenAIRE

    Kraft, Theresia; Mattei, Thomas; Radocaj, Ante; Piep, Birgit; Nocula, Christoph; Furch, Markus; Brenner, Bernhard

    2002-01-01

    Two-dimensional x-ray diffraction was used to investigate structural features of cross-bridges that generate force in isometrically contracting skeletal muscle. Diffraction patterns were recorded from arrays of single, chemically skinned rabbit psoas muscle fibers during isometric force generation, under relaxation, and in rigor. In isometric contraction, a rather prominent intensification of the actin layer lines at 5.9 and 5.1 nm and of the first actin layer line at 37 nm was found compared...

  6. Axial disposition of myosin heads in isometrically contracting muscles.

    Science.gov (United States)

    Juanhuix, J; Bordas, J; Campmany, J; Svensson, A; Bassford, M L; Narayanan, T

    2001-03-01

    Meridional x-ray diffraction diagrams, recorded with high angular resolution, from muscles contracting at the plateau of isometric tension show that the myosin diffraction orders are clusters of peaks. These clusters are due to pronounced interference effects between the myosin diffracting units on either side of the M-line. A theoretical analysis based on the polarity of the myosin (and actin) filaments shows that it is possible to extract phase information from which the axial disposition of the myosin heads can be determined. The results show that each head in a crown pair has a distinct structural disposition. It appears that only one of the heads in the pair stereospecifically interacts with the thin filament at any one time.

  7. [Assessment of the coronary circulation regulation by means of the so-called isometric contraction index].

    Science.gov (United States)

    Urbaszek, W; Löwe, H R; Rentsch, W; Pankau, H; Günther, K

    1976-08-01

    The index of isometric contraction formed from the quotient period of isometric contraction in the erect position by period of isometric contraction in lying position gives the possibility to separate between cardially sufficient and cardially insufficient patients with adequately disturbed regulation of the cardiac circulation. The recognition of early stages of the disturbed left-ventricular function is possible. The use of an adequate exact technique in gaining the primary data is to be presumed. Corrections of the frequency of the index of isometric contraction do not improve the evidence. In the borderline region of the index of isometric contraction with values between 1.03 and 1.1 in questionable cases a further differentiation into still normal or already latent insufficient will do by the analysis of the trend of the index of isometric contraction after the application of medicaments. The determination of the change of the direction of the index of isometric contraction after peroral application of nitroglycerin would be justifiable in routine work after the recognition of the initiaction increases in patients with latent heart insufficiency, in patients with a healthy heart it decreases. The clinical value of the index of isometric contraction as a simple test of the circulatory function is highly to be estimated.

  8. Significance of peripheral afferent input to the alpha-motoneurone pool for enhancement of tremor during an isometric fatiguing contraction.

    Science.gov (United States)

    Cresswell, A G; Löscher, W N

    2000-05-01

    The objective of this study was to investigate the contribution of peripheral afferent input to the enhancement of isometric tremor during a sustained submaximal isometric contraction. It was hypothesised that during muscle fatigue, when excitatory drive is high, peripheral afferent input may augment oscillations in the stretch reflex arc and result in bursting motor-unit activity and increased tremor. Nine healthy subjects maintained isometric plantar flexions at 30% of their maximum voluntary contraction until the limit of endurance, under three test conditions. Two paradigms were used to reduce afferent input to the triceps surae alpha-motoneurone pool: (1) continued vibration of the Achilles tendon, and (2) ischaemic partial block of the tibial nerve. These were compared to a control experiment, in which there was no intervention. By recording H-reflexes from the gastrocnemius and soleus muscles, it was possible to assess the effectiveness of reducing the afferent input. When H-reflex suppression had stabilised, the fatiguing contraction was commenced and tremor was computed from the continuously recorded torque signal. Superimposed maximum twitches were elicited as indirect measures of excitatory drive. The increase in tremor root mean square throughout the fatiguing contraction was significantly less for both the vibration and ischaemic conditions. Furthermore, tremor mean power frequency decreased significantly with endurance time in the control experiment, while no significant change was seen in the other two experimental conditions. It is concluded that the enhancement of isometric tremor seen during a fatiguing submaximal isometric contraction is facilitated by peripheral afferent input to the alpha-motoneurone pool.

  9. Two maximal isometric contractions attenuate the magnitude of eccentric exercise-induced muscle damage.

    Science.gov (United States)

    Chen, Hsin-Lian; Nosaka, Kazunori; Pearce, Alan J; Chen, Trevor C

    2012-08-01

    This study investigated whether maximal voluntary isometric contractions (MVC-ISO) would attenuate the magnitude of eccentric exercise-induced muscle damage. Young untrained men were placed into one of the two experimental groups or one control group (n = 13 per group). Subjects in the experimental groups performed either two or 10 MVC-ISO of the elbow flexors at a long muscle length (20° flexion) 2 days prior to 30 maximal isokinetic eccentric contractions of the elbow flexors. Subjects in the control group performed the eccentric contractions without MVC-ISO. No significant changes in maximal voluntary concentric contraction peak torque, peak torque angle, range of motion, upper arm circumference, plasma creatine kinase (CK) activity and myoglobin concentration, muscle soreness, and ultrasound echo intensity were evident after MVC-ISO. Changes in the variables following eccentric contractions were smaller (P MVC-ISO group (e.g., peak torque loss at 5 days after exercise, 23% ± 3%; peak CK activity, 1964 ± 452 IU·L(-1); peak muscle soreness, 46 ± 4 mm) or the 10 MVC-ISO group (13% ± 3%, 877 ± 198 IU·L(-1), 30 ± 4 mm) compared with the control (34% ± 4%, 6192 ± 1747 IU·L(-1), 66 ± 5 mm). The 10 MVC-ISO group showed smaller (P MVC-ISO group. Therefore, two MVC-ISO conferred potent protective effects against muscle damage, whereas greater protective effect was induced by 10 MVC-ISO, which can be used as a strategy to minimize muscle damage.

  10. ELECTROMYOGRAPHIC ACTIVITY OF THE VASTUS MEDIALIS OBLIQUE AND VASTUS LATERALIS DURING MAXIMUM VOLUNTARY ISOMETRICS IN DIFFERENT WEIGHT BEARING POSITIONS OF THE FOOT

    Directory of Open Access Journals (Sweden)

    Sreekar Kumar Reddy.R

    2014-09-01

    Full Text Available Background: Patellofemoral pain syndrome is a very common disorder. 90% of the general population has some degree of pathologic changes of the patellofemoral joint. Knowledge regarding the cause and prevention of patellofemoral pain syndrome is essential. Therefore the purpose of this study is intended to know whether different foot positions alter Vastus Medialis Oblique and Vastus Lateralis that leads to dysfunctions of knee joint. Method: 30 subjects are included in study and investigated foot in different foot positions are in neutral, pronated and supinated foot positions and performed maximum voluntary isometric contractions are recorded with electromyography. Results: EMG amplitudes (microvolts of VL and VMO at three different weight bearing positions of foot during maximum voluntary contraction analysis by using one-way Analysis of Variance. Mean amplitudes of foot positions in pronation shown significant difference while comparing with neutral and supination. Conclusion: The VMO and VL activity shows significant difference in the pronated foot weight bearing position compared to the neutral and supinated foot. Performing the maximum voluntary isometric contractions of VMO and VL with pronated foot elicited significantly higher EMG activity compared to Neutral or supinated weight bearing positions of foot. The results of this study also suggested that for patellofemoral pain which is caused by pronated foot can be treat with by using the soft foot orthoses

  11. Isokinetic and isometric muscle strength combined with transcutaneous electrical muscle stimulation in primary fibromyalgia syndrome

    DEFF Research Database (Denmark)

    Jacobsen, Søren; Wildschiødtz, Gordon; Danneskiold-Samsøe, B

    1991-01-01

    Twenty women with primary fibromyalgia syndrome and 20 age matched healthy women were investigated. The subjects performed maximum voluntary isokinetic contractions of the right quadriceps in an isokinetic dynamometer. Maximum voluntary isometric contractions of the right quadriceps were performe...

  12. Functional connectivity between core and shoulder muscles increases during isometric endurance contractions in judo competitors

    DEFF Research Database (Denmark)

    Kawczyński, Adam; Samani, Afshin; Mroczek, Dariusz

    2015-01-01

    regions during sustained isometric contraction. Methods: Twelve healthy, right-handed judo competitors participated in the study. The SEMG signals from the dominant trapezius (upper, middle and lower part), deltoideus anterior, serratus anterior, and pectoralis major muscles were recorded during isometric...

  13. Sub-sarcolemmal swelling of sarcoplasmic reticulum after isometric contractions in rat semimembranosus lateralis muscle

    NARCIS (Netherlands)

    Willems, M.E.T.; Huijing, P.A.J.B.M.; Friden, J.

    1999-01-01

    The decline in isometric force, swelling of sarcoplasmic reticulum and loss of desmin was measured in semimembranosus lateralis muscle of male Wistar rats immediately after a short series of brief (500 ms) maximal isometric contractions. For the active muscle, the series ended below (protocol A) and

  14. Blackcurrant Alters Physiological Responses and Femoral Artery Diameter during Sustained Isometric Contraction

    Directory of Open Access Journals (Sweden)

    Matthew David Cook

    2017-05-01

    Full Text Available Blackcurrant is rich in anthocyanins that may affect exercise-induced physiological responses. We examined tissue oxygen saturation, muscle activity, cardiovascular responses and femoral artery diameter during a submaximal sustained isometric contraction. In a randomised, double-blind, crossover design, healthy men (n = 13, age: 25 ± 4 years, BMI: 25 ± 3 kg·m−2, mean ± SD ingested New Zealand blackcurrant (NZBC extract (600 mg∙day−1 CurraNZ™ or placebo (PL for 7-days separated by 14-days washout. Participants produced isometric maximal voluntary contractions (iMVC and a 120-s 30%iMVC of the quadriceps with electromyography (EMG, near-infrared spectroscopy, hemodynamic and ultrasound recordings. There was no effect of NZBC extract on iMVC (NZBC: 654 ± 73, PL: 650 ± 78 N. During the 30%iMVC with NZBC extract, total peripheral resistance, systolic, diastolic, and mean arterial pressure were lower with increased cardiac output and stroke volume. With NZBC extract, EMG root mean square of the vastus medialis and muscle oxygen saturation were lower with higher total haemoglobin. During the 30%iMVC, femoral artery diameter was increased with NZBC extract at 30 (6.9%, 60 (8.2%, 90 (7.7% and 120 s (6.0%. Intake of NZBC extract for 7-days altered cardiovascular responses, muscle oxygen saturation, muscle activity and femoral artery diameter during a 120-s 30%iMVC of the quadriceps. The present study provides insight into the potential mechanisms for enhanced exercise performance with intake of blackcurrant.

  15. 偏瘫型脑瘫患儿腕屈伸肌群最大等长收缩时的表面肌电特征研究%Characteristic surface myoelectric signals of maximum isometric voluntary contraction of the wrist flexors and extensors in children with hemiplegic cerebral palsy

    Institute of Scientific and Technical Information of China (English)

    徐开寿; 何璐; 麦坚凝

    2014-01-01

    目的 观察偏瘫型脑瘫患儿腕屈伸肌群最大等长收缩时肌肉募集和协调功能的肌电信号特征.方法 选取痉挛型偏瘫患儿68例,年龄2~14岁,采用表面肌电图(sEMG)检测其健手和患手腕屈伸肌群最大等长收缩时的表面肌电信号,通过配对t检验和Pearson相关性分析确定其积分肌电值(iEMG)、均方根值(RMS)和协同收缩率的特征.结果 使用患手抓握时,患手腕部的RMS、iEMG均明显高于健手(P<0.05),患手与健手腕伸肌RMS、腕屈伸肌iEMG间具有良好的相关性(P<0.05).使用健手抓握时,健手腕部的RMS、iEMG均明显高于患手(P<0.05),健手与患手腕屈伸肌iEMG间具有良好的相关性(P<0.05).健手抓握时健手腕部的RMS、iEMG均明显高于患手抓握时患手腕部的RMS、iEMG,但健手腕部的协同收缩率(0.48±0.02)明显低于患手(0.54±0.04)(P<0.05).结论 偏瘫型脑瘫患儿使用患手时腕屈肌群存在过度协同激活,患手肌肉募集能力明显弱于健手,其双手的分离运动控制能力可能受限,提示增强腕伸肌收缩功能、抑制腕屈肌协同激活水平、合理引导患手开展功能锻炼应成为偏瘫患儿康复的重点之一.%Objective To study the characteristic surface myoelectric signals generated by children with hemiplegic cerebral palsy (HCP) during maximum isometric voluntary contraction (MIVC) of the wrist flexors and extensors.Methods Sixty-eight children with HCP 2 to 14 years of age were assessed with surface electromyography (sEMG).The electrodes were applied on the skin over the wrist flexors and extensors.The integrated EMG signals (iEMGs),root mean square amplitudes (RMSs) and co-contraction ratios during MIVC were recorded and analyzed.Results In a MIVC,the RMS,iEMG and co-contraction ratio were all significantly different between the involved and uninvolved hands,though the iEMGs of the wrists of the two hands were strongly correlated.The RMSs of the wrists of the

  16. Reliability of near-infrared spectroscopy for measuring biceps brachii oxygenation during sustained and repeated isometric contractions

    Science.gov (United States)

    Muthalib, Makii; Millet, Guillaume Y.; Quaresima, Valentina; Nosaka, Kazunori

    2010-01-01

    We examine the test-retest reliability of biceps brachii tissue oxygenation index (TOI) parameters measured by near-infrared spectroscopy during a 10-s sustained and a 30-repeated (1-s contraction, 1-s relaxation) isometric contraction task at 30% of maximal voluntary contraction (30% MVC) and maximal (100% MVC) intensities. Eight healthy men (23 to 33 yr) were tested on three sessions separated by 3 h and 24 h, and the within-subject reliability of torque and each TOI parameter were determined by Bland-Altman+/-2 SD limits of agreement plots and coefficient of variation (CV). No significant (P>0.05) differences between the three sessions were found for mean values of torque and TOI parameters during the sustained and repeated tasks at both contraction intensities. All TOI parameters were within+/-2 SD limits of agreement. The CVs for torque integral were similar between the sustained and repeated task at both intensities (4 to 7%) however, the CVs for TOI parameters during the sustained and repeated task were lower for 100% MVC (7 to 11%) than for 30% MVC (22 to 36%). It is concluded that the reliability of the biceps brachii NIRS parameters during both sustained and repeated isometric contraction tasks is acceptable.

  17. Time-dependent cortical activation in voluntary muscle contraction.

    Science.gov (United States)

    Yang, Qi; Wang, Xiaofeng; Fang, Yin; Siemionow, Vlodek; Yao, Wanxiang; Yue, Guang H

    2011-01-01

    This study was to characterize dynamic source strength changes estimated from high-density scalp electroencephalogram (EEG) at different phases of a submaximal voluntary muscle contraction. Eight healthy volunteers performed isometric handgrip contractions of the right arm at 20% maximal intensity. Signals of the handgrip force, electromyography (EMG) from the finger flexor and extensor muscles and 64-channel EEG were acquired simultaneously. Sources of the EEG were analyzed at 19 time points across preparation, execution and sustaining phases of the handgrip. A 3-layer boundary element model (BEM) based on the MNI (Montréal Neurological Institute) brain MRI was used to overlay the sources. A distributed current density model, LORETA L1 norm method was applied to the data that had been processed by independent component analysis (ICA). Statistical analysis based on a mixed-effects polynomial regression model showed a significant and consistent time-dependent non-linear source strength change pattern in different phases of the handgrip. The source strength increased at the preparation phase, peaked at the force onset time and decreased in the sustaining phase. There was no significant difference in the changing pattern of the source strength among Brodmann's areas 1, 2, 3, 4, and 6. These results show, for the first time, a high time resolution increasing-and-decreasing pattern of activation among the sensorimotor regions with the highest activity occurs at the muscle activity onset. The similarity in the source strength time courses among the cortical centers examined suggests a synchronized parallel function in controlling the motor activity.

  18. The effects of isometric contraction of shoulder muscles on cervical multifidus muscle dimensions in healthy office workers.

    Science.gov (United States)

    Rahnama, Leila; Rezasoltani, Asghar; Khalkhali Zavieh, Minoo; Noori Kochi, Farhang; Akbarzadeh Baghban, Alireza

    2014-07-01

    It is argued that cervical multifidus muscles (CMM) are responsible for providing neck stability. However, whether they are actually activated during the tasks performed by the upper extremities to the neck is still unknown. Therefore, the aim of this study was to examine the effects of isometric contraction of shoulder muscles on the dimensions of CMM. Twenty three healthy males voluntarily participated in this study. Ultrasonography imaging of CMM was conducted at rest and at 25%, 50%, 75%, and 100% of maximal voluntary contraction of shoulder muscles in 6 directions of shoulder movements. Anterior-posterior dimension (APD), lateral dimension (LD), shape ratio and multiplied linear dimension (MLD) of cervical multifidus were measured. The APD of CMM was increased while LD and shape ratio were decreased by shoulder muscles contraction (P < 0.01).

  19. Isometric contractions combined with eccentric contractions and stretching exercises on patient with subacromial impingement syndrome

    Directory of Open Access Journals (Sweden)

    Efstratiadis Anastasios

    2015-10-01

    Full Text Available Many people with shoulder pain and disability have signs of subacromial impingement syndrome. The subacromial impingement syndrome of the shoulder is a general term, which is often used to describe pain and dysfunction in the area around the shoulder. The aim of the present report is to find the effect of isometric contractions combined with eccentric contractions and stretching exercises on a patient with subacromial impingement syndrome. A patient with subacromial impingement syndrome for 1 year was included in the case report. The patient followed an exercise program consisted of stretching exercises of shoulder muscles extensors, isometric contractions of shoulder extensors and eccentric exercises of shoulder extensors, 4 times per week. The exercise program was individualized according to pain and symptoms of the patient. Outcome measures were pain, pain rest, pain activity, pain night measured on a visual analogue scale (VAS, disability index (DASH score and range of motion (Goniometer. The patient was evaluated at baseline and after 4 weeks. At the end of the program, there was a significant improvement pain, disability and range of motion. In this clinical case the patient was improved significantly in all outcome measures. Further studies based on better design, are needed to investigate the effect of those methods on a random population group with subacromial impingement syndrome.

  20. Reflex changes in muscle spindle discharge during a voluntary contraction.

    Science.gov (United States)

    Aniss, A M; Gandevia, S C; Burke, D

    1988-03-01

    1. This study was undertaken to determine whether low-threshold cutaneous and muscle afferents from mechanoreceptors in the foot reflexly affect fusimotor neurons innervating the plantar and dorsiflexors of the ankle during voluntary contractions. 2. Recordings were made from 29 identified muscle spindle afferents innervating triceps surae and the pretibial flexors. Trains of electrical stimuli (5 stimuli, 300 impulses per second) were delivered to the sural nerve at the ankle (intensity: 2-4 times sensory threshold) and to the posterior tibial nerve at the ankle (intensity: 1.5-3 times motor threshold for the small muscles of the foot). The stimuli were delivered while the subject maintained an isometric voluntary contraction of the receptor-bearing muscle, sufficient to accelerate the discharge of each spindle ending. This ensured that the fusimotor neurons directed to the ending were active and influencing the spindle discharge. The effects of these stimuli on muscle spindle discharge were assessed using raster displays, frequencygrams, poststimulus time histograms (PSTHs) and cumulative sums ("CUSUMs") of the PSTHs. Reflex effects onto alpha-motoneurons were determined from poststimulus changes in the averaged rectified electromyogram (EMG). Reflex effects of these stimuli onto single-motor units were assessed in separate experiments using PSTHs and CUSUMs. 3. Electrical stimulation of the sural or posterior tibial nerves at nonnoxious levels had no significant effect on the discharge of the 14 spindle endings in the pretibial flexor muscles. The electrical stimuli also produced no significant change in discharge of 11 of 15 spindle endings in triceps surae. With the remaining four endings in triceps surae, the overall change in discharge appeared to be an increase for two endings (at latencies of 60 and 68 ms) and a decrease for two endings (at latencies of 110 and 150 ms). The difference in the incidence of the responses of spindle endings in tibialis

  1. Mechanical compression during repeated sustained isometric muscle contractions and hyperemic recovery in healthy young males

    DEFF Research Database (Denmark)

    Osada, Takuya; Mortensen, Stefan P; Rådegran, Göran

    2015-01-01

    BACKGROUND: An elevated intramuscular pressure during a single forearm isometric muscle contraction may restrict muscle hyperemia. However, during repeated isometric exercise, it is unclear to what extent mechanical compression and muscle vasodilatation contribute to the magnitude and time course...... of beat-to-beat limb hemodynamics, due to alterations in leg vascular conductance (LVC). METHODS: In eight healthy male subjects, the time course of both beat-to-beat leg blood flow (LBF) and LVC in the femoral artery was determined between repeated 10-s isometric thigh muscle contractions and 10-s muscle...... (%). RESULTS: The exercise protocol was performed completely by all subjects (≤50 % MVC), seven subjects (≤70 % MVC), and two subjects (≤90 % MVC). During a 10-s isometric muscle contraction, the time course in both beat-to-beat LBF and LVC displayed a fitting curve with an exponential increase (P 

  2. Reactive oxygen species generation is not different during isometric and lengthening contractions of mouse muscle.

    Science.gov (United States)

    Sloboda, Darcée D; Brooks, Susan V

    2013-10-01

    Skeletal muscles can be injured by lengthening contractions, when the muscles are stretched while activated. Lengthening contractions produce structural damage that leads to the degeneration and regeneration of damaged muscle fibers by mechanisms that have not been fully elucidated. Reactive oxygen species (ROS) generated at the time of injury may initiate degenerative or regenerative processes. In the present study we hypothesized that lengthening contractions that damage the muscle would generate more ROS than isometric contractions that do not cause damage. To test our hypothesis, we subjected muscles of mice to lengthening contractions or isometric contractions and simultaneously monitored intracellular ROS generation with the fluorescent indicator 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein (CM-DCFH), which is oxidized by ROS to form the fluorescent product CM-DCF. We found that CM-DCF fluorescence was not different during or shortly after lengthening contractions compared with isometric controls, regardless of the amount of stretch and damage that occurred during the lengthening contractions. The only exception was that after severe stretches, the increase in CM-DCF fluorescence was impaired. We conclude that lengthening contractions that damage the muscle do not generate more ROS than isometric contractions that do not cause damage. The implication is that ROS generated at the time of injury are not the initiating signals for subsequent degenerative or regenerative processes.

  3. Fatigue reduces the complexity of knee extensor torque fluctuations during maximal and submaximal intermittent isometric contractions in man.

    Science.gov (United States)

    Pethick, Jamie; Winter, Samantha L; Burnley, Mark

    2015-04-15

    Neuromuscular fatigue increases the amplitude of fluctuations in torque output during isometric contractions, but the effect of fatigue on the temporal structure, or complexity, of these fluctuations is not known. We hypothesised that fatigue would result in a loss of temporal complexity and a change in fractal scaling of the torque signal during isometric knee extensor exercise. Eleven healthy participants performed a maximal test (5 min of intermittent maximal voluntary contractions, MVCs), and a submaximal test (contractions at a target of 40% MVC performed until task failure), each with a 60% duty factor (6 s contraction, 4 s rest). Torque and surface EMG signals were sampled continuously. Complexity and fractal scaling of torque were quantified by calculating approximate entropy (ApEn), sample entropy (SampEn) and the detrended fluctuation analysis (DFA) scaling exponent α. Fresh submaximal contractions were more complex than maximal contractions (mean ± SEM, submaximal vs. maximal: ApEn 0.65 ± 0.09 vs. 0.15 ± 0.02; SampEn 0.62 ± 0.09 vs. 0.14 ± 0.02; DFA α 1.35 ± 0.04 vs. 1.55 ± 0.03; all P contractions (ApEn to 0.24 ± 0.05; SampEn to 0.22 ± 0.04; DFA α to 1.55 ± 0.03; all P contractions (ApEn to 0.10 ± 0.02; SampEn to 0.10 ± 0.02; DFA α to 1.63 ± 0.02; all P < 0.01). This loss of complexity and shift towards Brownian-like noise suggests that as well as reducing the capacity to produce torque, fatigue reduces the neuromuscular system's adaptability to external perturbations.

  4. Optimal Combinations of Isometric Normalization Tests for the Production of Maximum Voluntary Activation of the Shoulder Muscles.

    Science.gov (United States)

    Dal Maso, Fabien; Marion, Patrick; Begon, Mickaël

    2016-09-01

    To identify the smallest combinations of maximum voluntary isometric contraction (MVIC) tests that produce near-maximum voluntary activation (MVA) for a large proportion of participants for the shoulder girdle muscles. Cross-sectional study. Research center. Healthy participants (N=38). Not applicable. The electromyography of 12 shoulder muscles was recorded while participants performed 15 MVIC tests. The smallest combinations of MVIC tests that met our acceptance criterion (ie, produce 90% of MVA for 90% of participants) were identified. Optimal combinations were identified for each of the 12 muscles individually and for the 12 muscles simultaneously. Electromyographic activation levels of the 95th highest percentile obtained with our optimal combinations and with the Four Normalization Tests previously recommended were compared using paired t tests. Between 2 and 6 MVIC tests were required for each of the 12 muscles, and 12 MVIC tests were required for the 12 muscles to meet the acceptance criterion. These optimal combinations produced electromyographic activation levels of the 95th highest percentile comprised between 97% and 100% of MVA. These electromyographic activation levels were significantly higher than the electromyographic activation levels obtained with the Four Normalization Tests. Although the number of MVIC tests to normalize 12 shoulder muscles was increased compared with previous recommendations, the proposed method ensures that near-MVA (>90%) was obtained for a large proportion of participants (>90%). Moreover, because electromyographic activation levels of the 95th highest percentile were at least 97% of MVA, the identified combinations could reduce the interparticipant variability. The proposed combinations could help to improve electromyographic normalization and therefore reduce the misinterpretations regarding shoulder muscle activation levels. Copyright © 2016 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All

  5. Relation between muscle and brain activity during isometric contractions of the first dorsal interosseus muscle

    NARCIS (Netherlands)

    van Duinen, Hiske; Renken, Remco; Maurits, Natasha M.; Zijdewind, Inge

    2008-01-01

    We studied the relationship between muscle activity (electromyography, EMG), force, and brain activity during isometric contractions of the index finger, on a group and individual level. Ten subjects contracted their right or left index finger at 5, 15, 30, 50, and 70% of their maximal force. Subjec

  6. M-wave potentiation after voluntary contractions of different durations and intensities in the tibialis anterior.

    Science.gov (United States)

    Rodriguez-Falces, Javier; Duchateau, Jacques; Muraoka, Yoshiho; Baudry, Stéphane

    2015-04-15

    The study was undertaken to provide insight into the mechanisms underlying the potentiation of the muscle compound action potential (M wave) after conditioning contractions. M waves were evoked in the tibialis anterior before and after isometric maximal voluntary contractions (MVC) of 1, 3, 6, 10, 30, and 60 s, and after 3-s contractions at 10, 30, 50, 70, 90, and 100% MVC. The amplitude, duration, and area of the first and second phases of the M wave, together with the median frequency (Fmedian) and muscle fiber conduction velocity (MFCV) were recorded. Furthermore, twitch force, muscle fascicle length, and pennation angle were measured at rest, before, and 1 s after the conditioning contractions. The results indicate that only the amplitude of the second phase of the M wave was significantly increased after conditioning contractions. The extent of this potentiation was similar for MVC durations ranging from 1 to 10 s and augmented progressively with contraction intensity from 30 to 70% MVC. After these conditioning contractions, the duration and area of the two M-wave phases decreased (P contraction. Changes in MFCV after the contractions were correlated with those in M-wave second-phase amplitude (r(2) = 0.42; P contractions. It is concluded that the potentiation of the second phase of the M wave is mainly due to an increased MFCV.

  7. Metabolically assessed muscle fibre recruitment in brief isometric contractions at different intensities.

    Science.gov (United States)

    Beltman, J G M; de Haan, A; Haan, H; Gerrits, H L; van Mechelen, W; Sargeant, A J

    2004-08-01

    This study investigated the recruitment of type I, IIA and IIAX fibres after seven isometric contractions at 40, 70 and 100% maximal voluntary knee extension torque (MVC, 1 s on/1 s off). Biopsies of the vastus lateralis muscle were collected from seven subjects at rest and immediately post-exercise. Fibre fragments were dissected from the freeze-dried samples and characterized as type I, IIA and IIAX using mATPase staining. Phosphocreatine (PCr) and creatine (Cr) content were measured in the remaining part of characterized fibres. A decline in the ratio of PCr to Cr (PCr/Cr) was used as an indication of activation. The mean peak torques were, respectively, 39 (2), 72 (2) and 87 (6)% MVC. Cumulative distributions of type I and IIA fibres were significantly shifted to lower PCr/Cr ratios at all intensities (Kolmogorov-Smirnov test, P<0.05). The cumulative distribution of type IIAX fibres showed a significant leftward shift only at 87% MVC ( P<0.05). A hierarchical order of fibre activation with increasing intensity of exercise was found, with some indication of rate coding for type I and IIA fibres. Evidence for activation of type IIAX fibres was only found at 87% MVC.

  8. Muscle fatigue-induced enhancement of corticomuscular coherence following sustained submaximal isometric contraction of the tibialis anterior muscle.

    Science.gov (United States)

    Ushiyama, Junichi; Katsu, Masanori; Masakado, Yoshihisa; Kimura, Akio; Liu, Meigen; Ushiba, Junichi

    2011-05-01

    Oscillatory activity of the sensorimotor cortex shows coherence with muscle activity within the 15- to 35-Hz frequency band (β-band) during weak to moderate sustained isometric contraction. We aimed to examine the acute changes in this corticomuscular coupling due to muscle fatigue and its effect on the steadiness of the exerted force. We quantified the coherence between the electroencephalogram (EEG) recorded over the sensorimotor cortex and the rectified surface electromyogram (EMG) of the tibialis anterior muscle as well as the coefficient of variance of the dorsiflexion force (Force(CV)) and sum of the auto-power spectral density function of the force within the β-band (Force(β-PSD)) during 30% of maximal voluntary contraction (MVC) for 60 s before (prefatiguing task) and after (postfatiguing task) muscle fatigue induced by sustained isometric contraction at 50% of MVC until exhaustion in seven healthy male subjects. The magnitude of the EEG-EMG coherence increased in the postfatiguing task in six of seven subjects. The maximal peak of EEG-EMG coherence stayed within the β-band in both pre- and postfatiguing tasks. Interestingly, two subjects, who had no significant EEG-EMG coherence in the prefatiguing task, showed significant coherence in the postfatiguing task. Additionally, Force(CV) and Force(β-PSD) significantly increased after muscle fatigue. These data suggest that when muscle fatigue develops, the central nervous system enhances oscillatory muscular activity in the β-band stronger coupled with the sensorimotor cortex activity accomplishing the sustained isometric contraction at lower performance levels.

  9. Muscular force production during non-isometric contractions: Towards numerical muscle modeling

    OpenAIRE

    Kosterina, Natalia

    2009-01-01

    The main objective of the study was to investigate skeletal muscle force production during isometric contractions, active muscle stretches and shortenings. The motivation behind this work is to improve the dominant model of muscle contraction force generation based on the theories of Hill. The effect of force modification was observed after concentric and eccentric contractions and also stretch-shortening cycles. It has been shown that this force modification is not related to lengthening/sho...

  10. Shear modulus estimation on vastus intermedius of elderly and young females over the entire range of isometric contraction.

    Directory of Open Access Journals (Sweden)

    Cong-Zhi Wang

    Full Text Available Elderly people often suffer from sarcopenia in their lower extremities, which gives rise to the increased susceptibility of fall. Comparing the mechanical properties of the knee extensor/flexors on elderly and young subjects is helpful in understanding the underlying mechanisms of the muscle aging process. However, although the stiffness of skeletal muscle has been proved to be positively correlated to its non-fatiguing contraction intensity by some existing methods, this conclusion has not been verified above 50% maximum voluntary contraction (MVC due to the limitation of their measurement range. In this study, a vibro-ultrasound system was set up to achieve a considerably larger measurement range on muscle stiffness estimation. Its feasibility was verified on self-made silicone phantoms by comparing with the mechanical indentation method. The system was then used to assess the stiffness of vastus intermedius (VI, one of the knee extensors, on 10 healthy elderly female subjects (56.7 ± 4.9 yr and 10 healthy young female subjects (27.6 ± 5.0 yr. The VI stiffness in its action direction was confirmed to be positively correlated to the % MVC level (R2 = 0.999 over the entire range of isometric contraction, i.e. from 0% MVC (relaxed state to 100% MVC. Furthermore, it was shown that there was no significant difference between the mean VI shear modulus of the elderly and young subjects in a relaxed state (p > 0.1. However, when performing step isometric contraction, the VI stiffness of young female subjects was found to be larger than that of elderly participants (p < 0.001, especially at the relatively higher contraction levels. The results expanded our knowledge on the mechanical property of the elderly's skeletal muscle and its relationship with intensity of active contraction. Furthermore, the vibro-ultrasound system has a potential to become a powerful tool for investigating the elderly's muscle diseases.

  11. Neck Muscle EMG-Force Relationship and Its Reliability During Isometric Contractions.

    Science.gov (United States)

    Lo Martire, Riccardo; Gladh, Kristofer; Westman, Anton; Äng, Björn O

    2017-12-01

    Susceptible to injury, the neck is subject to scientific investigations, frequently aiming to elucidate possible injury mechanisms via surface electromyography (EMG) by indirectly estimating cervical loads. Accurate estimation requires that the EMG-force relationship is known and that its measurement error is quantified. Hence, this study examined the relationship between EMG and isometric force amplitude of the anterior neck (AN), the upper posterior neck (UPN), and the lower posterior neck (LPN) and then assessed the relationships' test-retest reliability across force-percentiles within and between days. EMG and force data were sampled from 18 participants conducting randomly ordered muscle contractions at 5-90% of maximal voluntary force during three trials over 2 days. EMG-force relationships were modeled with general linear mixed-effects regression. Overall fitted lines' between-trial discrepancies were evaluated. Finally, the reliability of participants' fitted regression lines was quantified by an intraclass correlation coefficient (ICC) and the standard error of measurement (SEM). A rectilinear model had the best fit for AN while positively oriented quadratic models had the best fit for UPN and LPN, with mean adjusted conditional coefficients of determination and root mean square errors of 0.97-0.98 and 4-5%, respectively. Overall EMG-force relationships displayed a maximum 6% between-trial discrepancy and over 20% of maximal force, and mean ICC was above 0.79 within day and 0.27-0.61 between days across areas. Corresponding SEM was below 12% both within and between days across areas, excluding UPN between days, for which SEM was higher. EMG-force relationships were elucidated for three neck areas, and provided models allow inferences to be drawn from EMG to force on a group level. Reliability of EMG-force relationship models was higher within than between days, but typically acceptable for all but the lowest contraction intensities, and enables adjustment

  12. Structural features of cross-bridges in isometrically contracting skeletal muscle.

    Science.gov (United States)

    Kraft, Theresia; Mattei, Thomas; Radocaj, Ante; Piep, Birgit; Nocula, Christoph; Furch, Markus; Brenner, Bernhard

    2002-05-01

    Two-dimensional x-ray diffraction was used to investigate structural features of cross-bridges that generate force in isometrically contracting skeletal muscle. Diffraction patterns were recorded from arrays of single, chemically skinned rabbit psoas muscle fibers during isometric force generation, under relaxation, and in rigor. In isometric contraction, a rather prominent intensification of the actin layer lines at 5.9 and 5.1 nm and of the first actin layer line at 37 nm was found compared with those under relaxing conditions. Surprisingly, during isometric contraction, the intensity profile of the 5.9-nm actin layer line was shifted toward the meridian, but the resulting intensity profile was different from that observed in rigor. We particularly addressed the question whether the differences seen between rigor and active contraction might be due to a rigor-like configuration of both myosin heads in the absence of nucleotide (rigor), whereas during active contraction only one head of each myosin molecule is in a rigor-like configuration and the second head is weakly bound. To investigate this question, we created different mixtures of weak binding myosin heads and rigor-like actomyosin complexes by titrating MgATPgammaS at saturating [Ca2+] into arrays of single muscle fibers. The resulting diffraction patterns were different in several respects from patterns recorded under isometric contraction, particularly in the intensity distribution along the 5.9-nm actin layer line. This result indicates that cross-bridges present during isometric force generation are not simply a mixture of weakly bound and single-headed rigor-like complexes but are rather distinctly different from the rigor-like cross-bridge. Experiments with myosin-S1 and truncated S1 (motor domain) support the idea that for a force generating cross-bridge, disorder due to elastic distortion might involve a larger part of the myosin head than for a nucleotide free, rigor cross-bridge.

  13. Co-Activity during Maximum Voluntary Contraction: A Study of Four Lower-Extremity Muscles in Children with and without Cerebral Palsy

    Science.gov (United States)

    Tedroff, Kristina; Knutson, Loretta M.; Soderberg, Gary L.

    2008-01-01

    This study was designed to determine whether children with cerebral palsy (CP) showed more co-activity than comparison children in non-prime mover muscles with regard to the prime mover during maximum voluntary isometric contraction (MVIC) of four lower-extremity muscles. Fourteen children with spastic diplegic CP (10 males, four females; age…

  14. Protective effect by maximal isometric contractions against maximal eccentric exercise-induced muscle damage of the knee extensors.

    Science.gov (United States)

    Tseng, Kuo-Wei; Tseng, Wei-Chin; Lin, Ming-Ju; Chen, Hsin-Lian; Nosaka, Kazunori; Chen, Trevor C

    2016-01-01

    This study investigated whether maximal voluntary isometric contractions (MVIC) performed before maximal eccentric contractions (MaxEC) would attenuate muscle damage of the knee extensors. Untrained men were placed to an experimental group that performed 6 sets of 10 MVIC at 90° knee flexion 2 weeks before 6 sets of 10 MaxEC or a control group that performed MaxEC only (n = 13/group). Changes in muscle damage markers were assessed before to 5 days after each exercise. Small but significant changes in maximal voluntary concentric contraction torque, range of motion (ROM) and plasma creatine kinase (CK) activity were evident at immediately to 2 days post-MVIC (p < 0.05), but other variables (e.g. thigh girth, myoglobin concentration, B-mode echo intensity) did not change significantly. Changes in all variables after MaxEC were smaller (p < 0.05) by 45% (soreness)-67% (CK) for the experimental than the control group. These results suggest that MVIC conferred potent protective effect against MaxEC-induced muscle damage.

  15. Synergists activation pattern of the quadriceps muscle differs when performing sustained isometric contractions with different EMG biofeedback.

    Science.gov (United States)

    Place, Nicolas; Matkowski, Boris; Martin, Alain; Lepers, Romuald

    2006-10-01

    The aims of the present study were to examine (1) endurance time and (2) activation pattern of vastus lateralis (VL), vastus medialis (VM) and rectus femoris (RF) muscles during fatiguing isometric knee extensions performed with different EMG biofeedbacks. Thirteen men (27 +/- 5 year) volunteered to participate in three experimental sessions. Each session involved a submaximal isometric contraction held until failure at an EMG level corresponding to 40% maximal voluntary contraction torque (MVC), with visual EMG biofeedback provided for either (1) RF muscle (RF task), (2) VL and VM muscles (Vasti task) or (3) the sum of the VL, VM and RF muscles (Quadriceps task). EMG activity of VL, VM and RF muscles was recorded during each of the three tasks and further analyzed. Time to task failures and MVC loss (P 0.05) between the three sessions (182 s and approximately 28%, respectively) (P > 0.05). Moreover, the magnitude of central and peripheral fatigue was not different at failure of the three tasks. Activation pattern was similar for knee extensors at the beginning of each task (P > 0.05). However, RF EMG activity decreased (P pattern for the bi-articular RF muscle compared to the mono-articular vasti muscles during fatigue.

  16. Motor unit firing behaviour of soleus muscle in isometric and dynamic contractions.

    Directory of Open Access Journals (Sweden)

    Jouni Kallio

    Full Text Available INTRODUCTION: Understanding the detailed control of human locomotion and balance can be improved, when individual motor units can be isolated and their firing rates followed in natural movement of large, fuctionally important muscles. For this reason the present study investigated the motor unit discharge rate (MUDR in isometric and dynamic contractions of the soleus muscle. METHODS: Eleven males performed isometric (10-100% MVC and dynamic (10-40% MVC plantar flexions. Intramuscular EMG was measured from Soleus with bipolar wire-electrodes and decomposed with custom built "Daisy" software. RESULTS: The Soleus MUDR was significantly higher in concentric compared to isometric or eccentric contractions at all submaximal force levels (P<0.05. In isometric contractions MUDR increased up to 100% MVC. CONCLUSION: Motor unit discharge properties of a large plantarflexor can be measured in dynamic and maximal contractions. For a given torque output, MUDR is dependent upon contraction type, as set by the major mechanical differences between concentric and eccentric actions.

  17. Shear Modulus Estimation on Vastus Intermedius of Elderly and Young Females over the Entire Range of Isometric Contraction

    Science.gov (United States)

    Wang, Cong-Zhi; Li, Tian-Jie; Zheng, Yong-Ping

    2014-01-01

    Elderly people often suffer from sarcopenia in their lower extremities, which gives rise to the increased susceptibility of fall. Comparing the mechanical properties of the knee extensor/flexors on elderly and young subjects is helpful in understanding the underlying mechanisms of the muscle aging process. However, although the stiffness of skeletal muscle has been proved to be positively correlated to its non-fatiguing contraction intensity by some existing methods, this conclusion has not been verified above 50% maximum voluntary contraction (MVC) due to the limitation of their measurement range. In this study, a vibro-ultrasound system was set up to achieve a considerably larger measurement range on muscle stiffness estimation. Its feasibility was verified on self-made silicone phantoms by comparing with the mechanical indentation method. The system was then used to assess the stiffness of vastus intermedius (VI), one of the knee extensors, on 10 healthy elderly female subjects (56.7±4.9 yr) and 10 healthy young female subjects (27.6±5.0 yr). The VI stiffness in its action direction was confirmed to be positively correlated to the % MVC level (R2 = 0.999) over the entire range of isometric contraction, i.e. from 0% MVC (relaxed state) to 100% MVC. Furthermore, it was shown that there was no significant difference between the mean VI shear modulus of the elderly and young subjects in a relaxed state (p>0.1). However, when performing step isometric contraction, the VI stiffness of young female subjects was found to be larger than that of elderly participants (pmuscle and its relationship with intensity of active contraction. Furthermore, the vibro-ultrasound system has a potential to become a powerful tool for investigating the elderly’s muscle diseases. PMID:24991890

  18. Effects of Contract-Relax, Static Stretching, and Isometric Contractions on Muscle-Tendon Mechanics.

    Science.gov (United States)

    Kay, Anthony D; Husbands-Beasley, Jade; Blazevich, Anthony J

    2015-10-01

    Loading characteristics of stretching techniques likely influence the specific mechanisms responsible for acute increases in range of motion (ROM). Therefore, the effects of a version of contract-relax (CR) proprioceptive neuromuscular facilitation stretching, static stretching (SS), and maximal isometric contraction (Iso) interventions were studied in 17 healthy human volunteers. Passive ankle moment was recorded on an isokinetic dynamometer, with EMG recording from the triceps surae, simultaneous real-time motion analysis, and ultrasound-imaging-recorded gastrocnemius medialis muscle and Achilles tendon elongation. Subjects then performed each intervention randomly on separate days before reassessment. Significant increases in dorsiflexion ROM (2.5°-5.3°; P stretching (P stretching and Iso (17.7%-22.1%; P 0.05), whereas significant reductions in muscle stiffness occurred after CR stretching and SS (16.0%-20.5%; P 0.05). Increases in peak passive moment (stretch tolerance) occurred after Iso (6.8%; P stretching (10.6%; P = 0.08), and SS (5.2%; P = 0.08); no difference in changes between conditions was found (P > 0.05). Significant correlations (rs = 0.69-0.82; P stretching suggest a broader adaptive response that likely explains its superior efficacy in acutely increasing ROM. Although mechanical changes appear tissue-specific between interventions, similar increases in stretch tolerance after all interventions are strongly correlated with changes in ROM.

  19. Short-interval cortical inhibition and intracortical facilitation during submaximal voluntary contractions changes with fatigue.

    Science.gov (United States)

    Hunter, Sandra K; McNeil, Chris J; Butler, Jane E; Gandevia, Simon C; Taylor, Janet L

    2016-09-01

    This study determined whether short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) change during a sustained submaximal isometric contraction. On 2 days, 12 participants (6 men, 6 women) performed brief (7-s) elbow flexor contractions before and after a 10-min fatiguing contraction; all contractions were performed at the level of integrated electromyographic activity (EMG) which produced 25 % maximal unfatigued torque. During the brief 7-s and 10-min submaximal contractions, single (test) and paired (conditioning-test) transcranial magnetic stimuli were applied over the motor cortex (5 s apart) to elicit motor-evoked potentials (MEPs) in biceps brachii. SICI and ICF were elicited on separate days, with a conditioning-test interstimulus interval of 2.5 and 15 ms, respectively. On both days, integrated EMG remained constant while torque fell during the sustained contraction by ~51.5 % from control contractions, perceived effort increased threefold, and MVC declined by 21-22 %. For SICI, the conditioned MEP during control contractions (74.1 ± 2.5 % of unconditioned MEP) increased (less inhibition) during the sustained contraction (last 2.5 min: 86.0 ± 5.1 %; P contractions at 2 min (82.0 ± 3.8 %; P contractions (conditioned MEP 129.7 ± 4.8 % of unconditioned MEP) decreased (less facilitation) during the sustained contraction (last 2.5 min: 107.6 ± 6.8 %; P contractions after 2 min of recovery. Both intracortical inhibitory and facilitatory circuits become less excitable with fatigue when assessed during voluntary activity, but their different time courses of recovery suggest different mechanisms for the fatigue-related changes of SICI and ICF.

  20. Functional connectivity between core and shoulder muscles increases during isometric endurance contractions in judo competitors.

    Science.gov (United States)

    Kawczyński, Adam; Samani, Afshin; Mroczek, Dariusz; Chmura, Paweł; Błach, Wiesław; Migasiewicz, Juliusz; Klich, Sebastian; Chmura, Jan; Madeleine, Pascal

    2015-06-01

    The aim of this study was to assess the surface electromyogram (SEMG) changes within and between muscles of the torso and shoulder region during static endurance contraction in elite judokas. We hypothesized an increased functional connectivity of muscles from the shoulder and torso regions during sustained isometric contraction. Twelve healthy, right-handed judo competitors participated in the study. The SEMG signals from the dominant trapezius (upper, middle and lower part), deltoideus anterior, serratus anterior, and pectoralis major muscles were recorded during isometric endurance contraction consisting of bilateral arm abduction at 90°. The normalized mutual information (NMI) was computed between muscle pairs as an index indicating functional connectivity. The NMIs increased significantly during endurance test for 10 of the 15 muscle pairs (P shoulder muscles during an endurance contraction in elite judokas.

  1. Effects of Isometric Hand-Grip Muscle Contraction on Young Adults' Free Recall and Recognition Memory

    Science.gov (United States)

    Tomporowski, Phillip D.; Albrecht, Chelesa; Pendleton, Daniel M.

    2017-01-01

    Purpose: The purpose of this study was to determine if physical arousal produced by isometric hand-dynamometer contraction performed during word-list learning affects young adults' free recall or recognition memory. Method: Twenty-four young adults (12 female; M[subscript age] = 22 years) were presented with 4 20-item word lists. Moderate arousal…

  2. Relationship Between Erectores Spinae Voltage and Back-Lift Strength for Isometric, Concentric, and Eccentric Contractions

    Science.gov (United States)

    Ashton, T. Edwin J.; Singh, Mohan

    1975-01-01

    This study determined the maximal mean values for concentric and eccentric back-lift strength as well as isometric, and examined and compared the relationships between the mean peak voltage of the erectores spinae muscle(s) and maximal force exerted for the three types of muscle contractions. (RC)

  3. Motor unit firing behaviour of soleus muscle in isometric and dynamic contractions

    DEFF Research Database (Denmark)

    Kallio, Jouni; Søgaard, Karen; Avela, Janne

    2013-01-01

    Understanding the detailed control of human locomotion and balance can be improved, when individual motor units can be isolated and their firing rates followed in natural movement of large, fuctionally important muscles. For this reason the present study investigated the motor unit discharge rate...... (MUDR) in isometric and dynamic contractions of the soleus muscle....

  4. Alterations in Neural Control of Constant Isometric Contraction with the Size of Error Feedback

    Science.gov (United States)

    Hwang, Ing-Shiou; Lin, Yen-Ting; Huang, Wei-Min; Yang, Zong-Ru; Hu, Chia-Ling; Chen, Yi-Ching

    2017-01-01

    Discharge patterns from a population of motor units (MUs) were estimated with multi-channel surface electromyogram and signal processing techniques to investigate parametric differences in low-frequency force fluctuations, MU discharges, and force-discharge relation during static force-tracking with varying sizes of execution error presented via visual feedback. Fourteen healthy adults produced isometric force at 10% of maximal voluntary contraction through index abduction under three visual conditions that scaled execution errors with different amplification factors. Error-augmentation feedback that used a high amplification factor (HAF) to potentiate visualized error size resulted in higher sample entropy, mean frequency, ratio of high-frequency components, and spectral dispersion of force fluctuations than those of error-reducing feedback using a low amplification factor (LAF). In the HAF condition, MUs with relatively high recruitment thresholds in the dorsal interosseous muscle exhibited a larger coefficient of variation for inter-spike intervals and a greater spectral peak of the pooled MU coherence at 13–35 Hz than did those in the LAF condition. Manipulation of the size of error feedback altered the force-discharge relation, which was characterized with non-linear approaches such as mutual information and cross sample entropy. The association of force fluctuations and global discharge trace decreased with increasing error amplification factor. Our findings provide direct neurophysiological evidence that favors motor training using error-augmentation feedback. Amplification of the visualized error size of visual feedback could enrich force gradation strategies during static force-tracking, pertaining to selective increases in the discharge variability of higher-threshold MUs that receive greater common oscillatory inputs in the β-band. PMID:28125658

  5. Electromyographic, cerebral and muscle hemodynamic responses during intermittent, isometric contractions of the biceps brachii at three submaximal intensities

    Directory of Open Access Journals (Sweden)

    Yagesh eBhambhani

    2014-06-01

    Full Text Available This study examined the electromyographic, cerebral and muscle hemodynamic responses during intermittent isometric contractions of biceps brachii at 20%, 40% and 60% of maximal voluntary contraction (MVC. Eleven volunteers completed two minutes of intermittent isometric contractions (12/min at an elbow angle of 90° interspersed with three minutes rest between intensities in systematic order. Surface electromyography (EMG was recorded from the right biceps brachii and near infrared spectroscopy (NIRS was used to simultaneously measure left prefrontal and right biceps brachii oxyhemoglobin (HbO2, deoxyhemoglobin (HHb and total hemoglobin (Hbtot. Transcranial Doppler ultrasound was used to measure middle cerebral artery velocity (MCAv bilaterally. Finger photoplethysmography was used to record beat-to-beat blood pressure and heart rate. EMG increased with force output from 20% to 60% MVC (P0.05. MCAv increased from rest to exercise but was not different among intensities (P>0.05. Force output correlated with the root mean square EMG and changes in muscle HbO2 (P0.05 at all three intensities. Force output declined by 8% from the 1st to the 24th contraction only at 60% MVC and was accompanied by systematic increases in RMS, cerebral HbO2 and Hbtot with a levelling off in muscle HbO2 and Hbtot. These changes were independent of alterations in mean arterial pressure. Since cerebral blood flow and oxygenation were elevated at 60% MVC, we attribute the development of fatigue to reduced muscle oxygen availability rather than impaired central n

  6. Illusion caused by vibration of muscle spindles reveals an involvement of muscle spindle inputs in regulating isometric contraction of masseter muscles.

    Science.gov (United States)

    Tsukiboshi, Taisuke; Sato, Hajime; Tanaka, Yuto; Saito, Mitsuru; Toyoda, Hiroki; Morimoto, Toshifumi; Türker, Kemal Sitki; Maeda, Yoshinobu; Kang, Youngnam

    2012-11-01

    Spindle Ia afferents may be differentially involved in voluntary isometric contraction, depending on the pattern of synaptic connections in spindle reflex pathways. We investigated how isometric contraction of masseter muscles is regulated through the activity of their muscle spindles that contain the largest number of intrafusal fibers among skeletal muscle spindles by examining the effects of vibration of muscle spindles on the voluntary isometric contraction. Subjects were instructed to hold the jaw at resting position by counteracting ramp loads applied on lower molar teeth. In response to the increasing-ramp load, the root mean square (RMS) of masseter EMG activity almost linearly increased under no vibration, while displaying a steep linear increase followed by a slower increase under vibration. The regression line of the relationship between the load and RMS was significantly steeper under vibration than under no vibration, suggesting that the subjects overestimated the ramp load and excessively counteracted it as reflected in the emergence of bite pressure. In response to the decreasing-ramp load applied following the increasing one, the RMS hardly decreased under vibration unlike under no vibration, leading to a generation of bite pressure even after the offset of the negative-ramp load until the vibration was ceased. Thus the subjects overestimated the increasing rate of the load while underestimating the decreasing rate of the load, due to the vibration-induced illusion of jaw opening. These observations suggest that spindle Ia/II inputs play crucial roles both in estimating the load and in controlling the isometric contraction of masseter muscles in the jaw-closed position.

  7. Effect of shoulder angle on the activation pattern of the elbow extensors during a submaximal isometric fatiguing contraction.

    Science.gov (United States)

    Davidson, Andrew W; Rice, Charles L

    2010-10-01

    The aim of this study was to examine the effect of shoulder angle on the electromyographic (EMG) activation pattern of the elbow extensors during a fatiguing contraction. Ten young men (23.5 ± 1.7) were tested on two occasions with the elbow angle at 90° and the shoulder at either 0° or 90° of flexion. EMG was recorded by fine wire electrodes inserted into the lateral, medial, and long heads of the triceps brachii and the anconeus. An EMG-torque relationship was determined prior to a sustained isometric contraction at 20% of maximum voluntary contraction (MVC) until target failure. Endurance time was shorter, and postfatigue MVC torque was lower at 90° (40.4 ± 12.7 Nm) versus 0° (47.9 ± 14.7 Nm) of flexion. EMG activity of the long head during the final 10% of the fatiguing contraction was significantly greater at 90° versus 0° with no effect of shoulder angle on any other muscle portions. The findings suggest that measures from one muscle portion of the elbow extensors are not representative of the whole group, and the relative activation of the two-joint long head was changed depending on shoulder angle during a fatigue task.

  8. Differences in activation patterns in elbow flexor muscles during isometric, concentric and eccentric contractions.

    Science.gov (United States)

    Nakazawa, K; Kawakami, Y; Fukunaga, T; Yano, H; Miyashita, M

    1993-01-01

    To investigate the relative activation of the synergistic muscles during three different types of muscle contraction, the electromyograms (EMG) of two elbow flexor muscles, the biceps brachii (BB) and the brachioradialis (BR), have been compared. To accomplish this eight healthy human subjects performed the following elbow flexions against the same load--concentric, eccentric and isometric contractions. The isometric contractions were performed at three elbow angles: 10, 45 and 90 degrees (0 degree equal to full extension). The EMG were recorded by bipolar surface electrodes, and the relative activation between the two muscles was evaluated as the quotient of mean EMG activities (BR/BB). For the isotonic elbow flexions, BR/BB were calculated at three angle divisions: 0-30 degrees, 30-60 degrees and 60-90 degrees. Results indicated that the relative activation of the BR during the concentric contractions was higher than that of the eccentric contraction, particularly at the extended elbow angles, i.e. the BR/BB of the concentric contractions for the elbow joint angles ranging from 0-30 degrees and 30-60 degrees were significantly greater (P contractions. During the isometric and eccentric contractions, the BR/BB at the flexed joint angles tended to be greater than those at the extended angles. In contrast, there were no angle-dependent BR/BB variations during the concentric elbow flexions. Further, changing patterns in the EMG power spectra due to the type of contraction were different between BB and BR. These results indicated that the activation pattern in the two elbow flexor muscles varied with the muscle contraction pattern.

  9. Does the Length of Elbow Flexors and Visual Feedback Have Effect on Accuracy of Isometric Muscle Contraction in Men after Stroke?

    Directory of Open Access Journals (Sweden)

    Vilma Juodzbaliene

    2016-01-01

    Full Text Available The aim of the study was to determine the effect of different muscle length and visual feedback information (VFI on accuracy of isometric contraction of elbow flexors in men after an ischemic stroke (IS. Materials and Methods. Maximum voluntary muscle contraction force (MVMCF and accurate determinate muscle force (20% of MVMCF developed during an isometric contraction of elbow flexors in 90° and 60° of elbow flexion were measured by an isokinetic dynamometer in healthy subjects (MH, n=20 and subjects after an IS during their postrehabilitation period (MS, n=20. Results. In order to evaluate the accuracy of the isometric contraction of the elbow flexors absolute errors were calculated. The absolute errors provided information about the difference between determinate and achieved muscle force. Conclusions. There is a tendency that greater absolute errors generating determinate force are made by MH and MS subjects in case of a greater elbow flexors length despite presence of VFI. Absolute errors also increase in both groups in case of a greater elbow flexors length without VFI. MS subjects make greater absolute errors generating determinate force without VFI in comparison with MH in shorter elbow flexors length.

  10. Stimulated contractions delay and prolong central fatigue compared with voluntary contractions in men.

    Science.gov (United States)

    Chaubet, Vincent; Cormery, Bruno; Maitre, Julien; Paillard, Thierry

    2013-05-01

    Voluntary and stimulated contractions are commonly used in sports training and rehabilitation, and it is well known that both these kinds of contractions generate central fatigue. However, to date, there is a lack of research on the comparison of the mechanisms by which these 2 exercises induce central disturbances. Central fatigue can be characterized by central activation failure during maximal voluntary contraction (MVC). Superimposition of an electrical stimulation onto MVC has been used to detect central activation failure. Completeness of activation has been quantified by the central activation ratio (CAR) = MVC/(MVC + stimulated force). The aim was not only to evaluate the CAR immediately after fatiguing voluntary (VOL) and stimulated (STIM) contractions but also to compare recovery duration over different time periods (prefatigue: PRE condition; immediate postfatigue: POST condition; after a 5-minute recovery: POST 5 condition; after a 30-minute recovery: POST 30 condition) (n = 18). Results showed that in the POST condition, the CAR is more affected for the VOL contractions than for the STIM contractions (p contractions only in the POST 5 condition (p contractions, whereas it was complete for the VOL contractions (p contractions alter the CAR more than the STIM contractions immediately after their completion. However, the effects of the STIM contractions on the CAR are delayed and prolonged.

  11. Haemodynamic changes in human masseter and temporalis muscles induced by different levels of isometric contraction.

    Science.gov (United States)

    Kim, Y J; Kuboki, T; Tsukiyama, Y; Koyano, K; Clark, G T

    1999-08-01

    This study evaluated the influence of low contraction forces on intramuscular haemodynamics in human masseter and temporalis using near-infrared tissue spectroscopy. This method allowed the intramuscular haemoglobin (Hb) to be assessed dynamically before, during and after a 5, 15, 25 and 100% maximum voluntary contraction (MVC). Twenty volunteers, 10 males and 10 females, without pain or dysfunction in the masticatory system were included in this study. Data were recorded for 30 s before, 30 s during and 5 min after the four sustained contraction tasks. The results showed that all four levels of voluntary contraction produced a clear haemodynamic response (during and after contraction) in both muscles. For analytical purposes, the maximum Hb achieved after 100% MVC was set equal to 1.00. In the masseter the mean peak Hb during the 5, 15, 25 and 100% MVC was 0.49, 0.92, 1.30 and 1.73 while after the contractions it was 0.50, 0.65, 0.78 and 1.00, respectively. In the temporalis the peak Hb during the contractions was 0.23, 0.36, 0.48 and 0.66 and after the contractions 0.32, 0.45, 0.56 and 1.00, respectively. Repeated-measures analysis of variance revealed a significant main effect for the different contraction levels both in the masseter (during contraction, p = 0.001; after contraction, parchitecture between the two muscles contributes to these differences in blood flow.

  12. Impact of Isometric Contraction of Anterior Cervical Muscles on Cervical Lordosis.

    Science.gov (United States)

    Fedorchuk, Curtis A; McCoy, Matthew; Lightstone, Douglas F; Bak, David A; Moser, Jacque; Kubricht, Brett; Packer, John; Walton, Dustin; Binongo, Jose

    2016-09-01

    This study investigates the impact of isometric contraction of anterior cervical muscles on cervical lordosis. 29 volunteers were randomly assigned to an anterior head translation (n=15) or anterior head flexion (n=14) group. Resting neutral lateral cervical x-rays were compared to x-rays of sustained isometric contraction of the anterior cervical muscles producing anterior head translation or anterior head flexion. Paired sample t-tests indicate no significant difference between pre and post anterior head translation or anterior head flexion. Analysis of variance suggests that gender and peak force were not associated with change in cervical lordosis. Chamberlain's to atlas plane line angle difference was significantly associated with cervical lordosis difference during anterior head translation (p=0.01). This study shows no evidence that hypertonicity, as seen in muscle spasms, of the muscles responsible for anterior head translation and anterior head flexion have a significant impact on cervical lordosis.

  13. Cadmium block of isometric contractions of isolated bullfrog atrial cells.

    Science.gov (United States)

    Shepherd, N; Kavaler, F; Spielman, W

    1991-02-01

    We studied the effect of cadmium, verapamil, and quinacrine on the force of contraction (Fp) of isolated, single, field-stimulated bullfrog atrial cells. All agents were applied or removed rapidly (t1/2 approximately 15 ms) to minimize intracellular concentration changes other than intracellular calcium concentration. Two components of twitch force were observed, one blocked by micromolar Cd2+ and the other by millimolar Cd2+. The two contributed about equally to the activation of the twitch. The "cadmium-sensitive" portion of force (that affected by [Cd] less than or equal to 100 microM) had a K1/2 approximately 1 microM, was identical in magnitude to, and not additive with, a "verapamil-sensitive" (10 microM) component of force, was most strongly affected by 50-ms pulses of Cd2+ when they were applied in the mechanical latent period, and was potentiated by catecholamines. The cadmium-insensitive portion of force was abolished by the removal of extracellular calcium and was greatly potentiated by quinacrine (3 or 10 microM), a blocker of Na-Ca exchange. The results are consistent with the idea that activating calcium enters the cell via both an inactivating cadmium-sensitive L-type channel and a noninactivating cadmium-insensitive mechanism that is not Na-Ca exchange and leaves the cell via Na-Ca exchange.

  14. Image Based Calculation of Perfusion and Oxyhemoglobin Saturation in Skeletal Muscle during Submaximal Isometric Contractions

    Science.gov (United States)

    Elder, Christopher P.; Cook, Ryan N.; Chance, Marti A.; Copenhaver, Elizabeth A.; Damon, Bruce M.

    2015-01-01

    The relative oxygen saturation of hemoglobin (%HbO2) and the rate of perfusion (θ̇) are important physiological quantities, particularly in organs such as skeletal muscle in which oxygen delivery and use are tightly coupled. The purpose of this study was to demonstrate the image-based calculation of %HbO2 and quantification of perfusion in skeletal muscle during isometric contractions. This was accomplished by establishing an empirical relationship between the rate of RF-reversible dephasing (R2′) and near infrared spectroscopy (NIRS)-observed oxyhemoglobin saturation (%HbO2) under conditions of arterial occlusion and constant blood volume. A calibration curve was generated and used to calculate %HbO2 from R2′ changes measured during contraction. Twelve young healthy subjects underwent 300 seconds of arterial occlusion and performed isometric contractions of the dorsiflexors at 30% of maximal contraction for 120s. Muscle perfusion was quantified during contraction by arterial spin labeling and measures of muscle T1. Comparisons between the %HbO2 values predicted from R2′ and that measured by NIRS revealed no differences between methods (p = 0.760). Muscle perfusion reached a value of 34.7 mL 100g−1 min−1 during contraction. These measurements hold future promise in measuring muscle oxygen consumption in healthy and diseased skeletal muscle. PMID:20806379

  15. Effect of red bull energy drink on auditory reaction time and maximal voluntary contraction.

    Science.gov (United States)

    Goel, Vartika; Manjunatha, S; Pai, Kirtana M

    2014-01-01

    The use of "Energy Drinks" (ED) is increasing in India. Students specially use these drinks to rejuvenate after strenuous exercises or as a stimulant during exam times. The most common ingredient in EDs is caffeine and a popular ED available and commonly used is Red Bull, containing 80 mg of caffeine in 250 ml bottle. The primary aim of this study was to investigate the effects of Red Bull energy drink on Auditory reaction time and Maximal voluntary contraction. A homogeneous group containing twenty medical students (10 males, 10 females) participated in a crossover study in which they were randomized to supplement with Red Bull (2 mg/kg body weight of caffeine) or isoenergetic isovolumetric noncaffeinated control drink (a combination of Appy Fizz, Cranberry juice and soda) separated by 7 days. Maximal voluntary contraction (MVC) was recorded as the highest of the 3 values of maximal isometric force generated from the dominant hand using hand grip dynamometer (Biopac systems). Auditory reaction time (ART) was the average of 10 values of the time interval between the click sound and response by pressing the push button using hand held switch (Biopac systems). The energy and control drinks after one hour of consumption significantly reduced the Auditory reaction time in males (ED 232 ± 59 Vs 204 ± 34 s and Control 223 ± 57 Vs 210 ± 51 s; p caffeine in the beneficial effect seen after the drinks.

  16. Efeitos na medida do ângulo Q com a contração isométrica voluntária máxima do músculo quadricipital Efectos en la medida del ángulo Q con la contracción isométrica voluntária máxima del musculo cuadricipital Effects in the Q angle measurement with maximal voluntary isometric contraction of the quadriceps muscle

    Directory of Open Access Journals (Sweden)

    A.C.G. Belchior

    2006-02-01

    examination situations, having the quadriceps relaxed and in a maximal voluntary isometric contraction (MVIC through radiographic measurement, aiming to contribute to the assessment and treatment of patients with patelofemoral disorder (PFD. Through the standard radiological method twenty 21 years old mean women (40 knees were assessed. All individuals were positioned supine using a U-podalic stabilizer, having their lower limbs relaxed, using a plumb film on the anterior tuberosity of the tibia. For the statistical analysis, the averages for the asymptomatic and symptomatic groups in a relaxed and MVIC status, as well as the Student's t-test with p < 0.05 significance level were used. The mean values to the Q angle compared to the asymptomatic group were 17.15º on relaxation, and 14.5º on MVIC, while the asymptomatic group presented 21.45º, and 15.8º, respectively. The results in the equality analysis between the symptomatic and asymptomatic groups on the relaxed status attained a p = 0.004, and to the maximal voluntary isometric contraction, p = 0.29. Considering the data attained in the present study, it can be verified that in a relaxing status, there is a difference between the value of the Q angle among symptomatic and asymptomatic individuals, being found a higher value in the FPD bearers, while in a maximal isometric contraction of the quadriceps muscle no statistical difference was found in the present study, with a reduction in the angle in both groups.

  17. Differences in cervical multifidus muscle thickness during isometric contraction of shoulder muscles: a comparison between patients with chronic neck pain and healthy controls.

    Science.gov (United States)

    Rahnama, Leila; Rezasoltani, Asghar; Zavieh, Minoo Khalkhali; NooriKochi, Farhang; Baghban, Alireza Akbarzadeh

    2015-01-01

    The purposes of this study were to (1) measure the thickness of cervical multifidus muscle (CMM) in different maximal voluntary contraction percentages of isometric contraction of shoulder muscles, (2) evaluate the differences of the CMM thickness in different directions of the shoulder movement, and (3) compare the changes in the CMM thickness of participants with neck pain and also of healthy individuals. Twenty healthy men (age, 27.45 ± 4.37 years; height, 177 ± 4.66 cm; weight, 72.85 ± 6.46 kg) and 20 men with chronic mechanical neck pain (age, 28.90 ± 5.53 years; height, 176 ± 5.98 cm; weight, 73.15 ± 7.82 kg) participated in the study. Both the right and left CMM thicknesses were measured using an ultrasound device while participants performed isometric contraction of shoulder muscles in 6 movement directions. In both groups, an increment of CMM thickness followed as the increase of isometric force (P muscle thickness of healthy participants was substantially more than the chronic mechanical neck pain participants (P = .03). Although no significant difference of CMM thickness was seen among the effects of the 6 force directions (P > .05), there was a significant difference of activity noted between the left and right sides (P = .047). The results of the present study indicate that isometric contraction of shoulder muscles caused an increase in the CMM thickness regardless of force direction. This increase was seen in both groups of healthy participants and patients with neck pain. However, less thickness changes were observed in participants with neck pain, which may be interpreted as reduced CMM activity in such people. Copyright © 2015 National University of Health Sciences. Published by Elsevier Inc. All rights reserved.

  18. Muscle oxygenation of superficial and deep regions in knee extensor and plantar flexor muscles during repeated isometric contractions.

    Science.gov (United States)

    Kubo, K

    2015-04-01

    The purpose of this study was to investigate changes in muscle oxygenation of knee extensor and plantar flexor muscles during repeated muscle contractions under the same condition. In addition, we compared changes in muscle oxygenation between superficial and deep regions of both muscles. Eleven healthy males participated in this study. During repeated knee extensions and plantar flexions (50 repetitions at 50% of the isometric maximum voluntary contraction for 3 s with 3 s relaxations), blood volume and oxygen saturation (StO₂) of the vastus lateralis and medial gastrocnemius muscles (superficial and deep region of each muscle) were measured using near infrared spectroscopy. The decrement of StO₂at the end of exercises was greater in plantar flexor muscle than in knee extensor muscle (Pmuscles, the decrement of StO₂at the end of exercises was greater in the deep region than in the superficial one (both Pmuscle and deep regions of each muscle were higher than that of knee extensor muscle and superficial regions of each muscle.

  19. LONG-LASTING SUPERNORMAL CONDUCTION-VELOCITY AFTER SUSTAINED MAXIMAL ISOMETRIC CONTRACTION IN HUMAN MUSCLE

    NARCIS (Netherlands)

    VANDERHOEVEN, JH; VANWEERDEN, TW; ZWARTS, MJ

    1993-01-01

    Local muscle fatigue (1 min maximal voluntary contraction) and recovery were studied by means of surface and invasive EMG on elbow flexors to record the changes in muscle fiber conduction velocity (MFCV), median power frequency (MPF), integrated EMG (IEMG), and force. The main finding was a long-las

  20. LONG-LASTING SUPERNORMAL CONDUCTION-VELOCITY AFTER SUSTAINED MAXIMAL ISOMETRIC CONTRACTION IN HUMAN MUSCLE

    NARCIS (Netherlands)

    VANDERHOEVEN, JH; VANWEERDEN, TW; ZWARTS, MJ

    1993-01-01

    Local muscle fatigue (1 min maximal voluntary contraction) and recovery were studied by means of surface and invasive EMG on elbow flexors to record the changes in muscle fiber conduction velocity (MFCV), median power frequency (MPF), integrated EMG (IEMG), and force. The main finding was a long-las

  1. Three-dimensional geometrical changes of the human tibialis anterior muscle and its central aponeurosis measured with three-dimensional ultrasound during isometric contractions.

    Science.gov (United States)

    Raiteri, Brent J; Cresswell, Andrew G; Lichtwark, Glen A

    2016-01-01

    Background. Muscles not only shorten during contraction to perform mechanical work, but they also bulge radially because of the isovolumetric constraint on muscle fibres. Muscle bulging may have important implications for muscle performance, however quantifying three-dimensional (3D) muscle shape changes in human muscle is problematic because of difficulties with sustaining contractions for the duration of an in vivo scan. Although two-dimensional ultrasound imaging is useful for measuring local muscle deformations, assumptions must be made about global muscle shape changes, which could lead to errors in fully understanding the mechanical behaviour of muscle and its surrounding connective tissues, such as aponeurosis. Therefore, the aims of this investigation were (a) to determine the intra-session reliability of a novel 3D ultrasound (3DUS) imaging method for measuring in vivo human muscle and aponeurosis deformations and (b) to examine how contraction intensity influences in vivo human muscle and aponeurosis strains during isometric contractions. Methods. Participants (n = 12) were seated in a reclined position with their left knee extended and ankle at 90° and performed isometric dorsiflexion contractions up to 50% of maximal voluntary contraction. 3DUS scans of the tibialis anterior (TA) muscle belly were performed during the contractions and at rest to assess muscle volume, muscle length, muscle cross-sectional area, muscle thickness and width, fascicle length and pennation angle, and central aponeurosis width and length. The 3DUS scan involved synchronous B-mode ultrasound imaging and 3D motion capture of the position and orientation of the ultrasound transducer, while successive cross-sectional slices were captured by sweeping the transducer along the muscle. Results. 3DUS was shown to be highly reliable across measures of muscle volume, muscle length, fascicle length and central aponeurosis length (ICC ≥ 0.98, CV contraction conditions and progressively

  2. Mechanomyographic responses during voluntary ramp contractions of the human first dorsal interosseous muscle.

    Science.gov (United States)

    Akataki, Kumi; Mita, Katsumi; Watakabe, Makoto; Itoh, Kunihiko

    2003-08-01

    The aim of this study was to examine the mechanomyogram (MMG) and force relationship of the first dorsal interosseous (FDI) muscle as well as the biceps brachii (BB) muscle during voluntary isometric ramp contractions, and to elucidate the MMG responses resulting from the intrinsic motor unit (MU) activation strategy of FDI muscle with reference to the MMG of BB muscle. The subjects were asked to exert ramp contractions of FDI and BB muscle from 5% to 70% of the maximal voluntary contraction (MVC) at a constant rate of 10% MVC/s. In FDI muscle, the root-mean-squared amplitude (RMS) of the MMG decreased slowly with force up to 21%, and then a progressive increase was followed by a relatively rapid decrease beyond 41% MVC. The RMS/%MVC relationship in BB muscle consisted of an initial slow increase followed by a rapid increase from 23% MVC and a progressive decrease beyond 61% MVC. With respect to the mean power frequency (MPF), FDI muscle demonstrated no obvious inflection point in the MPF/%MVC relationship compared with that in BB muscle. Namely, the MPF of FDI muscle increased linearly through the force levels exerted. In contrast to FDI muscle, the MPF/%MVC relationship in BB muscle was decomposed into four specific regions: (1) a relative rapidly increase (62% MVC). The different MMG responses between FDI and BB muscles are considered to reflect the fact that the MU activation strategy varies among different muscles in relation to their morphology and histochemical type. Namely, the rate coding of the MUs plays a more prominent role in force production in relatively small FDI muscle than does MU recruitment compared with their respective roles in the relatively large BB muscle.

  3. The effect of temperature on eccentric contraction-induced isometric force loss in isolated perfused rat medial gastrocnemius muscle

    Directory of Open Access Journals (Sweden)

    Vasaghi Gharamaleki B

    2008-09-01

    Full Text Available "nBackground: The typical features of eccentric exercise-induced muscle damage are delayed-onset muscle soreness (DOMS and prolonged loss of muscle strength. It has been shown that passive warmth is effective in reducing muscle injury. Due to the interaction of different systems in vivo, we used isolated perfused medial gastrocnemius skeletal muscle to study the direct effect of temperature on the eccentric contraction-induced force loss. "nMethods: After femoral artery cannulation of a rat, the left medial gastrocnemius muscle was separated and then the entire lower limb was transferred into a prewarmed (35oC chamber. With the chamber temperature at 31, 35 and 39oC before and during eccentric contraction. Isometric force loss was measured after 15 eccentric contractions (N=7-9. "nResults: Maximum contraction force reduction has been used as an index for eccentric contraction-induced force loss. In this study eccentric contraction caused a significant reduction in maximum isometric tension (p<0.01, but no significant difference was seen in isometric force loss at 31oC and 39oC compared with that at 35oC. "nConclusions: Our results suggest that temperature changes before or during eccentric contractions have no effect on eccentric contraction-induced force loss. "nKeywords: Isolated perfused muscle, skeletal muscle, eccentric contractions, isometric force, gastrocnemius muscle, temperature.

  4. Individual finger contribution in submaximal voluntary contraction of gripping.

    Science.gov (United States)

    Kong, Yong-Ku; Lee, Kyung-Sun; Kim, Dae-Min; Jung, Myung-Chul

    2011-11-01

    The objective of this study was to evaluate individual finger force and contribution to a gripping force, the difference between actual and expected finger forces and subjective discomfort rating at 10 different submaximal voluntary contraction (%MVC) levels (10-100% in 10 increments). Seventy-two participants randomly exerted gripping force with a multi-finger force measurement system. The individual finger force, gripping force and discomfort increased as %MVC levels increased. The middle and ring fingers exerted more force and contributed to a gripping force more than the index and little fingers due to their larger mass fractions of the digit flexor muscles. It was apparent at MVC; however, the index finger increased its contribution and exerted even more force than expected at more than 50% MVC. Subjective discomfort supported the results of the objective measures. This could explain the conflicting findings between index and ring fingers in previous finger contribution studies. STATEMENT OF RELEVANCE: Hand tool design is of special interest in ergonomics due to its association with musculoskeletal disorders in the hand. This study reveals a different contribution pattern of the fingers in submaximal voluntary contraction of gripping exertion.

  5. Combined application of neuromuscular electrical stimulation and voluntary muscular contractions.

    Science.gov (United States)

    Paillard, Thierry

    2008-01-01

    Electromyostimulation (EMS) and voluntary muscle contraction (VC) constitute different modes of muscle activation and induce different acute physiological effects on the neuromuscular system. Long-term application of each mode of muscle activation can produce different muscle adaptations. It seems theoretically possible to completely or partially cumulate the muscle adaptations induced by each mode of muscle activation applied separately. This work consisted of examining the literature concerning the muscle adaptations induced by long-term application of the combined technique (CT) [i.e. EMS is combined with VC - non-simultaneously] compared with VC and/or EMS alone in healthy subjects and/or athletes and in post-operative knee-injured subjects. In general, CT induced greater muscular adaptations than VC whether in sports training or rehabilitation. This efficiency would be due to the fact that CT can facilitate cumulative effects of training completely or partially induced by VC and EMS practiced alone. CT also provides a greater improvement of the performance of complex dynamic movements than VC. However, EMS cannot improve coordination between different agonistic and antagonistic muscles and thus does not facilitate learning the specific coordination of complex movements. Hence, EMS should be combined with specific sport training to generate neuromuscular adaptations, but also allow the adjustment of motor control during a voluntary movement. Likewise, in a therapeutic context, CT was particularly efficient to accelerate recovery of muscle contractility during a rehabilitation programme. Strength loss and atrophy inherent in a traumatism and/or a surgical operation would be more efficiently compensated with CT than with VC. Furthermore, CT also restored more functional abilities than VC. Finally, in a rehabilitation context, EMS is complementary to voluntary exercise because in the early phase of rehabilitation it elicits a strength increase, which is necessary

  6. Predicting blood flow responses to rhythmic handgrip exercise from one second isometric contractions.

    Science.gov (United States)

    Cook, M; Smart, N A; Van der Touw, T

    2016-11-08

    The aim of this work was to predict blood flow responses to rhythmic handgrip exercise from one second isometric contractions. Seven healthy men were studied. Each subject performed a single 1 s handgrip contraction at 10 %, 20 % and 40 % of the maximum handgrip strength. We then repeatedly summed hyperaemic responses from single contractions to predict hyperaemic response to a prolonged bout of rhythmic exercise. There was similarity between steady state brachial blood flow velocity (BBV) extrapolated from single handgrip contractions and during 2 min of rhythmic exercise for 20 % (10.0+/-3.8 cm/s vs. 10.2+/-2.6 cm/s, r=0.93, p=0.003) and 40 % of maximum contractions (14.2+/-5.5 cm/s vs. 15.6+/-3.4 cm/s, r=0.88, p=0.009), but not for 10 % (7.5+/-4.1 cm/s vs. 5.7+/-3.3 cm/s, r=0.94, p=0.018). BBV progressively rose substantially higher during rhythmic contractions than peak BBV observed during single contractions at matched intensity. Respective peak BBV during single contractions and steady state BBV rhythmic contractions were 4.4+/-2.1 and 5.7+/-3.3 cm.s(-1) at 10 % forearm strength (p=0.14), 5.6+/-2.4 and 10.2+/-2.8 cm.s(-1) at 20 % (p=0.002), and 7.0+/-2.5 and 15.6+/-3.6 cm.s(-1) at 40 % (p=0.003). In conclusion, there is similarity between the summated blood flow velocity calculated from a single 1 s muscle contraction and the steady state blood flow velocity response of rhythmic exercise.

  7. Real-time changes in corticospinal excitability during voluntary contraction with concurrent electrical stimulation.

    Directory of Open Access Journals (Sweden)

    Tomofumi Yamaguchi

    Full Text Available While previous studies have assessed changes in corticospinal excitability following voluntary contraction coupled with electrical stimulation (ES, we sought to examine, for the first time in the field, real-time changes in corticospinal excitability. We monitored motor evoked potentials (MEPs elicited by transcranial magnetic stimulation and recorded the MEPs using a mechanomyogram, which is less susceptible to electrical artifacts. We assessed the MEPs at each level of muscle contraction of wrist flexion (0%, 5%, or 20% of maximum voluntary contraction during voluntary wrist flexion (flexor carpi radialis (FCR voluntary contraction, either with or without simultaneous low-frequency (10 Hz ES of the median nerve that innervates the FCR. The stimulus intensity corresponded to 1.2 × perception threshold. In the FCR, voluntary contraction with median nerve stimulation significantly increased corticospinal excitability compared with FCR voluntary contraction without median nerve stimulation (p<0.01. In addition, corticospinal excitability was significantly modulated by the level of FCR voluntary contraction. In contrast, in the extensor carpi radialis (ECR, FCR voluntary contraction with median nerve stimulation significantly decreased corticospinal excitability compared with FCR voluntary contraction without median nerve stimulation (p<0.05. Thus, median nerve stimulation during FCR voluntary contraction induces reciprocal changes in cortical excitability in agonist and antagonist muscles. Finally we also showed that even mental imagery of FCR voluntary contraction with median nerve stimulation induced the same reciprocal changes in cortical excitability in agonist and antagonist muscles. Our results support the use of voluntary contraction coupled with ES in neurorehabilitation therapy for patients.

  8. Characteristics of fast voluntary and electrically evoked isometric knee extensions during 56 days of bed rest with and without exercise countermeasure.

    NARCIS (Netherlands)

    Mulder, E.R.; Gerrits, K.H.; Rittweger, J.; Felsenberg, D.; Stegeman, D.F.; Haan, A. de

    2008-01-01

    The contractile characteristics of fast voluntary and electrically evoked unilateral isometric knee extensions were followed in 16 healthy men during 56 days of horizontal bed rest and assessed at bed rest days 4, 7, 10, 17, 24, 38 and 56. Subjects were randomized to either an inactive control group

  9. Quantifying thigh muscle co-activation during isometric knee extension contractions: within- and between-session reliability.

    Science.gov (United States)

    Katsavelis, Dimitrios; Threlkeld, A Joseph

    2014-08-01

    Muscle co-activation around the knee is important during ambulation and balance. The wide range of methodological approaches for the quantification of co-activation index (CI) makes comparisons across studies and populations difficult. The present study determined within- and between-session reliability of different methodological approaches for the quantification of the CI of the knee extensor and flexor muscles during maximum voluntary isometric contractions (MVICs). Eight healthy volunteers participated in two repeated testing sessions. A series of knee extension MVICs of the dominant leg with concomitant torque and electromyographic (EMG) recordings were captured. CI was calculated utilizing different analytical approaches. Intraclass correlation coefficient (ICC) showed that within-session measures displayed higher reliability (ICC>0.861) and lower variability (Coefficient of variation; CV24.2%). A selection of a 500ms or larger window of RMS EMG activity around the PT delivered more reliable and less variable results than other approaches. Our findings suggest that the CI can provide a reliable measure for comparisons among conditions and is best utilized for within-session experimental designs.

  10. Less indication of muscle damage in the second than initial electrical muscle stimulation bout consisting of isometric contractions of the knee extensors.

    Science.gov (United States)

    Aldayel, Abdulaziz; Jubeau, Marc; McGuigan, Michael R; Nosaka, Kazunori

    2010-03-01

    This study compared the first and second exercise bouts consisting of electrically evoked isometric contractions for muscle damage profile. Nine healthy men (31 +/- 4 years) had two electrical muscle stimulation (EMS) bouts separated by 2 weeks. The knee extensors of one leg were stimulated by biphasic rectangular pulses (75 Hz, 400 mus, on-off ratio 5-15 s) at the knee joint angle of 100 degrees (0 degrees , full extension) to induce 40 isometric contractions, while the current amplitude was increased to maintain maximal force generation. Maximal voluntary isometric contraction (MVC) torque of the knee extensors at 100 degrees , muscle soreness, pressure pain threshold and plasma creatine kinase (CK) activity were used as indirect markers of muscle damage, and measured before and 1, 24, 48, 72 and 96 h after EMS bout, and the changes over time were compared between bouts. The torque produced during exercise was approximately 30% of MVC, and no significant difference between bouts was evident for the changes in peak and average torque over 40 contractions. MVC decreased significantly (P < 0.05) by 26% immediately and 1 h after both bouts, but the recovery was significantly (P < 0.05) faster after the second bout (100% at 96 h) compared with the first bout (81% at 96 h). Development of muscle soreness and tenderness, and increases in plasma CK activity were significantly (P < 0.05) smaller after the second than the first bout. These results show that changes in muscle damage markers were attenuated in the second EMS bout compared with the initial EMS bout.

  11. Sustained maximal voluntary contraction produces independent changes in human motor axons and the muscle they innervate.

    Directory of Open Access Journals (Sweden)

    David A Milder

    Full Text Available The repetitive discharges required to produce a sustained muscle contraction results in activity-dependent hyperpolarization of the motor axons and a reduction in the force-generating capacity of the muscle. We investigated the relationship between these changes in the adductor pollicis muscle and the motor axons of its ulnar nerve supply, and the reproducibility of these changes. Ten subjects performed a 1-min maximal voluntary contraction. Activity-dependent changes in axonal excitability were measured using threshold tracking with electrical stimulation at the wrist; changes in the muscle were assessed as evoked and voluntary electromyography (EMG and isometric force. Separate components of axonal excitability and muscle properties were tested at 5 min intervals after the sustained contraction in 5 separate sessions. The current threshold required to produce the target muscle action potential increased immediately after the contraction by 14.8% (p<0.05, reflecting decreased axonal excitability secondary to hyperpolarization. This was not correlated with the decline in amplitude of muscle force or evoked EMG. A late reversal in threshold current after the initial recovery from hyperpolarization peaked at -5.9% at ∼35 min (p<0.05. This pattern was mirrored by other indices of axonal excitability revealing a previously unreported depolarization of motor axons in the late recovery period. Measures of axonal excitability were relatively stable at rest but less so after sustained activity. The coefficient of variation (CoV for threshold current increase was higher after activity (CoV 0.54, p<0.05 whereas changes in voluntary (CoV 0.12 and evoked twitch (CoV 0.15 force were relatively stable. These results demonstrate that activity-dependent changes in motor axon excitability are unlikely to contribute to concomitant changes in the muscle after sustained activity in healthy people. The variability in axonal excitability after sustained activity

  12. Removal of visual feedback alters muscle activity and reduces force variability during constant isometric contractions.

    Science.gov (United States)

    Baweja, Harsimran S; Patel, Bhavini K; Martinkewiz, Julie D; Vu, Julie; Christou, Evangelos A

    2009-07-01

    The purpose of this study was to compare force accuracy, force variability and muscle activity during constant isometric contractions at different force levels with and without visual feedback and at different feedback gains. In experiment 1, subjects were instructed to accurately match the target force at 2, 15, 30, 50, and 70% of their maximal isometric force with abduction of the index finger and maintain their force even in the absence of visual feedback. Each trial lasted 22 s and visual feedback was removed from 8-12 to 16-20 s. Each subject performed 6 trials at each target force, half with visual gain of 51.2 pixels/N and the rest with a visual gain of 12.8 pixels/N. Force error was calculated as the root mean square error of the force trace from the target line. Force variability was quantified as the standard deviation and coefficient of variation (CVF) of the force trace. The EMG activity of the agonist (first dorsal interosseus; FDI) was measured with bipolar surface electrodes placed distal to the innervation zone. Independent of visual gain and force level, subjects exhibited lower force error with the visual feedback condition (2.53 +/- 2.95 vs. 2.71 +/- 2.97 N; P feedback was removed (CVF: 4.06 +/- 3.11 vs. 4.47 +/- 3.14, P feedback condition and this difference increased especially at higher force levels (70%: 370 +/- 149 vs. 350 +/- 143 microV, P feedback. Subjects performed constant isometric contractions with the abduction of the index finger at an absolute force of 2 N, with two distinct feedback gains of 15 and 3,000 pixels/N. In agreement with the findings of experiment 1, subjects exhibited lower force error in the presence of visual feedback especially when the feedback gain was high (0.057 +/- 0.03 vs. 0.095 +/- 0.05 N). However, force variability was not affected by the vastly distinct feedback gains at this force, which supported and extended the findings from experiment 1. Our findings demonstrate that although removal of visual

  13. Depression of corticomotor excitability after muscle fatigue induced by electrical stimulation and voluntary contraction

    Directory of Open Access Journals (Sweden)

    Shinichi eKotan

    2015-06-01

    Full Text Available In this study, we examined the effect of muscle fatigue induced by tetanic electrical stimulation (ES and submaximal isometric contraction on corticomotor excitability. Experiments were performed in a cross-over design. Motor-evoked potentials (MEPs were elicited by transcranial magnetic stimulation. Corticomotor excitability was recorded before and after thumb opposition muscle fatigue tasks, in which 10% of the maximal tension intensity was induced by tetanic ES or voluntary contraction (VC. The participants were 10 healthy individuals who performed each task for 10 min. Surface electrodes placed over the abductor pollicis brevis (APB muscle recorded MEPs. F- and M-waves were elicited from APB by supramaximal ES of the median nerve. After the ES1-and VC tasks, MEP amplitudes were significantly lower than before the task. However, F-and M-wave amplitudes remained unchanged. These findings suggest that corticospinal excitability is reduced by muscle fatigue as a result of intracortical inhibitory mechanisms. Our results also suggest that corticomotor excitability is reduced by muscle fatigue caused by both VC and tetanic ES.

  14. Cortical and spinal excitability during and after lengthening contractions of the human plantar flexor muscles performed with maximal voluntary effort.

    Directory of Open Access Journals (Sweden)

    Daniel Hahn

    Full Text Available This study was designed to investigate the sites of potential specific modulations in the neural control of lengthening and subsequent isometric maximal voluntary contractions (MVCs versus purely isometric MVCs of the plantar flexor muscles, when there is enhanced torque during and following stretch. Ankle joint torque during maximum voluntary plantar flexion was measured by a dynamometer when subjects (n = 10 lay prone on a bench with the right ankle tightly strapped to a foot-plate. Neural control was analysed by comparing soleus motor responses to electrical nerve stimulation (M-wave, V-wave, electrical stimulation of the cervicomedullary junction (CMEP and transcranial magnetic stimulation of the motor cortex (MEP. Enhanced torque of 17 ± 8% and 9 ± 8% was found during and 2.5-3 s after lengthening MVCs, respectively. Cortical and spinal responsiveness was similar to that in isometric conditions during the lengthening MVCs, as shown by unchanged MEPs, CMEPs and V-waves, suggesting that the major voluntary motor pathways are not subject to substantial inhibition. Following the lengthening MVCs, enhanced torque was accompanied by larger MEPs (p ≤ 0.05 and a trend to greater V-waves (p ≤ 0.1. In combination with stable CMEPs, increased MEPs suggest an increase in cortical excitability, and enlarged V-waves indicate greater motoneuronal output or increased stretch reflex excitability. The new results illustrate that neuromotor pathways are altered after lengthening MVCs suggesting that the underlying mechanisms of the enhanced torque are not purely mechanical in nature.

  15. sEMG Feature Analysis on Forearm Muscle Fatigue During Isometric Contractions

    Institute of Scientific and Technical Information of China (English)

    明东; 王欣; 徐瑞; 邱爽; 赵欣; 綦宏志; 周鹏; 张力新; 万柏坤

    2014-01-01

    In order to detect and assess the muscle fatigue state with the surface electromyography (sEMG) character-istic parameters, this paper carried out a series of isometric contraction experiments to induce the fatigue on the fore-arm muscles from four subjects, and recorded the sEMG signals of the flexor carpi ulnaris. sEMG's median frequency (MDF) and mean frequency (MF) were extracted by short term Fourier transform (STFT), and the root mean square (RMS) of wavelet coefficients in the frequency band of 5-45 Hz was obtained by continuous wavelet transform (CWT). The results demonstrate that both MDF and MF show downward trends within 1 min;however, RMS shows an upward trend within the same time. The three parameters are closely correlated with absolute values of mean corre-lation coefficients greater than 0.8. It is suggested that the three parameters above can be used as reliable indicators to evaluate the level of muscle fatigue during isometric contractions.

  16. Local Muscle Metabolic Demand Induced by Neuromuscular Electrical Stimulation and Voluntary Contractions at Different Force Levels: A NIRS Study.

    Science.gov (United States)

    Muthalib, Makii; Kerr, Graham; Nosaka, Kazunori; Perrey, Stephane

    2016-06-13

    Functional Muscle metabolic demand during contractions evoked by neuromuscular electrical stimulation (NMES) has been consistently documented to be greater than voluntary contractions (VOL) at the same force level (10-50% maximal voluntary contraction-MVC). However, we have shown using a near-infrared spectroscopy (NIRS) technique that local muscle metabolic demand is similar between NMES and VOL performed at MVC levels, thus controversy exists. This study therefore compared biceps brachii muscle metabolic demand (tissue oxygenation index-TOI and total hemoglobin volume-tHb) during a 10s isometric contraction of the elbow flexors between NMES (stimulation frequency of 30Hz and current level to evoke 30% MVC) and VOL at 30% MVC (VOL-30%MVC) and MVC (VOL-MVC) level in 8 healthy men (23-33-y). Greater changes in TOI and tHb induced by NMES than VOL-30%MVC confirm previous studies of a greater local metabolic demand for NMES than VOL at the same force level. The same TOI and tHb changes for NMES and VOL-MVC suggest that local muscle metabolic demand and intramuscular pressure were similar between conditions. In conclusion, these findings indicate that NMES induce a similar local muscle metabolic demand as that of maximal VOL.

  17. Increased spinal reflex excitability is associated with enhanced central activation during voluntary lengthening contractions in human spinal cord injury

    Science.gov (United States)

    Kim, Hyosub E.; Corcos, Daniel M.

    2015-01-01

    This study of chronic incomplete spinal cord injury (SCI) subjects investigated patterns of central motor drive (i.e., central activation) of the plantar flexors using interpolated twitches, and modulation of soleus H-reflexes during lengthening, isometric, and shortening muscle actions. In a recent study of the knee extensors, SCI subjects demonstrated greater central activation ratio (CAR) values during lengthening (i.e., eccentric) maximal voluntary contractions (MVCs), compared with during isometric or shortening (i.e., concentric) MVCs. In contrast, healthy controls demonstrated lower lengthening CAR values compared with their isometric and shortening CARs. For the present investigation, we hypothesized SCI subjects would again produce their highest CAR values during lengthening MVCs, and that these increases in central activation were partially attributable to greater efficacy of Ia-α motoneuron transmission during muscle lengthening following SCI. Results show SCI subjects produced higher CAR values during lengthening vs. isometric or shortening MVCs (all P reflex testing revealed normalized H-reflexes (maximal SOL H-reflex-to-maximal M-wave ratios) were greater for SCI than controls during passive (P = 0.023) and active (i.e., 75% MVC; P = 0.017) lengthening, suggesting facilitation of Ia transmission post-SCI. Additionally, measures of spinal reflex excitability (passive lengthening maximal SOL H-reflex-to-maximal M-wave ratio) in SCI were positively correlated with soleus electromyographic activity and CAR values during lengthening MVCs (both P < 0.05). The present study presents evidence that patterns of dynamic muscle activation are altered following SCI, and that greater central activation during lengthening contractions is partly due to enhanced efficacy of Ia-α motoneuron transmission. PMID:25972590

  18. Repeatability study of mechanomyography in submaximal isometric contractions using coefficient of variation and intraclass correlation coefficient.

    Science.gov (United States)

    Akataki, K; Mita, K; Itoh, Y

    1999-01-01

    The within-day and between-day repeatability of the mechanomyogram (MMG) was assessed using the coefficient of variation (CV) and the intraclass correlation coefficient (ICC) and was compared with that of the electromyogram (EMG). The MMG and EMG were recorded simultaneously during isometric elbow flexion trials at different submaximal levels of 10% to 90% MVC. The testing session consisting of 9 submaximal trials was repeated 8 times on the same day for estimation of the within-day variation. In order to examine the between-day variation, the same testing session was also performed 8 times over 3 weeks with a 2-day rest interval between each session. The CVs within-day and between-day in both the MMG and EMG did not demonstrate any significant differences relating to the magnitude of force exerted. The CVs combined over all the force levels were approximately 10% within the same day and 25% between days for both the MMG and EMG. These corresponded to the within-day ICC of approximately 0.95 and the between-day ICC of 0.80. The repeatability of the MMG during submaximal isometric contractions of biceps brachii muscles is considered to be similar to that of the more established EMG.

  19. Hierarchical control of motor units in voluntary contractions.

    Science.gov (United States)

    De Luca, Carlo J; Contessa, Paola

    2012-01-01

    For the past five decades there has been wide acceptance of a relationship between the firing rate of motor units and the afterhyperpolarization of motoneurons. It has been promulgated that the higher-threshold, larger-soma, motoneurons fire faster than the lower-threshold, smaller-soma, motor units. This relationship was based on studies on anesthetized cats with electrically stimulated motoneurons. We questioned its applicability to motor unit control during voluntary contractions in humans. We found that during linearly force-increasing contractions, firing rates increased as exponential functions. At any time and force level, including at recruitment, the firing rate values were inversely related to the recruitment threshold of the motor unit. The time constants of the exponential functions were directly related to the recruitment threshold. From the Henneman size principle it follows that the characteristics of the firing rates are also related to the size of the soma. The "firing rate spectrum" presents a beautifully simple control scheme in which, at any given time or force, the firing rate value of earlier-recruited motor units is greater than that of later-recruited motor units. This hierarchical control scheme describes a mechanism that provides an effective economy of force generation for the earlier-recruited lower force-twitch motor units, and reduces the fatigue of later-recruited higher force-twitch motor units-both characteristics being well suited for generating and sustaining force during the fight-or-flight response.

  20. Maximum isometric knee flexor and extensor muscle contractions: normal patterns of torque versus time.

    Science.gov (United States)

    Murray, M P; Baldwin, J M; Gardner, G M; Sepic, S B; Downs, W J

    1977-06-01

    Isometric torque of the knee flexor and extensor muscles were recorded for 5 seconds at three knee joint positions. The subjects included healthy men in age groups from 20 to 35 and 45 to 65 years of age. The amplitudes and duration of peak torque and the time to peak torque were measured for each contraction. Peak torque was usually maintaned less than 0.1 second and never longer than 0.9 second. At each of the three angles, the mean extensor muscle torque was higher than the mean flexor muscle torque in both age groups, and the mean torque for both muscle group was higher among the younger than among the older man. The highest average torque was recorded at the knee angle of 60 degrees for the extensor muscles and 45 degrees for the flexor muscles, but this was not always a stereotyped response either for a given individual or among individuals.

  1. Electron Tomography of Cryofixed, Isometrically Contracting Insect Flight Muscle Reveals Novel Actin-Myosin Interactions

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Shenping; Liu, Jun; Reedy, Mary C.; Tregear, Richard T.; Winkler, Hanspeter; Franzini-Armstrong, Clara; Sasaki, Hiroyuki; Lucaveche, Carmen; Goldman, Yale E.; Reedy, Michael K.; Taylor, Kenneth A. (UPENN); (Duke); (MRCLMB); (FSU); (Jikei-Med)

    2010-10-22

    Isometric muscle contraction, where force is generated without muscle shortening, is a molecular traffic jam in which the number of actin-attached motors is maximized and all states of motor action are trapped with consequently high heterogeneity. This heterogeneity is a major limitation to deciphering myosin conformational changes in situ. We used multivariate data analysis to group repeat segments in electron tomograms of isometrically contracting insect flight muscle, mechanically monitored, rapidly frozen, freeze substituted, and thin sectioned. Improved resolution reveals the helical arrangement of F-actin subunits in the thin filament enabling an atomic model to be built into the thin filament density independent of the myosin. Actin-myosin attachments can now be assigned as weak or strong by their motor domain orientation relative to actin. Myosin attachments were quantified everywhere along the thin filament including troponin. Strong binding myosin attachments are found on only four F-actin subunits, the 'target zone', situated exactly midway between successive troponin complexes. They show an axial lever arm range of 77{sup o}/12.9 nm. The lever arm azimuthal range of strong binding attachments has a highly skewed, 127{sup o} range compared with X-ray crystallographic structures. Two types of weak actin attachments are described. One type, found exclusively in the target zone, appears to represent pre-working-stroke intermediates. The other, which contacts tropomyosin rather than actin, is positioned M-ward of the target zone, i.e. the position toward which thin filaments slide during shortening. We present a model for the weak to strong transition in the myosin ATPase cycle that incorporates azimuthal movements of the motor domain on actin. Stress/strain in the S2 domain may explain azimuthal lever arm changes in the strong binding attachments. The results support previous conclusions that the weak attachments preceding force generation are

  2. Coherent source and connectivity analysis on simultaneously measured EEG and MEG data during isometric contraction.

    Science.gov (United States)

    Muthuraman, M; Hellriegel, H; Hoogenboom, N; Anwar, A R; Mideksa, K G; Krause, H; Schnitzler, A; Raethjen, J; Deuschl, G

    2014-01-01

    The most well-known non-invasive electric and magnetic field measurement modalities are the electroencephalography (EEG) and magnetoencephalography (MEG). The first aim of the study was to implement the recently developed realistic head model which uses an integrative approach for both the modalities. The second aim of this study was to find the network of coherent sources and the modes of interactions within this network during isometric contraction (ISC) at (15-30 Hz) in healthy subjects. The third aim was to test the effective connectivity revealed by both the modalities analyzing them separately and combined. The Welch periodogram method was used to estimate the coherence spectrum between the EEG and the electromyography (EMG) signals followed by the realistic head modelling and source analysis method dynamic imaging of coherent sources (DICS) to find the network of coherent sources at the individual peak frequency within the beta band in healthy subjects. The last step was to identify the effective connectivity between the identified sources using the renormalized partial directed coherence method. The cortical and sub-cortical network comprised of the primary sensory motor cortex (PSMC), secondary motor area (SMA), and the cerebellum (C). The cortical and sub-cortical network responsible for the isometric contraction was similar in both the modalities when analysing them separately and combined. The SNR was not significantly different between the two modalities separately and combined. However, the coherence values were significantly higher in the combined modality in comparison to each of the modality separately. The effective connectivity analysis revealed plausible additional connections in the combined modality analysis.

  3. Electron tomography of cryofixed, isometrically contracting insect flight muscle reveals novel actin-myosin interactions.

    Directory of Open Access Journals (Sweden)

    Shenping Wu

    Full Text Available Isometric muscle contraction, where force is generated without muscle shortening, is a molecular traffic jam in which the number of actin-attached motors is maximized and all states of motor action are trapped with consequently high heterogeneity. This heterogeneity is a major limitation to deciphering myosin conformational changes in situ.We used multivariate data analysis to group repeat segments in electron tomograms of isometrically contracting insect flight muscle, mechanically monitored, rapidly frozen, freeze substituted, and thin sectioned. Improved resolution reveals the helical arrangement of F-actin subunits in the thin filament enabling an atomic model to be built into the thin filament density independent of the myosin. Actin-myosin attachments can now be assigned as weak or strong by their motor domain orientation relative to actin. Myosin attachments were quantified everywhere along the thin filament including troponin. Strong binding myosin attachments are found on only four F-actin subunits, the "target zone", situated exactly midway between successive troponin complexes. They show an axial lever arm range of 77°/12.9 nm. The lever arm azimuthal range of strong binding attachments has a highly skewed, 127° range compared with X-ray crystallographic structures. Two types of weak actin attachments are described. One type, found exclusively in the target zone, appears to represent pre-working-stroke intermediates. The other, which contacts tropomyosin rather than actin, is positioned M-ward of the target zone, i.e. the position toward which thin filaments slide during shortening.We present a model for the weak to strong transition in the myosin ATPase cycle that incorporates azimuthal movements of the motor domain on actin. Stress/strain in the S2 domain may explain azimuthal lever arm changes in the strong binding attachments. The results support previous conclusions that the weak attachments preceding force generation are very

  4. Behavior of human gastrocnemius muscle fascicles during ramped submaximal isometric contractions.

    Science.gov (United States)

    Héroux, Martin E; Stubbs, Peter W; Herbert, Robert D

    2016-09-01

    Precise estimates of muscle architecture are necessary to understand and model muscle mechanics. The primary aim of this study was to estimate continuous changes in fascicle length and pennation angle in human gastrocnemius muscles during ramped plantar flexor contractions at two ankle angles. The secondary aim was to determine whether these changes differ between proximal and distal fascicles. Fifteen healthy subjects performed ramped contractions (0-25% MVC) as ultrasound images were recorded from the medial (MG, eight sites) and lateral (LG, six sites) gastrocnemius muscle with the ankle at 90° and 120° (larger angles correspond to shorter muscle lengths). In all subjects, fascicles progressively shortened with increasing torque. MG fascicles shortened 5.8 mm (11.1%) at 90° and 4.5 mm (12.1%) at 120°, whereas LG muscle fascicles shortened 5.1 mm (8.8%) at both ankle angles. MG pennation angle increased 1.4° at 90° and 4.9° at 120°, and LG pennation angle decreased 0.3° at 90° and increased 2.6° at 120°. Muscle architecture changes were similar in proximal and distal fascicles at both ankle angles. This is the first study to describe continuous changes in fascicle length and pennation angle in the human gastrocnemius muscle during ramped isometric contractions. Very similar changes occurred in proximal and distal muscle regions. These findings are relevant to studies modeling active muscle mechanics.

  5. Effects of proprioceptive neuromuscular facilitation stretching and static stretching on maximal voluntary contraction.

    Science.gov (United States)

    Miyahara, Yutetsu; Naito, Hisashi; Ogura, Yuji; Katamoto, Shizuo; Aoki, Junichiro

    2013-01-01

    This study was undertaken to investigate and compare the effects of proprioceptive neuromuscular facilitation (PNF) stretching and static stretching on maximal voluntary contraction (MVC). Thirteen male university students (age, 20 ± 1 years; height, 172.2 ± 4.6 cm; weight, 68.4 ± 6.7 kg; mean ± SD) completed 3 different conditions on 3 nonconsecutive days in randomized order: static stretching (SS), PNF stretching (PNF), and no stretching (control, CON). Each condition consisted of a 5-minute rest accompanied by one of the following activities: (a) control, (b) SS, or (c) PNF stretching. The hip flexion range of motion (ROM) was evaluated immediately before and after the activity. The MVC of knee flexion was then measured. Surface electromyography was recorded from the biceps femoris and vastus lateralis muscles during MVC tests and stretching. Although increases in ROM were significantly greater after PNF than after SS (p stretching increases ROM more than SS, PNF stretching and SS is detrimental to isometric maximal strength.

  6. Superimposed electrical stimulation comfortably improves the endurance of maximal voluntary contractions.

    OpenAIRE

    Boisgontier, Matthieu; Moineau, Bastien; Nougier, Vincent

    2012-01-01

    International audience; AIM: Electrical stimulation has shown to improve muscle endurance in sub-maximal contractions but sessions were painful due to the electric stimuli parameters. Therefore, the present study tested the effects of the superimposed electrical stimulation technique using comfortable current on endurance in repetitions of maximal voluntary contraction. METHODS: Seventeen young healthy subjects performed fifty maximal voluntary contractions of the triceps brachii in two condi...

  7. Different Effects of Startling Acoustic Stimuli (SAS) on TMS-Induced Responses at Rest and during Sustained Voluntary Contraction.

    Science.gov (United States)

    Chen, Yen-Ting; Li, Shengai; Zhou, Ping; Li, Sheng

    2016-01-01

    Previous studies have shown that a habituated startling acoustic stimulus (SAS) can cause a transient suppression of motor evoked potentials (MEPs) induced by transcranial magnetic stimulation (TMS) during light muscle contraction. However, it is still unknown whether this phenomenon persists when at rest or during a sustained voluntary contraction task. Therefore, the purpose of this study was to determine whether a conditioning SAS has different effects. TMS was delivered to the hot spot for the left biceps on 11 subjects at rest both with and without a conditioning SAS. Of the 11subjects, 9 also had TMS delivered during isometric flexion of the left elbow, also with and without a conditioning SAS. TMS-induced MEPs, TMS-induced force, and silent periods were used to determine the effect of conditioning SAS. Consistent with previous findings, TMS-induced MEPs were smaller with a conditioning SAS (0.49 ± 0.37 mV) as compared without the SAS (0.69 ± 0.52 mV) at rest. However, a conditioning SAS during the voluntary contraction tasks resulted in a significant shortening of the MEP silent period (187.22 ± 22.99 ms with SAS vs. 200.56 ± 29.71 ms without SAS) without any changes in the amplitude of the MEP (1.37 ± 0.9 mV with SAS V.S. 1.32 ± 0.92 mV without SAS) or the TMS-induced force (3.11 ± 2.03 N-m with SAS V.S. 3.62 ± 1.33 N-m without SAS). Our results provide novel evidence that a conditioning SAS has different effects on the excitability of the motor cortex when at rest or during sustained voluntary contractions.

  8. A Review of Classification Techniques of EMG Signals during Isotonic and Isometric Contractions.

    Science.gov (United States)

    Nazmi, Nurhazimah; Abdul Rahman, Mohd Azizi; Yamamoto, Shin-Ichiroh; Ahmad, Siti Anom; Zamzuri, Hairi; Mazlan, Saiful Amri

    2016-08-17

    In recent years, there has been major interest in the exposure to physical therapy during rehabilitation. Several publications have demonstrated its usefulness in clinical/medical and human machine interface (HMI) applications. An automated system will guide the user to perform the training during rehabilitation independently. Advances in engineering have extended electromyography (EMG) beyond the traditional diagnostic applications to also include applications in diverse areas such as movement analysis. This paper gives an overview of the numerous methods available to recognize motion patterns of EMG signals for both isotonic and isometric contractions. Various signal analysis methods are compared by illustrating their applicability in real-time settings. This paper will be of interest to researchers who would like to select the most appropriate methodology in classifying motion patterns, especially during different types of contractions. For feature extraction, the probability density function (PDF) of EMG signals will be the main interest of this study. Following that, a brief explanation of the different methods for pre-processing, feature extraction and classifying EMG signals will be compared in terms of their performance. The crux of this paper is to review the most recent developments and research studies related to the issues mentioned above.

  9. A Review of Classification Techniques of EMG Signals during Isotonic and Isometric Contractions

    Directory of Open Access Journals (Sweden)

    Nurhazimah Nazmi

    2016-08-01

    Full Text Available In recent years, there has been major interest in the exposure to physical therapy during rehabilitation. Several publications have demonstrated its usefulness in clinical/medical and human machine interface (HMI applications. An automated system will guide the user to perform the training during rehabilitation independently. Advances in engineering have extended electromyography (EMG beyond the traditional diagnostic applications to also include applications in diverse areas such as movement analysis. This paper gives an overview of the numerous methods available to recognize motion patterns of EMG signals for both isotonic and isometric contractions. Various signal analysis methods are compared by illustrating their applicability in real-time settings. This paper will be of interest to researchers who would like to select the most appropriate methodology in classifying motion patterns, especially during different types of contractions. For feature extraction, the probability density function (PDF of EMG signals will be the main interest of this study. Following that, a brief explanation of the different methods for pre-processing, feature extraction and classifying EMG signals will be compared in terms of their performance. The crux of this paper is to review the most recent developments and research studies related to the issues mentioned above.

  10. Trainability of muscular activity level during maximal voluntary co-contraction: comparison between bodybuilders and nonathletes.

    Directory of Open Access Journals (Sweden)

    Sumiaki Maeo

    Full Text Available Antagonistic muscle pairs cannot be fully activated simultaneously, even with maximal effort, under conditions of voluntary co-contraction, and their muscular activity levels are always below those during agonist contraction with maximal voluntary effort (MVE. Whether the muscular activity level during the task has trainability remains unclear. The present study examined this issue by comparing the muscular activity level during maximal voluntary co-contraction for highly experienced bodybuilders, who frequently perform voluntary co-contraction in their training programs, with that for untrained individuals (nonathletes. The electromyograms (EMGs of biceps brachii and triceps brachii muscles during maximal voluntary co-contraction of elbow flexors and extensors were recorded in 11 male bodybuilders and 10 nonathletes, and normalized to the values obtained during the MVE of agonist contraction for each of the corresponding muscles (% EMGMVE. The involuntary coactivation level in antagonist muscle during the MVE of agonist contraction was also calculated. In both muscles, % EMGMVE values during the co-contraction task for bodybuilders were significantly higher (P<0.01 than those for nonathletes (biceps brachii: 66±14% in bodybuilders vs. 46±13% in nonathletes, triceps brachii: 74±16% vs. 57±9%. There was a significant positive correlation between a length of bodybuilding experience and muscular activity level during the co-contraction task (r = 0.653, P = 0.03. Involuntary antagonist coactivation level during MVE of agonist contraction was not different between the two groups. The current result indicates that long-term participation in voluntary co-contraction training progressively enhances muscular activity during maximal voluntary co-contraction.

  11. Attenuation of eccentric exercise-induced muscle damage conferred by maximal isometric contractions: a mini review

    Directory of Open Access Journals (Sweden)

    Leonardo Coelho Rabello Lima

    2015-10-01

    Full Text Available Although beneficial in determined contexts, eccentric exercise-induced muscle damage (EIMD might be unwanted during training regimens, competitions and daily activities. There are a vast number of studies investigating strategies to attenuate EIMD response after damaging exercise bouts. Many of them consist of performing exercises that induce EIMD, consuming supplements or using equipment that are not accessible for most people. It appears that performing maximal isometric contractions (ISOs 2-4 days prior to damaging bouts promotes significant attenuation of EIMD symptoms that are not related to muscle function. It has been shown that the volume of ISOs, muscle length in which they are performed, and interval between them and the damaging bout influence the magnitude of this protection. Additionally, it appears that this protection is not long-lived, lasting no longer than 4 days. Although no particular mechanisms for these adaptations were identified, professionals should consider applying this non-damaging stimulus before submitting their patients to unaccustomed exercised. However, it seems not to be the best option for athletes or relatively trained individuals. Future studies should focus on establishing if ISOs protect other populations (i.e., trained individuals or muscle groups (i.e., knee extensors against EIMD, as well as investigate different mechanisms for ISO-induced protection.

  12. The origin of activity in the biceps brachii muscle during voluntary contractions of the contralateral elbow flexor muscles

    NARCIS (Netherlands)

    Zijdewind, Inge; Butler, Jane E.; Gandevia, Simon C.; Taylor, Janet L.

    2006-01-01

    During strong voluntary contractions, activity is not restricted to the target muscles. Other muscles, including contralateral muscles, often contract. We used transcranial magnetic stimulation (TMS) to analyse the origin of these unintended contralateral contractions (termed "associated" contractio

  13. The origin of activity in the biceps brachii muscle during voluntary contractions of the contralateral elbow flexor muscles

    NARCIS (Netherlands)

    Zijdewind, Inge; Butler, Jane E.; Gandevia, Simon C.; Taylor, Janet L.

    2006-01-01

    During strong voluntary contractions, activity is not restricted to the target muscles. Other muscles, including contralateral muscles, often contract. We used transcranial magnetic stimulation (TMS) to analyse the origin of these unintended contralateral contractions (termed "associated"

  14. Is cardiac autonomic modulation during upper limb isometric contraction and Valsalva maneuver impaired in COPD patients?

    Directory of Open Access Journals (Sweden)

    Goulart CL

    2017-03-01

    Full Text Available Cássia da Luz Goulart,1 Ramona Cabiddu,2 Paloma de Borba Schneiders,1 Elisabete Antunes San Martin,1 Renata Trimer,3 Audrey Borghi-Silva,2 Andréa Lúcia Gonçalves da Silva4,5 1Course of Physiotherapy, University of Santa Cruz do Sul, Rio Grande do Sul, Brazil; 2Cardiopulmonary Physiotherapy Laboratory, Nucleus of Research in Physical Exercise, Federal University of São Carlos, São Carlos, Brazil; 3Department of Physiotherapy, Federal University of Amazonas, Manaus, AM, Brazil; 4Course of Physiotherapy, Department of Health and Physical Education, University of Santa Cruz do Sul, Rio Grande do Sul, Brazil; 5Pulmonary Rehabilitation Program, Santa Cruz Hospital, Santa Cruz do Sul, Rio Grande do Sul, Brazil Purpose: To evaluate the heart rate variability (HRV indices and heart rate (HR responses during isometric contraction (IC and Valsalva maneuver (VM in COPD patients. Methods: Twenty-two stable moderate to severe COPD patients were evaluated. R-R intervals were recorded (monitor Polar® S810i during dominant upper limb IC (2 minutes. Stable signals were analyzed by Kubios HRV® software. Indices of HRV were computed in the time domain (mean HR; square root of the mean squared differences of successive RR intervals [RMSSD] and HRV triangular index [RR tri index] and in the frequency domain (high frequency [HF]; low frequency [LF] and LF/HF ratio. The HR responses were evaluated at rest, at the peak and at the nadir of the VM (15 seconds. The Valsalva index was also calculated. Results: During IC: time domain indices (mean HR increased [P=0.001], RMSSD, and RR tri index decreased [P=0.005 and P=0.005, respectively]; frequency domain indices (LF increased [P=0.033] and HF decreased [P=0.002]; associations were found between forced expiratory volume in 1 second (FEV1 vs RMSSD (P=0.04; r=–0.55, FEV1 vs HR (P=0.04; r=–0.48, forced vital capacity (FVC vs RMSSD (P=0.05; r=–0.62, maximum inspiratory pressure (MIP vs HF (P=0.02; r=0.68. FEV1

  15. Tension and heat production during isometric contractions and shortening in the anterior byssus retractor muscle of Mytilus edulis.

    Science.gov (United States)

    Gilbert, S H

    1978-09-01

    1. Tension and heat production were measured during phasic isometric contractions and isovelocity shortening in the anterior byssus retractor muscle (ABRM) of Mytilus edulis at 20 degrees C. 2. Isometric tension at lo was 550 +/- 40 mN/mm2 (S.D. for 173 observations in nine muscles), while the isometric maintenance heat rate was 1.0 +/- 0.2 mW/g wet wt. (S.D. for seventy-eight observations in eight muscles). 3. Isometric tension and heat production were measured as functions of muscle length over a range of 0.79--1.14 lo and were found to bear a linear relation to each other. 4. The force-velocity relation was determined in isovelocity releases imposed during tetanic stimulation and was found to fit the Hill equation with parameters alpha/Po = 0.07 +/- 0.01 and b/lo = 0.016 +/- 0.0007 sec-1 (S.E. from non-linear least-squares regression of the pooled data from seven experiments). 5. Heat production measured in the same experiments showed that shortening heat is produced with a shortening heat coefficient alpha/Po of 0.15. Shortening heat does not appear to be force-dependent, and separate experiments confirmed that it is a linear function of the amount of shortening.

  16. Real-time muscle state estimation from EMG signals during isometric contractions using Kalman filters.

    Science.gov (United States)

    Menegaldo, Luciano L

    2017-08-01

    State-space control of myoelectric devices and real-time visualization of muscle forces in virtual rehabilitation require measuring or estimating muscle dynamic states: neuromuscular activation, tendon force and muscle length. This paper investigates whether regular (KF) and extended Kalman filters (eKF), derived directly from Hill-type muscle mechanics equations, can be used as real-time muscle state estimators for isometric contractions using raw electromyography signals (EMG) as the only available measurement. The estimators' amplitude error, computational cost, filtering lags and smoothness are compared with usual EMG-driven analysis, performed offline, by integrating the nonlinear Hill-type muscle model differential equations (offline simulations-OS). EMG activity of the three triceps surae components (soleus, gastrocnemius medialis and gastrocnemius lateralis), in three torque levels, was collected for ten subjects. The actualization interval (AI) between two updates of the KF and eKF was also varied. The results show that computational costs are significantly reduced (70x for KF and 17[Formula: see text] for eKF). The filtering lags presented sharp linear relationships with the AI (0-300 ms), depending on the state and activation level. Under maximum excitation, amplitude errors varied in the range 10-24% for activation, 5-8% for tendon force and 1.4-1.8% for muscle length, reducing linearly with the excitation level. Smoothness, measured by the ratio between the average standard variations of KF/eKF and OS estimations, was greatly reduced for activation but converged exponentially to 1 for the other states by increasing AI. Compared to regular KF, extended KF does not seem to improve estimation accuracy significantly. Depending on the particular application requirements, the most appropriate KF actualization interval can be selected.

  17. Planckian Power Spectral Densities from Human Calves during Posture Maintenance and Controlled Isometric Contractions.

    Directory of Open Access Journals (Sweden)

    J E Lugo

    Full Text Available The relationship between muscle anatomy and physiology and its corresponding electromyography activity (EMGA is complex and not well understood. EMGA models may be broadly divided in stochastic and motor-unit-based models. For example, these models have successfully described many muscle physiological variables such as the value of the muscle fiber velocity and the linear relationship between median frequency and muscle fiber velocity. However they cannot explain the behavior of many of these variables with changes in intramuscular temperature, or muscle PH acidity, for instance. Here, we propose that the motor unit action potential can be treated as an electromagnetic resonant mode confined at thermal equilibrium inside the muscle. The motor units comprising the muscle form a system of standing waves or modes, where the energy of each mode is proportional to its frequency. Therefore, the power spectral density of the EMGA is well described and fit by Planck's law and from its distribution we developed theoretical relationships that explain the behavior of known physiological variables with changes in intramuscular temperature or muscle PH acidity, for instance.EMGA of the calf muscle was recorded during posture maintenance in seven participants and during controlled isometric contractions in two participants. The power spectral density of the EMGA was then fit with the Planckian distribution. Then, we inferred nine theoretical relationships from the distribution and compared the theoretically derived values with experimentally obtained values.The power spectral density of EMGA was fit by Planckian distributions and all the theoretical relationships were validated by experimental results.Only by considering the motor unit action potentials as electromagnetic resonant modes confined at thermal equilibrium inside the muscle suffices to predict known or new theoretical relationships for muscle physiological variables that other models have failed

  18. Is cardiac autonomic modulation during upper limb isometric contraction and Valsalva maneuver impaired in COPD patients?

    Science.gov (United States)

    Goulart, Cássia da Luz; Cabiddu, Ramona; Schneiders, Paloma de Borba; Antunes San Martin, Elisabete; Trimer, Renata; Borghi-Silva, Audrey; da Silva, Andréa Lúcia Gonçalves

    2017-01-01

    Purpose To evaluate the heart rate variability (HRV) indices and heart rate (HR) responses during isometric contraction (IC) and Valsalva maneuver (VM) in COPD patients. Methods Twenty-two stable moderate to severe COPD patients were evaluated. R-R intervals were recorded (monitor Polar® S810i) during dominant upper limb IC (2 minutes). Stable signals were analyzed by Kubios HRV® software. Indices of HRV were computed in the time domain (mean HR; square root of the mean squared differences of successive RR intervals [RMSSD] and HRV triangular index [RR tri index]) and in the frequency domain (high frequency [HF]; low frequency [LF] and LF/HF ratio). The HR responses were evaluated at rest, at the peak and at the nadir of the VM (15 seconds). The Valsalva index was also calculated. Results During IC: time domain indices (mean HR increased [P=0.001], RMSSD, and RR tri index decreased [P=0.005 and P=0.005, respectively]); frequency domain indices (LF increased [P=0.033] and HF decreased [P=0.002]); associations were found between forced expiratory volume in 1 second (FEV1) vs RMSSD (P=0.04; r=−0.55), FEV1 vs HR (P=0.04; r=−0.48), forced vital capacity (FVC) vs RMSSD (P=0.05; r=−0.62), maximum inspiratory pressure (MIP) vs HF (P=0.02; r=0.68). FEV1 and FVC justified 30% of mean HR. During VM: HR increased (P=0.01); the nadir showed normal bradycardic response; the Valsalva index was =0.7. Conclusion COPD patients responded properly to the upper limb IC and to the VM; however, HR recovery during VM was impaired in these patients. The severity of the disease and MIP were associated with increased parasympathetic modulation and higher chronotropic response.

  19. Changes in tetrodotoxin-resistant C-fibre activity during fatiguing isometric contractions in the rat.

    Directory of Open Access Journals (Sweden)

    Ivana Kalezic

    Full Text Available It is by now well established that tetrodotoxin-resistant (TTX-R afferent fibres from muscle in the rat exhibit a multisensitive profile, including nociception. TTX-R afferent fibres play an important role in motor control, via spinal and supraspinal loops, but their activation and function during muscle exercise and fatigue are still unknown. Therefore, the specific effect of isometric fatiguing muscle contraction on the responsiveness of TTX-R C-fibres has been investigated in this study. To quantify the TTX-R afferent input we recorded the cord dorsum potential (CDP, which is the result of the electrical fields set up within the spinal cord by the depolarisation of the interneurons located in the dorsal horn, activated by an incoming volley of TTX-R muscle afferents. The changes in TTX-R CDP size before, during and after fatiguing electrical stimulation of the gastrocnemius-soleus (GS muscle have been taken as a measure of TTX-R C-unit activation. At the end of the fatiguing protocol, following an exponential drop in force, TTX-R CDP area decreased in the majority of trials (9/14 to 0.75 ± 0.03% (mean ± SEM of the pre-fatigue value. Recovery to the control size of the TTX-R CDP was incomplete after 10 min. Furthermore, fatiguing trials could sensitise a fraction of the TTX-R C-fibres responding to muscle pinch. The results suggest a long-lasting activation of the TTX-R muscle afferents after fatiguing stimulation. The role of this behaviour in chronic muscle fatigue in connection with pain development is discussed. Accumulation of metabolites released into the interstitium during fatiguing stimulation might be one of the reasons underlying the C-fibres' long-lasting activation.

  20. Representing a product system representation as a contractive semigroup and applications to regular isometric dilations

    CERN Document Server

    Shalit, Orr

    2007-01-01

    In this paper we propose a new technical tool for analyzing representations of Hilbert $C^*$-product systems. Using this tool, we give a new proof that every doubly commuting representation over $\\mathbb{N}^k$ has a regular isometric dilation, and we also prove sufficient conditions for the existence of a regular isometric dilation of representations over more general subsemigroups of $\\mathbb{R}_+^k$.

  1. Electrically evoked and voluntary maximal isometric tension in relation to dynamic muscle performance in elderly male subjects, aged 69 years.

    Science.gov (United States)

    Davies, C T; White, M J; Young, K

    1983-01-01

    The dynamic performance and electrically evoked mechanical properties of elderly triceps surae muscle have been investigated in 9 men, aged 69 yr. Dynamic performance consisted of cycling on a force bicycle and a vertical jump off two feet from a force platform. The results showed that the time to peak tension (TPT) and half relaxation time (1/2 RT) were significantly greater (p less than 0.001) by 30 ms and 22 ms and the supramaximal twitch (Pt) and tetanic (20 Hz-P020) tensions and maximal voluntary contraction (MVC) were less by 45 N (-33%), 708 N (-49%), and 899 N (-43%) in the elderly compared with young male control subjects. On the force platform, the height jumped (Ht), maximal force exerted (P), take-off velocity (VT), net impulse (NI) and peak power output (W) were less by 18.6 cm, 173 N, 0.9 ms-1, 52 Ns and 1120 w respectively. Similar differences of power, force and velocity were observed on the force bicycle. The reduction of W in the elderly was associated with the contractile characteristics of the leg muscle. The loss of contractile speed and capacity to to generate force in old people was reflected in their inability to develop power during the performance of a maximal vertical jump and cycling.

  2. An automated method to control preload by compensation for stress relaxation in spontaneously contracting, isometric rat mesenteric lymphatics.

    Science.gov (United States)

    Davis, Michael J; Lane, Megan M; Scallan, Joshua P; Gashev, Anatoliy A; Zawieja, David C

    2007-08-01

    Our objective was to devise a system to automatically correct for stress relaxation of isometric rat mesenteric lymphatics (90-120 microm, ID). Stress relaxation is a particular problem in isometric studies of highly distensible vessels and is evident as a time-dependent, secondary decline in force after an abrupt length increase. Because the phasic contraction pattern of lymphatics is exquisitely sensitive to changes in preload, stress relaxation makes stable contraction patterns difficult to achieve and analyze. A DMT wire myograph was modified to accommodate an Inchworm piezo stack in series with a standard micrometer drive to permit automated control of vessel caliber/force. The force output of the myograph was digitized and computer algorithms were devised to servo control force by changing vessel diameter. The system was tested on passive lymphatics, passive small veins, and lymphatics exhibiting spontaneous force transients. The software was designed to temporarily disable servo control during a spontaneous force transient. For both active and passive lymphatics, stable preloads were very well maintained, indicating that the system was adequately compensating for stress relaxation. The method works well with isometric rat mesenteric lymphatics without disturbing spontaneous activity. It should be applicable to arterial, venous, and lymphatic vessels (80-500 microm in diameter) isolated from other tissues and species.

  3. Anisotropy of human muscle via non invasive impedance measurements. Frequency dependence of the impedance changes during isometric contractions

    Science.gov (United States)

    Kashuri, Hektor

    In this thesis we present non invasive muscle impedance measurements using rotatable probes extending the work done by Aaron et al. (1997) by measuring not only the real part of the impedance but the imaginary part as well. The results reveal orientations of underlying muscle fibers via minima in resistance and reactance versus angle curves, suggesting this method as potentially useful for studying muscle properties in clinical and physiological research. Calculations of the current distribution for a slab of material with anisotropic conductivity show that the current distribution depends strongly on the separation of two current electrodes and as well as on its conducting anisotropy. Forearm muscle impedance measurements at 50 kHz done by Shiffman et al. (2003) had shown that both resistance (R) and reactance (X) increase during isometric contraction. We have extended these measurements in the 3 to 100 kHz range and we found that resistance (R) and reactance (X) both increase and their changes increased or decreased at frequency dependent rates. Analysis based on circuit models of changes in R and X during the short contraction pulses showed that the extra cellular fluid resistance increased by 3.9 +/- 1.4 %, while the capacitance increased by 5.6 +/- 2 %. For long contraction pulses at very low frequencies: (1) there was practically no change in R during contraction, which implies that these changes are due to cellular membrane or intracellular effects with the extra cellular water component not participating, and (2) in post contraction stage there were no morphological changes which means that drifts in R can only be due to physiological changes. Following Shiffman et al. (2003) we measured impedance changes of R and X during a triangular shaped pulse of force generated via isometric forearm muscle contraction at 50 kHz. We measured these changes in 3-100 kHz frequency range for a stair case pulse of forces and the results showed that they are frequency

  4. Torque and mechanomyogram relationships during electrically-evoked isometric quadriceps contractions in persons with spinal cord injury.

    Science.gov (United States)

    Ibitoye, Morufu Olusola; Hamzaid, Nur Azah; Hasnan, Nazirah; Abdul Wahab, Ahmad Khairi; Islam, Md Anamul; Kean, Victor S P; Davis, Glen M

    2016-08-01

    The interaction between muscle contractions and joint loading produces torques necessary for movements during activities of daily living. However, during neuromuscular electrical stimulation (NMES)-evoked contractions in persons with spinal cord injury (SCI), a simple and reliable proxy of torque at the muscle level has been minimally investigated. Thus, the purpose of this study was to investigate the relationships between muscle mechanomyographic (MMG) characteristics and NMES-evoked isometric quadriceps torques in persons with motor complete SCI. Six SCI participants with lesion levels below C4 [(mean (SD) age, 39.2 (7.9) year; stature, 1.71 (0.05) m; and body mass, 69.3 (12.9) kg)] performed randomly ordered NMES-evoked isometric leg muscle contractions at 30°, 60° and 90° knee flexion angles on an isokinetic dynamometer. MMG signals were detected by an accelerometer-based vibromyographic sensor placed over the belly of rectus femoris muscle. The relationship between MMG root mean square (MMG-RMS) and NMES-evoked torque revealed a very high association (R(2)=0.91 at 30°; R(2)=0.98 at 60°; and R(2)=0.97 at 90° knee angles; Pcontractions. The strong positive relationship between MMG signal and NMES-evoked torque production suggested that the MMG might be deployed as a direct proxy for muscle torque or fatigue measurement during leg exercise and functional movements in the SCI population.

  5. Approximate entropy based on attempted steady isometric contractions with the ankle dorsal- and plantarflexors: Reliability and optimal sampling frequency

    DEFF Research Database (Denmark)

    Rose, Martin Høyer; Bandholm, Thomas; Jensen, Bente Rona

    2009-01-01

    healthy young subjects (13+/-3 years, mean+/-1 S.D.) performed attempted steady isometric submaximal contractions with the ankle dorsal- and plantarflexors at two different days. Relative (ICC(3.1)) and absolute (standard error of measurement [S.E.M.], and S.E.M.%) test-retest reliability was assessed...... for the ApEn values calculated for torque time-series down-sampled to 30 and 100Hz, respectively. The relative reliability was generally moderate (0.360...

  6. Motor unit activity during isometric and concentric-eccentric contractions of the human first dorsal interosseus muscle.

    Science.gov (United States)

    Howell, J N; Fuglevand, A J; Walsh, M L; Bigland-Ritchie, B

    1995-08-01

    1. Motor unit activity was recorded with intramuscular fine wire electrodes during isometric, concentric, and eccentric activity in the human first dorsal interosseus muscle. Twenty-one units from 11 subjects were sampled. 2. During isotonic cycles of shortening and lengthening, 18 of 21 units were recruited during the concentric phase, increased their discharge rates as the concentric movement progressed, then decreased their discharge rate during the eccentric phase, and were derecruited. 3. A different pattern of recruitment was observed in recordings from three units. These units were recruited during the eccentric phase, at a time when other units were decreasing their discharge rate or being derecruited. In two of the units selectively recruited during the eccentric phase, it was possible to determine their isometric thresholds, which were higher than those of units exhibiting the more common pattern of recruitment. 4. For two of the three units exhibiting selective recruitment during eccentric contraction, the unit was recorded simultaneously with different pairs of recording wires separated by 5-10 mm. Each discharge of these units was detected by both electrodes, making it unlikely that movement artifact was responsible for the initiation or cessation of discharge. 5. The recruitment patterns observed suggest that changes in the type or distribution of synaptic inputs to motoneurons during movement can, in some instances, override pre- and postsynaptic factors that shape recruitment order in isometric conditions.

  7. Changes in conformation of myosin heads during the development of isometric contraction and rapid shortening in single frog muscle fibres.

    Science.gov (United States)

    Piazzesi, G; Reconditi, M; Dobbie, I; Linari, M; Boesecke, P; Diat, O; Irving, M; Lombardi, V

    1999-01-15

    1. Two-dimensional X-ray diffraction patterns were recorded at the European Synchrotron Radiation Facility from central segments of intact single muscle fibres of Rana temporaria with 5 ms time resolution during the development of isometric contraction. Shortening at ca 0.8 times the maximum velocity was also imposed at the isometric tetanus plateau. 2. The first myosin-based layer line (ML1) and the second myosin-based meridional reflection (M2), which are both strong in resting muscle, were completely abolished at the plateau of the isometric tetanus. The third myosin-based meridional reflection (M3), arising from the axial repeat of the myosin heads along the filaments, remained intense but its spacing changed from 14.34 to 14.56 nm. The intensity change of the M3 reflection, IM3, could be explained as the sum of two components, I14.34 and I14.56, arising from myosin head conformations characteristic of rest and isometric contraction, respectively. 3. The amplitudes (A) of the X-ray reflections, which are proportional to the fraction of myosin heads in each conformation, changed with half-times that were similar to that of isometric force development, which was 33.5 +/- 2. 0 ms (mean +/- s.d., 224 tetani from three fibres, 4 C), measured from the end of the latent period. We conclude that the myosin head conformation changes synchronously with force development, at least within the 5 ms time resolution of these measurements. 4. The changes in the X-ray reflections during rapid shortening have two temporal components. The rapid decrease in intensity of the 14.56 nm reflection at the start of shortening is likely to be due to tilting of myosin heads attached to actin. The slower changes in the other reflections were consistent with a return to the resting conformation of the myosin heads that was about 60 % complete after shortening of 70 nm per half-sarcomere.

  8. In-Vivo Measurement of Muscle Tension: Dynamic Properties of the MC Sensor during Isometric Muscle Contraction

    Directory of Open Access Journals (Sweden)

    Srđan Đorđević

    2014-09-01

    Full Text Available Skeletal muscle is the largest tissue structure in our body and plays an essential role for producing motion through integrated action with bones, tendons, ligaments and joints, for stabilizing body position, for generation of heat through cell respiration and for blood glucose disposal. A key function of skeletal muscle is force generation. Non-invasive and selective measurement of muscle contraction force in the field and in clinical settings has always been challenging. The aim of our work has been to develop a sensor that can overcome these difficulties and therefore enable measurement of muscle force during different contraction conditions. In this study, we tested the mechanical properties of a “Muscle Contraction” (MC sensor during isometric muscle contraction in different length/tension conditions. The MC sensor is attached so that it indents the skin overlying a muscle group and detects varying degrees of tension during muscular contraction. We compared MC sensor readings over the biceps brachii (BB muscle to dynamometric measurements of force of elbow flexion, together with recordings of surface EMG signal of BB during isometric contractions at 15° and 90° of elbow flexion. Statistical correlation between MC signal and force was very high at 15° (r = 0.976 and 90° (r = 0.966 across the complete time domain. Normalized SD or σN = σ/max(FMC was used as a measure of linearity of MC signal and elbow flexion force in dynamic conditions. The average was 8.24% for an elbow angle of 90° and 10.01% for an elbow of angle 15°, which indicates high linearity and good dynamic properties of MC sensor signal when compared to elbow flexion force. The next step of testing MC sensor potential will be to measure tension of muscle-tendon complex in conditions when length and tension change simultaneously during human motion.

  9. The Combined Effect of Electrical Stimulation and High-Load Isometric Contraction on Protein Degradation Pathways in Muscle Atrophy Induced by Hindlimb Unloading

    OpenAIRE

    Naoto Fujita; Shinichiro Murakami; Hidemi Fujino

    2011-01-01

    High-load isometric exercise is considered an effective countermeasure against muscle atrophy, but therapeutic electrical stimulation for muscle atrophy is often performed without loading. In the present study, we investigated the combined effectiveness of electrical stimulation and high-load isometric contraction in preventing muscle atrophy induced by hindlimb unloading. Electrical stimulation without loading resulted in slight attenuation of muscle atrophy. Moreover, combining electrical s...

  10. On isometric dilations of product systems of C*-correspondences and applications to families of contractions associated to higher-rank graphs

    CERN Document Server

    Skalski, Adam

    2008-01-01

    Let E be a product system of C*-correspondences over N^r. Some sufficient conditions for the existence of a not necessarily regular isometric dilation of a completely contractive representation of E are established and difference between regular and *-regular dilations discussed. It is in particular shown that a minimal isometric dilation is *-regular if and only if it is doubly commuting. The case of product systems associated with higher-rank graphs is analysed in detail.

  11. A comparison of customized strategies to manage muscle fatigue in isometric artificially elicited muscle contractions for incomplete SCI subjects

    Directory of Open Access Journals (Sweden)

    del-Ama Antonio J.

    2013-01-01

    Full Text Available Muscle fatigue due to functional electrical stimulation still prevents its widespread use as a gait rehabilitation tool for spinal cord injured subjects. Although there is an active research towards optimization of pulse parameters to delay muscle fatigue, changes in stimulated muscle's performance during repeated contractions due to fatigue have not been yet determined. In this work, a study conducted in two phases with a sample of incomplete spinal cord injured patients is presented. In the first phase, a fatigue protocol based on submaximal isometric contractions allowed to obtain an objective criterion for estimation of fatigue of knee muscles from initial changes in muscle performance. The criterion is incorporated in the fatigue protocol in the second phase of the study, to compare two novel customized fatigue management strategies. Results showed that knee flexor muscles develop less force and lower fatigue than extensor muscles. Muscle fatigue management strategies based on customized modulations of stimulation frequency are valid to delay muscle fatigue.

  12. Behaviour of the electrical impedance myography in isometric contraction of biceps brachii at different elbow joint angles

    Science.gov (United States)

    Coutinho, A. B. B.; Jotta, B.; Pino, A. V.; Souza, M. N.

    2012-12-01

    Electrical impedance myography (EIM) can be understood as an experimental technique applied to evaluate bioelectrical impedance associated to the muscular activity. With the development of technique, some studies are trying to associate the EIM parameters with the morphological and physiological changes that occur in the muscle during contraction. In this context this work sought to associate EIM parameters observed during isometric contractions of the biceps brachii muscle at different elbow joint angles with the correspondent muscular force. Differently from previous works that did not observe significant correlation between those data, our findings point to high correlations between the some EIM resistive parameters and the muscle force. Despite the need of further investigation, our results indicated that EIM technique can be used to estimate muscle force in a noninvasive way.

  13. Medial gastrocnemius architectural properties during isometric contractions in boys and men.

    Science.gov (United States)

    Kannas, Theodoros; Kellis, Eleftherios; Arampatzi, Fotini; de Villarreal, Eduardo Saez Saez

    2010-02-01

    The aim of this study was to examine the differences in muscle architecture during isometric tests between children and adults. Eight boys (age= 11.2 +/- 0.26 years) and eight men (age= 22.3 +/- 2.01 years) performed plantar flexion isometric efforts at angles of -15 degrees, 0 degrees, 15 degrees at 0%, 40%, 60%, 80% of MVC. Analysis of variance tests indicated that adults showed greater fascicle length from rest to 80% of MVC (p MVC (p MVC (p < .05). These differences observed in MG would appear to favor better utilization of the force-length and the force-velocity relationships, of the muscle in adults compared with children.

  14. Maximal intermittent contractions of the first dorsal interosseous inhibits voluntary activation of the contralateral homologous muscle.

    Science.gov (United States)

    Kavanagh, Justin J; Feldman, Matthew R; Simmonds, Michael J

    2016-09-07

    The aim of this study was to investigate how maximal intermittent contractions for a hand muscle influence cortical and reflex activity, as well as the ability to voluntarily activate, the homologous muscle in the opposite limb. Twelve healthy subjects (age: 24 ± 3 years, all right hand dominant) performed maximal contractions of the dominant limb first dorsal interosseous (FDI), and activity of the contralateral FDI was examined in a series of experiments. Index finger abduction force, FDI EMG, motor evoked potentials and heteronomous reflexes were obtained from the contralateral limb during brief non-fatiguing contractions. The same measures, as well as the ability to voluntarily activate the contralateral FDI, were then assessed in an extended intermittent contraction protocol that elicited fatigue. Brief contractions under non-fatigued conditions increased index finger abduction force, FDI EMG, and motor evoked potential amplitude of the contralateral limb. However, when intermittent maximal contractions were continued until fatigue, there was an inability to produce maximal force with the contralateral limb (~30%) which was coupled to a decrease in the level of voluntary activation (~20%). These declines were present without changes in reflex activity, and regardless of whether cortical or motor point stimulation was used to assess voluntary activation. It is concluded that performing maximal intermittent contractions with a single limb causes an inability of the CNS to maximally drive the homologous muscle of the contralateral limb. This was, in part, mediated by mechanisms that involve the motor cortex ipsilateral to the contracting limb.

  15. Voluntary activation during maximal contraction with advancing age: a brief review.

    Science.gov (United States)

    Klass, Malgorzata; Baudry, Stéphane; Duchateau, Jacques

    2007-07-01

    It is well established that the loss of muscle mass (i.e. sarcopenia) is the primary factor contributing to the reduction in muscle force with ageing. Based on the observation that force declines at a faster rate than muscle mass, neural alterations are also thought to contribute to muscle weakness by reducing central drive to the agonist muscles and by increasing coactivation of the antagonist muscles. Researchers have attempted to quantify the contribution of impaired voluntary drive to the decline in muscle force using superimposed electrical stimulation during maximal voluntary contractions (MVCs) and by recording surface electromyographic (EMG) activity. Although reduced voluntary activation of agonist muscles and increased coactivation of antagonist muscles during a MVC have been reported with advancing age, such changes are not supported by all studies. These discrepancies may be explained by differences in sensitivity between the methods used to assess voluntary activation, as well as differences between the characteristics of the study population, the muscle group that is tested, and the type of contraction that is performed. The objective of this review is to summarize current knowledge regarding the activation of agonist and antagonist muscles during MVC in elderly and to try to clarify the disparities in literature concerning the influence of a possible deficit in voluntary activation on the maximal force capacity of muscles in elderly adults.

  16. Functional imaging of muscle oxygenation and oxygen consumption in the knee extensor muscles during isometric contractions by spatially resolved near-infrared spectroscopy

    Science.gov (United States)

    Kek, Khai Jun; Miyakawa, Takahiro; Kudo, Nobuki; Yamamoto, Katsuyuki

    2007-02-01

    In this study, we showed that exercise type- and intensity-dependent regional differences in muscle oxygenation and oxygen consumption rate (Vo II) of the knee extensor muscles could be imaged in real time with a multi-channel spatially resolved near-infrared spectroscopy (SR-NIRS) imaging device. Healthy subjects performed isometric knee extension exercise for 30 s (without- or with-leg-press action) at different exercise intensities [10%, 40% and 70% of maximum voluntary contraction (MVC)]. "Separation-type" probes were attached to the skin over the major knee extensor muscles: vastus lateralis (VL), rectus femoris (RF) and vastus medialis (VM). Placement of the probes enabled simultaneously measurement of 12 sites over a skin area of about 30 cm2 (temporal resolution = 0.25 s). Local Vo II of each muscle, resting Vo II (Vo II, rest) and recovery Vo II (Vo II, rec ), were determined with arterial occlusion before the start and after the end of contraction, respectively. There was no significant difference between the values of Vo II rest, in the muscles. However, during knee extension exercise without-leg-press action, Vo II rec, value of the RF was significantly greater than the values of the VL and VM at all exercise intensities. In contrast, during exercise with-leg-press action, Vo II rec, values of the RF and VM were greater than those of the VL, especially during exercise at 40% and 70% MVC. In summary, the regional differences in muscle oxygenation and Vo II of the knee extensor muscles, probably due to the differences in relative contributions of muscles to exercise and in muscle architecture, were imaged using SR-NIRS.

  17. Evidence of skeletal muscle damage following electrically stimulated isometric muscle contractions in humans

    DEFF Research Database (Denmark)

    Mackey, Abigail; Bojsen-Moller, Jens; Qvortrup, Klaus

    2008-01-01

    It is unknown whether muscle damage at the level of the sarcomere can be induced without lengthening contractions. To investigate this, we designed a study where seven young, healthy men underwent 30 min of repeated electrical stimulated contraction of m. gastrocnemius medialis, with the ankle an...

  18. Electromyographic Responses during Elbow Movement at Two Angles with Voluntary Contraction: Influences of Muscle Activity on Upper Arm Biceps Brachii

    Directory of Open Access Journals (Sweden)

    Nizam Uddin Ahamed

    2012-11-01

    Full Text Available Analysis of Electromyography (EMG signals generated by individuals is part of human musculoskeletal system research and signals are always influenced by the electrode placement in the muscle. This characteristic is also obvious at Biceps Brachii (BB muscles during the movement of elbow at different angles. The purpose of this study was to monitor and determine the BB muscle function in 3 conditions: (i electrodes were placed at 3 locations on the BB, (ii elbow was fixed at the two angles (90° and 150° and (iii isometric contractions were performed to record EMG data. EMG data were obtained from six healthy subjects (n = 6, mean±SD age = 24.4±3.1 years, body mass = 68±6.3 kg, height = 164±4.1 cm, BMI = 21.2±2.3, right arm dominated. A Bluetooth-enabled laptop, wireless EMG sensors, digital dynamometer and angle meter were used for data recording. EMG data were calculated and analyzed by average value, standard deviation, Root Mean Square (RMS and highest peak of the signal during maximum voluntary contraction. All the dependent variables were calculated using repeated measures Analysis of Variance (ANOVA. The results from the research showed that (i according to the calculation of average RMS and the maximum peaks of EMG signals, there was a significant difference between 2 angles (p = 0.047, i.e., p<0.05, but no interaction at the same angles when overall average EMG and standard deviation value are considered and (ii majority of the outcomes showed that EMG activity is higher in the order of middle, upper and lower BB muscle. It is therefore important that electrical signals generated upon different electrode placements and angles on the BB muscle are used for biceps rehabilitation and other physiological measurements on upper arm.

  19. An EEG-based study of discrete isometric and isotonic human lower limb muscle contractions

    Directory of Open Access Journals (Sweden)

    Gwin Joseph T

    2012-06-01

    Full Text Available Abstract Background Electroencephalography (EEG combined with independent component analysis enables functional neuroimaging in dynamic environments including during human locomotion. This type of functional neuroimaging could be a powerful tool for neurological rehabilitation. It could enable clinicians to monitor changes in motor control related cortical dynamics associated with a therapeutic intervention, and it could facilitate noninvasive electrocortical control of devices for assisting limb movement to stimulate activity dependent plasticity. Understanding the relationship between electrocortical dynamics and muscle activity will be helpful for incorporating EEG-based functional neuroimaging into clinical practice. The goal of this study was to use independent component analysis of high-density EEG to test whether we could relate electrocortical dynamics to lower limb muscle activation in a constrained motor task. A secondary goal was to assess the trial-by-trial consistency of the electrocortical dynamics by decoding the type of muscle action. Methods We recorded 264-channel EEG while 8 neurologically intact subjects performed isometric and isotonic, knee and ankle exercises at two different effort levels. Adaptive mixture independent component analysis (AMICA parsed EEG into models of underlying source signals. We generated spectrograms for all electrocortical source signals and used a naïve Bayesian classifier to decode exercise type from trial-by-trial time-frequency data. Results AMICA captured different electrocortical source distributions for ankle and knee tasks. The fit of single-trial EEG to these models distinguished knee from ankle tasks with 80% accuracy. Electrocortical spectral modulations in the supplementary motor area were significantly different for isometric and isotonic tasks (p  Conclusions Independent component analysis of EEG reveals unique spatial and spectro-temporal electrocortical properties for different

  20. Later stages of diabetic neuropathy affect the complexity of the neuromuscular system at the knee during low-level isometric contractions

    DEFF Research Database (Denmark)

    Suda, Eneida Y.; Sacco, Isabel C. N.; Hirata, Rogerio P.

    2017-01-01

    INTRODUCTION: The aim of this study was to evaluate the complexity of force and surface electromyography (sEMG) during knee extension and flexion at low-level isometric contractions in individuals with different degrees of diabetic peripheral neuropathy (DPN). METHODS: Ten control and 38 diabetic...

  1. Neural activation during submaximal contractions seems more reflective of neuromuscular ageing than maximal voluntary activation

    Directory of Open Access Journals (Sweden)

    Gil eScaglioni

    2016-02-01

    Full Text Available This study aimed at testing the hypothesis that differences in neural activation strategy during submaximal but not maximal plantarflexions exist between young and older men. Eleven young men (YM, 26±4 yr and 13 OM (76±3 yr volunteered for the investigation. Maximal voluntary torque (MVT was 38.2%, lower (P<0.001 in OM than in YM, while voluntary activation was equivalent (~97%. The relationship between the interpolated twitch-torque and the voluntary torque (IT-VT relationship was composite (curvilinear+exponential for both age-groups. However, the OM showed accentuated concavity, as attested by the occurrence of the deviation from linearity at a lower contraction intensity (OM: 54.9 vs. YM: 71.9% MVT. In conclusion, ageing does not affect the capacity to fully activate the plantar flexors during maximal performances, but it alters the activation pattern for submaximal levels of effort. The greater age-related concavity of the IT-VT relationship suggests that, during submaximal contractions, OM need to reach a level of activation higher than YM to develop an equivalent relative torque.

  2. Differential displacement of the human soleus and medial gastrocnemius aponeuroses during isometric plantar flexor contractions in vivo.

    Science.gov (United States)

    Bojsen-Møller, Jens; Hansen, Philip; Aagaard, Per; Svantesson, Ulla; Kjaer, Michael; Magnusson, S Peter

    2004-11-01

    The human triceps surae muscle-tendon complex is a unique structure with three separate muscle compartments that merge via their aponeuroses into the Achilles tendon. The mechanical function and properties of these structures during muscular contraction are not well understood. The purpose of the study was to investigate the extent to which differential displacement occurs between the aponeuroses of the medial gastrocnemius (MG) and soleus (Sol) muscles during plantar flexion. Eight subjects (mean +/- SD; age 30 +/- 7 yr, body mass 76.8 +/- 5.5 kg, height 1.83 +/- 0.06 m) performed maximal isometric ramp contractions with the plantar flexor muscles. The experiment was performed in two positions: position 1, in which the knee joint was maximally extended, and position 2, in which the knee joint was maximally flexed (125 degrees ). Plantarflexion moment was assessed with a strain gauge load cell, and the corresponding displacement of the MG and Sol aponeuroses was measured by ultrasonography. Differential shear displacement of the aponeurosis was quantified by subtracting displacement of Sol from that of MG. Maximal plantar flexion moment was 36% greater in position 1 than in position 2 (132 +/- 20 vs. 97 +/- 11 N.m). In position 1, the displacement of the MG aponeurosis at maximal force exceeded that of the Sol (12.6 +/- 1.7 vs. 8.9 +/- 1.5 mm), whereas in position 2 displacement of the Sol was greater than displacement of the MG (9.6 +/- 1.0 vs. 7.9 +/- 1.2 mm). The amount and "direction" of shear between the aponeuroses differed significantly between the two positions across the entire range of contraction, indicating that the Achilles tendon may be exposed to intratendinous shear and stress gradients during human locomotion.

  3. The effect of sustained low-intensity contractions on supraspinal fatigue in human elbow flexor muscles

    DEFF Research Database (Denmark)

    Søgaard, Karen; Gandevia, Simon C; Todd, Gabrielle

    2006-01-01

    contractions is not clear. This study investigated whether central fatigue developed during prolonged low-force voluntary contractions. Subjects (n=9) held isometric elbow flexions of 15% MVC for 43 min. Voluntary activation was measured during brief MVCs every 3 min. During each MVC, transcranial magnetic...

  4. Changes in Systolic Blood Pressure during Isometric Contractions of Different Size Muscle Groups.

    Science.gov (United States)

    1979-05-01

    flexion), fine motor control is required to produce index finger adduction as an isolated i contraction (37,38). with this in mind , one should...efficacy of drugs used for treating I hypertension. Clinicians, using biofeedback techniques, could teach individuals hcw to relax certain muscles. i...I APP ~NDhX E CLLIBRATION CF FO~C~ £~EASIJBING TR&NSDUC~B5 I I ii I I H. I I’ I.. I 106 The calibration for each ’t0" ring force transducer I was

  5. Descending pain modulation and its interaction with peripheral sensitization following sustained isometric muscle contraction in fibromyalgia

    DEFF Research Database (Denmark)

    Ge, Hong-You; Nie, HongLing; Graven-Nielsen, Thomas

    2012-01-01

    facilitation and that the effect of descending pain modulation be dependent on peripheral muscle pain sensitivity. METHODS: Pressure pain thresholds (PPT) were measured from 13 points bilaterally in the upper trapezius muscle and from the mid-point bilaterally in the tibialis anterior before-, immediately......) than healthy control groups (286.2±24.1s) (P0.05). Following the contraction, PPTs were increased significantly and heterogeneously in the upper trapezius over time, but not, in the tibialis anterior muscle in healthy controls. However, PPT were significantly decreased over time in the tibialis...

  6. Brain Functional Connectivity is Different during VoluntaryConcentric and Eccentric Muscle Contraction

    Directory of Open Access Journals (Sweden)

    Wan X Yao

    2016-11-01

    Full Text Available Previous studies report greater activation in the cortical motor network in controlling eccentric contraction (EC than concentric contraction (CC of human skeletal muscles despite lower activation level of the muscle associated with EC. It is unknown, however, whether the strength of functional coupling between the primary motor cortex (M1 and other involved areas in the brain differs as voluntary movements are controlled by a network of regions in the primary, secondary and association cortices. Examining fMRI-based functional connectivity (FC offers an opportunity to measure strength of such coupling. To address the question, we examined functional MRI (fMRI data acquired during EC and CC (20 contractions each with similar movement distance and speed of the right first dorsal interosseous (FDI muscle in 11 young (20-32 years and healthy individuals and estimated FC between the M1 and a number of cortical regions in the motor control network. The major findings from the behavioral and fMRI-based FC analysis were that (1 no significant differences were seen in movement distance, speed and stability between the EC and CC; (2 significantly stronger mean FC was found for CC than EC. Our finding provides novel insights for a better understanding of the control mechanisms underlying voluntary movements produced by EC and CC. The finding is potentially helpful for guiding the development of targeted sport training and/or therapeutic programs for performance enhancement and injury prevention.

  7. Voluntary low-force contraction elicits prolonged low-frequency fatigue and changes in surface electromyography and mechanomyography

    DEFF Research Database (Denmark)

    Blangsted, Anne Katrine; Sjøgaard, Gisela; Madeleine, Pascal

    2005-01-01

    ) and in particular mechanomyography (MMG) during low-force rather than high-force test contractions. Seven subjects performed static wrist extension at 10% maximal voluntary contraction (MVC) for 10 min (10%MVC10 min). Wrist force response to electrical stimulation of extensor carpi radialis muscle (ECR) quantified...

  8. Ultrasonographic analysis of dorsal neck muscles thickness changes induced by isometric contraction of shoulder muscles: A comparison between patients with chronic neck pain and healthy controls.

    Science.gov (United States)

    Karimi, Noureddin; Rezasoltani, Asghar; Rahnama, Leila; Noori-Kochi, Farhang; Jaberzadeh, Shapour

    2016-04-01

    Altered pattern of muscle activity is commonly seen with chronic neck pain (CNP). However, limited investigations have been done on dorsal neck muscles' activity pattern while performing upper limb tasks in patients with CNP. To investigate dorsal neck muscles' thickness changes during isometric contraction of shoulder muscles. Case-control study. This study investigated dorsal neck muscles' thickness changes during isometric contraction of shoulder muscles in 20 healthy participants (mean age 27 ± 4.37) and 17 patients with CNP (mean age 29 ± 5.50). Effects of isometric force of shoulder muscles on dorsal neck muscles' thickness changes were also evaluated. Significant muscle × group interaction was observed for the dorsal neck muscles thickness changes (p = 0.008) indicating different pattern of muscle activity in terms of changes in muscle thickness of two groups. Significant main effects of direction was observed (P = 0.003), with the abduction had the greatest impact on changing the dorsal neck muscles thickness. patients with CNP showed altered pattern of muscle thickness changes in comparison to healthy participants. Isometric abduction of shoulder muscles induced the greatest changes of dorsal neck muscles thickness among other force directions. Copyright © 2015 Elsevier Ltd. All rights reserved.

  9. SUPERNORMAL MUSCLE-FIBER CONDUCTION-VELOCITY DURING INTERMITTENT ISOMETRIC-EXERCISE IN HUMAN MUSCLE

    NARCIS (Netherlands)

    VANDERHOEVEN, JH; LANGE, F

    1994-01-01

    Muscle fiber conduction velocity (MFCV) and surface electromyographic parameters were studied in the brachial biceps muscle of healthy males during voluntary intermittent isometric contractions at 50% of maximum force. Recovery in the following 15 min was then observed. The measurements were perform

  10. Oxygenation and EMG in the proximal and distal vastus lateralis during submaximal isometric knee extension

    DEFF Research Database (Denmark)

    Crenshaw, Albert G.; Bronee, Lars; Krag, Ida

    2010-01-01

    /or (2) fatigue development. Nine males performed 2-min sustained isometric knee extensions at 15% and 30% maximum voluntary contraction during which oxygenation and EMG were recorded simultaneously from proximal and distal locations of the vastus lateralis muscle. Near infrared spectroscopy variables...

  11. Temporal muscle activation assessment by ultrasound imaging during flexor withdrawal reflex and voluntary contraction.

    Science.gov (United States)

    Jose, Gomez-Tames; Shuto, Nakamura; Jose, Gonzalez; Wenwei, Yu

    2013-01-01

    Activating flexor reflexes by electrical stimulation has been used as a mechanism to initiate the swing phase or to enhance it for spinal cord injured patients. However, it is necessary to know their contraction dynamics in order to artificially induce them at the right moment of a walking cycle. This requires understanding the temporal activation pattern of both surface and deep muscles simultaneously. This study aimed at developing a system to measure and analyze the temporal activation of both surface and deep muscles during voluntary contraction and flexor reflexes (also called withdrawal reflexes) using ultrasound imaging. A set of experiments were done to verify the validity of the system, while exploring the temporal pattern of muscle activation during flexor reflexes. As a result, we were able to quantify the surface and deep muscle activity by measuring the muscle thickness, pennation angle and long-axis displacement, from the ultrasound images.

  12. Isometric exercise in the denervated heart: a Doppler echocardiographic study.

    OpenAIRE

    Robson, S C; Furniss, S.S.; Heads, A; Boys, R J; McGregor, C.; Bexton, R S

    1989-01-01

    The haemodynamic responses to isometric exercise of eight recipients of orthotopic heart transplants and eight healthy controls were studied. Each performed sustained exercise at 30% of maximal voluntary contraction for three minutes on a handgrip dynamometer. Cardiac output was measured by combined Doppler and cross sectional echocardiography before exercise and every 30 seconds during and after exercise. In the controls cardiac output and blood pressure increased significantly owing to an i...

  13. Clinical Value of the Assessment of Changes in MEP Duration with Voluntary Contraction.

    Science.gov (United States)

    Brum, Marisa; Cabib, Christopher; Valls-Solé, Josep

    2015-01-01

    Transcranial magnetic stimulation (TMS) gives rise to muscle responses, known as motor evoked potentials (MEP), through activation of the motor pathways. Voluntary contraction causes facilitation of MEPs, which consists of shortening MEP latency, increasing MEP amplitude and widening MEP duration. While an increase in excitability of alpha motorneurons and the corticospinal tract can easily explain latency shortening and amplitude increase, other mechanisms have to be accounted for to explain the increase in duration. We measured the increase in duration of the MEP during contraction with respect to rest in a group of healthy volunteers and retrospectively assessed this parameter in patients who were examined in a standardized fashion during the past 5 years. We included 25 healthy subjects, 21 patients with multiple sclerosis, 33 patients with acute stroke, 5 patients with hereditary spastic paraparesis, and 5 patients with signs suggesting psychogenic paresis. We found already significant differences among groups in the MEP duration at rest, patients with MS had a significantly longer duration, and patients with stroke had significantly shorter duration, than the other two groups. The increase in MEP duration during voluntary contraction was different in patients and in healthy subjects. It was significantly shorter in MS and significantly longer in stroke patients. It was absent in the five patients with suspected psychogenic weakness. In patients with HSP, an abnormally increase in duration occurred only in leg muscles. Our results suggest that the increase in duration of the MEP during contraction may reveal the contribution of propriospinal interneurons to the activation of alpha motorneurons. This mechanism may be altered in some diseases and, therefore, the assessment proposed in this work may have clinical applicability for the differential diagnosis of weakness.

  14. Clinical value of the assessment of changes in MEP duration with voluntary contraction

    Directory of Open Access Journals (Sweden)

    Josep eValls-Sole

    2016-01-01

    Full Text Available Transcranial magnetic stimulation (TMS gives rise to muscle responses, known as motor evoked potentials (MEP, through activation of the motor pathways. Voluntary contraction causes facilitation of MEPs, which consists of shortening MEP latency, increasing MEP amplitude and widening MEP duration. While an increase in excitability of alpha motorneurons and the corticospinal tract can easily explain latency shortening and amplitude increase, other mechanisms have to be accounted for to explain the increase in duration. We measured the extent of the increase in duration that adds at the end of the MEP during contraction with respect to rest in a group of healthy volunteers and retrospectively assessed this parameter in patients who were examined in a standardized fashion during the past 5 years. We included 25 healthy subjects, 21 patients with multiple sclerosis, 33 patients with acute stroke, 5 patients with hereditary spastic paraparesis and 5 patients with signs suggesting psychogenic paresis. We found already significant differences among groups in the MEP duration at rest, patients with MS had a significantly longer duration, and patients with stroke had significantly shorter duration, than the other two groups. The increase in MEP duration during voluntary contraction was different in patients and in healthy subjects. It was significantly shorter in MS and significantly longer in stroke patients. It was absent in the 5 patients with suspected psychogenic weakness. In patients with HSP, an abnormally increase in duration occurred only in leg muscles. Our results suggest that the increase in duration of the MEP during contraction may reveal the contribution of propriospinal interneurons to the activation of alpha motorneurons. This mechanism may be altered in some diseases and, therefore, the assessment proposed in this work may have clinical applicability for the differential diagnosis of weakness.

  15. The nature of corticospinal paths driving human motoneurones during voluntary contractions.

    Science.gov (United States)

    Butler, Jane E; Larsen, Thomas S; Gandevia, Simon C; Petersen, Nicolas T

    2007-10-15

    The properties of the human motor cortex can be studied non-invasively using transcranial magnetic stimulation (TMS). Stimulation at high intensity excites corticospinal cells with fast conducting axons that make direct connections to motoneurones of human upper limb muscles, while low-intensity stimulation can suppress ongoing EMG. To assess whether these cells are used in normal voluntary contractions, we used TMS at very low intensities to suppress the firing of single motor units in biceps brachii (n = 14) and first dorsal interosseous (FDI, n = 6). Their discharge was recorded with intramuscular electrodes and cortical stimulation was delivered at multiple intensities at appropriate times during sustained voluntary firing at approximately 10 Hz. For biceps, high-intensity stimulation produced facilitation at 17.1 +/- 2.1 ms (lasting 2.4 +/- 0.9 ms), while low-intensity stimulation (below motor threshold) produced suppression (without facilitation) at 20.2 +/- 2.1 ms (lasting 7.6 +/- 2.2 ms). For FDI, high-intensity stimulation produced facilitation at 23.3 +/- 1.2 ms (lasting 1.8 +/- 0.4 ms), with suppression produced by low-intensity stimulation at 25.2 +/- 2.6 ms (lasting 7.5 +/- 2.6 ms). The difference between the onsets of facilitation and suppression was short: 3.1 +/- 1.2 ms for biceps and 2.0 +/- 1.5 ms for FDI. This latency difference is much less than that previously reported using surface EMG recordings ( approximately 10 ms). These data suggest that low-intensity cortical stimulation inhibits ongoing activity in fast-conducting corticospinal axons through an oligosynaptic (possibly disynaptic) path, and that this activity is normally contributing to drive the motoneurones during voluntary contractions.

  16. Relaxation from a voluntary contraction is preceded by increased excitability of motor cortical inhibitory circuits.

    Science.gov (United States)

    Buccolieri, Alessandro; Abbruzzese, Giovanni; Rothwell, John C

    2004-07-15

    Termination of a muscle contraction is as important a part of movement as muscle activation yet the mechanisms responsible are less well understood. In the present experiments we examined the possible role of intracortical inhibitory circuits in terminating a 20% maximum isometric contraction of the first dorsal interosseous muscle (FDI) in eight healthy subjects. Subjects performed the task simultaneously with both hands and received single or pairs (at an interstimulus interval of 3 ms to evaluate short interval intracortical inhibition, SICI) of transcranial magnetic stimuli (TMS) via a focal coil over the motor hand area of the left hemisphere at different times before and after the onset of relaxation. The amplitude of the motor-evoked potential (MEP) following a single or a pair of TMS pulses was measured in the right FDI and plotted relative to the onset of relaxation as estimated from the surface electromyogram (EMG) of the left FDI. MEPs were larger during contraction than after relaxation whereas SICI was absent during contraction and reappeared after relaxation. We found that in all subjects, the time course of MEP changes during relaxation was closely fitted by a Boltzmann sigmoidal curve which allowed us to estimate the mean MEP amplitudes as well as the ratio of the amplitudes after single or pairs of TMS pulses (i.e.%SICI) at any time in the task. The data showed that the amplitude of MEPs to single pulse TMS had started to decline at about the same time as the onset of EMG silence. Furthermore, the size of the MEPs evoked by paired pulses decreased up to 30 ms beforehand. The latter suggests that an increase in SICI occurs prior to the onset of MEP changes, and hence that increased cortical inhibition may play a role in suppressing corticospinal excitability during relaxation. A subsidiary experiment showed that the time relations of changes in SICI and MEP were unchanged by a period of 10 min training on the task.

  17. Voluntary activation of the trapezius muscle in cases with neck/shoulder pain compared to healthy controls

    DEFF Research Database (Denmark)

    Bech, Katrine Tholstrup; Larsen, Camilla Marie; Sjøgaard, Gisela

    2017-01-01

    Subjects reporting neck/shoulder pain have been shown to generate less force during maximal voluntary isometric contractions (MVC) of the shoulder muscles compared to healthy controls. This has been suggested to be caused by a pain-related decrease in voluntary activation (VA) rather than lack of...

  18. Voluntary activation of human knee extensors measured using transcranial magnetic stimulation.

    Science.gov (United States)

    Goodall, S; Romer, L M; Ross, E Z

    2009-09-01

    The aim of this study was to determine the applicability and reliability of a transcranial magnetic stimulation twitch interpolation technique for measuring voluntary activation of a lower limb muscle group. Cortical voluntary activation of the knee extensors was determined in nine healthy men on two separate visits by measuring superimposed twitch torques evoked by transcranial magnetic stimulation during isometric knee extensions of varying intensity. Superimposed twitch amplitude decreased linearly with increasing voluntary torque between 50 and 100% of mean maximal torque, allowing estimation of resting twitch amplitude and subsequent calculation of voluntary activation. There were no systematic differences for maximal voluntary activation within day (mean +/- s.d. 90.9 +/- 6.2 versus 90.7 +/- 5.9%; P = 0.98) or between days (90.8 +/- 6.0 versus 91.2 +/- 5.7%; P = 0.92). Systematic bias and random error components of the 95% limits of agreement were 0.23 and 9.3% within day versus 0.38 and 7.5% between days. Voluntary activation was also determined immediately after a 2 min maximal voluntary isometric contraction; in four of these subjects, voluntary activation was determined 30 min after the sustained contraction. Immediately after the sustained isometric contraction, maximal voluntary activation was reduced from 91.2 +/- 5.7 to 74.2 +/- 12.0% (P knee extensors.

  19. Effect of motor imagery and voluntary muscle contraction on the F wave.

    Science.gov (United States)

    Hara, Motohiko; Kimura, Jun; Walker, D David; Taniguchi, Shinichirou; Ichikawa, Hiroo; Fujisawa, Reiko; Shimizu, Hiroshi; Abe, Tatsuya; Yamada, Thoru; Kayamori, Ryoji; Mizutani, Tomohiko

    2010-08-01

    We tested the validity of instructing patients to minimally contract the muscle to facilitate F-wave recording in clinical practice. In 12 healthy subjects, F waves were recorded from the first dorsal interosseous muscle at rest, during motor imagery, and at up to 30% of the maximal voluntary contraction (MVC). F-wave persistence increased significantly from 32.5 +/- 11.9% (mean +/- SD) at rest to 58.3 +/- 15.2% during motor imagery and 90.0 +/- 8.7% during 3% MVC. It then remained the same during stepwise changes to and from 30% MVC before decreasing significantly from 80.8 +/- 18.5% during 3% MVC to 48.7 +/- 23.8% during motor imagery and 27.0 +/- 16.0% at rest. The trial average of F-wave amplitude showed a similar pattern of facilitation. Motor imagery enhances F-wave persistence and amplitude, which further increase with a slight muscle contraction and show no additional change with a stronger effort.

  20. Motor unit firing during and after voluntary contractions of human thenar muscles weakened by spinal cord injury

    NARCIS (Netherlands)

    Zijdewind, Inge; Thomas, CK

    2003-01-01

    Spinal cord injury may change both the distribution and the strength of the synaptic input within a motoneuron pool and therefore alter force gradation. Here, we have studied the relative contributions of motor unit recruitment and rate modulation to force gradation during voluntary contractions of

  1. An additional phase in PCr use during sustained isometric exercise at 30% MVC in the tibialis anterior muscle.

    NARCIS (Netherlands)

    Houtman, C.J.; Heerschap, A.; Zwarts, M.J.; Stegeman, D.F.

    2002-01-01

    The occurrence of an abrupt acceleration in phosphocreatine hydrolysis in the tibial anterior muscle during the last part of a sustained isometric exercise at 30% maximal voluntary contraction until fatigue is demonstrated in seven out of eight healthy subjects by applying in vivo 31P NMR spectrosco

  2. Between-subject variance in the magnitude of corticomuscular coherence during tonic isometric contraction of the tibialis anterior muscle in healthy young adults.

    Science.gov (United States)

    Ushiyama, Junichi; Suzuki, Tatsuya; Masakado, Yoshihisa; Hase, Kimitaka; Kimura, Akio; Liu, Meigen; Ushiba, Junichi

    2011-09-01

    Oscillatory activity of the sensorimotor cortex has been reported to show coherence with muscle activity in the 15- to 35-Hz frequency band (β-band) during weak to moderate intensity of isometric contraction. The present study examined the variance of the magnitude of the corticomuscular coherence across a large number of subjects. We quantified the coherence between EEG over the sensorimotor cortex and rectified electromyogram (EMG) from the tibialis anterior muscle during tonic isometric contraction at 30% of maximal effort in 100 healthy young individuals. We estimated the maximal peak of EEG-EMG coherence (Cohmax) and the ratio of the sum of the autopower spectral density function within the β-band to that of all frequency ranges for both EEG (EEGβ-PSD) and EMG (EMGβ-PSD) signals. The frequency histogram of Cohmax across all subjects showed a broad bell-shaped continuous distribution (range, 0.048-0.816). When the coherence was thresholded at the estimated significance level of P < 0.05 (0.114), 46 out of 100 subjects showed significant EEG-EMG coherence. Cohmax occurred within the β-band in the majority of subjects who showed significant EEG-EMG coherence (n = 43). Furthermore, Cohmax showed significant positive correlations with both EEGβ-PSD (r = 0.575, P < 0.001) and EMGβ-PSD (r = 0.606, P < 0.001). These data suggest that even during simple tonic isometric contraction, the strength of oscillatory coupling between the sensorimotor cortex and spinal motoneurons varies among individuals and is a contributory factor determining muscle activation patterns such as the degree of grouped discharge in muscle activity within the β-band for each subject.

  3. Postactivation Potentiation Biases Maximal Isometric Strength Assessment

    Directory of Open Access Journals (Sweden)

    Leonardo Coelho Rabello Lima

    2014-01-01

    Full Text Available Postactivation potentiation (PAP is known to enhance force production. Maximal isometric strength assessment protocols usually consist of two or more maximal voluntary isometric contractions (MVCs. The objective of this study was to determine if PAP would influence isometric strength assessment. Healthy male volunteers (n=23 performed two five-second MVCs separated by a 180-seconds interval. Changes in isometric peak torque (IPT, time to achieve it (tPTI, contractile impulse (CI, root mean square of the electromyographic signal during PTI (RMS, and rate of torque development (RTD, in different intervals, were measured. Significant increases in IPT (240.6 ± 55.7 N·m versus 248.9 ± 55.1 N·m, RTD (746 ± 152 N·m·s−1versus 727 ± 158 N·m·s−1, and RMS (59.1 ± 12.2% RMSMAX  versus 54.8 ± 9.4% RMSMAX were found on the second MVC. tPTI decreased significantly on the second MVC (2373 ± 1200 ms versus 2784 ± 1226 ms. We conclude that a first MVC leads to PAP that elicits significant enhancements in strength-related variables of a second MVC performed 180 seconds later. If disconsidered, this phenomenon might bias maximal isometric strength assessment, overestimating some of these variables.

  4. Effect of remote voluntary contractions on knee extensor torque and rate of velocity development.

    Science.gov (United States)

    Cherry, Emily A; Brown, Lee E; Coburn, Jared W; Noffal, Guillermo J

    2010-09-01

    Remote voluntary contractions (RVCs) are described as a muscle action of the prime mover while performing a simultaneous muscle action with another part of the body. Previous studies have shown that RVCs may elicit augmented performance of the prime mover. The purpose of this study was to evaluate the effect of RVCs on knee extensor rate of velocity development (RVD) and peak torque. Fourteen men and 16 women who were regularly active and free of any knee pathology for the past year took part in this study. Subjects performed 3 maximal dynamic knee extensions at 3 velocities with and without an RVC condition. The RVC condition consisted of holding hand dynamometers in each hand and maximally gripping while performing a maximal knee extension movement. The NO-RVC condition was the same only without gripping. Men produced greater peak torque and RVD than did women across speeds and conditions. Analysis demonstrated that RVC had no effect on knee extension peak torque, but RVD decreased in the RVC condition (NO-RVC 2,012.07 [46.52] degrees xs-1xs-1; RVC 1,882.61 [51.84] degrees xs-1xs-1). Grip strength of the left hand at 180 degrees xs-1decreased from 42.03 (14.40) to 38.83 (14.65) kg in the RVC condition. In conclusion, RVC should not be used when attempting to maximize RVD, because it may hinder results when performing a single joint movement.

  5. Transcranial Magnetic Stimulation with the Maximum Voluntary Muscle Contraction Facilitates Motor Neuron Excitability and Muscle Force

    Directory of Open Access Journals (Sweden)

    Tetsuo Touge

    2012-01-01

    Full Text Available Three trials of transcranial magnetic stimulation (TMS during the maximum voluntary muscle contraction (MVC were repeated at 15-minute intervals for 1 hour to examine the effects on motor evoked potentials (MEPs in the digital muscles and pinching muscle force before and after 4 high-intensity TMSs (test 1 condition or sham TMS (test 2 condition with MVC. Under the placebo condition, real TMS with MVC was administered only before and 1 hour after the sham TMS with MVC. Magnetic stimulation at the foramen magnum level (FMS with MVC was performed by the same protocol as that for the test 2 condition. As a result, MEP sizes in the digital muscles significantly increased after TMS with MVC under test conditions compared with the placebo conditions (P<0.05. Pinching muscle force was significantly larger 45 minutes and 1 hour after TMS with MVC under the test conditions than under the placebo condition (P<0.05. FMS significantly decreased MEP amplitudes 60 minutes after the sham TMS with MVC (P<0.005. The present results suggest that intermittently repeated TMS with MVC facilitates motor neuron excitabilities and muscle force. However, further studies are needed to confirm the effects of TMS with MVC and its mechanism.

  6. Transcranial magnetic stimulation with the maximum voluntary muscle contraction facilitates motor neuron excitability and muscle force.

    Science.gov (United States)

    Touge, Tetsuo; Urai, Yoshiteru; Ikeda, Kazuyo; Kume, Kodai; Deguchi, Kazushi

    2012-01-01

    Three trials of transcranial magnetic stimulation (TMS) during the maximum voluntary muscle contraction (MVC) were repeated at 15-minute intervals for 1 hour to examine the effects on motor evoked potentials (MEPs) in the digital muscles and pinching muscle force before and after 4 high-intensity TMSs (test 1 condition) or sham TMS (test 2 condition) with MVC. Under the placebo condition, real TMS with MVC was administered only before and 1 hour after the sham TMS with MVC. Magnetic stimulation at the foramen magnum level (FMS) with MVC was performed by the same protocol as that for the test 2 condition. As a result, MEP sizes in the digital muscles significantly increased after TMS with MVC under test conditions compared with the placebo conditions (P MVC under the test conditions than under the placebo condition (P MVC (P MVC facilitates motor neuron excitabilities and muscle force. However, further studies are needed to confirm the effects of TMS with MVC and its mechanism.

  7. Strength Training to Contraction Failure Increases Voluntary Activation of the Quadriceps Muscle Shortly After Total Knee Arthroplasty

    DEFF Research Database (Denmark)

    Mikkelsen, Elin Karin; Jakobsen, Thomas Linding; Holsgaard-Larsen, Anders;

    2016-01-01

    OBJECTIVE: The objective of this study was to investigate voluntary activation of the quadriceps muscle during one set of knee extensions performed until contraction failure in patients shortly after total knee arthroplasty. DESIGN: This was a cross-sectional study of 24 patients with total knee...... arthroplasty. One set of knee extensions was performed until contraction failure, using a predetermined 10 repetition maximum loading. In the operated leg, electromyographic (EMG) activity of the lateral and medial vastus, semitendinosus, and biceps femoris muscles was recorded during the set. Muscle activity...... (%EMGmax) and median power frequency of the EMG power spectrum were calculated for each repetition decile (10%-100% contraction failure). RESULTS: Muscle activity increased significantly over contractions from a mean of 90.0 and 93.6 %EMGmax (lateral vastus and medial vastus, respectively) at 10...

  8. Activation of selected shoulder muscles during unilateral wall and bench press tasks under submaximal isometric effort.

    Science.gov (United States)

    Tucci, Helga T; Ciol, Marcia A; de Araújo, Rodrigo C; de Andrade, Rodrigo; Martins, Jaqueline; McQuade, Kevin J; Oliveira, Anamaria S

    2011-07-01

    Controlled laboratory study. To assess the activation of 7 shoulder muscles under 2 closed kinetic chain (CKC) tasks for the upper extremity using submaximal isometric effort, thus providing relative quantification of muscular isometric effort for these muscles across the CKC exercises, which may be applied to rehabilitation protocols for individuals with shoulder weakness. CKC exercises favor joint congruence, reduce shear load, and promote joint dynamic stability. Additionally, knowledge about glenohumeral and periscapular muscle activity elicited during CKC exercises may help clinicians to design protocols for shoulder rehabilitation. Using surface electromyography, activation level was measured across 7 shoulder muscles in 20 healthy males, during the performance of a submaximal isometric wall press and bench press. Signals were normalized to the maximal voluntary isometric contraction, and, using paired t tests, data were analyzed between the exercises for each muscle. Compared to the wall press, the bench press elicited higher activity for most muscles, except for the upper trapezius. Levels of activity were usually low but were above 20% maximal voluntary isometric contraction for the serratus anterior on both tasks, and for the long head triceps brachii on the bench press. Both the bench press and wall press, as performed in this study, led to relatively low EMG activation levels for the muscles measured and may be considered for use in the early phases of rehabilitation.

  9. Training-related changes in the EMG-moment relationship during isometric contractions: Further evidence of improved control of muscle activation in strength-trained men?

    Science.gov (United States)

    Amarantini, David; Bru, Bertrand

    2015-08-01

    The possibility of using electromyography (EMG) to track muscle activity has raised the question of its relationship with the effort exerted by the muscles around the joints. However, the EMG-moment relationship is yet to be fully defined, and increasing knowledge of this topic could contribute to research in motor control and to the development of EMG-based algorithms and devices. With regards the training-related adaptations at the peripheral and central level, the present study investigated the effect of strength training on EMG-moment relationship. Our aim was to clarify its nature and gain further understanding of how morphological and neural factors may affect its form. The EMG-moment relationship was determined during knee flexion and extension isometric contractions performed by strength-trained male athletes and untrained male participants. The results showed that strength training induced linearity of the EMG-moment relationship concomitantly with enhanced maximum force production capacity and decreased co-activation of knee agonist-antagonist muscle pair. These results clarified discordant results regarding the linear or curved nature of the EMG-moment in isometric conditions and suggested that the remarkable linearity of the EMG-moment found in trained participants could indicate improved control of muscle activation.

  10. Effects of myofascial release leg pull and sagittal plane isometric contract-relax techniques on passive straight-leg raise angle.

    Science.gov (United States)

    Hanten, W P; Chandler, S D

    1994-09-01

    Experimental evidence does not currently exist to support the claims of clinical effectiveness for myofascial release techniques. This presents an obvious need to document the effects of myofascial release. The purpose of this study was to compare the effects of two techniques, sagittal plane isometric contract-relax and myofascial release leg pull for increasing hip flexion range of motion (ROM) as measured by the angle of passive straight-leg raise. Seventy-five nondisabled, female subjects 18-29 years of age were randomly assigned to contract-relax, leg pull, or control groups. Pretest hip flexion ROM was measured for each subject's right hip with a passive straight-leg raise test using a fluid-filled goniometer. Subjects in the treatment groups received either contract-relax or leg pull treatment applied to the right lower extremity; subjects in the control group remained supine quietly for 5 minutes. Following treatment, posttest straight-leg raise measurements were performed. A one-way analysis of variance followed by a Newman-Keuls post hoc comparison of mean gain scores showed that subjects receiving contract-relax treatment increased their ROM significantly more than those who received leg pull treatment, and the increase in ROM of subjects in both treatment groups was significantly higher than those of the control group. The results suggest that while both contract-relax and leg pull techniques can significantly increase hip flexion ROM in normal subjects, contract-relax treatment may be more effective and efficient than leg pull treatment.

  11. Motor unit firing rates and synchronisation affect the fractal dimension of simulated surface electromyogram during isometric/isotonic contraction of vastus lateralis muscle.

    Science.gov (United States)

    Mesin, Luca; Dardanello, Davide; Rainoldi, Alberto; Boccia, Gennaro

    2016-12-01

    During fatiguing contractions, many adjustments in motor units behaviour occur: decrease in muscle fibre conduction velocity; increase in motor units synchronisation; modulation of motor units firing rate; increase in variability of motor units inter-spike interval. We simulated the influence of all these adjustments on synthetic EMG signals in isometric/isotonic conditions. The fractal dimension of the EMG signal was found mainly influenced by motor units firing behaviour, being affected by both firing rate and synchronisation level, and least affected by muscle fibre conduction velocity. None of the calculated EMG indices was able to discriminate between firing rate and motor units synchronisation. Copyright © 2016 IPEM. Published by Elsevier Ltd. All rights reserved.

  12. The relationships between exercise intensity, heart rate, and blood pressure during an incremental isometric exercise test.

    Science.gov (United States)

    Wiles, Jonathan D; Allum, Simon R; Coleman, Damian A; Swaine, Ian L

    2008-01-15

    Currently, it is not possible to prescribe isometric exercise at an intensity that corresponds to given heart rates or systolic blood pressures. This might be useful in optimizing the effects of isometric exercise training. Therefore, the aim of this study was to explore the relationships between isometric exercise intensity and both heart rate and systolic blood pressure during repeated incremental isometric exercise tests. Fifteen participants performed seated isometric double-leg knee extension, during which maximum voluntary contraction (MVC) was assessed, using an isokinetic dynamometer. From this, a corresponding peak electromyographic activity (EMG(peak)) was determined. Subsequently, participants performed two incremental isometric exercise tests (at least 48 h apart) at 10, 15, 20, 25, and 30% EMG(peak), during which steady-state heart rate and systolic blood pressure were recorded. In all participants, there were linear relationships between %EMG(peak) and heart rate (r at least 0.91; P blood pressure (r at least 0.92; P 0.50) or elevations (P > 0.10) for either of the relationships. Therefore, these linear relationships could be used to identify isometric exercise training intensities that correspond to precise heart rates or systolic blood pressures. Training performed in this way might provide greater insight into the underlying mechanisms for the cardiovascular adaptations that are known to occur as a result.

  13. Mapping of spatial and temporal heterogeneity of plantar flexor muscle activity during isometric contraction: correlation of velocity-encoded MRI with EMG.

    Science.gov (United States)

    Csapo, Robert; Malis, Vadim; Sinha, Usha; Sinha, Shantanu

    2015-09-01

    The aim of this study was to assess the correlation between contraction-associated muscle kinematics as measured by velocity-encoded phase-contrast (VE-PC) magnetic resonance imaging (MRI) and activity recorded via electromyography (EMG), and to construct a detailed three-dimensional (3-D) map of the contractile behavior of the triceps surae complex from the MRI data. Ten axial-plane VE-PC MRI slices of the triceps surae and EMG data were acquired during submaximal isometric contractions in 10 subjects. MRI images were analyzed to yield the degree of contraction-associated muscle displacement on a voxel-by-voxel basis and determine the heterogeneity of muscle movement within and between slices. Correlational analyses were performed to determine the agreement between EMG data and displacements. Pearson's coefficients demonstrated good agreement (0.84 muscle revealed significant heterogeneity in displacement values both in-plane and along the cranio-caudal axis, with highest values in the mid-muscle regions. By contrast, no significant differences between muscle regions were found in the soleus muscle. Substantial differences among displacements were also observed within slices, with those in static areas being only 17-39% (maximum) of those in the most mobile muscle regions. The good agreement between EMG data and displacements suggests that VE-PC MRI may be used as a noninvasive, high-resolution technique for quantifying and modeling muscle activity over the entire 3-D volume of muscle groups. Application to the triceps surae complex revealed substantial heterogeneity of contraction-associated muscle motion both within slices and between different cranio-caudal positions.

  14. Increase in heterogeneity of biceps brachii activation during isometric submaximal fatiguing contractions: a multichannel surface EMG study

    NARCIS (Netherlands)

    Staudenmann, D.; Dieen, J.H. van; Stegeman, D.F.; Enoka, R.M.

    2014-01-01

    The effects of fatigue emerge from the beginning of sustained submaximal contractions, as shown by an increase in the amplitude of the surface electromyogram (EMG). The increase in EMG amplitude is attributed to an augmentation of the excitatory drive to the motor neuron pool that, more importantly

  15. Pattern classification of Myo-Electrical signal during different Maximum Voluntary Contractions: A study using BSS techniques

    Science.gov (United States)

    Naik, Ganesh R.; Kumar, Dinesh K.; Arjunan, Sridhar P.

    2010-01-01

    The presence of noise and cross-talk from closely located and simultaneously active muscles is exaggerated when the level of muscle contraction is very low. Due to this the current applications of surface electromyogram (sEMG) are infeasible and unreliable in pattern classification. This research reports a new technique of sEMG using Independent Component Analysis (ICA). The technique uses blind source separation (BSS) methods to classify the patterns of Myo-electrical signals during different Maximum Voluntary Contraction (MVCs) at different low level finger movements. The results of the experiments indicate that patterns using ICA of sEMG is a reliable (pMVC. The authors propose that ICA is a useful indicator of muscle properties and is a useful indicator of the level of muscle activity.

  16. Continuous monitoring of electromyography (EMG), mechanomyography (MMG), sonomyography (SMG) and torque output during ramp and step isometric contractions.

    Science.gov (United States)

    Guo, Jing-Yi; Zheng, Yong-Ping; Xie, Hong-Bo; Chen, Xin

    2010-11-01

    In this study we simultaneously collected ultrasound images, EMG, MMG from the rectus femoris (RF) muscle and torque signal from the leg extensor muscle group of nine male subjects (mean±SD, age=30.7±.4.9 years; body weight=67.0±8.4kg; height=170.4±6.9cm) during step, ramp increasing, and decreasing at three different rates (50%, 25% and 17% MVC/s). The muscle architectural parameters extracted from ultrasound imaging, which reflect muscle contractions, were defined as sonomyography (SMG) in this study. The cross-sectional area (CSA) and aspect ratio between muscle width and thickness (width/thickness) were extracted from ultrasound images. The results showed that the CSA of RF muscles decreased by 7.25±4.07% when muscle torque output changed from 0% to 90% MVC, and the aspect ratio decreased by 41.66±7.96%. The muscle contraction level and SMG data were strongly correlated (R(2)=0.961, P=0.003, for CSA and R(2)=0.999, PEMG RMS in ramp increasing was 8.25±4.00% higher than step (P=0.002). The normalized MMG RMS of step contraction was significantly lower than ramp increasing and decreasing, with averaged differences of 12.22±3.37% (P=0.001) and 12.06±3.37% (P=0.001), respectively. The results of this study demonstrated that the CSA and aspect ratio, i.e., SMG signals, can provide useful information about muscle contractions. They may therefore complement EMG and MMG for studying muscle activation strategies under different conditions.

  17. Effectiveness of adding voluntary pelvic floor muscle contraction to a Pilates exercise program: an assessor-masked randomized controlled trial.

    Science.gov (United States)

    Torelli, Luiza; de Jarmy Di Bella, Zsuzsanna Ilona Katalin; Rodrigues, Claudinei Alves; Stüpp, Liliana; Girão, Manoel João Batista Castello; Sartori, Marair Gracio Ferreira

    2016-11-01

    The purpose of this study was to evaluate the effectiveness of adding voluntary pelvic floor muscle contraction (PFMC) to a Pilates exercise program in sedentary nulliparous women. Fifty-seven healthy nulliparous and physically inactive women were randomized to a Pilates exercise program (PEP) with or without PFMC. Forty-eight women concluded this study (24 participants for each group). Each woman was evaluated before and after the PEP, by a physiotherapist and an urogynecologist (UG). Neither of the professionals was revealed to them. This physiotherapist measured their pelvic floor muscle strength by using both a perineometer (Peritron) and vaginal palpation (Oxford Scale). The UG, who performed 3D perineal ultrasound examinations, collected their data and evaluated the results for pubovisceral muscle thickness and the levator hiatus area (LA). Both professionals were blinded to the group allocation. The protocol for both groups consisted of 24 bi-weekly 1-h individual sessions of Pilates exercises, developed by another physiotherapist who specializes in PFM rehabilitation and the Pilates technique. The PEP+ PFMC group showed significantly greater strength improvements than the PEP group when comparing the Oxford scale, vaginal pressure and pubovisceral muscle thickness during contraction measurements at baseline and post-treatment. Our findings suggest that adding a voluntary PFMC to a Pilates exercise program is more effective than Pilates alone in improving PFM strength in sedentary nulliparous women.

  18. Muscle tissue oxygenation, pressure, electrical, and mechanical responses during dynamic and static voluntary contractions

    DEFF Research Database (Denmark)

    Vedsted, Pernille; Blangsted, Anne Katrine; Søgaard, Karen

    2006-01-01

    Dynamic muscle contractions have been shown to cause greater energy turnover and fatigue than static contractions performed at a corresponding force level. Therefore, we hypothesized that: (1) electro- (EMG) and mechanomyography (MMG), intramuscular pressure (IMP), and reduction in muscle oxygen...... similar in spite of major differences in the MMG and EMG responses of the muscle during contraction periods. This may relate to the surprisingly lower IMP in DYN than IST....

  19. [Changes in the position of the ureterovesical junction during maximal voluntary contractions and during maximal vaginal electric stimulation of the pelvic floor muscles].

    Science.gov (United States)

    Martan, A; Masata, J; Halaska, M; Voigt, R

    1998-06-01

    The objective of the study was to evaluate and compare the effect of the maximal voluntary muscle contraction of the pelvic floor (PFM) and contractions of the PFM evoked by maximal electric stimulation using an electrostimulation apparatus Conmax by monitoring the position of the urethrovesical junction by ultrasound. The trial comprised 20 women with confirmed stress incontinence of urine. With the patients in a supine position with abducted lower extremities an electrostimulation probe was inserted into the vagina. This was followed by perineal ultrasound (US) examination using an ACUSON 128 XP-10 apparatus and a convex tube 5 MHz. The ultrasound examination was made using the electrostimulation probe--at rest and during maximal voluntary contraction of the PFM. This was followed by maximal electric stimulation and after five minutes during stimulation the US examination was repeated. It was performed also during maximal electric stimulation (MES) concurrently with maximal voluntary contraction of the PFM. For electrostimulation a Conmax appartus was used. The applied frequency was 50 Hz, amplitude from 0 to 90 mA (grade 0-6), duration of pulse 0.75 ms. The maximum intensity of stimulation was determined by the patient, i.e. when stimulation was not yet painful. During US the authors investigated the gamma angle, i.e. the angle between the axis of the symphysis and the connecting line between the UV junction and the lower borderline of the symphysis. The mean difference of the gamma angle during voluntary contraction of the PFM and at rest was 13.6. During contraction caused by maximal electric stimulation of the PFM and at rest this difference was 21.3. The difference did not differ significantly during maximal electric stimulation of the PFM and during maximal electric stimulation and voluntary contraction of the PFM. From the trial ensues that contraction of the pelvic floor muscles during maximal electric stimulation is stronger as compared with the

  20. Influences of Fascicle Length During Isometric Training on Improvement of Muscle Strength.

    Science.gov (United States)

    Tanaka, Hiroki; Ikezoe, Tome; Umehara, Jun; Nakamura, Masatoshi; Umegaki, Hiroki; Kobayashi, Takuya; Nishishita, Satoru; Fujita, Kosuke; Araki, Kojiro; Ichihashi, Noriaki

    2016-11-01

    Tanaka, H, Ikezoe, T, Umehara, J, Nakamura, M, Umegaki, H, Kobayashi, T, Nishishita, S, Fujita, K, Araki, K, and Ichihashi, N. Influences of fascicle length during isometric training on improvement of muscle strength. J Strength Cond Res 30(11): 3249-3255, 2016-This study investigated whether low-intensity isometric training would elicit a greater improvement in maximum voluntary contraction (MVC) at the same fascicle length, rather than the joint angle, adopted during training. Sixteen healthy women (21.8 ± 1.5 years) were randomly divided into an intervention group and a control group. Before (Pre) and after (Post) training, isometric plantarflexion MVCs were measured every 10° through the range of ankle joint position from 20° dorsiflexion to 30° plantarflexion (i.e., 6 ankle angles). Medial gastrocnemius fascicle length was also measured at each position, using B-mode ultrasound under 3 conditions of muscle activation: at rest, 30%MVC at respective angles, and MVC. Plantarflexion resistance training at an angle of 20° plantarflexion was performed 3 days a week for 4 weeks at 30%MVC using 3 sets of twenty 3-second isometric contractions. Maximum voluntary contraction in the intervention group increased at 0 and 10° plantarflexion (0°; Pre: 81.2 ± 26.5 N·m, Post: 105.0 ± 21.6 N·m, 10°; Pre: 63.0 ± 23.6 N·m, Post: 81.3 ± 20.3 N·m), which was not the angle used in training (20°). However, the fascicle length adopted in training at 20° plantarflexion and 30%MVC was similar to the value at 0 or 10° plantarflexion at MVC. Low-intensity isometric training at a shortened muscle length may be effective for improving MVC at a lengthened muscle length because of specificity of the fascicle length than the joint angle.

  1. Time-resolved X-ray diffraction studies of myosin head movements in live frog sartorius muscle during isometric and isotonic contractions.

    Science.gov (United States)

    Martin-Fernandez, M L; Bordas, J; Diakun, G; Harries, J; Lowy, J; Mant, G R; Svensson, A; Towns-Andrews, E

    1994-06-01

    Using the facilities at the Daresbury Synchrotron Radiation Source, meridional diffraction patterns of muscles at ca 8 degrees C were recorded with a time resolution of 2 or 4 ms. In isometric contractions tetanic peak tension (P0) is reached in ca 400 ms. Under such conditions, following stimulation from rest, the timing of changes in the major reflections (the 38.2 nm troponin reflection, and the 21.5 and 14.34/14.58 nm myosin reflections) can be explained in terms of four types of time courses: K1, K2, K3 and K4. The onset of K1 occurs immediately after stimulation, but that of K2, K3 and K4 is delayed by a latent period of ca 16 ms. Relative to the end of their own latent periods the half-times for K1, K2, K3 and K4 are 14-16, 16, 32 and 52 ms, respectively. In half-times, K1, K2, K3 lead tension rise by 52, 36 and 20 ms, respectively. K4 parallels the time course of tension rise. From an analysis of the data we conclude that K1 reflects thin filament activation which involves the troponin system; K2 arises from an order-disorder transition during which the register between the filaments is lost; K3 is due to the formation of an acto-myosin complex which (at P0) causes 70% or more of the heads to diffract with actin-based periodicities; and K4 is caused by a change in the axial orientation of the myosin heads (relative to thin filament axis) which is estimated to be from 65-70 degrees at rest to ca 90 degrees at P0. Isotonic contraction experiments showed that during shortening under a load of ca 0.27 P0, at least 85% of the heads (relative to those forming an acto-myosin complex at P0) diffract with actin-based periodicities, whilst their axial orientation does not change from that at rest. During shortening under a negligible load, at most 5-10% of the heads (relative to those forming an acto-myosin complex at P0) diffract with actin-based periodicities, and their axial orientation also remains the same as that at rest. This suggests that in isometric

  2. Neuromuscular electrical stimulation versus volitional isometric strength training in children with spastic diplegic cerebral palsy: a preliminary study.

    Science.gov (United States)

    Stackhouse, Scott K; Binder-Macleod, Stuart A; Stackhouse, Carrie A; McCarthy, James J; Prosser, Laura A; Lee, Samuel C K

    2007-01-01

    To date, no reports have investigated neuromuscular electrical stimulation (NMES) to increase muscle force production of children with cerebral palsy (CP) using high-force contractions and low repetitions. The aims of this study were to determine if isometric NMES or volitional training in children with CP could increase muscle strength and walking speed and to examine the mechanisms that may contribute to increased force production. Eleven children with spastic diplegia were assigned to an NMES training group or to a volitional training group. Participants in the NMES group had electrodes implanted percutaneously to activate the quadriceps femoris and triceps surae muscles. The volitional group trained with maximal effort contractions. Both groups performed a 12-week isometric strength-training program. Maximum voluntary isometric contraction (MVIC) force, voluntary muscle activation, quadriceps and triceps surae cross-sectional area (CSA), and walking speed were measured pre- and post-strength training. The NMES-trained group had greater increases in normalized force production for both the quadriceps femoris and triceps surae. Similarly, only the NMES group showed an increase in walking speed after training. Changes in voluntary muscle activation explained approximately 67% and 37% of the changes seen in the MVIC of the NMES and volitional groups, respectively. Quadriceps femoris maximum CSA increased significantly for the NMES group only. This study was the first to quantitatively show strength gains with the use of NMES in children with CP. These results support the need for future experimental studies that will examine the clinical effectiveness of NMES strength training.

  3. RELATIONSHIP BETWEEN ELECTRICAL AND VIBRATORY OUTPUT OF MUSCLE DURING VOLUNTARY CONTRACTION AND FATIGUE

    NARCIS (Netherlands)

    ZWARTS, MJ; KEIDEL, M

    1991-01-01

    Measurements were done on the biceps muscles of 6 healthy volunteers to record simultaneously the surface electromyogram (EMG) and vibromyogram (VMG) by means of a piezoelectric device (accelerometer). The VMG is generated by mechanical waves due to the contraction mechanism and often measured as so

  4. Acute effect of static stretching on rate of force development and maximal voluntary contraction in older women.

    Science.gov (United States)

    Gurjão, André L D; Gonçalves, Raquel; de Moura, Rodrigo F; Gobbi, Sebastião

    2009-10-01

    The purpose of this study was to investigate, in older women, the acute effect of static stretching (SS) on both muscle activation and force output. Twenty-three older women (64.6 +/- 7.1 yr) participated in the study. The maximal voluntary contraction (MVC), rate of force development (RFD) (50, 100, 150, and 200 ms relative to onset of muscular contraction), and peak RFD (PRFD) (the steepest slope of the curve during the first 200 ms) were tested under 2 randomly separate conditions: SS and control (C). Electromyographic (EMG) activity of the vastus medialis (VM), vastus lateralis (VL), and biceps femoris (BF) muscles also was assessed. The MVC was significantly lower (p force decreased after their performance of SS exercises. The mechanisms responsible for this effect do not appear to be related to muscle activation. Thus, if flexibility is to be trained, it is recommended that SS does not occur just before the performance of activities that require high levels of muscular force.

  5. Time-Course of Neuromuscular Changes during and after Maximal Eccentric Contractions.

    Science.gov (United States)

    Doguet, Valentin; Jubeau, Marc; Dorel, Sylvain; Couturier, Antoine; Lacourpaille, Lilian; Guével, Arnaud; Guilhem, Gaël

    2016-01-01

    This study tested the relationship between the magnitude of muscle damage and both central and peripheral modulations during and after eccentric contractions of plantar flexors. Eleven participants performed 10 sets of 30 maximal eccentric contractions of the plantar flexors at 45°·s(-1). Maximal voluntary torque, evoked torque (peripheral component) and voluntary activation (central component) were assessed before, during, immediately after (POST) and 48 h after (48 h) the eccentric exercise. Voluntary eccentric torque progressively decreased (up to -36%) concomitantly to a significant alteration of evoked torque (up to -34%) and voluntary activation (up to -13%) during the exercise. Voluntary isometric torque (-48 ± 7%), evoked torque (-41 ± 14%) and voluntary activation (-13 ± 11%) decreased at POST, but only voluntary isometric torque (-19 ± 6%) and evoked torque (-10 ± 18%) remained depressed at 48 h. Neither changes in voluntary activation nor evoked torque during the exercise were related to the magnitude of muscle damage markers, but the evoked torque decrement at 48 h was significantly correlated with the changes in voluntary activation (r = -0.71) and evoked torque (r = 0.77) at POST. Our findings show that neuromuscular responses observed during eccentric contractions were not associated with muscle damage. Conversely, central and peripheral impairments observed immediately after the exercise reflect the long-lasting reduction in force-generating capacity.

  6. Ischemic Preconditioning Enhances Muscle Endurance during Sustained Isometric Exercise.

    Science.gov (United States)

    Tanaka, D; Suga, T; Tanaka, T; Kido, K; Honjo, T; Fujita, S; Hamaoka, T; Isaka, T

    2016-07-01

    Ischemic preconditioning (IPC) enhances whole-body exercise endurance. However, it is poorly understood whether the beneficial effects originate from systemic (e. g., cardiovascular system) or peripheral (e. g., skeletal muscle) adaptations. The present study examined the effects of IPC on local muscle endurance during fatiguing isometric exercise. 12 male subjects performed sustained isometric unilateral knee-extension exercise at 20% of maximal voluntary contraction until failure. Prior to the exercise, subjects completed IPC or control (CON) treatments. During exercise trial, electromyography activity and near-infrared spectroscopy-derived deoxygenation in skeletal muscle were continuously recorded. Endurance time to task failure was significantly longer in IPC than in CON (mean±SE; 233±9 vs. 198±9 s, PIPC and CON. In contrast, deoxygenation dynamics in the quadriceps vastus lateralis muscle was significantly faster in IPC than in CON (27.1±3.4 vs. 35.0±3.6 s, PIPC can enhance muscular endurance during fatiguing isometric exercise. Moreover, IPC accelerated muscle deoxygenation dynamics during the exercise. Therefore, we suggest that the origin of beneficial effects of IPC on exercise performance may be the enhanced mitochondrial metabolism in skeletal muscle.

  7. Methodology to Customize Maximal Isometric Forces for Hill-Type Muscle Models.

    Science.gov (United States)

    Dal Maso, Fabien; Begon, Mickaël; Raison, Maxime

    2017-02-01

    One approach to increasing the confidence of muscle force estimation via musculoskeletal models is to minimize the root mean square error (RMSE) between joint torques estimated from electromyographic-driven musculoskeletal models and those computed using inverse dynamics. We propose a method that reduces RMSE by selecting subsets of combinations of maximal voluntary isometric contraction (MVIC) trials that minimize RMSE. Twelve participants performed 3 elbow MVIC in flexion and in extension. An upper-limb electromyographic-driven musculoskeletal model was created to optimize maximum muscle stress and estimate the maximal isometric force of the biceps brachii, brachialis, brachioradialis, and triceps brachii. Maximal isometric forces were computed from all possible combinations of flexion-extension trials. The combinations producing the smallest RMSE significantly reduced the normalized RMSE to 7.4% compared with the combination containing all trials (9.0%). Maximal isometric forces ranged between 114-806 N, 64-409 N, 236-1511 N, and 556-3434 N for the brachii, brachialis, brachioradialis, and triceps brachii, respectively. These large variations suggest that customization is required to reduce the difference between models and actual participants' maximal isometric force. While the smallest previously reported RMSE was 10.3%, the proposed method reduced the RMSE to 7.4%, which may increase the confidence of muscle force estimation.

  8. Myofibrillar proteolysis in response to voluntary or electrically stimulated muscle contractions in humans

    DEFF Research Database (Denmark)

    Hansen, M; Trappe, T; Crameri, R M;

    2008-01-01

    Knowledge about the effects of exercise on myofibrillar protein breakdown in human subjects is limited. Our purpose was to measure the changes in the degradation of myofibrillar proteins in response to different ways of eliciting muscle contractions using the local interstitial 3-methyl-histidine......Knowledge about the effects of exercise on myofibrillar protein breakdown in human subjects is limited. Our purpose was to measure the changes in the degradation of myofibrillar proteins in response to different ways of eliciting muscle contractions using the local interstitial 3-methyl....... Only after ES did the histochemical stainings show significant disruption of cytoskeletal proteins. Furthermore, intracellular disruption and destroyed Z-lines were markedly more pronounced in ES vs VOL. In conclusion, the local level of interstitial 3-MH in the skeletal muscle was significantly...... enhanced after ES compared with VOL immediately after exercise, while the level of 3-MH did not change in the post-exercise period after VOL. These results indicate that the local myofibrillar breakdown is accelerated after ES associated with severe myofiber damage....

  9. Comparison of sympathetic nerve responses to neck and forearm isometric exercise

    Science.gov (United States)

    Steele, S. L. Jr; Ray, C. A.

    2000-01-01

    PURPOSE: Although the autonomic and cardiovascular responses to arm and leg exercise have been studied, the sympathetic adjustments to exercise of the neck have not. The purpose of the present study was twofold: 1) to determine sympathetic and cardiovascular responses to isometric contractions of the neck extensors and 2) to compare sympathetic and cardiovascular responses to isometric exercise of the neck and forearm. METHODS: Muscle sympathetic nerve activity (MSNA), mean arterial pressure (MAP), and heart rate were measured in nine healthy subjects while performing isometric neck extension (INE) and isometric handgrip (IHG) in the prone position. After a 3-min baseline period, subjects performed three intensities of INE for 2.5 min each: 1) unloaded (supporting head alone), 2) 10% maximal voluntary contraction (MVC), and 3) 30% MVC, then subjects performed two intensities (10% and 30% MVC) of IHG for 2.5 min. RESULTS: Supporting the head by itself did not significantly change any of the variables. During [NE, MAP significantly increased by 10 +/- 2 and 31 +/- 4 mm Hg and MSNA increased by 67 +/- 46 and 168 +/- 36 units/30 s for 10% and 30% MVC, respectively. IHG and INE evoked similar responses at 10% MVC, but IHG elicited higher peak MAP and MSNA at 30% MVC (37 +/- 7 mm Hg (P architecture of the neck and forearm are responsible for these differences in peak responses.

  10. Comparison of sympathetic nerve responses to neck and forearm isometric exercise

    Science.gov (United States)

    Steele, S. L. Jr; Ray, C. A.

    2000-01-01

    PURPOSE: Although the autonomic and cardiovascular responses to arm and leg exercise have been studied, the sympathetic adjustments to exercise of the neck have not. The purpose of the present study was twofold: 1) to determine sympathetic and cardiovascular responses to isometric contractions of the neck extensors and 2) to compare sympathetic and cardiovascular responses to isometric exercise of the neck and forearm. METHODS: Muscle sympathetic nerve activity (MSNA), mean arterial pressure (MAP), and heart rate were measured in nine healthy subjects while performing isometric neck extension (INE) and isometric handgrip (IHG) in the prone position. After a 3-min baseline period, subjects performed three intensities of INE for 2.5 min each: 1) unloaded (supporting head alone), 2) 10% maximal voluntary contraction (MVC), and 3) 30% MVC, then subjects performed two intensities (10% and 30% MVC) of IHG for 2.5 min. RESULTS: Supporting the head by itself did not significantly change any of the variables. During [NE, MAP significantly increased by 10 +/- 2 and 31 +/- 4 mm Hg and MSNA increased by 67 +/- 46 and 168 +/- 36 units/30 s for 10% and 30% MVC, respectively. IHG and INE evoked similar responses at 10% MVC, but IHG elicited higher peak MAP and MSNA at 30% MVC (37 +/- 7 mm Hg (P type composition, muscle mass, and/or muscle architecture of the neck and forearm are responsible for these differences in peak responses.

  11. Comparison of sympathetic nerve responses to neck and forearm isometric exercise

    Science.gov (United States)

    Steele, S. L. Jr; Ray, C. A.

    2000-01-01

    PURPOSE: Although the autonomic and cardiovascular responses to arm and leg exercise have been studied, the sympathetic adjustments to exercise of the neck have not. The purpose of the present study was twofold: 1) to determine sympathetic and cardiovascular responses to isometric contractions of the neck extensors and 2) to compare sympathetic and cardiovascular responses to isometric exercise of the neck and forearm. METHODS: Muscle sympathetic nerve activity (MSNA), mean arterial pressure (MAP), and heart rate were measured in nine healthy subjects while performing isometric neck extension (INE) and isometric handgrip (IHG) in the prone position. After a 3-min baseline period, subjects performed three intensities of INE for 2.5 min each: 1) unloaded (supporting head alone), 2) 10% maximal voluntary contraction (MVC), and 3) 30% MVC, then subjects performed two intensities (10% and 30% MVC) of IHG for 2.5 min. RESULTS: Supporting the head by itself did not significantly change any of the variables. During [NE, MAP significantly increased by 10 +/- 2 and 31 +/- 4 mm Hg and MSNA increased by 67 +/- 46 and 168 +/- 36 units/30 s for 10% and 30% MVC, respectively. IHG and INE evoked similar responses at 10% MVC, but IHG elicited higher peak MAP and MSNA at 30% MVC (37 +/- 7 mm Hg (P muscle fiber type composition, muscle mass, and/or muscle architecture of the neck and forearm are responsible for these differences in peak responses.

  12. [Reliability and validity of the analysis of hand grip and pinch force in isometric and isokinetic conditions].

    Science.gov (United States)

    Benaglia, P G; Franchignoni, F; Ferriero, G; Zebellin, G; Sartorio, F

    1999-01-01

    Strength measurement of the hand grip is at the core of most protocols of functional assessment of the upper limb and in rehabilitation plays a major role in the analysis of treatment efficacy and patients' occupational ability. The aims of this study were to: a) verify the repeatability of strength measurements made during performance of the hand grip and three types of pinch, carried out under isometric and isokinetic conditions; b) compare maximal isometric strength with the corresponding isokinetic value for each of the manoeuvres studied; c) investigate the correlations between the strength expressed in the different manoeuvres, under both isometric and isokinetic conditions. We studied 14 voluntary subjects over three sessions conducted at 48-hr intervals, employing a computerized isokinetic dynamometer Lido WorkSet equipped with device N(o) 21 for the study of pinch (lateral pinch, pulp pinch, chuck pinch) and device N(o) 52 for the grip study. Isometric contractions resulted stronger than isokinetic ones, and the hand grip was found to be the manoeuvre able to produce most strength. The repeatability of each strength measurement test over the three days was high (Intraclass Correlation Coefficients: 0.89-0.93). Correlations between the isometric and isokinetic performance for each of the manoeuvres examined were always high (Pearson's r coefficients: 0.89-0.95) as were those between the different manoeuvres, whether performed in isometric or isokinetic modality (r: 0.60-0.94).

  13. ANODAL TRANSCRANIAL DIRECT CURRENT STIMULATION (TDCS) INCREASES ISOMETRIC STRENGTH OF SHOULDER ROTATORS MUSCLES IN HANDBALL PLAYERS.

    Science.gov (United States)

    Hazime, Fuad Ahmad; da Cunha, Ronaldo Alves; Soliaman, Renato Rozenblit; Romancini, Ana Clara Bezerra; Pochini, Alberto de Castro; Ejnisman, Benno; Baptista, Abrahão Fontes

    2017-06-01

    Weakness of the rotator cuff muscles can lead to imbalances in the strength of shoulder external and internal rotators, change the biomechanics of the glenohumeral joint and predispose an athlete to injury. Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that has demonstrated promising results in a variety of health conditions. However few studies addressed its potential approach in the realm of athletics. The purpose of this study was to investigate if transcranial direct current stimulation (tDCS) technique increases the isometric muscle strength of shoulder external and internal rotators in handball athletes. Randomized, double-blind, placebo-controlled, crossover study. Eight female handball players aged between 17 and 21 years (Mean=19.65; SD=2.55) with 7.1 ± 4.8 years of experience in training, participating in regional and national competitions were recruited. Maximal voluntary isometric contraction (MVIC) of shoulder external and internal rotator muscles was evaluated during and after 30 and 60 minutes post one session of anodal and sham current (2mA; 0.057mA/cm(2)) with a one-week interval between stimulations. Compared to baseline, MVIC of shoulder external and internal rotators significantly increased after real but not sham tDCS. Between-group differences were observed for external and internal rotator muscles. Maximal voluntary isometric contraction of external rotation increased significantly during tDCS, and 30 and 60 minutes post-tDCS for real tDCS compared to that for sham tDCS. For internal rotation MVIC increased significantly during and 60 minutes post-tDCS. The results indicate that transcranial direct current stimulation temporarily increases maximal isometric contractions of the internal and external rotators of the shoulder in handball players. 2.

  14. [Motor unit activities of human masseter muscle during sustained voluntary contractions].

    Science.gov (United States)

    Shimizu, T

    1990-02-01

    The purpose of this paper is to investigate the motor unit activities of the human masseter muscle during sustained the bite force at a constant level. The electrical activities recorded with surface and inserted electrodes were studied, with the following results. 1. The masseter muscle had the changes of activities in two phases as a contraction progressed. 2. In the first phase, surface EMG activities decreased and discharge frequency of motor units also decreased. 3. In the second phase, surface EMG activities increased and discharge frequency of motor units also increased. 4. In the first phase, it was suggested that the bite force was maintained by an increase in the twitch tension produced by a motor unit and that there were no recruitment of additional motor units. 5. In the second phase, it was indicated that the bite force was maintained by the recruitment of new motor units and an increase in the discharge frequency of motor units to compensate a loss of force resulted from the contractile element fatigue.

  15. The effects of verbal encouragement and conscientiousness on maximal voluntary contraction of the triceps surae muscle in elite athletes.

    Science.gov (United States)

    Binboğa, Erdal; Tok, Serdar; Catikkas, Fatih; Guven, Senol; Dane, Senol

    2013-01-01

    We investigated the effect of verbal encouragement on maximal voluntary contraction (MVC) level of the triceps surae muscle group. Our secondary focus was to examine whether the effect of verbal encouragement on MVC level varies as a result of conscientiousness. While the participants performed plantar flexion, MVCs of the triceps surae muscle group were measured using rectified and smoothed surface electromyography (rsEMG) during the absence and presence of verbal encouragement. Participants completed questions from the Five Factor Personality Inventory concerning conscientiousness and were divided into high- and low-conscientiousness groups according to a median split. The sample included 30 female and 53 male elite athletes. In the entire cohort, there was no significant difference in MVCs with and without verbal encouragement. When the sample was partitioned by conscientiousness scores, verbal encouragement led to a significant increase in MVC in the low-conscientiousness group, whereas verbal encouragement led to a non-significant decrease in MVC in the high-conscientiousness group. Percentage change in MVC across experimental conditions was significantly different between the groups, with a 9.72% increase during verbal encouragement of the low-conscientiousness group, and a 2.47% decrease during verbal encouragement of the high-conscientiousness group.

  16. Comparison of two isometric handgrip protocols on sympathetic arousal in women.

    Science.gov (United States)

    Nielsen, Shawn E; Mather, Mara

    2015-04-01

    Isometric handgrip is commonly used in stress research because the task reliably increases sympathetic arousal. Various handgrip protocols have been used; they vary in handgrip strength, duration of grip, and the number of cycles of handgrip and rest. However, most protocols require the calibration of a maximum voluntary contraction (MVC) prior to the handgrip task, which is not always convenient (i.e., in a functional magnetic resonance imaging study). Here, we wanted to test whether two handgrip protocols with different strength, duration and cycle protocols would reliably elicit sympathetic arousal in the absence of calibrating an MVC. Sixty-two healthy naturally cycling women and women on hormonal contraception participated in one of the two isometric handgrip protocols using a hand therapy ball of medium resistance. Women completed one of the following handgrip protocols: 1) 30% of a perceived maximum voluntary contraction for 3 min or 2) 3 cycles of maximum voluntary contraction for 18s with a one minute rest in between. All handgrip blocks were counterbalanced with a control condition. Sympathetic arousal was measured throughout the session via pupil diameter changes and salivary alpha-amylase. Results indicate that in the absence of calibrating an MVC, the handgrip tasks elicited different changes in sympathetic arousal. Pupil dilation responses increased significantly in the handgrip versus control blocks only in participants in the 18-s protocol. Additionally, more participants exhibited a salivary alpha-amylase response to the handgrip block in the 18-s condition compared to the 3-min condition. Thus, these results suggest that neuroimaging and behavioral studies with isometric handgrip should be able to successfully induce sympathetic nervous activity with the 18-s paradigm, regardless of the handgrip device and the ability to calibrate an MVC. Published by Elsevier Inc.

  17. Fast unilateral isometric knee extension torque development and bilateral jump height.

    Science.gov (United States)

    de Ruiter, Cornelis J; Van Leeuwen, Daniel; Heijblom, Arjan; Bobbert, Maarten F; de Haan, Arnold

    2006-10-01

    We hypothesized that the initial rate (first 40 ms) of unilateral knee extensor torque development during a maximally fast isometric contraction would depend on the subjects' ability for fast neural activation and that it would predict bilateral jumping performance. Nine males (21.8 +/- 0.9 yr, means +/- SD) performed unilateral fast isometric knee extensions (120 degrees knee angle) without countermovement on a dynamometer and bilateral squat jumps (SJ) and countermovement jumps (CMJ) starting from 90 and 120 degrees knee angles (full extension = 180 degrees ). The dynamometer contractions started either from full relaxation or from an isometric pre-tension (15% maximal isometric torque, Tmax). Torque time integral for the first 40 ms after torque onset (TTI-40, normalized to Tmax) and averaged normalized rectified knee extensor EMG for 40 ms before fast torque onset (EMG-40) were used to quantify initial torque rise and voluntary muscle activation. TTI-40 without pre-tension (range: 0.02-0.19% Tmax per second) was significantly lower than TTI-40 with pre-tension, and both were significantly (r = 0.81 and 0.80) related to EMG-40. During jumping, similar significant positive relations were found between jump height and knee extensor EMG during the first 100 ms of the rise in ground reaction force. There also were significant positive linear relations between dynamometer TTI-40 and jump height (r = 0.75 (SJ 90), 0.84 (SJ 120), 0.76 (CMJ 90), and 0.86 (CMJ 120)) but not between dynamometer Tmax and jump height (-0.16 < r < 0.02). One-legged TTI-40 to a large extent explained the variation in jump height. The ability to produce a high efferent neural drive before muscle contraction seemed to dominate performance in both the simple single-joint isometric task and the complex multijoint dynamic task.

  18. Isometric knee extensor fatigue following a Wingate test: peripheral and central mechanisms.

    Science.gov (United States)

    Fernandez-del-Olmo, M; Rodriguez, F A; Marquez, G; Iglesias, X; Marina, M; Benitez, A; Vallejo, L; Acero, R M

    2013-02-01

    Central and peripheral fatigue have been explored during and after running or cycling exercises. However, the fatigue mechanisms associated with a short maximal cycling exercise (30 s Wingate test) have not been investigated. In this study, 10 volunteer subjects performed several isometric voluntary contractions using the leg muscle extensors before and after two bouts of cycling at 25% of maximal power output and two bouts of Wingate tests. Transcranial magnetic stimulation (TMS) and electrical motor nerve stimulation (NM) were applied at rest and during the voluntary contractions. Maximal voluntary contraction (MVC), voluntary activation (VA), twitch amplitude evoked by electrical nerve stimulation, M wave and motor potential evoked by TMS (MEP) were recorded. MVC, VA and twitch amplitude evoked at rest by NM decreased significantly after the first and second Wingate tests, indicating central and peripheral fatigue. MVC and VA, but not the twitch amplitude evoked by NM, recovered before the second Wingate test. These results suggest that the Wingate test results in a decrease in MVC associated with peripheral and central fatigue. While the peripheral fatigue is associated with an intramuscular impairment, the central fatigue seems to be the main reason for the Wingate test-induced impairment of MVC.

  19. 表面肌电信号指标评价低负荷等长收缩诱发屈肘肌疲劳的敏感性和稳定性分析%Sensitivity and Stability of sEMG in Evaluating Muscle Fatigue Caused by Isometric Contractions

    Institute of Scientific and Technical Information of China (English)

    王乐军; 陆爱云; 范年春; 郑樊慧; 董菲; 张磊

    2013-01-01

    目的:分析表面肌电(sEMG)信号指标评定低负荷等长收缩诱发运动性肌肉疲劳的敏感性和稳定性,为疲劳评价提供参考.方法:以15名男性青年志愿者为研究对象,先测试受试者屈肘关节最大自主收缩力矩(Maximal Voluntary Contration,MVC),令受试者右臂腕部拉住可在肘关节处产生20%MVC的重物,记录右侧肱桡肌和肱二头肌sEMG,至不能坚持负荷时结束实验.计算时域指标均方根振幅(RMS),基于傅里叶变换计算中值频率(MF)和平均功率频率(MPF),基于小波包分析计算中值频率(MDF)和平均功率频率(MNF),基于非线性分析计算Lempel-Ziv复杂度C(n).评定上述指标在低负荷等长收缩诱发屈肘肌疲劳方面的敏感性和稳定性.结果:肱二头肌与肱桡肌sEMG的RMS随负荷实验持续时间延长表现出逐渐增加的趋势,而MF、MPF、MDF、MNF、C(n)则表现出逐渐减小的趋势.MF、MPF、MDF、MNF、C(n)与负荷运动持续时间之间具有显著负相关,RMS与负荷运动持续时间之间具有显著的正相关.肱二头肌与肱桡肌RMS反映疲劳的敏感性和稳定性优于其他指标.结论:由于低负荷收缩诱发疲劳引起募集运动单位数量增加等因素作用,RMS表现出较显著的增加趋势,是评定由低负荷等长收缩诱发屈肘肌疲劳的较好指标.%Objective The sensitivity and stability of sEMG during muscle fatigue induced by isometric contraction was evaluated. Methods Fifteen young man participated in this experiment. The isomeric contraction of elbow flexion was performed with the load of 20% individual maximal voluntary contraction. At the same time, sEMG signals were collected from biceps brachi (BB) and brachioradialis (BR), then root mean square (RMS),Fourier transformation-based medium frequency (MF) and mean power frequency (MPF) .wavelet packet transformation-based medium frequency (MDF) and mean power frequency (MNF), and nonlinear Lempel-Ziv complexity (Cn) were

  20. Coherent motor unit rhythms in the 6-10 Hz range during time-varying voluntary muscle contractions: neural mechanism and relation to rhythmical motor control.

    Science.gov (United States)

    Erimaki, Sophia; Christakos, Constantinos N

    2008-02-01

    In quasi-sinusoidal (0.5-3.0 Hz) voluntary muscle contractions, we studied the 6- to 10-Hz motor unit (MU) firing synchrony and muscle force oscillation with emphasis on their neural substrate and relation to rhythmical motor control. Our analyses were performed on data from 121 contractions of a finger muscle in 24 human subjects. They demonstrate that coherent 6- to 10-Hz components of MU discharges coexist with carrier components and coherent modulation components underlying the voluntary force variations. The 6- to 10-Hz synchrony has the frequency of the tremor synchrony in steady contractions and is also widespread and in-phase. Its strength ranges from very small to very large (MU/MU coherence >0.50) among contractions; moreover, it is not related to the contraction parameters, in accord with the notion of a distinct 6- to 10-Hz synaptic input to the MUs. Unlike the coherent MU modulations and the voluntary force variations, the in-phase 6- to 10-Hz MU components are suppressed or even eliminated during ischemia, while the respective force component is drastically reduced. These findings agree with the widely assumed supraspinal origin of the MU modulations, but they also strongly suggest a key role for muscle spindle feedback in the generation of the 6- to 10-Hz synaptic input. They therefore provide important information for the study of generators of the 6- to 10-Hz rhythm which subserves the postulated rhythmical control and is manifested as force and movement components. Moreover, they argue for a participation of oscillating spinal stretch reflex loops in the rhythm generation, possibly in interaction with supraspinal oscillators.

  1. Voluntary Slavery

    Directory of Open Access Journals (Sweden)

    Danny Frederick

    2014-06-01

    Full Text Available The permissibility of actions depends upon facts about the flourishing and separateness of persons. Persons differ from other creatures in having the task of discovering for themselves, by conjecture and refutation, what sort of life will fulfil them. Compulsory slavery impermissibly prevents some persons from pursuing this task. However, many people may conjecture that they are natural slaves. Some of these conjectures may turn out to be correct. In consequence, voluntary slavery, in which one person welcomes the duty to fulfil all the commands of another, is permissible. Life-long voluntary slavery contracts are impermissible because of human fallibility; but fixed-term slavery contracts should be legally enforceable. Each person has the temporarily alienable moral right to direct her own life.

  2. Voluntary Slavery

    Directory of Open Access Journals (Sweden)

    Danny Frederick

    2014-06-01

    Full Text Available The permissibility of actions depends upon facts about the flourishing and separateness of persons. Persons differ from other creatures in having the task of discovering for themselves, by conjecture and refutation, what sort of life will fulfil them. Compulsory slavery impermissibly prevents some persons from pursuing this task. However, many people may conjecture that they are natural slaves. Some of these conjectures may turn out to be correct. In consequence, voluntary slavery, in which one person welcomes the duty to fulfil all the commands of another, is permissible. Life-long voluntary slavery contracts are impermissible because of human fallibility; but fixed-term slavery contracts should be legally enforceable. Each person has the temporarily alienable moral right to direct her own life.

  3. Contributions of central command and muscle feedback to sympathetic nerve activity in contracting human skeletal muscle

    Directory of Open Access Journals (Sweden)

    Daniel eBoulton

    2016-05-01

    Full Text Available During voluntary contractions, muscle sympathetic nerve activity (MSNA to contracting muscles increases in proportion to force but the underlying mechanisms are not clear. To shed light on these mechanisms, particularly the influences of central command and muscle afferent feedback, the present study tested the hypothesis that MSNA is greater during voluntary compared with electrically-evoked contractions. Seven male subjects performed a series of 1-minute isometric dorsiflexion contractions (left leg separated by 2-minute rest periods, alternating between voluntary and electrically-evoked contractions at similar forces (5-10 % of maximum. MSNA was recorded continuously (microneurography from the left peroneal nerve and quantified from cardiac-synchronised, negative-going spikes in the neurogram. Compared with pre-contraction values, MSNA increased by 51 ± 34 % (P 0.05. MSNA analysed at 15-s intervals revealed that this effect of voluntary contraction appeared 15-30 s after contraction onset (P < 0.01, remained elevated until the end of contraction, and disappeared within 15 s after contraction. These findings suggest that central command, and not feedback from contracting muscle, is the primary mechanism responsible for the increase in MSNA to contracting muscle. The time-course of MSNA suggests that there is a longer delay in the onset of this effect compared with its cessation after contraction.

  4. Impaired dynamic cerebral autoregulation at rest and during isometric exercise in type 2 diabetes patients.

    Science.gov (United States)

    Vianna, Lauro C; Deo, Shekhar H; Jensen, Areum K; Holwerda, Seth W; Zimmerman, Matthew C; Fadel, Paul J

    2015-04-01

    Type 2 diabetes mellitus patients (T2D) have elevated risk of stroke, suggesting that cerebrovascular function is impaired. Herein, we examined dynamic cerebral autoregulation (CA) at rest and during exercise in T2D patients and determined whether underlying systemic oxidative stress is associated with impairments in CA. Middle cerebral artery blood velocity and arterial blood pressure (BP) were measured at rest and during 2-min bouts of low- and high-intensity isometric handgrip performed at 20% and 40% maximum voluntary contraction, respectively, in seven normotensive and eight hypertensive T2D patients and eight healthy controls. Dynamic CA was estimated using the rate of regulation (RoR). Total reactive oxygen species (ROS) and superoxide levels were measured at rest. There were no differences in RoR at rest or during exercise between normotensive and hypertensive T2D patients. However, when compared with controls, T2D patients exhibited lower RoR at rest and during low-intensity handgrip indicating impaired dynamic CA. Moreover, the RoR was further reduced by 29 ± 4% during high-intensity handgrip in T2D patients (0.307 ± 0.012/s rest vs. 0.220 ± 0.014/s high intensity; P < 0.01), although well maintained in controls. T2D patients demonstrated greater baseline total ROS and superoxide compared with controls, both of which were negatively related to RoR during handgrip (e.g., total ROS: r = -0.71, P < 0.05; 40% maximum voluntary contraction). Collectively, these data demonstrate impaired dynamic CA at rest and during isometric handgrip in T2D patients, which may be, in part, related to greater underlying systemic oxidative stress. Additionally, dynamic CA is blunted further with high intensity isometric contractions potentially placing T2D patients at greater risk for cerebral events during such activities. Copyright © 2015 the American Physiological Society.

  5. 等长收缩训练治疗下颈椎失稳交感神经症状的效果①%Effect of Isometric Contraction on Sympathetic Nervous Symptoms Followed Subaxial Cervical Instability

    Institute of Scientific and Technical Information of China (English)

    郄淑燕; 张夏琳; 潘钰; 马全胜; 张丽华; 丁永红

    2013-01-01

    Objective To study the effect of isometric contraction on subaxial cervical instability with sympathetic nervous symptoms. Methods 41 subaxial cervical instability patients with sympathetic nervous symptoms were assigned to experimental group (n=21) and con-trol group (n=20). Both groups received manipulation therapy. Experimental group received isometric contraction in addition. They were as-sessed with Visual Analogue Scale (VAS) and heart rate variability (HRV), including total power (TP), low frequency power (LF), high fre-quency power (HF), and LF/HF before and 3 weeks after treatment. Results The scores of VAS, LF and LF/HF decreased in both groups af-ter treatment (P<0.05), which decreased more in the experiement group than in the control group (P<0.05). Conclusion Isometric contrac-tion can release the sympathetic nervous symptoms post subaxial cervical instability.%  目的探讨颈部肌群等长收缩训练对下颈椎失稳交感神经症状的临床疗效。方法41例下颈椎失稳并发交感神经症状的患者分为试验组(n=21)和对照组(n=20)。两组均接受为期3周的手法治疗,试验组同时行颈部肌群等长收缩训练。治疗前后采用视觉模拟评分法(VAS)评价临床症状,采用短程频谱分析法检测心率变异性,包括总功率(TP)、低频成分(LF)、高频成分(HF)、低频高频比(LF/HF)。结果治疗后,两组 VAS 评分、LF、LF/HF 均下降(P<0.05);试验组 VAS 评分、LF、LF/HF 均低于对照组(P<0.05)。结论等长收缩训练可改善下颈椎失稳患者交感神经症状。

  6. Maximal voluntary contraction force, SR function and glycogen resynthesis during the first 72 h after a high-level competitive soccer game

    DEFF Research Database (Denmark)

    Krustrup, Peter; Ortenblad, Niels; Nielsen, Joachim

    2011-01-01

    The aim of this study was to examine maximal voluntary knee-extensor contraction force (MVC force), sarcoplasmic reticulum (SR) function and muscle glycogen levels in the days after a high-level soccer game when players ingested an optimised diet. Seven high-level male soccer players had a vastus...... lateralis muscle biopsy and a blood sample collected in a control situation and at 0, 24, 48 and 72 h after a competitive soccer game. MVC force, SR function, muscle glycogen, muscle soreness and plasma myoglobin were measured. MVC force sustained over 1 s was 11 and 10% lower (P ...

  7. Autonomic nervous control of the heart rate during isometric exercise in normal man.

    Science.gov (United States)

    Maciel, B C; Gallo Júnior, L; Marin Neto, J A; Martins, L E

    1987-02-01

    The relative contribution of the efferent components of the autonomic nervous system to the regulation of tachycardia induced by isometric exercise was assessed in 23 normal males. The isometric exercise (handgrip) was performed at the maximum intensity tolerated by the individual over a period of 10 s (maximal voluntary contraction-MVC) and at levels equivalent to 75, 50 and 25% of MVC for 20, 40 and 10 s, respectively. The study was performed both under control conditions and after pharmacological blockade with atropine (12 individuals) or propranolol (11 individuals). Under control conditions, the heart rate (HR) responses to isometric effort were dependent on the intensity and duration of the exercise, showing a tendency towards progressive elevation with the maintenance of muscular contraction at the levels studied. The tachycardia evoked by this effort was of considerable magnitude and of rapid onset, especially at the more intense levels of activity. Parasympathetic blockade markedly decreased tachycardia, which manifested itself during the first 10 s of exercise at all levels of intensity, whereas sympathetic blockade markedly modified the HR response after 10 s of effort at the 75 and 50% MVC levels. A slight depression of the tachycardiac response could be observed already after 10 s of maximum effort after propranolol. The present results suggest that the autonomic regulation of these responses is based on a biphasic mechanism, with the initial phase depending on the rapid withdrawal of the parasympathetic influence, followed by a marked sympathetic contribution to the induction of tachycardia after 10 s of isometric contraction or even a little before at maximum exertion.

  8. Optimal Control of Isometric Muscle Dynamics

    Directory of Open Access Journals (Sweden)

    Robert Rockenfeller

    2015-03-01

    Full Text Available We use an indirect optimal control approach to calculate the optimal neural stimulation needed to obtain measured isometric muscle forces. The neural stimulation of the nerve system is hereby considered to be a control function (input of the system ’muscle’ that solely determines the muscle force (output. We use a well-established muscle model and experimental data of isometric contractions. The model consists of coupled activation and contraction dynamics described by ordinary differential equations. To validate our results, we perform a comparison with commercial optimal control software.

  9. 等长收缩负荷对家兔股动脉固有侧支循环开放的影响%The effect of isometric contraction in opening femoral artery collateral circulation in rabbits

    Institute of Scientific and Technical Information of China (English)

    韩良; 励建安; 余滨宾

    2010-01-01

    Objective To explore the effect of isometric contraction-induced ischemic burden for evoking maximal intrinsic femoral artery collateral circulation. Methods Twenty-four adult New Zealand rabbits weighing (2.0±0.5) kg were subjected to a model of isometric contraction-induced ischemia. An electrode was implanted in the sciatic nerve of the left hind limb for evoking isometric contraction of the gastrocnemius, which blocked local blood flow and induced local ischemia. Femoral artery collateral blood flow (FCBF) was measured using a micro-sphere technique. Results Local blood flow was the lowest at 40% of the maximal isometric contraction (IEmax), and reached plateau at 60% of IEmax. FCBF increased gradually and reached a plateau at 40% of IEmax in the 4th min. After 4 minutes at 40% of IEmax, FCBF had increased to higher than pre-stimulus, peaking in the 2nd minute, and then decreasing gradually to baseline at the 5th minute after reperfusion. It ceased to increase when reperfusion was prolonged to 8 or 10 min. Conclusions The minimal ischemic burden for full obstruction of the femoral artery is 40% of IEmax, and the shortest stimulus duration is 4 min. The maximal FCBF opening duration is no more than 5 min.%目的 观察不同等长收缩负荷对股动脉同有侧支循环开放的影响,为研究生理性缺血训练对侧支循环生成的影响奠定基础.方法 选择健康成年家兔24只,体重(2.0±0.5)kg,于左下肢坐骨神经植入电极,电刺激产生等长收缩造成缺血,预先设定不同收缩强度和时间.实验终止时取坐骨神经支配区-腓肠肌组织,微球技术定量检测股动脉固有侧支血流(FCBF).结果 ①采用40%最大等长收缩强度(IEmax)时缺血区局部血流降低程度最大(P<0.01);采用60%IEmax和80%IEmax的局部血流下降率相比,差异无统计学意义.②采用40%IEmax刺激0~4 min,FCBF呈增加趋势,第4分钟时达峰值,较刺激即刻、刺激后第2,3分钟明显增加(P<0.01),至第5

  10. Maximal force, voluntary activation and muscle soreness after eccentric damage to human elbow flexor muscles

    Science.gov (United States)

    Prasartwuth, O; Taylor, JL; Gandevia, SC

    2005-01-01

    Muscle damage reduces voluntary force after eccentric exercise but impaired neural drive to the muscle may also contribute. To determine whether the delayed-onset muscle soreness, which develops ∼1 day after exercise, reduces voluntary activation and to identify the possible site for any reduction, voluntary activation of elbow flexor muscles was examined with both motor cortex and motor nerve stimulation. We measured maximal voluntary isometric torque (MVC), twitch torque, muscle soreness and voluntary activation in eight subjects before, immediately after, 2 h after, 1, 2, 4 and 8 days after eccentric exercise. Motor nerve stimulation and motor cortex stimulation were used to derive twitch torques and measures of voluntary activation. Eccentric exercise immediately reduced the MVC by 38 ± 3% (mean ±s.d., n = 8). The resting twitch produced by motor nerve stimulation fell by 82 ± 6%, and the estimated resting twitch by cortical stimulation fell by 47 ± 15%. While voluntary torque recovered after 8 days, both measures of the resting twitch remained depressed. Muscle tenderness occurred 1–2 days after exercise, and pain during contractions on days 1–4, but changes in voluntary activation did not follow this time course. Voluntary activation assessed with nerve stimulation fell 19 ± 6% immediately after exercise but was not different from control values after 2 days. Voluntary activation assessed by motor cortex stimulation was unchanged by eccentric exercise. During MVCs, absolute increments in torque evoked by nerve and cortical stimulation behaved differently. Those to cortical stimulation decreased whereas those to nerve stimulation tended to increase. These findings suggest that reduced voluntary activation contributes to the early force loss after eccentric exercise, but that it is not due to muscle soreness. The impairment of voluntary activation to nerve stimulation but not motor cortical stimulation suggests that the activation deficit lies in the

  11. Evaluation of electromyographic activity and heart rate responses to isometric exercise. The role played by muscular mass and type

    Directory of Open Access Journals (Sweden)

    E. Silva

    1999-01-01

    Full Text Available The purpose of the present study was to examine the relationship between the electromyographic (EMG activity and heart rate (HR responses induced by isometric exercise performed by knee extension (KE and flexion (KF in men. Fifteen healthy male subjects, 21 ± 1.3 years (mean ± SD, were submitted to KE and KF isometric exercise tests at 100% of maximal voluntary contraction (MVC. The exercises were performed with one leg (right or left and with two legs simultaneously, for 10 s in the sitting position with the hip and knee flexed at 90o. EMG activity (root mean square values and HR (beats/min were recorded simultaneously both at rest and throughout the sustained contraction. The HR responses to isometric exercise in KE and KF were similar when performed with one and two legs. However, the HR increase was always significantly higher in KE than KF (P0.05 and KF (r = 0.15, P>0.05 contractions were not significant. These results suggest that the predominant mechanism responsible for the larger increase in HR response to KE as compared to KF in our study could be dependent on qualitative and quantitative differences in the fiber type composition found in each muscle group. This mechanism seems to demand a higher activation of motor units with a corresponding increase in central command to the cardiovascular centers that modulate HR control.

  12. Quantification of muscle co-contraction using supersonic shear wave imaging.

    Science.gov (United States)

    Raiteri, Brent J; Hug, François; Cresswell, Andrew G; Lichtwark, Glen A

    2016-02-01

    Muscle stiffness estimated using shear wave elastography can provide an index of individual muscle force during isometric contraction and may therefore be a promising method for quantifying co-contraction. We estimated the shear modulus of the lateral gastrocnemius (LG) muscle using supersonic shear wave imaging and measured its myoelectrical activity using surface electromyography (sEMG) during graded isometric contractions of plantar flexion and dorsiflexion (n=7). During dorsiflexion, the average shear modulus was 26 ± 6 kPa at peak sEMG amplitude, which was significantly less (P=0.02) than that measured at the same sEMG level during plantar flexion (42 ± 10 kPa). The passive tension during contraction was estimated using the passive LG muscle shear modulus during a passive ankle rotation measured at an equivalent ankle angle to that measured during contraction. The passive shear modulus increased significantly (Pmuscle shear modulus due to active contraction was significantly greater (Pmuscle, despite measured sEMG activity of 19% of maximal voluntary plantar flexion contraction. This strongly suggests that the sEMG activity recorded from the LG muscle during isometric dorsiflexion was primarily due to cross-talk. However, it is clear that passive muscle tension changes can contribute to joint torque during isometric dorsiflexion.

  13. The surface EMG-force relationship during isometric dorsiflexion in males and females.

    Science.gov (United States)

    Lenhardt, S A; McIntosh, K C; Gabriel, D A

    2009-01-01

    This study compared the tibialis anterior (TA) surface electromyographic (sEMG) to force relationship for males and females. One-hundred participants (50 males and 50 females) performed three isometric contractions at 20, 40, 60, 80, and 100% of maximal voluntary contraction (MVC) in an apparatus designed to isolate the action of the dorsiflexors. The sEMG signal was amplified (1000x), band-pass filtered (10-500 Hz), and sampled at 2048 Hz. The load cell signal was low-pass filtered at 100 Hz and sampled at the same rate. Males were stronger than females (p MVC (p MVC, the frequency values for the females plateaued while males showed a decrease (p pattern of means for RMS and MNF between males and females revealed no differences between groups in the sEMG-force relationship. We therefore conclude that there are no differences between males and females in the gradation of muscle force.

  14. Physiological alterations of maximal voluntary quadriceps activation by changes of knee joint angle.

    Science.gov (United States)

    Becker, R; Awiszus, F

    2001-05-01

    The purpose of this study was to investigate the influence of different angles of the knee joint on voluntary activation of the quadriceps muscle, estimating the ability of a subject to activate a muscle maximally by means of voluntary contraction. Isometric torque measurement was performed on 6 healthy subjects in 5 degrees intervals between 30 degrees and 90 degrees of knee joint flexion. Superimposed twitches at maximal voluntary contraction (MVC) and at a level of 60% and 40% of the MVC were applied and the voluntary activation estimated. At between 30 degrees and 75 degrees of knee flexion, the maximal extension torque increased at an average rate of 2.67 +/- 0.6 Nm/degree, followed by a decline with further flexion. However, throughout the joint-angle range tested, voluntary activation increased on average by 0.37%/degree with a maximum at 90 degrees of flexion. Due to the influence of joint position it is not possible to generalize results obtained at the knee joint angle of 90 degrees of flexion, which is usually used for the quadriceps twitch-interpolation technique. Consequently, it is useful to investigate voluntary activation deficits in knee joint disorders at a range of knee joint angles that includes, in particular, the more extended joint angles used frequently during daily activity.

  15. Obtaining maximum muscle excitation for normalizing shoulder electromyography in dynamic contractions.

    Science.gov (United States)

    Hodder, Joanne N; Keir, Peter J

    2013-10-01

    Muscle specific maximal voluntary isometric contractions (MVIC) are commonly used to elicit reference amplitudes to normalize electromyographic signals (EMG). It has been questioned whether this is appropriate for normalizing EMG from dynamic contractions. This study compares EMG amplitude when shoulder muscle activity from dynamic contractions is normalized to isometric and isokinetic maximal excitation as well as a hybrid approach currently used in our laboratory. Anterior, middle and posterior deltoid, upper and lower trapezius, pectoralis major, latissimus dorsi and infraspinatus were monitored during (1) manually resisted MVICs, and (2) maximum voluntary dynamic concentric contractions (MVDC) on an isokinetic dynamometer. Dynamic contractions were performed (a) at 30°/s about the longitudinal, frontal and sagittal axes of the shoulder, and (b) during manual bi-rotation of a tilted wheel at 120°/s. EMG from the wheel task was normalized to the maximum excitation from (i) the muscle specific MVIC, (ii) from any MVIC (MVICALL), (iii) for any MVDC, (iv) from any exertion (maximum experimental excitation, MEE). Mean EMG from the wheel task was up to 45% greater when normalized to muscle specific isometric contractions (method i) than when normalized to MEE (method iv). Seventy-five percent of MEE's occurred during MVDCs. This study presents an 20 useful and effective process for obtaining the greatest excitation from the shoulder muscles when normalizing dynamic efforts.

  16. An examination of cross-talk among surface mechanomyographic signals from the superficial quadriceps femoris muscles during isometric muscle actions.

    Science.gov (United States)

    Beck, Travis W; DeFreitas, Jason M; Stock, Matt S

    2010-04-01

    The purpose of this study was to examine cross-talk among the mechanomyographic (MMG) signals from the superficial quadriceps femoris muscles during submaximal to maximal isometric muscle actions of the leg extensors. Eleven healthy men (age=20.1+/-1.1yr, mean+/-SD) volunteered to randomly perform isometric muscle actions in 10% increments from 10% to 90% of the maximum voluntary contraction (MVC). During each muscle action, MMG signals were detected from the vastus lateralis, rectus femoris, and vastus medialis with three separate accelerometers. Cross-correlation was used to quantify cross-talk among the vastus lateralis, rectus femoris, and vastus medialis during each muscle action. The results showed cross-correlation coefficients that ranged from R(x,y)=.124-.714, but generally speaking, the coefficients were between .1 and .3. In addition, there were no consistent differences among the cross-talk levels for the three muscles, and the cross-correlation coefficients generally did not increase with isometric torque. Thus, MMG can be used to examine muscle function from each of the superficial quadriceps femoris muscles during isometric muscle actions.

  17. The isometric athlete.

    Science.gov (United States)

    Longhurst, J C; Stebbins, C L

    1992-05-01

    A number of normal daily and athletic activities require isometric or static exercise. Such sports as weight lifting and other high-resistance activities are used by athletes to gain strength and skeletal muscle bulk. However, static exercise also causes significant increases in blood pressure, heart rate, myocardial contractility, and cardiac output. These changes occur in response to central neural irradiation, called central command, as well as a reflex originating from statically contracting muscle. Studies have demonstrated that blood pressure appears to be the regulated variable, presumably because the increased pressure provides blood flow into muscles that have compressed their arterial inflow as a result of increases in intramuscular pressure created by contraction. Thus, static exercise is characterized by a pressure load to the heart and can be differentiated from dynamic (isotonic) exercise, which involves a volume load to the heart. Physical training with static exercise leads to concentric cardiac, particularly left ventricular, hypertrophy, whereas training with dynamic exercise leads to eccentric hypertrophy. Furthermore, the magnitude of cardiac hypertrophy is much less in athletes training with static than dynamic exercise. Neither systolic nor diastolic function is altered by the hypertrophic process associated with static exercise training. Many of the energy requirements for static exercise, particularly during more severe levels of exercise, are met by anaerobic glycolysis because the contracting muscle becomes deprived of blood flow. Training with repetitive static exercise therefore causes little increase in oxygen transport capacity, so that maximal oxygen consumption is either not or only minimally increased. Peripheral cardiovascular adaptations also can occur in response to static exercise training. Although controversial, these adaptations include modest decreases in resting blood pressure, smaller increases in blood pressure during a

  18. A Spatially Detailed Model of Isometric Contraction Based on Competitive Binding of Troponin I Explains Cooperative Interactions between Tropomyosin and Crossbridges.

    Directory of Open Access Journals (Sweden)

    Sander Land

    2015-08-01

    Full Text Available Biophysical models of cardiac tension development provide a succinct representation of our understanding of force generation in the heart. The link between protein kinetics and interactions that gives rise to high cooperativity is not yet fully explained from experiments or previous biophysical models. We propose a biophysical ODE-based representation of cross-bridge (XB, tropomyosin and troponin within a contractile regulatory unit (RU to investigate the mechanisms behind cooperative activation, as well as the role of cooperativity in dynamic tension generation across different species. The model includes cooperative interactions between regulatory units (RU-RU, between crossbridges (XB-XB, as well more complex interactions between crossbridges and regulatory units (XB-RU interactions. For the steady-state force-calcium relationship, our framework predicts that: (1 XB-RU effects are key in shifting the half-activation value of the force-calcium relationship towards lower [Ca(2+], but have only small effects on cooperativity. (2 XB-XB effects approximately double the duty ratio of myosin, but do not significantly affect cooperativity. (3 RU-RU effects derived from the long-range action of tropomyosin are a major factor in cooperative activation, with each additional unblocked RU increasing the rate of additional RU's unblocking. (4 Myosin affinity for short (1-4 RU unblocked stretches of actin of is very low, and the resulting suppression of force at low [Ca(2+] is a major contributor in the biphasic force-calcium relationship. We also reproduce isometric tension development across mouse, rat and human at physiological temperature and pacing rate, and conclude that species differences require only changes in myosin affinity and troponin I/troponin C affinity. Furthermore, we show that the calcium dependence of the rate of tension redevelopment k(tr is explained by transient blocking of RU's by a temporary decrease in XB-RU effects.

  19. An examination of the frequency-specific behavior of the mechanomyographic amplitude versus isometric torque relationship.

    Science.gov (United States)

    Beck, T W

    2009-01-01

    The purpose of this study was to examine the patterns of responses for mechanomyographic (MMG) amplitude versus isometric torque in different frequency bands for the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) muscles. Eleven men (mean +/- SD age = 20.1 +/- 1.1 yrs) performed submaximal to maximal isometric step muscle actions of the dominant leg extensors from 10% to 100% of the maximum voluntary contraction (MVC). During each muscle action, three separate surface mechanomyographic (MMG) signals were detected from the VL, RF and VM. Each MMG signal was decomposed into 9 different frequency bands (5-15, 15-25, 25-35, 35-45, 45-55, 55-65, 65-75, 75-85, and 85-95 Hz), and the root-mean-square amplitude of the signal in each frequency band was calculated. The results showed that for the VL and RF muscles, MMG amplitude plateaued from 80-100% MVC in the 15-25 and 25-35 Hz frequency bands. For the VM, however, the plateau in MMG amplitude from 80-100% MVC occurred in the 5-15 and 15-25 Hz bands. These findings indicated that there were both muscle- and frequency-specific discrepancies in the MMG amplitude versus isometric torque relationship that could be due to differences in muscle architecture and/or fiber type composition.

  20. Effect of age on the hemodynamic and sympathetic responses at the onset of isometric handgrip exercise.

    Science.gov (United States)

    Lalande, Sophie; Sawicki, Carolyn P; Baker, Jacquie R; Shoemaker, J Kevin

    2014-01-15

    Cardiac and peripheral vasomotor factors contribute to the rapid pressor response at the onset of isometric handgrip exercise. We tested the hypothesis that age enhances the sympathetic and vasoconstrictor response at the onset of isometric handgrip exercise so that the pressor response is maintained, despite a diminished cardiac function. Twelve young and twelve older (24 ± 3 and 63 ± 8 yr) individuals performed 20-s isometric handgrip exercise at 30, 40, or 50% of maximal voluntary contraction force. Muscle sympathetic nerve activity (MSNA) was measured using microneurography. Mean arterial pressure (MAP) and cardiac output (Q) were assessed continuously by finger plethysmography and total peripheral resistance was calculated. MAP increased with the onset of handgrip; this increase was associated with handgrip intensity and was similar in both groups. Heart rate and Q increased with increasing handgrip intensity in both groups, but increases were greater in young vs. older individuals (age × handgrip intensity interaction, P change in MSNA between baseline and handgrip, for both frequency and incidence, increased with increasing handgrip intensity for both groups. There was no effect of handgrip intensity or age on total peripheral resistance. The smaller heart rate and Q response during the first 20 s of handgrip exercise in older individuals was not accompanied by a greater sympathetic activation or vasoconstrictor response. However, increases in MAP were similar between groups, indicating that the pressor response at the onset of handgrip exercise is preserved with aging.

  1. Effects of experimental muscle pain on force variability during task-related and three directional isometric force task

    DEFF Research Database (Denmark)

    Mista, Christian Ariel; Graven-Nielsen, Thomas

    2013-01-01

    -dimensional force task during acute muscle pain. Twelve right-handed healthy volunteers participated in the experiment. Three-dimensional force signals were acquired during isometric elbow flexion at 5%, 15%, and 30% of the maximum voluntary contraction (MVC). The force components were represented by a circle...... the sense of effort and motor output during contractions. However, little is known about the pain effects on the force components when task-related or three-dimensional force matching task are required. The aim of this study was to quantify changes in the force variability during task-related and three...... on a computer screen, and a moving square was used for the visual target. Subjects were asked to match the main direction of the contraction during the task-related (1D) or all the force components during the three-dimensional (3D) force matching tasks. Isotonic and hypertonic saline injections were randomly...

  2. 股四头肌等长等张收缩锻炼在治疗膝骨关节炎中的作用%Quadriceps isometric isotonic contraction in the role of exercise in the treatment of knee osteoarthritis

    Institute of Scientific and Technical Information of China (English)

    刘福英; 刘卫华

    2013-01-01

    目的观察通过股四头肌等长、等张收缩练习治疗膝骨性关节炎中的临床效果,并建立膝骨性关节炎运动处方。方法将60例膝关节骨性关节炎患者同期分为观察组30例(透明质酸钠关节腔注射+股四头肌等长等张收缩训练)、对照组30例(透明质酸钠关节腔注射),治疗前及治疗后、3个月、6个月、1年用Lysholms膝关节功能评分方法观察膝关节功能及临床疗效。结果两组治疗均可减轻疼痛,改善患膝功能,同治疗前相比差异有统计学意义(P<0.05);组间对比,观察组疗效优于对照组,差异有统计学意义(P<0.05)。结论坚持等长、等张收缩练习,能有效缓解关节疼痛,增强关节稳定性,改善关节功能,其远期效果优于玻璃酸钠。%Objective To observe clinical effects of knee osteoarthritis with the treatment of the isometric quadriceps femoris contraction exercises, which aims at establishing the exercise prescription of knee osteoarthritis, and promoting its clinical application. Methods 60 patients with knee osteoarthritis were divided into two groups according to visiting sequence. There were 30 patients in the therapeutic group. The patients were treated with intra-articular injection of sodium hyaluronate and isometric quadriceps femoris contraction exercises for treatment. There were 30 patients in the control group. The patients were treated with conventional intra-articular injection of sodium hyaluronate. In our study, by measuring the diameter, daily function and HSS score to evaluate the clinical effect of treatment and make statistical analysis in pretreatment group and posttreatment groups at 3 and 6 months. Results Treatment of two groups reduced pain and improved knee function. Compared with pre-treatment difference was statistically significant (P < 0.05). Comparison between groups, observation group was better than the control group, the difference was

  3. Fatigue and recovery from dynamic contractions in men and women differ for arm and leg muscles.

    Science.gov (United States)

    Senefeld, Jonathon; Yoon, Tejin; Bement, Marie Hoeger; Hunter, Sandra K

    2013-09-01

    Whether there is a gender difference in fatigue and recovery from maximal velocity fatiguing contractions and across muscles is not understood. Sixteen men and 19 women performed 90 isotonic contractions at maximal voluntary shortening velocity (maximal velocity concentric contractions, MVCC) with the elbow flexor and knee extensor muscles (separate days) at a load equivalent to 20% maximal voluntary isometric contraction (MVIC). Power (from MVCCs) decreased similarly for men and women for both muscles (P > 0.05). Men and women had similar declines in MVIC of elbow flexors, but men had greater reductions in knee extensor MVIC force and MVIC electromyogram activity than women (P contractions for upper and lower limb muscles. Copyright © Published 2013 by Wiley Periodicals, Inc. This article is a US Government wmusork and, as such, is in the public domain in the United States of America.

  4. Motor imagery muscle contraction strength influences spinal motor neuron excitability and cardiac sympathetic nerve activity

    OpenAIRE

    2015-01-01

    [Purpose] The aim of this study was to investigate the changes in spinal motor neuron excitability and autonomic nervous system activity during motor imagery of isometric thenar muscle activity at 10% and 50% maximal voluntary contraction (MVC). [Methods] The F-waves and low frequency/high frequency (LF/HF) ratio were recorded at rest, during motor imagery, and post-trial. For motor imagery trials, subjects were instructed to imagine thenar muscle activity at 10% and 50% MVC while holding the...

  5. A linear description of shortening induced changes in isometric length-force characteristics of rat muscle

    OpenAIRE

    Meijer, K; Grootenboer, H.J.; Koopman, H.F.J.M.; Huijing, P.A.

    1996-01-01

    Active muscle shortening reduces the isometric force potential of muscle. This observation indicates that the isometric length-force characteristics are altered during muscle shortening. Post-shortening decrease in isometric force depends on starting length, shortening amplitude and shortening velocity. In the present study, post-shortening decrease in isometric force was determined after isokinetic contractions with various shortening amplitudes initiated from different lengths of rat medial...

  6. Behaviour of the human gastrocnemius muscle architecture during submaximal isometric fatigue.

    Science.gov (United States)

    Mademli, Lida; Arampatzis, Adamantios

    2005-08-01

    The purpose of this study was to examine whether the human gastrocnemius medialis (GM) fascicle length and pennation angle alter during a sustained submaximal isometric plantar flexion. Fourteen male subjects performed maximal voluntary plantar flexions (MVC) on a dynamometer before and after a fatiguing task. This task consisted of a sustained submaximal isometric fatiguing contraction (40% MVC) until failure to hold the defined moment. Ultrasonography was used to visualise the muscle belly of the GM. Leg kinematics were recorded (120 Hz) to calculate the joint moment using inverse dynamics. The exerted moments and the EMG signals from GM and lateralis, soleus and tibialis anterior were measured at 1,080 Hz. The root mean square (RMS) of the EMG signal of the three triceps surae muscles increased significantly (P < or = 0.05) between 17% and 28% with fatigue. Further, the fascicle length of the GM significantly decreased from 47.1 +/- 8.0 mm at the beginning to 41.8 +/- 6.7 mm at the end of fatigue and the pennation angle increased from 23.5 +/- 4.1 degrees to 26.3 +/- 2.2 degrees (P < or = 0.05). The changes in fascicle length and pennation angle of the GM during the contraction can influence the force potential of the muscle due to the force-length relationship and the force transmission to the tendon. This provides evidence on that an additional mechanical mechanism, namely tendon creep, can contribute to the increase in the EMG activity of the GM during submaximal isometric sustained contractions.

  7. Superficial aponeurosis of human gastrocnemius is elongated during contraction: implications for modeling muscle-tendon unit.

    Science.gov (United States)

    Muramatsu, Tadashi; Muraoka, Tetsuro; Kawakami, Yasuo; Fukunaga, Tetsuo

    2002-02-01

    Two questions were addressed in this study: (1) how much strain of the superficial aponeurosis of the human medial gastrocnemius muscle (MG) was obtained during voluntary isometric contractions in vivo, (2) whether there existed inhomogeneity of the strain along the superficial aponeurosis. Seven male subjects, whose knees were extended and ankles were flexed at right angle, performed isometric plantar flexion while elongation of superficial aponeurosis of MG was determined from the movements of the intersections made by the superficial aponeurosis and fascicles using ultrasonography. The strain of the superficial aponeurosis at the maximum voluntary contraction, estimated from the elongation and length data, was 5.6+/-1.2%. There was no significant difference in strain between the proximal and distal parts of the superficial aponeurosis. Based on the present result and that of our previous study for the same subjects (J. Appl. Physiol 90 (2001) 1671), a model was formulated for a contracting uni-pennate muscle-tendon unit. This model, which could be applied to isometric contractions at other angles and therefore of wide use, showed that similar strain between superficial and deep aponeuroses of MG contributed to homogeneous fascicle length change within MG during contractions. These findings would contribute to clarifying the functions of the superficial aponeurosis and the effects of the superficial aponeurosis elongation on the whole muscle behavior.

  8. Contraction level-related modulation of corticomuscular coherence differs between the tibialis anterior and soleus muscles in humans.

    Science.gov (United States)

    Ushiyama, Junichi; Masakado, Yoshihisa; Fujiwara, Toshiyuki; Tsuji, Tetsuya; Hase, Kimitaka; Kimura, Akio; Liu, Meigen; Ushiba, Junichi

    2012-04-01

    The sensorimotor cortex activity measured by scalp EEG shows coherence with electromyogram (EMG) activity within the 15- to 35-Hz frequency band (β-band) during weak to moderate intensity of isometric voluntary contraction. This coupling is known to change its frequency band to the 35- to 60-Hz band (γ-band) during strong contraction. This study aimed to examine whether such contraction level-related modulation of corticomuscular coupling differs between muscles with different muscle compositions and functions. In 11 healthy young adults, we quantified the coherence between EEG over the sensorimotor cortex and rectified EMG during tonic isometric voluntary contraction at 10-70% of maximal voluntary contraction of the tibialis anterior (TA) and soleus (SOL) muscles, respectively. In the TA, the EEG-EMG coherence shifted from the β-band to the γ-band with increasing contraction level. Indeed, the magnitude of β-band EEG-EMG coherence was significantly decreased, whereas that of γ-band coherence was significantly increased, when the contraction level was above 60% of maximal voluntary contraction. In contrast to the TA, the SOL showed no such frequency changes of EEG-EMG coherence with alterations in the contraction levels. In other words, the maximal peak of EEG-EMG coherence in the SOL existed within the β-band, irrespective of the contraction levels. These findings suggest that the central nervous system regulates the frequency of corticomuscular coupling to exert the desired levels of muscle force and, notably, that the applicable rhythmicity of the coupling for performing strong contractions differs between muscles, depending on the physiological muscle compositions and functions of the contracting muscle.

  9. Insights into the neural control of eccentric contractions.

    Science.gov (United States)

    Duchateau, Jacques; Baudry, Stéphane

    2014-06-01

    The purpose of this brief review is to examine our current knowledge of the neural control of eccentric contractions. The review focuses on three main issues. The first issue considers the ability of individuals to activate muscles maximally during eccentric contractions. Most studies indicate that, regardless of the experimental approach (surface EMG amplitude, twitch superimposition, and motor unit recordings), it is usually more difficult to achieve full activation of a muscle by voluntary command during eccentric contractions than during concentric and isometric contractions. The second issue is related to the specificity of the control strategy used by the central nervous system during submaximal eccentric contractions. This part underscores that although the central nervous system appears to employ a single size-related strategy to activate motoneurons during the different types of contractions, the discharge rate of motor units is less during eccentric contractions across different loading conditions. The last issue addresses the mechanisms that produce this specific neural activation. This section indicates that neural adjustments at both supraspinal and spinal levels contribute to the specific modulation of voluntary activation during eccentric contractions. Although the available information on the control of eccentric contractions has increased during the last two decades, this review indicates that the exact mechanisms underlying the unique neural modulation observed in this type of contraction at spinal and supraspinal levels remains unknown and their understanding represents, therefore, a major challenge for future research on this topic.

  10. Characterizing rapid-onset vasodilation to single muscle contractions in the human leg.

    Science.gov (United States)

    Credeur, Daniel P; Holwerda, Seth W; Restaino, Robert M; King, Phillip M; Crutcher, Kiera L; Laughlin, M Harold; Padilla, Jaume; Fadel, Paul J

    2015-02-15

    Rapid-onset vasodilation (ROV) following single muscle contractions has been examined in the forearm of humans, but has not yet been characterized in the leg. Given known vascular differences between the arm and leg, we sought to characterize ROV following single muscle contractions in the leg. Sixteen healthy men performed random ordered single contractions at 5, 10, 20, 40, and 60% of their maximum voluntary contraction (MVC) using isometric knee extension made with the leg above and below heart level, and these were compared with single isometric contractions of the forearm (handgrip). Single thigh cuff compressions (300 mmHg) were utilized to estimate the mechanical contribution to leg ROV. Continuous blood flow was determined by duplex-Doppler ultrasound and blood pressure via finger photoplethysmography (Finometer). Single isometric knee extensor contractions produced intensity-dependent increases in peak leg vascular conductance that were significantly greater than the forearm in both the above- and below-heart level positions (e.g., above heart level: leg 20% MVC, +138 ± 28% vs. arm 20% MVC, +89 ± 17%; P contractions in the leg. Collectively, these data demonstrate the presence of a rapid and robust vasodilation to single muscle contractions in the leg that is largely independent of mechanical factors, thus establishing the leg as a viable model to study ROV in humans.

  11. Muscle sympathetic nerve activity during cold stress and isometric exercise in healthy older adults.

    Science.gov (United States)

    Greaney, Jody L; Stanhewicz, Anna E; Kenney, W Larry; Alexander, Lacy M

    2014-09-15

    Cardiovascular mortality increases in cold weather in older adults, and physical activity may impart even greater cardiovascular risk than cold exposure alone. Human aging is associated with exaggerated pressor responses to whole body cooling; however, the sympathetic response to cold stress alone and in combination with isometric exercise is unknown. We hypothesized that cold stress would 1) increase muscle sympathetic nerve activity (MSNA) and 2) augment the MSNA response to isometric handgrip in older adults. Whole body cooling (water-perfused suit) was conducted in 11 young (23 ± 1 yr) and 12 healthy older adults (60 ± 2 yr). Blood pressure (BP; Finometer) and MSNA (microneurography) were measured throughout cooling and during isometric handgrip at 30% maximal voluntary contraction performed at a mean skin temperature (Tsk) of 34 and 30.5°C. MSNA was greater in older adults at Tsk = 34.0°C and throughout cooling (P 0.05) or older adults (Δ12 ± 1 Tsk 34°C vs. Δ8 ± 1 Tsk 30.5°C bursts/min; Δ18 ± 3 Tsk 34°C vs. Δ17 ± 2 Tsk 30.5°C mmHg; both P > 0.05). In summary, MSNA increased during cold stress in older, but not young, adults. Furthermore, concomitant cold stress did not alter the sympathetic responses to isometric exercise in either age group, suggesting preserved sympathetic responsiveness during exercise in the cold in healthy aging. Copyright © 2014 the American Physiological Society.

  12. β-alanine supplementation improves isometric endurance of the knee extensor muscles

    Directory of Open Access Journals (Sweden)

    Sale Craig

    2012-06-01

    Full Text Available Abstract Background We examined the effect of four weeks of β-alanine supplementation on isometric endurance of the knee extensors at 45% maximal voluntary isometric contraction (MVIC. Methods Thirteen males (age 23 ± 6 y; height 1.80 ± 0.05 m; body mass 81.0 ± 10.5 kg, matched for pre-supplementation isometric endurance, were allocated to either a placebo (n = 6 or β-alanine (n = 7; 6.4 g·d-1 over 4 weeks supplementation group. Participants completed an isometric knee extension test (IKET to fatigue, at an intensity of 45% MVIC, before and after supplementation. In addition, two habituation tests were completed in the week prior to the pre-supplementation test and a further practice test was completed in the week prior to the post-supplementation test. MVIC force, IKET hold-time, and impulse generated were recorded. Results IKET hold-time increased by 9.7 ± 9.4 s (13.2% and impulse by 3.7 ± 1.3 kN·s-1 (13.9% following β-alanine supplementation. These changes were significantly greater than those in the placebo group (IKET: t(11 = 2.9, p ≤0.05; impulse: t(11 = 3.1, p ≤ 0.05. There were no significant changes in MVIC force in either group. Conclusion Four weeks of β-alanine supplementation at 6.4 g·d-1 improved endurance capacity of the knee extensors at 45% MVIC, which most likely results from improved pH regulation within the muscle cell as a result of elevated muscle carnosine levels.

  13. Time course of central and peripheral alterations after isometric neuromuscular electrical stimulation-induced muscle damage.

    Directory of Open Access Journals (Sweden)

    Alexandre Fouré

    Full Text Available Isometric contractions induced by neuromuscular electrostimulation (NMES have been shown to result in a prolonged force decrease but the time course of the potential central and peripheral factors have never been investigated. This study examined the specific time course of central and peripheral factors after isometric NMES-induced muscle damage. Twenty-five young healthy men were subjected to an NMES exercise consisting of 40 contractions for both legs. Changes in maximal voluntary contraction force of the knee extensors (MVC, peak evoked force during double stimulations at 10 Hz (Db(10 and 100 Hz (Db(100, its ratio (10:100, voluntary activation, muscle soreness and plasma creatine kinase activity were assessed before, immediately after and throughout four days after NMES session. Changes in knee extensors volume and T2 relaxation time were also assessed at two (D2 and four (D4 days post-exercise. MVC decreased by 29% immediately after NMES session and was still 19% lower than the baseline value at D4. The decrease in Db(10 was higher than in Db(100 immediately and one day post-exercise resulting in a decrease (-12% in the 10:100 ratio. On the contrary, voluntary activation significantly decreased at D2 (-5% and was still depressed at D4 (-5%. Muscle soreness and plasma creatine kinase activity increased after NMES and peaked at D2 and D4, respectively. T2 was also increased at D2 (6% and D4 (9%. Additionally, changes in MVC and peripheral factors (e.g., Db(100 were correlated on the full recovery period, while a significant correlation was found between changes in MVC and VA only from D2 to D4. The decrease in MVC recorded immediately after the NMES session was mainly due to peripheral changes while both central and peripheral contributions were involved in the prolonged force reduction. Interestingly, the chronological events differ from what has been reported so far for voluntary exercise-induced muscle damage.

  14. The number of active motor units and their firing rates in voluntary contraction of human brachialis muscle.

    Science.gov (United States)

    Kanosue, K; Yoshida, M; Akazawa, K; Fujii, K

    1979-01-01

    To make clear the control mechanism of force generation in human muscle, the electrical activity of the brachialis muscle was studied at various levels of contraction force by recording single motor unit discharges as well as mass electromyograms (EMGs). The firing rate of motor units increased with force along an S-shaped curve. At low levels of force, motor units increased their firing rates steeply with force. At intermediate levels of force, each motor unit increased its firing rate linearly with force at lower rates. As the maximum of force was approached, the firing rate increased very steeply, reaching as high as 50 Hz or more. By applying a new method of statistical processing to mass EMGs, the number of active motor units and the size of action potential were estimated at each level of force. The number of active motor units increased monotonously with muscle force. Motor units recruited at high levels of force had larger amplitudes of action potentials than those recruited at lower levels. Calculations were made to determine how the relative contribution to an increase in muscle force is varied between recruitment and the increase in firing rate. The contribution of recruitment gradually decreased with the increase in force. Up to about 70% of the maximum force, recruitment is the major mechanism for increasing the force of contraction.

  15. Contractions

    Science.gov (United States)

    ... the opening to the uterus through which the baby passes during delivery). The contractions tend to increase in the weeks ... experience cramps, contractions and discomfort for weeks before delivery. ... The feeling that the baby has settled lower in your belly. This can ...

  16. Differential contributions of ankle plantarflexors during submaximal isometric muscle action

    DEFF Research Database (Denmark)

    Masood, Tahir; Bojsen-Møller, Jens; Kalliokoski, Kari K

    2014-01-01

    healthy volunteers (27.3±4.2yrs). A tracer ([(18)F]-FDG) was injected during the exercise and PET scanning was done immediately afterwards. The examined muscles included soleus (Sol), medial gastrocnemius (MG), lateral gastrocnemius (LG), and flexor hallucis longus (FHL). It was found that isometric...... maximal voluntary contraction (MVC) force, muscle glucose uptake (GU) rate, and SEMG of various plantarflexors were comparable bilaterally. In terms of %EMG MVC, FHL and MG displayed the highest activity (∼34%), while LG (∼21%) had the lowest activity. Cumulative SEMG from all parts of the triceps surae...... (TS) muscle accounted for ∼70% of the combined EMG signal of all four plantarflexors. As for GU, the highest quantity was observed in MG (2.4±0.8μmol*100g(-1)*min(-1)), whereas FHL (1.8±0.6μmol*100g(-1)*min(-1)) had the lowest uptake. Cumulative GU of TS constituted nearly 80% of the combined GU...

  17. The modulatory effect of electrical stimulation on the excitability of the corticospinal tract varies according to the type of muscle contraction being performed.

    Science.gov (United States)

    Saito, Kei; Sugawara, Kenichi; Miyaguchi, Shota; Matsumoto, Takuya; Kirimoto, Hikari; Tamaki, Hiroyuki; Onishi, Hideaki

    2014-01-01

    Afferent input caused by electrical stimulation of a peripheral nerve increases corticospinal excitability during voluntary contractions, indicating that proprioceptive sensory input arriving at the cortex plays a fundamental role in modulating corticospinal excitability. The purpose of this study was to investigate whether the effect of electrical stimulation on the corticospinal excitability varies according to the type of muscle contraction being performed. Motor-evoked potentials (MEPs) were elicited by transcranial magnetic stimulation (TMS) during a shortening contraction, an isometric contraction, or no contraction of the first dorsal interosseous (FDI) muscle. In some trials, electrical stimulation of the ulnar nerve was performed at 110% of the sensory threshold or 110% of the motor threshold prior to TMS. Electrical stimulation involved either a train of 50 pulses at 10 Hz or a single pulse. Shortening contraction with the train of electrical stimuli significantly increased MEP amplitudes, and the increase was dependent on the type of stimulation. Isometric contraction with the train of electrical stimuli and electrical stimulation without voluntary contraction did not affect MEP amplitudes. A single pulse of electrical stimulation did not affect MEP amplitudes in any condition. Thus, electrical-stimulation-induced modulation of corticospinal excitability varied according to the type of muscle contraction performed and the type of stimulation. These results show that the type of contraction should be considered when using electrical stimulation for rehabilitation in patients with central nervous system lesions.

  18. The Effects of Positive and Negative Feedback on Maximal Voluntary Contraction Level of the Biceps Brachii Muscle: Moderating Roles of Gender and Conscientiousness.

    Science.gov (United States)

    Sarıkabak, Murat; Yaman, Çetin; Tok, Serdar; Binboga, Erdal

    2016-11-02

    We investigated the effect of positive and negative feedback on maximal voluntary contraction (MVC) of the biceps brachii muscle and explored the mediating effects of gender and conscientiousness. During elbow flexion, MVCs were measured in positive, negative, and no-feedback conditions. Participants were divided into high- and low-conscientiousness groups based on the median split of their scores on Tatar's five-factor personality inventory. Considering all participants 46 college student athletes (21 female, 28 male), positive feedback led to a greater MVC percentage change (-5.76%) than did negative feedback (2.2%). MVC percentage change in the positive feedback condition differed significantly by gender, but the negative feedback condition did not. Thus, positive feedback increased female athletes' MVC level by 3.49%, but decreased male athletes' MVC level by 15.6%. For conscientiousness, MVC percentage change in the positive feedback condition did not differ according to high and low conscientiousness. However, conscientiousness interacted with gender in the positive feedback condition, increasing MVC in high-conscientiousness female athletes and decreasing MVC in low-conscientiousness female athletes. Positive feedback decreased MVC in both high- and low-conscientiousness male athletes.

  19. A comparison of two formulas of topical menthol on vascular responses and perceived intensity prior to and follow a bout of maximum voluntary muscular contractions (MVMCs).

    Science.gov (United States)

    Topp, Robert; Ng, Alex; Cybulski, Alyson; Skelton, Katalin; Papanek, Paula

    2014-07-01

    The purpose of this study was to compare the vascular responses in the brachial artery and perceived intensity of two different formulas of topical menthol gels prior to and following a bout of maximum voluntary muscular contractions (MVMCs). 18 adults completed the same protocol on different days using blinded topical menthol gels (Old Formula and New Formula). Heart rate, brachial artery blood flow (ml/min), vessel diameter and reported intensity of sensation were measured at baseline (T1), at 5 min after application of the gel to the upper arm (T2), and immediately following five MVMCs hand grips (T3). The New Formula exhibited a significant decline in blood flow (-22.6%) between T1 and T2 which was not different than the nonsignificant declines under the Old Formula 1 (-21.8%). Both formulas resulted in a significant increase in perceived intensity of sensation between T1 and T2. Blood flow increased significantly with the New Formula (488%) between T2 and T3 and nonsignificantly with the Old Formula (355%).

  20. Brain-imaging during an isometric leg extension task at graded intensities

    Directory of Open Access Journals (Sweden)

    Vera eAbeln

    2013-10-01

    Full Text Available Imaging the brain during complex and intensive movements is challenging due to the susceptibility of brain-imaging methods for motion and myogenic artifacts. A few studies measured brain activity during either single-joint or low-intensity exercises; however, the cortical activation state during larger movements with increases up to maximal intensity has barely been investigated so far. Eleven right-handed volunteers (22-45 years in age performed isometric leg extensions with their right leg at 20%, 40%, 60%, 80% and 100% of their maximal voluntary contraction. Contractions were hold for 20 seconds respectively. Electroencephalographic (EEG and electromyographic (EMG activity was recorded. Standardized low-resolution brain electromagnetic tomography (sLORETA was used to localize the cortical current density within the premotor (PMC, primary motor (M1, primary somatosensory (S1 and somatosensory association cortex (SAC. ANOVA was used for repeated measures for comparison of intensities and between the left and right hemispheres.The quality of the EEG signal was satisfying up to 80% intensity. At 100% half of the participants were not able to keep their neck and face muscles relaxed, leading to myogenic artifacts. Higher contralateral versus ipsilateral hemispheric activity was found for the S1, SAC and PMC. M1 possessed higher ipsilateral activity. The highest activity was localized in the M1, followed by S1, PMC and SAC. EMG activity and cortical current density within the M1 increased with exercise intensity. EEG recordings during bigger movements up to submaximal intensity (80% are possible, but maximal intensities are still hard to investigate when subjects contracted their neck and face muscles at the same time. Isometric contractions mainly involve the M1, whereas the S1, PMC and SAC seem not to be involved in the force output. Limitations and recommendations for future studies are discussed.

  1. Brain-imaging during an isometric leg extension task at graded intensities.

    Science.gov (United States)

    Abeln, Vera; Harig, Alexandra; Knicker, Axel; Vogt, Tobias; Schneider, Stefan

    2013-01-01

    Imaging the brain during complex and intensive movements is challenging due to the susceptibility of brain-imaging methods for motion and myogenic artifacts. A few studies measured brain activity during either single-joint or low-intensity exercises; however, the cortical activation state during larger movements with increases up to maximal intensity has barely been investigated so far. Eleven right-handed volunteers (22-45 years in age) performed isometric leg extensions with their right leg at 20, 40, 60, 80, and 100% of their maximal voluntary contraction. Contractions were hold for 20 s respectively. Electroencephalographic (EEG) and electromyographic (EMG) activity was recorded. Standardized low-resolution brain electromagnetic tomography (sLORETA) was used to localize the cortical current density within the premotor (PMC), primary motor (M1), primary somatosensory (S1) and somatosensory association cortex (SAC). ANOVA was used for repeated measures for comparison of intensities and between the left and right hemispheres. The quality of the EEG signal was satisfying up to 80% intensity. At 100% half of the participants were not able to keep their neck and face muscles relaxed, leading to myogenic artifacts. Higher contralateral vs. ipsilateral hemispheric activity was found for the S1, SAC and, PMC. M1 possessed higher ipsilateral activity. The highest activity was localized in the M1, followed by S1, PMC, and SAC. EMG activity and cortical current density within the M1 increased with exercise intensity. EEG recordings during bigger movements up to submaximal intensity (80%) are possible, but maximal intensities are still hard to investigate when subjects contracted their neck and face muscles at the same time. Isometric contractions mainly involve the M1, whereas the S1, PMC, and SAC seem not to be involved in the force output. Limitations and recommendations for future studies are discussed.

  2. Validity and reliability of isometric, isokinetic and isoinertial modalities for the assessment of quadriceps muscle strength in patients with total knee arthroplasty.

    Science.gov (United States)

    Lienhard, K; Lauermann, S P; Schneider, D; Item-Glatthorn, J F; Casartelli, N C; Maffiuletti, N A

    2013-12-01

    Reliability of isometric, isokinetic and isoinertial modalities for quadriceps strength evaluation, and the relation between quadriceps strength and physical function was investigated in 29 total knee arthroplasty (TKA) patients, with an average age of 63 years. Isometric maximal voluntary contraction torque, isokinetic peak torque, and isoinertial one-repetition maximum load of the involved and uninvolved quadriceps were evaluated as well as objective (walking parameters) and subjective physical function (WOMAC). Reliability was good and comparable for the isometric, isokinetic, and isoinertial strength outcomes on both sides (intraclass correlation coefficient range: 0.947-0.966; standard error of measurement range: 5.1-9.3%). Involved quadriceps strength was significantly correlated to walking speed (r range: 0.641-0.710), step length (r range: 0.685-0.820) and WOMAC function (r range: 0.575-0.663), independent from the modality (P torque (P > 0.05). In conclusion, isometric, isokinetic, and isoinertial modalities ensure valid and reliable assessment of quadriceps muscle strength in TKA patients.

  3. Muscle activation and blood flow do not explain the muscle length-dependent variation in quadriceps isometric endurance.

    Science.gov (United States)

    Kooistra, R D; de Ruiter, C J; de Haan, A

    2005-03-01

    We investigated the role of central activation in muscle length-dependent endurance. Central activation ratio (CAR) and rectified surface electromyogram (EMG) were studied during fatigue of isometric contractions of the knee extensors at 30 and 90 degrees knee angles (full extension = 0 degree). Subjects (n = 8) were tested on a custom-built ergometer. Maximal voluntary isometric knee extension with supramaximal superimposed burst stimulation (three 100-mus pulses; 300 Hz) was performed to assess CAR and maximal torque capacity (MTC). Surface EMG signals were obtained from vastus lateralis and rectus femoris muscles. At each angle, intermittent (15 s on 6 s off) isometric exercise at 50% MTC with superimposed stimulation was performed to exhaustion. During the fatigue task, a sphygmomanometer cuff around the upper thigh ensured full occlusion (400 mmHg) of the blood supply to the knee extensors. At least 2 days separated fatigue tests. MTC was not different between knee angles (30 degrees : 229.6 +/- 39.3 N.m vs. 90 degrees: 215.7 +/- 13.2 N.m). Endurance times, however, were significantly longer (P muscle length-related differences in metabolic cost.

  4. Impairment of voluntary control of finger motion following stroke: role of inappropriate muscle coactivation.

    Science.gov (United States)

    Kamper, D G; Rymer, W Z

    2001-05-01

    Subjects with chronic hemiplegia following stroke attempted to perform voluntary isometric, isokinetic, and free contractions of the extensor muscles of the metacarpophalangeal (MCP) joints. We recorded torque, metacarpophalangeal joint angle and velocity, and electromyographic (EMG) activity of the extrinsic extensors and flexors and the first dorsal interosseous (FDI). We found that voluntary MCP joint extension in hemiparetic subjects was greatly impaired in comparison with control subjects: only two of the 11 stroke subjects were able to generate even 0.21 N-m of isometric extension torque, only two could produce positive finger extension with no load, and none could develop an isokinetic concentric extension. Deficits seemed to result from a combination of coactivation of the finger flexor and extensor muscles and decreased voluntary excitation of the extensors, as normalized flexor and FDI EMG activity were greater for stroke than for control subjects (P < 0.001), but normalized extensor activity was reduced (P < 0.001). Copyright 2001 John Wiley & Sons, Inc.

  5. Knee Extensor Electromyographic Activity-to-Work Ratio is Greater With Isotonic Than Isokinetic Contractions.

    Science.gov (United States)

    Schmitz, Randy J.; Westwood, Kevin C.

    2001-12-01

    OBJECTIVE: To determine whether isotonic or isokinetic contractions produced greater electromyographic (EMG) activity per unit of work during isotonic and isokinetic knee-extension exercise. DESIGN AND SETTING: Subjects performed three 3-second maximal voluntary isometric contractions of the dominant knee extensors for EMG normalization. Exercise testing performed on the Biodex System 3 Dynamometer involved 10 isokinetic contractions at 180 degrees.s(-1) and 10 isotonic contractions with the resistance set at 50% of the previously recorded maximal voluntary isometric contraction. SUBJECTS: Recreationally active college students (10 men and 11 women). MEASUREMENTS: Surface EMG signals were collected from the vastus medialis and lateralis muscles and then integrated (IEMG) over the concentric phase of each repetition for both exercises. The IEMG was divided by the total work performed during the concentric phase for each exercise (IEMG/W). RESULTS: We analyzed the IEMG/W data using a 1-between (sex), 2-within (exercise and muscle) repeated-measures analysis of variance. There was a significant main effect for exercise, with the isotonic IEMG/W value being significantly greater than the isokinetic IEMG/W value. Additionally, the IEMG/W relationship did not appear to be affected by sex or individual muscle tested. CONCLUSIONS: Per unit of work performed, the isotonic contractions resulted in greater motor unit recruitment or an increased rate of firing, or both. This finding may have implications for the early phase of rehabilitation, when goals include complete motor unit recruitment of injured or atrophied muscles.

  6. Isometric strength training lowers the O2 cost of cycling during moderate-intensity exercise.

    Science.gov (United States)

    Zoladz, Jerzy A; Szkutnik, Zbigniew; Majerczak, Joanna; Grandys, Marcin; Duda, Krzysztof; Grassi, Bruno

    2012-12-01

    The effect of maximal voluntary isometric strength training of knee extensor muscles on pulmonary V'O(2) on-kinetics, the O(2) cost of cycling and peak oxygen uptake (V'O(2peak)) in humans was studied. Seven healthy males (mean ± SD, age 22.3 ± 2.0 years, body weight 75.0 ± 9.2 kg, V'O(2peak) 49.5 ± 3.8 ml kg(-1) min(-1)) performed maximal isometric strength training lasting 7 weeks (4 sessions per week). Force during maximal voluntary contraction (MVC) increased by 15 % (P < 0.001) after 1 week of training, and by 19 % (P < 0.001) after 7 weeks of training. This increase in MVC was accompanied by no significant changes in the time constant of the V'O(2) on-kinetics during 6 min of moderate and heavy cycling intensities. Strength training resulted in a significant decrease (by ~7 %; P < 0.02) in the amplitude of the fundamental component of the V'O(2) on-kinetics, and therefore in a lower O(2) cost of cycling during moderate cycling intensity. The amplitude of the slow component of V'O(2) on-kinetics during heavy cycling intensity did not change with training. Training had no effect on the V'O(2peak), whereas the maximal power output reached at V'O(2peak) was slightly but significantly increased (P < 0.05). Isometric strength training rapidly (i.e., after 1 week) decreases the O(2) cost of cycling during moderate-intensity exercise, whereas it does not affect the amplitude of the slow component of the V'O(2) on-kinetics during heavy-intensity exercise. Isometric strength training can have beneficial effects on performance during endurance events.

  7. Excitability changes in primary motor cortex just prior to voluntary muscle relaxation.

    Science.gov (United States)

    Suzuki, Tomotaka; Sugawara, Kenichi; Takagi, Mineko; Higashi, Toshio

    2015-01-01

    We postulated that primary motor cortex (M1) activity does not just decrease immediately prior to voluntary muscle relaxation; rather, it is dynamic and acts as an active cortical process. Thus we investigated the detailed time course of M1 excitability changes during muscle relaxation. Ten healthy participants performed a simple reaction time task. After the go signal, they rapidly terminated isometric abduction of the right index finger from a constant muscle force output of 20% of their maximal voluntary contraction force and performed voluntary muscle relaxation. Transcranial magnetic stimulation pulses were randomly delivered before and after the go signal, and motor evoked potentials (MEPs) were recorded from the right first dorsal interosseous muscle. We selected the time course relative to an appropriate reference point, the onset of voluntary relaxation, to detect excitability changes in M1. MEP amplitude from 80 to 60 ms before the estimated electromyographic offset was significantly greater than that in other intervals. Dynamic excitability changes in M1 just prior to quick voluntary muscle relaxation indicate that cortical control of muscle relaxation is established through active processing and not by simple cessation of activity. The cortical mechanisms underlying muscle relaxation need to be reconsidered in light of such dynamics. Copyright © 2015 the American Physiological Society.

  8. Motor unit properties from three synergistic muscles during ramp isometric elbow extensions.

    Science.gov (United States)

    Harwood, B; Dalton, B H; Power, G A; Rice, C L

    2013-12-01

    Many tasks require synergistic activation of muscles that possess different architectural, mechanical, and neural control properties. However, investigations of the motor unit (MU) mechanisms which modulate force are mostly restricted to individual muscles and low forces. To explore the pattern of MU recruitment and discharge behavior among three elbow extensors (lateral and long heads of the triceps brachii, and anconeus) during ramp isometric contractions, recruitment thresholds of 77 MUs in five young men were determined and corresponding MU discharge rates were tracked in 1-s epochs over forces ranging from 0 to 75 % of maximal voluntary isometric force (MVC). Across all forces, MUs in the lateral head discharged at higher rates than those in the anconeus (p MVC), recruitment thresholds were lower in the anconeus than in both heads of the triceps brachii consistent with the expected twitch contractile and fiber type differences among these muscles. These findings illustrate the importance of considering synergistic relations among muscles used for a coordinated task, and the sensitivity of synergies to muscle architectural, mechanical, and possibly specific synaptic input factors.

  9. Cerebral mechanisms underlying the effects of music during a fatiguing isometric ankle-dorsiflexion task.

    Science.gov (United States)

    Bigliassi, Marcelo; Karageorghis, Costas I; Nowicky, Alexander V; Orgs, Guido; Wright, Michael J

    2016-10-01

    The brain mechanisms by which music-related interventions ameliorate fatigue-related symptoms during the execution of fatiguing motor tasks are hitherto under-researched. The objective of the present study was to investigate the effects of music on brain electrical activity and psychophysiological measures during the execution of an isometric fatiguing ankle-dorsiflexion task performed until the point of volitional exhaustion. Nineteen healthy participants performed two fatigue tests at 40% of maximal voluntary contraction while listening to music or in silence. Electrical activity in the brain was assessed by use of a 64-channel EEG. The results indicated that music downregulated theta waves in the frontal, central, and parietal regions of the brain during exercise. Music also induced a partial attentional switching from associative thoughts to task-unrelated factors (dissociative thoughts) during exercise, which led to improvements in task performance. Moreover, participants experienced a more positive affective state while performing the isometric task under the influence of music. © 2016 Society for Psychophysiological Research.

  10. Corticospinal interaction during isometric compensation for modulated forces with different frequencies

    Directory of Open Access Journals (Sweden)

    Maurer Christoph

    2010-12-01

    Full Text Available Abstract Background During isometric compensation of modulated low-level forces corticomuscular coherence (CMC has been shown to occur in high-beta or gamma-range. The influence of the frequency of force modulation on CMC has up to now remained unexplored. We addressed this question by investigating CMC, motor performance, and cortical spectral power during a visuomotor task in which subjects had to compensate a modulated force of 8% of the maximum voluntary contraction exerted on their right index finger. The effect of three frequencies of force modulation (0.6, 1.0 and 1.6 Hz was tested. EEG, EMG from first dorsal interosseus, hand flexor and extensor muscles, and finger position were recorded in eight right-handed women. Results Five subjects showed CMC in gamma- (28-45 Hz and three in beta-range (15-30 Hz. Beta- and gamma-range CMC and cortical motor spectral power were not modulated by the various frequencies. However, a sharp bilateral CMC peak at 1.6 Hz was observed, but only in the five gamma-range CMC subjects. The performance error increased linearly with the frequency. Conclusions Our findings suggest that the frequency of force modulation has no effect on the beta- and gamma-range CMC during isometric compensation for modulated forces at 8% MVC. The beta- and gamma-range CMC may be related to interindividual differences and possibly to strategy differences.

  11. Isometric torque-angle relationships of the elbow flexors and extensors in the transverse plane.

    Science.gov (United States)

    Pinter, Ilona J; Bobbert, Maarten F; van Soest, A J Knoek; Smeets, Jeroen B J

    2010-10-01

    Maximal voluntary isometric torque-angle relationships of elbow extensors and flexors in the transverse plane (humerus elevation angle of 90 degrees ) were measured at two different horizontal adduction angles of the humerus compared to thorax: 20 degrees and 45 degrees . For both elbow flexors and extensors, the torque-angle relationship was insensitive to this 25 degrees horizontal adduction of the humerus. The peak in torque-angle relationship of elbow extensors was found at 55 degrees (0 degrees is full extension). This is closer to full elbow extension than reported by researchers who investigated this relationship in the sagittal plane. Using actual elbow angles during contraction, as we did in this study, instead of angles set by the dynamometer, as others have done, can partly explain this difference. We also measured electromyographic activity of the biceps and triceps muscles with pairs of surface electrodes and found that electromyographic activity level of the agonistic muscles was correlated to measured net torque (elbow flexion torque: Pearson's r=0.21 and extension torque: Pearson's r=0.53). We conclude that the isometric torque-angle relationship of the elbow extensors found in this study provides a good representation of the force-length relationship and the moment arm-angle relationship of the elbow extensors, but angle dependency of neural input gives an overestimation of the steepness. Copyright (c) 2010 Elsevier Ltd. All rights reserved.

  12. The strength of the corticospinal coherence depends on the predictability of modulated isometric forces.

    Science.gov (United States)

    Mendez-Balbuena, Ignacio; Naranjo, Jose Raul; Wang, Xi; Andrykiewicz, Agnieska; Huethe, Frank; Schulte-Mönting, Jürgen; Hepp-Reymond, Marie-Claude; Kristeva, Rumyana

    2013-03-01

    Isometric compensation of predictably frequency-modulated low forces is associated with corticomuscular coherence (CMC) in beta and low gamma range. It remains unclear how the CMC is influenced by unpredictably modulated forces, which create a mismatch between expected and actual sensory feedback. We recorded electroencephalography from the contralateral hand motor area, electromyography (EMG), and the motor performance of 16 subjects during a visuomotor task in which they had to isometrically compensate target forces at 8% of the maximum voluntary contraction with their right index finger. The modulated forces were presented with predictable or unpredictable frequencies. We calculated the CMC, the cortical motor alpha-, beta-, and gamma-range spectral powers (SP), and the task-related desynchronization (TRD), as well as the EMG SP and the performance. We found that in the unpredictable condition the CMC was significantly lower and associated with lower cortical motor SP, stronger TRD, higher EMG SP, and worse performance. The findings suggest that due to the mismatch between predicted and actual sensory feedback leading to higher computational load and less stationary motor state, the unpredictable modulation of the force leads to a decrease in corticospinal synchrony, an increase in cortical and muscle activation, and a worse performance.

  13. Corticospinal interaction during isometric compensation for modulated forces with different frequencies.

    Science.gov (United States)

    Naranjo, José R; Wang, Xi; Schulte-Mönting, Jürgen; Huethe, Frank; Maurer, Christoph; Hepp-Reymond, Marie-Claude; Kristeva, Rumyana

    2010-12-31

    During isometric compensation of modulated low-level forces corticomuscular coherence (CMC) has been shown to occur in high-beta or gamma-range. The influence of the frequency of force modulation on CMC has up to now remained unexplored. We addressed this question by investigating CMC, motor performance, and cortical spectral power during a visuomotor task in which subjects had to compensate a modulated force of 8% of the maximum voluntary contraction exerted on their right index finger. The effect of three frequencies of force modulation (0.6, 1.0 and 1.6 Hz) was tested. EEG, EMG from first dorsal interosseus, hand flexor and extensor muscles, and finger position were recorded in eight right-handed women. Five subjects showed CMC in gamma- (28-45 Hz) and three in beta-range (15-30 Hz). Beta- and gamma-range CMC and cortical motor spectral power were not modulated by the various frequencies. However, a sharp bilateral CMC peak at 1.6 Hz was observed, but only in the five gamma-range CMC subjects. The performance error increased linearly with the frequency. Our findings suggest that the frequency of force modulation has no effect on the beta- and gamma-range CMC during isometric compensation for modulated forces at 8% MVC. The beta- and gamma-range CMC may be related to interindividual differences and possibly to strategy differences.

  14. Isometric handgrip does not elicit cardiovascular overload or post-exercise hypotension in hypertensive older women

    Directory of Open Access Journals (Sweden)

    Olher RR

    2013-06-01

    Full Text Available Rafael dos Reis Vieira Olher,1,2,* Danilo Sales Bocalini,3,* Reury Frank Bacurau,4 Daniel Rodriguez,5 Aylton Figueira Jr,5 Francisco Luciano Pontes Jr,4 Francisco Navarro,6 Herbert Gustavo Simões,1 Ronaldo Carvalho Araujo,7 Milton Rocha Moraes8 1Universidade Católica de Brasília, Distrito Federal, 2Universidade Gama Filho, Rio de Janeiro, 3Universidade Nove de Julho (UNINOVE, São Paulo, 4Universidade de São Paulo – Escola de Artes, Ciências e Humanidades, São Paulo, 5Universidade São Judas Tadeu (USJT, São Paulo, Brazil, 6Universidade Federal do Maranhão, Maranhão, 7Universidade de São Paulo, Instituto de Ciências Biomédicas, São Paulo, 8Universidade Federal de São Paulo – Escola Paulista de Medicina, São Paulo, Brazil *These authors contributed equally to this work Background: Arterial hypertension is a serious health problem affecting mainly the elderly population. Recent studies have considered both aerobic and resistance exercises as a non-pharmacological aid for arterial hypertension treatment. However, the cardiovascular responses of the elderly to isometric resistance exercise (eg, isometric handgrip [IHG] have not yet been documented. Objective: The purpose of this study was to investigate cardiovascular responses to different intensities of isometric exercise, as well as the occurrence of post-isometric exercise hypotension in hypertensive elderly people under antihypertensive medication treatment. Patients and methods: Twelve women volunteered to participate in the study after a maximal voluntary contraction test (MVC and standardization of the intervention workload consisting of two sessions of IHG exercise performed in four sets of five contractions of a 10-second duration. Sessions were performed both at 30% of the MVC and 50% of the MVC, using a unilateral IHG protocol. Both intensities were compared with a control session without exercise. Systolic blood pressure (SBP and diastolic blood pressure (DBP at rest

  15. Mechanomyographic amplitude and mean power frequency responses during isometric ramp vs. step muscle actions.

    Science.gov (United States)

    Ryan, Eric D; Beck, Travis W; Herda, Trent J; Hartman, Michael J; Stout, Jeffrey R; Housh, Terry J; Cramer, Joel T

    2008-03-15

    The purpose of the present study was to compare the mechanomyographic amplitude (MMG(RMS)) and mean power frequency (MMG(MPF)) vs. torque relationships during isometric ramp and step muscle actions for the vastus lateralis (VL) and rectus femoris (RF) muscles. Nineteen subjects (mean+/-S.D. age=24+/-4 years) performed 2 isometric maximal voluntary contractions (MVCs) before and after 2 or 3 isometric ramp muscle actions from (5-95% MVC) to 9 submaximal step muscle actions (15, 25, 35, 45, 55, 65, 75, 85, and 95% MVC). MMG signals were recorded from the VL and RF muscles, and MMG(RMS) and MMG(MPF) values were computed for each corresponding percentage of the MVC. Absolute and normalized MMG(RMS) and MMG(MPF) vs. torque relationships were analyzed and interpreted on a subject-by-subject and composite pattern basis using polynomial regression and repeated measures ANOVAs. For MMG(RMS) and MMG(MPF), only 16-53% and 11-26% of the individual responses were consistent with the composite polynomial models, respectively. In addition, the normalized composite MMG(RMS) values were greater for the RF than the VL from 35 to 85% MVC. Only 47% of the MMG(RMS) and 5% of the MMG(MPF) individual patterns of responses were the same for the ramp and step muscle actions, and differences were also observed for the composite MMG(RMS) and MMG(MPF) patterns between the ramp and step muscle actions. Overall, these findings indicated that the torque-related patterns of responses for MMG(RMS) and MMG(MPF) were different among subjects (i.e., inter-individual variability) and were muscle- (VL vs. RF) and mode-specific (ramp vs. step).

  16. Relationships between skinfold thickness and electromyographic and mechanomyographic amplitude recorded during voluntary and non-voluntary muscle actions.

    Science.gov (United States)

    Cooper, Michael A; Herda, Trent J; Vardiman, John P; Gallagher, Phillip M; Fry, Andrew C

    2014-04-01

    The purpose of this study was to examine possible correlations between skinfold thicknesses and the a terms from the log-transformed electromyographic (EMGRMS) and mechanomyographic amplitude (MMGRMS)-force relationships, EMG M-Waves, and MMG gross lateral movements (GLM). Forty healthy subjects performed a 6-s isometric ramp contraction from 5% to 85% of their maximal voluntary contraction with EMG and MMG sensors placed on the vastus lateralis (VL) and rectus femoris (RF). A single electrical stimulus was applied to the femoral nerve to record the EMG M-waves and MMG GLMs. Skinfold thickness was assessed at the site of each electrode. Pearson's product correlation coefficients were calculated comparing skinfold thicknesses with the a terms from the log-transformed EMGRMS-and MMGRMS-force relationships, EMG M-waves, and MMG GLMs. There were no significant cor1relations (p>0.05) between the a terms and skinfold thicknesses for the RF and VL from the EMGRMS and MMGRMS-force relationships. However, there were significant correlations (pskinfold thicknesses and the EMG M-waves and MMG GLMs for the RF (r=-0.521, -0.376) and VL (r=-0.479, -0.484). Relationships were only present between skinfold thickness and the amplitudes of the EMG and MMG signals during the non-voluntary muscle actions. Copyright © 2014 Elsevier Ltd. All rights reserved.

  17. Effect of increased maxillo-mandibular relationship on isometric strength in TMD patients with loss of vertical dimension of occlusion.

    Science.gov (United States)

    Abduljabbar, T; Mehta, N R; Forgione, A G; Clark, R E; Kronman, J H; Munsat, T L; George, P

    1997-01-01

    The effect on isometric strength of the shoulders and limbs while biting in habitual occlusion, on a bite-elevating appliance and on a placebo appliance was analyzed. Twenty female volunteer patients, presenting with temporomandibular pain dysfunction syndrome and obvious loss of vertical dimension, served as subjects. All were weaker to the manual application of the isometric Deltoid Press (IDP) when biting, as opposed to maintaining the mandible in an unsupported rest position. Two intraoral appliances were fabricated for each subject: a bite-elevating appliance (BEA) set by a functional criterion of peak strength to the IDP and a placebo appliance which did not interfere with occlusion but was "set" with a mock IDP procedure. Testing was carried out by the Neuromuscular Research Testing Laboratory of the Neurology Department of Tufts New England Medical Center. Testing was independent of the dentist who fabricated and set the appliances. A standard neuromuscular test with the Maximal Voluntary Isometric Contraction apparatus was used to assess strength of right and left shoulder, elbow and knee flexion and extension as is routinely performed with all neuromuscular disease patients. Twelve strength tests were carried out for each of three conditions: 1. Baseline-biting in habitual occlusion; 2. Elevated-biting on the BEA; and 3. Placebo-biting with the placebo appliance inserted. The order of conditions 2 and 3 was counterbalanced without knowledge of the subjects. Twelve repeated measures ANOVAs (each subject as their own control) were conducted for each of the 12 strength measures. All F-tests indicated a significant main effect for treatment differences (p TMD Center: individuals with loss of vertical dimension of occlusion respond to a bite raising appliance by increased isometric-strength.

  18. Learning Isometric Separation Maps

    CERN Document Server

    Vasiloglou, Nikolaos; Anderson, David V

    2008-01-01

    Maximum Variance Unfolding (MVU) and its variants have been very successful in embedding data-manifolds in lower dimensionality spaces, often revealing the true intrinsic dimensions. In this paper we show how to also incorporate supervised class information into an MVU-like method without breaking its convexity. We call this method the Isometric Separation Map and we show that the resulting kernel matrix can be used for a binary/multiclass Support Vector Machine in a semi-supervised (transductive) framework. We also show that the method always finds a kernel matrix that linearly separates the training data exactly without projecting them in infinite dimensional spaces.

  19. Effects of experimental muscle pain on force variability during task-related and three directional isometric force task

    DEFF Research Database (Denmark)

    Mista, Christian Ariel; Graven-Nielsen, Thomas

    2013-01-01

    injected into the biceps brachii muscle. The coefficient of variation (CV) was used to analyze the variability on the task-related force direction. The total excursion of the center of pressure (CoP) was used to quantify the variability on the tangential force directions. Complexity of the force......Experimentally muscle pain induces changes in the distribution of muscle activity and affects the muscle coordination. The force steadiness is impaired during muscle pain in the task-related force direction as well as in the tangential directions. In addition, pain lead to a mismatch between......-dimensional force task during acute muscle pain. Twelve right-handed healthy volunteers participated in the experiment. Three-dimensional force signals were acquired during isometric elbow flexion at 5%, 15%, and 30% of the maximum voluntary contraction (MVC). The force components were represented by a circle...

  20. Single motor unit firing rate after stroke is higher on the less-affected side during stable low-level voluntary contractions

    Directory of Open Access Journals (Sweden)

    Penelope A Mcnulty

    2014-07-01

    Full Text Available Muscle weakness is the most common outcome after stroke and a leading cause of adult-acquired motor disability. Single motor unit properties provide insight into the mechanisms of post-stroke motor impairment. Motor units on the more-affected side are reported to have lower peak firing rates, reduced discharge variability and a more compressed dynamic range than healthy subjects. The activity of 169 motor units was discriminated from surface EMG in 28 stroke patients during sustained voluntary contractions 10% of maximal and compared to 110 units recorded from 16 healthy subjects. Motor units were recorded in three series: ankle dorsiflexion, wrist flexion and elbow flexion. Mean firing rates after stroke were significantly lower on the more-affected than the less-affected side (p< 0.001 with no between-side differences for controls. When data were combined, firing rates on the less-affected side were significantly higher than those either on the more-affected side or healthy subjects (p< 0.001. Motor unit mean firing rate was higher in the upper-limb than the lower-limb (p< 0.05. The coefficient of variation of motor unit discharge rate was lower for motor units after stroke compared to controls for wrist flexion (p< 0.05 but not ankle dorsiflexion. However, the dynamic range of motor units was compressed only for motor units on the more-affected side during wrist flexion. Our results show that the pathological change in motor unit firing rate occurs on the less-affected side after stroke and not the more-affected side as previously reported, and suggest that motor unit behavior recorded in a single muscle after stroke cannot be generalized to muscles acting on other joints even within the same limb. These data emphasize that the less-affected side does not provide a valid control for physiological studies on the more-affected side after stroke and that both sides should be compared to data from age- and sex-matched healthy subjects.

  1. Effect of muscle contraction strength on gating of somatosensory magnetic fields.

    Science.gov (United States)

    Sugawara, Kazuhiro; Onishi, Hideaki; Yamashiro, Koya; Kotan, Shinichi; Kojima, Sho; Miyaguchi, Shota; Tsubaki, Atsuhiro; Kirimoto, Hikari; Tamaki, Hiroyuki; Shirozu, Hiroshi; Kameyama, Shigeki

    2016-11-01

    Afferent somatosensory information is modulated before the afferent input arrives at the primary somatosensory cortex during voluntary movement. The aim of the present study was to clarify the effect of muscular contraction strength on somatosensory evoked fields (SEFs) during voluntary movement. In addition, we examined the differences in gating between innervated and non-innervated muscle during contraction. We investigated the changes in gating effect by muscular contraction strength and innervated and non-innervated muscles in human using 306-channel magnetoencephalography. SEFs were recorded following the right median nerve stimulation in a resting condition and during isometric muscular contractions from 10 % electromyographic activity (EMG), 20 and 30 % EMG of the right extensor indicis muscle and abductor pollicis brevis muscle. Our results showed that the equivalent current dipole (ECD) strength for P35m decreased with increasing strength of muscular contraction of the right abductor pollicis brevis muscle. However, changes were observed only at 30 % EMG contraction level of the right extensor indicis muscle, which was not innervated by the median nerve. There were no significant changes in the peak latencies and ECD locations of each component in all conditions. The ECD strength did not differ significantly for N20m and P60m regardless of the strength of muscular contraction and innervation. Therefore, we suggest that the gating of SEF waveforms following peripheral nerve stimulation was affected by the strength of muscular contraction and innervation of the contracting muscle.

  2. 不同负荷水平颈部肌肉等长收缩的平均肌电变化特征%The Changes of AEMG of Neck Muscles Under Isometric Contraction at Different Load Levels

    Institute of Scientific and Technical Information of China (English)

    陈谦; 杨红春; 王健

    2010-01-01

    目的:采用表面肌电信号(Surface Electromyographic Signal,sEMG)分析技术研究不同负荷水平颈部两侧头夹肌、胸锁乳突肌和斜方肌上部肌肉等长收缩对相关肌肉平均肌电((Average EMG,AEMG)活动的影响,为进一步开展颈部肌肉功能和康复训练效果评价提供科学依据.方法:16名无颈部疾病的健康青年男性志愿者,分别在颈椎屈曲、后伸、左侧屈和右侧屈4个运动方向上完成20%最大随意收缩力(Maximal Voluntary Contraction,MVC)、40%MVC、60%MVC、80%MVC和100%MVC的等长收缩实验,期间采集被检肌肉的sEMG信号,计算标准化的AEMG.结果:①受试者最大颈椎后伸力量显著大于颈椎屈曲、颈左侧屈及右侧屈力量,而后三者之间没有显著差异;②递增负荷水平等长收缩条件下与运动方向同侧的颈部肌肉出现收缩增强效应,而对侧拮抗肌表现出明显的共收缩现象;③运动方向和负荷水平均对各被检肌肉的AEMG有明显作用,且以上两因素对各被检肌肉AEMG有明显交互作用.结论:人体颈部最大伸颈力量显著大于屈颈、颈左侧屈和右侧屈力量,完成矢状面屈伸和额状面侧屈运动时各被检肌肉的AEMG值与负荷水平成正比.

  3. Avaliação da inibição recíproca em humanos durante contrações isométricas dos músculos tibial anterior e sóleo Assessment of reciprocal inhibition in humans during isometric contractions of the tibialis anterior and soleus muscles

    Directory of Open Access Journals (Sweden)

    José Eduardo Pompeu

    2009-09-01

    Full Text Available Os objetivos do presente trabalho foram: (1 desenvolver um método para estimar o grau de inibição recíproca (IR entre músculos antagonistas em humanos (sóleo e tibial anterior e (2 comparar os níveis de IR no repouso, na dorsiflexão (DF e na flexão plantar (FP. Participaram nove sujeitos saudáveis com idade entre 20 e 30 anos, quatro homens e cinco mulheres. Os sujeitos permaneceram sentados numa cadeira com o pé direito apoiado e fixo num pedal acoplado a um torquímetro; as medições foram feitas no repouso e durante contração isométrica dos músculos dorsiflexores e flexores plantares do tornozelo. A onda H do músculo sóleo foi captada por eletrodos de superfície. O reflexo H (RH "teste" do músculo sóleo foi medido aplicando-se um estímulo na fossa poplítea (nervo tibial. O reflexo H "condicionado" foi obtido pelo pareamento de dois estímulos: o primeiro aplicado sobre a cabeça da fíbula e o segundo, na fossa poplítea, após 1 a 3 ms.. As amplitudes pico-a-pico dos RH teste e condicionado foram utilizadas para o cálculo da IR. Os valores de IR foram: 16,41%±8,68 no repouso; 21,94%±5,39 na DF e 3,12%±11,84 na FP. Foi constatada menor inibição recíproca na FP quando comparada às demais condições (pThe purposes of the present study were (1 to develop a method to estimate the level of reciprocal inhibition (RI between antagonist (soleus and anterior tibial muscles in humans, and (2 to compare RI levels during rest, dorsiflexion (DF and plantar flexion (PF. Nine healthy subjects (four men, five women aged between 20 and 30 years were assessed. Each subject remained seated with his/her right foot strapped to a rigid foot plate coupled to a torquemeter; measurements were taken at rest and during isometric contraction of the ankle dorsiflexor and plantar flexor muscles. The soleus muscle H-wave was captured by surface electrodes. A "test" H- reflex was elicited by a stimulus (electrical pulse to the popliteal fossa

  4. Power output, isometric strength and steadiness in the leg muscles of pre- and postmenopausal women; the effects of hormone replacement therapy.

    Science.gov (United States)

    Carville, Serena F; Rutherford, Olga M; Newham, Di J

    2006-02-01

    There are conflicting reports of the effects of hormone replacement therapy (HRT) on strength preservation in postmenopausal women, while any effect on power output has received little attention. Decreased steadiness of force generation has been reported in older muscles and may be related to the hormonal changes associated with the menopause, but the effect of HRT has not been investigated. We have studied the effect of HRT on strength, power output and isometric force steadiness in healthy women. Sixteen young (aged 27.4 +/- 1.4 years, mean +/- SEM) and 29 postmenopausal women were studied. Fifteen of the latter were taking HRT (68.1 +/- 1.4 years, HRT+) and 14 (70.5 +/- 1.5 years, HRT-) had never done so. During isometric quadriceps contractions the force steadiness (coefficient of variation of force) was measured at 10, 25, 50 and 100% maximum voluntary contraction (MVC). The average power generated by an explosive leg extension was recorded. The HRT- group generated less power (110.2 +/- 7.2 W) than both the HRT+ (136.5 +/- 10.9 W, P = 0.027) and young (136.2 +/- 5.8 W, P = 0.027) subjects. Power output was similar in the HRT+ and younger subjects. The HRT- subjects were weaker than the younger ones (241.3 +/- 14.0 N vs. 297.6 +/- 13 N, P = 0.006). The strength of the HRT+ group (255.5 +/- 14 N) was not significantly different to the other two groups. There was no difference in steadiness between the three groups at any of the force levels. HRT appears to maintain power output to a greater extent than isometric strength in postmenopausal women. There was no evidence for an effect of either age or HRT on isometric steadiness in the quadriceps.

  5. Isometric handgrip training lowers blood pressure and increases heart rate complexity in medicated hypertensive patients.

    Science.gov (United States)

    Millar, P J; Levy, A S; McGowan, C L; McCartney, N; MacDonald, M J

    2013-10-01

    Hypertension is characterized by elevated blood pressure (BP) and autonomic dysfunction, both thought to be improved with exercise training. Isometric handgrip (IHG) training may represent a beneficial, time-effective exercise therapy. We investigated the effects of IHG training on BP and traditional and nonlinear measures of heart rate variability (HRV). Pre- and post-measurements of BP and HRV were determined in 23 medicated hypertensive participants (mean ± SEM, 66 ± 2 years) following either 8 weeks of IHG training (n = 13) or control (n = 10). IHG exercise consisted of four unilateral 2-min isometric contractions at 30% of maximal voluntary contraction, each separated by 4 min of rest. IHG training was performed 3 days/week for 8 weeks. IHG training decreased systolic BP (125 ± 3 mmHg to 120 ± 2 mmHg, P < 0.05) and mean BP (90 ± 2 mmHg to 87 ± 2 mmHg, P < 0.05), while sample entropy was increased (1.07 ± 0.1 to 1.35 ± 0.1, P < 0.05) and the fractal scaling distance score was decreased (0.34 ± 0.1 to 0.19 ± 0.1, P < 0.05). No significant changes were observed in traditional spectral or time-domain measures of HRV or control participants. IHG training improves nonlinear HRV, but not traditional HRV, while reducing systolic and mean BP. These results may highlight the benefits of IHG training for patients with primary hypertension.

  6. Electromyographic analysis of the infraspinatus and scapular stabilizing muscles during isometric shoulder external rotation at various shoulder elevation angles

    Science.gov (United States)

    Uga, Daisuke; Endo, Yasuhiro; Nakazawa, Rie; Sakamoto, Masaaki

    2016-01-01

    [Purpose] This study aimed to clarify activation of the infraspinatus and scapular stabilizing muscles during shoulder external rotation at various shoulder elevation angles. [Subjects] Twenty subjects participated in this study and all measurements were performed on the right shoulder. [Methods] Isometric shoulder external rotation strength and surface electromyographic data were measured with the shoulder at 0°, 45°, 90°, and 135° elevation in the scapular plane. The electromyographic data were collected from the infraspinatus, upper trapezius, middle trapezius, lower trapezius, and serratus anterior muscles. These measurements were compared across the various shoulder elevation angles. [Results] The strength measurements did not differ significantly by angulation. The infraspinatus activity was 92%, 75%, 68%, and 57% of the maximum voluntary contraction, which significantly decreased as shoulder elevation increased. The serratus anterior activity was 24%, 48%, 53%, and 62% of the maximum voluntary contraction, which significantly increased as shoulder elevation increased. [Conclusion] Shoulder external rotation torque was maintained regardless of shoulder elevation angle. The shoulder approximated to the zero position as the shoulder elevation increased so that infraspinatus activity decreased and the scapular posterior tilting by the serratus anterior might generate shoulder external rotation torque. PMID:26957748

  7. The repeated bout effect of eccentric exercise is not associated with changes in voluntary activation.

    Science.gov (United States)

    Kamandulis, Sigitas; Skurvydas, Albertas; Brazaitis, Marius; Skikas, Laimutis; Duchateau, Jacques

    2010-04-01

    The aim of this study was to compare the possible changes in muscle activation level between a first and second bout of damaging eccentric exercise performed at 2 weeks interval (i.e. repeated bout effect). To that purpose, ten physically active males took part in this study. The eccentric exercise consisted of 10 sets of 12 maximal voluntary contractions (MVC) produced by the knee extensors during movements performed at a constant speed of 160 degrees s(-1). Changes in voluntary and electrically evoked torque in concentric and/or isometric conditions were assessed at the following time points: pre-exercise, and 2 min, 1 and 24 h after each eccentric exercise. At the same time points, voluntary activation was quantified by the superimposed electrical stimulation technique. Muscle soreness and plasma CK activity were measured within 48 h after the eccentric exercise. The results showed that the decrease in eccentric peak torque was linear throughout the exercise protocol. At the end of bouts 1 and 2, torque was significantly reduced by 27.7 +/- 9.1 and 23.4 +/- 11.2, respectively, with no difference between bouts (P > 0.05). At 24 h post-exercise, a lower reduction (P eccentric exercise appears to reduce muscle damage, but does not influence the level of voluntary activation.

  8. Transcranial magnetic stimulation during voluntary action: directional facilitation of outputs and relationships to force generation.

    Science.gov (United States)

    Cros, Didier; Soto, Oscar; Chiappa, Keith H

    2007-12-14

    Single-pulse transcranial magnetic stimulation (TMS) of the human motor cortex evokes simple muscle jerks whose physiological significance is unclear. Indeed, in subjects performing a motor task, there is uncertainty as to whether TMS-evoked outputs reflect the ongoing behavior or, alternatively, a disrupted motor plan. Considering force direction and magnitude to reflect qualitative and quantitative features of the motor plan respectively, we studied the relationships between voluntary forces and those evoked by TMS. In five healthy adults, we recorded the isometric forces acting a hand joint and the electromyographic activity in the first dorsal interosseous (FDI) muscle. Responses obtained at rest were highly invariant. Evoked responses obtained while subjects generated static and dynamic contractions were highly codirectional with the voluntary forces. Such directional relationships were independent of stimulation intensity, stimulated cortical volume, or magnitude of voluntary force exerted. Dynamic force generation was associated with a marked increase in the magnitude of the evoked force that was linearly related to the rate of force generation. The timing of central conduction was different depending on functional role of the target muscle, as either agonist or joint fixator. These results indicate that the architecture of motor plans remain grossly undisrupted by cortical stimulation applied during voluntary motor behavior. The significant magnitude modulation of responses during dynamic force generation suggests an essential role of the corticospinal system in the specification of force changes. Finally, the corticospinal activation depends on the functional role assumed by the target muscle, either postural or agonist.

  9. ABSENCE OF GENDER DIFFERENCES IN THE FATIGABILITY OF THE FOREARM MUSCLES DURING INTERMITTENT ISOMETRIC HANDGRIP EXERCISE

    Directory of Open Access Journals (Sweden)

    Joaquin U. Gonzales

    2007-03-01

    Full Text Available Previous studies have reported women to have a greater resistance to fatigue than men during sustained handgrip exercise, however, observed gender differences in fatigue has been shown to be a function of contraction type. The purpose of the present study was to determine if gender differences exist in forearm muscle fatigue during intermittent handgrip contractions. Women [n = 11, 23.5 ± 1.5 (SE yr] and men (n = 11, 24.1 ± 1.5 yr performed intermittent isometric handgrip contractions at a target force of 50% of maximal voluntary contraction (MVC for 5 s followed by 5 s rest until task failure. Rate of fatigue was calculated from MVCs taken every 2 min during exercise, and recovery of muscle strength was measured in 5 min increments until 45 min post-task failure. Forearm muscle strength was less for women than men (W: 341.5 ± 11.9 N; M: 480.2 ± 28.0 N; p < 0.05. No gender difference was present in time to task failure (W: 793.3 ± 92.5 s; M: 684.8 ± 76.3 s or in the decrease in muscle force generating capacity at task failure (W: -47.6 ± 1.0%; M: -49.9 ± 1.3%. Rate of muscle fatigue was found to be similar between women and men (W: -3.6 ± 0.5 %·min-1; M: -4.3 ± 0.6 %·min-1 and no gender difference was found in the recovery of muscle strength following task failure. In summary, no gender difference was found in the fatigability of the forearm muscles during intermittent submaximal handgrip contractions, independent of muscle strength

  10. Electromyographic response of global abdominal stabilizers in response to stable- and unstable-base isometric exercise.

    Science.gov (United States)

    Atkins, Stephen J; Bentley, Ian; Brooks, Darrell; Burrows, Mark P; Hurst, Howard T; Sinclair, Jonathan K

    2015-06-01

    Core stability training traditionally uses stable-base techniques. Less is known as to the use of unstable-base techniques, such as suspension training, to activate core musculature. This study sought to assess the neuromuscular activation of global core stabilizers when using suspension training techniques, compared with more traditional forms of isometric exercise. Eighteen elite level, male youth swimmers (age, 15.5 ± 2.3 years; stature, 163.3 ± 12.7 cm; body mass, 62.2 ± 11.9 kg) participated in this study. Surface electromyography (sEMG) was used to determine the rate of muscle contraction in postural musculature, associated with core stability and torso bracing (rectus abdominus [RA], external obliques [EO], erector spinae [ES]). A maximal voluntary contraction test was used to determine peak amplitude for all muscles. Static bracing of the core was achieved using a modified "plank" position, with and without a Swiss ball, and held for 30 seconds. A mechanically similar "plank" was then held using suspension straps. Analysis of sEMG revealed that suspension produced higher peak amplitude in the RA than using a prone or Swiss ball "plank" (p = 0.04). This difference was not replicated in either the EO or ES musculature. We conclude that suspension training noticeably improves engagement of anterior core musculature when compared with both lateral and posterior muscles. Further research is required to determine how best to activate both posterior and lateral musculature when using all forms of core stability training.

  11. Properties of Force Output and Spectral EMG in Young Patients with Nonspecific Low Back Pain during Isometric Trunk Extension.

    Science.gov (United States)

    Miura, Tatsuhiro; Sakuraba, Keishoku

    2014-03-01

    [Purpose] To clarify the influence of nonspecific low back pain (NSLBP) on force fluctuation and the myoelectric data of back muscles during isometric trunk extension at low to high force levels. [Subjects] Fourteen male subjects with NSLBP and 14 healthy male control subjects participated in this study. [Methods] All participants extended their trunk isometrically maintaining 10 levels of target force [2, 5, 10, 15, 20, 30, 50, 70, 80 and 90% of maximal voluntary contraction (MVC) in a random order] for about 4 seconds with visual feedback. A force transducer and tri-axis force sensor were positioned at the 7th thoracic vertebra to measure force output and the direction of force. Myoelectric activities of the back muscles (longissimus thoracis, L2 level; multifidus, S1 level) were recorded by surface electromyography. [Results] Force output of NSLBP subjects fluctuated more than that of healthy subjects at 30% and 50%MVC. Higher median power frequency in the multifidus was observed in NSLBP subjects at moderate to high force levels. [Conclusion] These results show that the properties of force output in NSLBP subjects differ from those in healthy subjects, suggesting that the assessment of force fluctuation of back muscles at moderate force levels is a useful index for evaluating and discriminating NSLBP.

  12. Muscular activity and torque of the foot dorsiflexor muscles during decremental isometric test: A cross-sectional study.

    Science.gov (United States)

    Ruiz-Muñoz, Maria; González-Sánchez, Manuel; Martín-Martín, Jaime; Cuesta-Vargas, Antonio I

    2017-06-01

    To analyse the torque variation level that could be explained by the muscle activation (EMG) amplitude of the three major foot dorsiflexor muscles (tibialis anterior (TA), extensor digitorum longus (EDL), extensor hallucis longus (EHL)) during isometric foot dorsiflexion at different intensities. In a cross-sectional study, forty-one subjects performed foot dorsiflexion at 100%, 75%, 50% and 25% of maximal voluntary contractions (MVC) with the hip and knee flexed 90° and the ankle in neutral position (90° between leg and foot). Three foot dorsiflexions were performed for each intensity. Outcome variables were: maximum (100% MVC) and relative torque (75%, 50%, 25% MVC), maximum and relative EMG amplitude. A linear regression analysis was calculated for each intensity of the isometric foot dorsiflexion. The degree of torque variation (dependent variable) from the independent variables explain (EMG amplitude of the three major foot dorsiflexor muscles) the increases when the foot dorsiflexion intensity is increased, with values of R(2) that range from 0.194 (during 25% MVC) to 0.753 (during 100% MVC). The reliability of the outcome variables was excellent. The EMG amplitude of the three main foot dorsiflexors exhibited more variance in the dependent variable (torque) when foot dorsiflexion intensity increases. Copyright © 2016 Elsevier Ltd. All rights reserved.

  13. Motor variability during sustained contractions increases with cognitive demand in older adults

    Directory of Open Access Journals (Sweden)

    Marnie L Vanden Noven

    2014-05-01

    Full Text Available To expose cortical involvement in age-related changes in motor performance, we compared steadiness (force fluctuations and fatigability of submaximal isometric contractions with the ankle dorsiflexor muscles in older and young adults and with varying levels of cognitive demand imposed. Sixteen young (20 ± 2 yr: 8 men, 8 women and 17 older adults (69 ±4 yr: 9 men, 8 women attended three sessions and performed a 40 s isometric contraction at 5% maximal voluntary contraction (MVC force followed by an isometric contraction at 30% MVC until task failure. The cognitive demand required during the submaximal contractions in each session differed as follows: 1 high-cognitive demand session where difficult mental math was imposed (counting backward by 13 from a 4-digit number; 2 low-cognitive demand session which involved simple mental math (counting backward by one; and 3 control session with no mental math. Anxiety was elevated during the high-cognitive demand session compared with other sessions for both age groups but more so for the older adults than young adults (p0.05, but the variability between sessions (standard deviation [SD] of 3 sessions was greater for older adults than young (2.02 ± 1.05 min vs. 1.25 ± 0.51 min, P<0.05. Thus, variability in lower limb motor performance for low and moderate force isometric tasks increased with age and was exacerbated when cognitive demand was imposed, and may be related to modulation of synergist and antagonist muscles and an altered neural strategy with age originating from central sources. These data have significant implications for cognitively demanding low-force motor tasks that are relevant to functional and ergonomic in an aging workforce.

  14. Age-related differences in muscle fatigue vary by contraction type: a meta-analysis.

    Science.gov (United States)

    Avin, Keith G; Law, Laura A Frey

    2011-08-01

    During senescence, despite the loss of strength (force-generating capability) associated with sarcopenia, muscle endurance may improve for isometric contractions. The purpose of this study was to perform a systematic meta-analysis of young versus older adults, considering likely moderators (ie, contraction type, joint, sex, activity level, and task intensity). A 2-stage systematic review identified potential studies from PubMed, CINAHL, PEDro, EBSCOhost: ERIC, EBSCOhost: Sportdiscus, and The Cochrane Library. Studies reporting fatigue tasks (voluntary activation) performed at a relative intensity in both young (18-45 years of age) and old (≥ 55 years of age) adults who were healthy were considered. Sample size, mean and variance outcome data (ie, fatigue index or endurance time), joint, contraction type, task intensity (percentage of maximum), sex, and activity levels were extracted. Effect sizes were (1) computed for all data points; (2) subgrouped by contraction type, sex, joint or muscle group, intensity, or activity level; and (3) further subgrouped between contraction type and the remaining moderators. Out of 3,457 potential studies, 46 publications (with 78 distinct effect size data points) met all inclusion criteria. A lack of available data limited subgroup analyses (ie, sex, intensity, joint), as did a disproportionate spread of data (most intensities ≥ 50% of maximum voluntary contraction). Overall, older adults were able to sustain relative-intensity tasks significantly longer or with less force decay than younger adults (effect size=0.49). However, this age-related difference was present only for sustained and intermittent isometric contractions, whereas this age-related advantage was lost for dynamic tasks. When controlling for contraction type, the additional modifiers played minor roles. Identifying muscle endurance capabilities in the older adult may provide an avenue to improve functional capabilities, despite a clearly established decrement in

  15. No Critical Peripheral Fatigue Threshold during Intermittent Isometric Time to Task Failure Test with the Knee Extensors

    Science.gov (United States)

    Froyd, Christian; Beltrami, Fernando G.; Millet, Guillaume Y.; Noakes, Timothy D.

    2016-01-01

    It has been proposed that group III and IV muscle afferents provide inhibitory feedback from locomotor muscles to the central nervous system, setting an absolute threshold for the development of peripheral fatigue during exercise. The aim of this study was to test the validity of this theory. Thus, we asked whether the level of developed peripheral fatigue would differ when two consecutive exercise trials were completed to task failure. Ten trained sport students performed two exercise trials to task failure on an isometric dynamometer, allowing peripheral fatigue to be assessed 2 s after maximal voluntary contraction (MVC) post task failure. The trials, separated by 8 min, consisted of repeated sets of 10 × 5-s isometric knee extension followed by 5-s rest between contractions. In each set, the first nine contractions were performed at a target force at 60% of the pre-exercise MVC, while the 10th contraction was a MVC. MVC and evoked force responses to supramaximal electrical femoral nerve stimulation on relaxed muscles were assessed during the trials and at task failure. Stimulations at task failure consisted of single stimulus (SS), paired stimuli at 10 Hz (PS10), paired stimuli at 100 Hz (PS100), and 50 stimuli at 100 Hz (tetanus). Time to task failure for the first trial (12.84 ± 5.60 min) was longer (P < 0.001) than for the second (5.74 ± 1.77 min). MVC force was significantly lower at task failure for both trials compared with the pre-exercise values (both P < 0.001), but there were no differences in MVC at task failure in the first and second trials (P = 1.00). However, evoked peak force for SS, PS100, and tetanus were all reduced more at task failure in the second compared to the first trial (P = 0.014 for SS, P < 0.001 for PS100 and tetanus). These results demonstrate that subjects do not terminate exercise at task failure because they have reached a critical threshold in peripheral fatigue. The present data therefore question the existence of a

  16. Regular physical exercise improves cardiac autonomic and muscle vasodilatory responses to isometric exercise in healthy elderly

    Directory of Open Access Journals (Sweden)

    Sarmento AO

    2017-06-01

    Full Text Available Adriana de Oliveira Sarmento,1–3 Amilton da Cruz Santos,1,4 Ivani Credidio Trombetta,2,5 Marciano Moacir Dantas,1 Ana Cristina Oliveira Marques,1,4 Leone Severino do Nascimento,1,4 Bruno Teixeira Barbosa,1,2 Marcelo Rodrigues Dos Santos,2 Maria do Amparo Andrade,3 Anna Myrna Jaguaribe-Lima,3,6 Maria do Socorro Brasileiro-Santos1,3,4 1Laboratory of Physical Training Studies Applied to Health, Department of Physical Education, Federal University of Paraiba, João Pessoa, Brazil; 2Unit of Cardiovascular Rehabilitation and Exercise Physiology – Heart Institute (InCor/HC-FMUSP, University of São Paulo, São Paulo, Brazil; 3Graduate Program in Physiotherapy, Federal University of Pernambuco, Recife, Brazil; 4Associate Graduate Program in Physical Education UPE/UFPB, João Pessoa, Brazil; 5Graduate Program in Medicine, Universidade Nove de Julho (UNINOVE, São Paulo, Brazil; 6Department of Morphology and Animal Physiology, Federal Rural University of Pernambuco, Recife, Brazil Abstract: The objective of this study was to evaluate cardiac autonomic control and muscle vasodilation response during isometric exercise in sedentary and physically active older adults. Twenty healthy participants, 10 sedentary and 10 physically active older adults, were evaluated and paired by gender, age, and body mass index. Sympathetic and parasympathetic cardiac activity (spectral and symbolic heart rate analysis and muscle blood flow (venous occlusion plethysmography were measured for 10 minutes at rest (baseline and during 3 minutes of isometric handgrip exercise at 30% of the maximum voluntary contraction (sympathetic excitatory maneuver. Variables were analyzed at baseline and during 3 minutes of isometric exercise. Cardiac autonomic parameters were analyzed by Wilcoxon and Mann–Whitney tests. Muscle vasodilatory response was analyzed by repeated-measures analysis of variance followed by Tukey’s post hoc test. Sedentary older adults had higher cardiac

  17. Time course of human motoneuron recovery after sustained low-level voluntary activity.

    Science.gov (United States)

    Héroux, Martin E; Butler, Annie A; Gandevia, Simon C; Taylor, Janet L; Butler, Jane E

    2016-02-01

    Motoneurons often fire repetitively and for long periods. In sustained voluntary contractions the excitability of motoneurons declines. We provide the first detailed description of the time course of human motoneuron recovery after sustained activity at a constant discharge rate. We recorded the discharge of single motor units (MUs, n = 30) with intramuscular wire electrodes inserted in triceps brachii during weak isometric contractions. Subjects (n = 15) discharged single MUs at a constant frequency (∼10 Hz) with visual feedback for prolonged durations (3-7 min) until rectified surface electromyogram (sEMG) of triceps brachii increased by ∼100%. After a rest of 1-2, 15, 30, 60, 120, or 240 s, subjects briefly resumed the contraction with the target MU at the same discharge rate. Each MU was tested with three to four rest periods. The magnitude of sEMG was increased when contractions were resumed, and the target motoneuron discharged at the test frequency following rest intervals of 2-60 s (P = 0.001-0.038). The increased sEMG indicates that greater excitatory drive was needed to discharge the motoneuron at the test rate. The increase in EMG recovered exponentially with a time constant of 28 s but did not return to baseline even after a rest period of ∼240 s. Thus the decline in motoneuron excitability from a weak contraction takes several minutes to recover fully.

  18. Optimal work-rest cycles for an isometric intermittent gripping task as a function of force, posture and grip span.

    Science.gov (United States)

    Eksioglu, Mahmut

    2006-02-10

    The aim of this study was to investigate the maximum acceptable contraction frequencies (i.e. work-rest cycles) for an isometric-intermittent handgrip task as a function of grip span, applied force and shoulder posture using psychophysical and physiological approaches. Twelve healthy males served as subjects. The three grip spans investigated were the optimal, 2 cm narrower than the optimal, and 2 cm wider than the optimal. The grip force levels studied were 15% and 30% of maximum voluntary grip force and the two shoulder postures were 25 degrees flexion and 30 degrees abduction. The psychophysical results indicate that subjects work faster with the narrower grip span at 15% of maximum voluntary grip force level in comparison to working with the optimal and the wider spans. However, when the task required 30% of maximum grip force level, the subjects worked faster with the optimal grip span. These findings were supported by the results of electromyography, heart rate, blood pressure and perceived discomfort. The study suggests that grip span of a tool is an important factor to be considered in predicting optimal work-rest cycles for hand grip tasks, and the optimum setting of grip span of the hand-tool depends on the required task force level. That is, the optimality is relative rather than absolute. In addition, it appears that weaker subjects can work at a higher rate than stronger ones at the same relative force level.

  19. The effect of shortening history on isometric and dynamic muscle function.

    Science.gov (United States)

    McDaniel, John; Elmer, Steven J; Martin, James C

    2010-03-03

    Despite numerous reports on isometric force depression, few reports have quantified force depression during active muscle shortening (dynamic force depression). The purpose of this investigation was to determine the influence of shortening history on isometric force following active shortening, force during isokinetic shortening, and velocity during isotonic shortening. The soleus muscles of four cats were subjected to a series of isokinetic contractions at three shortening velocities and isotonic contractions under three loads. Muscle excursions initiated from three different muscle lengths but terminated at a constant length. Isometric force produced subsequent to active shortening, and force or shortening velocity produced at a specific muscle length during shortening, were compared across all three conditions. Results indicated that shortening history altered isometric force by up to 5%, force during isokinetic shortening up to 30% and shortening velocity during isotonic contractions by up to 63%. Furthermore, there was a load by excursion interaction during isotonic contractions such that excursion had the most influence on shortening velocity when the loads were the greatest. There was not a velocity by excursion interaction during isokinetic contractions. Isokinetic and isotonic power-velocity relationships displayed a downward shift in power as excursions increased. Thus, to discuss force depression based on differences in isometric force subsequent to active shortening may underestimate its importance during dynamic contractions. The presence of dynamic force depression should be realized in sport performance, motor control modeling and when controlling paralyzed limbs through artificial stimulation.

  20. Central fatigue of the first dorsal interosseous muscle during low-force and high-force sustained submaximal contractions.

    Science.gov (United States)

    Eichelberger, Tamara D; Bilodeau, Martin

    2007-09-01

    The aim of this study was to compare the extent of central fatigue in the first dorsal interosseous (FDI) muscle of healthy adults in low, moderate and high-force submaximal contractions. Nine healthy adults completed four experimental sessions where index finger abduction force was recorded during voluntary contractions and in response to brief trains (five pulses at 100 Hz) of electrical stimulation. The ability to maximally activate FDI under volition, or voluntary activation, and its change with sustained activity (central fatigue) was assessed using the twitch interpolation technique. The fatigue tasks consisted of continuous isometric index finger abduction contractions held until exhaustion at four target force levels: 30%, 45%, 60% and 75% of the maximal voluntary contraction. The main finding was the presence of central fatigue for the 30% task, but not for the three other fatigue tasks. The extent of central fatigue was also associated with changes in a measure reflecting the status of peripheral structures/mechanisms. It appears that central fatigue contributed to task failure for the lowest force fatigue task (30%), but not for the other (higher) contraction intensities.

  1. Energy cost of isometric force production after active shortening in skinned muscle fibres.

    Science.gov (United States)

    Joumaa, V; Fitzowich, A; Herzog, W

    2017-02-23

    The steady state isometric force after active shortening of a skeletal muscle is lower than the purely isometric force at the corresponding length. This property of skeletal muscle is known as force depression. The purpose of this study was to investigate whether the energy cost of force production at the steady state after active shortening was reduced compared to the energy cost of force production for a purely isometric contraction performed at the corresponding length (same length, same activation). Experiments were performed in skinned fibres isolated from rabbit psoas muscle. Skinned fibres were actively shortened from an average sarcomere length of 3.0 µm to an average sarcomere length of 2.4 µm. Purely isometric reference contractions were performed at an average sarcomere length of 2.4 µm. Simultaneously with the force measurements, the ATP cost was measured during the last 30 seconds of isometric contractions using an enzyme-coupled assay. Stiffness was calculated during a quick stretch-release cycle of 0.2% fibre length performed once the steady state had been reached after active shortening and during the purely isometric reference contractions. Force and stiffness following active shortening were decreased by 10.0±1.8% and 11.0±2.2%, respectively compared to the isometric reference contractions. Similarly, ATPase activity per second (not normalized to the force) showed a decrease of 15.6±3.0% in the force depressed state compared to the purely isometric reference state. However, ATPase activity per second per unit of force was similar for the isometric contractions following active shortening (28.7±2.4 mM/mN.s.mm(3)) and the corresponding purely isometric reference contraction (30.9±2.8 mM/mN.s.mm(3)). Furthermore, the reduction in absolute ATPase activity per second was significantly correlated with force depression and stiffness depression. These results are in accordance with the idea that force depression following active shortening is

  2. Latency of saccadic eye movement during contraction of bilateral and unilateral shoulder girdle elevators.

    Science.gov (United States)

    Fujiwara, Katsuo; Kunita, Kenji; Toyama, Hiroshi

    2003-02-01

    We compared the timed latencies of saccadic eye movement during isometric contraction of the bilateral and unilateral shoulder girdle elevators in a sitting posture. Muscle contraction force was increased in 10% increments from 0% to 60% of the maximal voluntary contraction (MVC) of each side. Saccadic latency was measured as the latency to the beginning of eye movement toward the lateral target that was moved at random intervals in 20 degree amplitude jumps. Eye movement was measured using the electro-oculogram technique. During bilateral contraction, saccadic latency decreased until 30% MVC and then began to increase at 40% MVC. During unilateral contraction, saccadic latency decreased until 30% MVC in a similar pattern as in bilateral condition, was constant from 30% MVC to 50% MVC, followed by a slight increase at 60% MVC. The saccadic latencies at 10% and 40-60% MVC were significantly shorter during unilateral contraction than bilateral contraction. Thus, the relative force for producing a marked shortening of saccadic latency is observed within a wider range during unilateral contraction than bilateral contraction.

  3. An additional phase in PCr use during sustained isometric exercise at 30% MVC in the tibialis anterior muscle.

    Science.gov (United States)

    Houtman, C J; Heerschap, A; Zwarts, M J; Stegeman, D F

    2002-06-01

    The occurrence of an abrupt acceleration in phosphocreatine hydrolysis in the tibial anterior muscle during the last part of a sustained isometric exercise at 30% maximal voluntary contraction until fatigue is demonstrated in seven out of eight healthy subjects by applying in vivo 31P NMR spectroscopy at 1.5 T field strength. This additional third phase in PCr hydrolysis, is preceded by a common biphasic pattern (first fast then slow) in PCr use. The NMR spectra, as localized by a surface coil and improved by proton irradiation, were collected at a time resolution of 16 s. Mean rates of PCr hydrolysis during exercise were -0.44 +/- 0.19% s(-1), -0.07 +/- 0.04% s(-1), and -0.29 +/- 0.10% s(-1) for the three successive phases. The increased rate of PCr hydrolysis, and also the loss of fine force control evident in the force records are consistent with increased involvement of large, fast-fatiguable units later in the contraction.

  4. Isometric fatigue patterns in time and time-frequency domains of triceps surae muscle in different knee positions.

    Science.gov (United States)

    Pereira, Glauber Ribeiro; de Oliveira, Liliam Fernandes; Nadal, Jurandir

    2011-08-01

    The occurrence of fatigue in triceps surae (TS) muscles during sustained plantar flexion contraction is investigated by means of the RMS electromyogram (EMG) and the instantaneous median frequency (IMF) of the short time Fourier transform (STFT). Six male subjects realized a 40% maximal plantar flexion isometric voluntary contraction until fatigue in two knee positions. Electrodes were positioned on gastrocnemius medialis, gastrocnemius lateralis and soleus muscles. The torque (TO) and EMG signals were synchronized. The RMS and the median of the IMF values were obtained, respectively, for each 250 ms and 1s windows of signal. Each signal was segmented into 10 epochs, from which the mean values of IMF, RMS and TO were obtained and submitted to linear regressions to determine parameter trends. Friedman test with the Dunn's post hoc were used to test for differences among muscles activation for each knee position and among slopes of regression curves, as well as to observe changes in TS RMS values over time. The results indicate different activation strategies with the knee extended (KE) in contrast to knee flexed (KF). With the KE, the gastrocnemii showed typical fatigue behavior with significant (p<0.05) IMF reductions and RMS increases over time, while soleus showed concomitant RMS and IMF increases (p<0.05) suggesting an increased soleus contribution to the torque production. With KF, the gastrocnemii were under activated, increasing the role of soleus. Thus, time-frequency analysis represented an important tool for TS muscular fatigue evaluation, allowing differentiates the role of soleus muscle.

  5. Effect of neck muscle isometric contraction training on axial symptom postoperative of laminoplasty%颈部肌肉等长收缩训练对颈椎管扩大成形术后颈部轴性症状的影响

    Institute of Scientific and Technical Information of China (English)

    郭永传; 张益宏; 马守战; 贾思明

    2016-01-01

    目的:探讨颈部肌肉等长收缩训练对颈椎管扩大成型术后轴性症状的影响作用。方法2011年7月至2013年7月收治符合纳入标准条件的患者100例,随机分组A、B组,均采用椎管扩大成型术式,术后3 d B组开始实施颈部肌肉等长收缩训练3个月,分两个阶段进行。术后随访1.5年,记录术后3个月、6个月、1年、1.5年4个时间点患者轴性症状的罹患率及疼痛程度VAS评分,并进行统计分析。结果术后随访3个月、6个月、1年、1.5年4个时间点,A、B两组患者轴性症状疼痛VAS评分及轴性症状发生率比较差异有统计学意义( P<0.05)。结论早期肌肉等长收缩训练能够促进颈椎椎管扩大成型术后轴性症状的恢复,是预防治疗颈椎管扩大成型术后轴性症状的一种有效方法,值得在临床上推广应用。%Objective To investigate the effect of neck muscle isometric contraction training on axial symptom postoperative of laminoplasty. Methods One hundred patients from July 2011 to July 2013 were selected, they were ran-domly divided into group A and group B, both adopted laminoplasty. Three days after surgery, patients in group B began to implement neck muscle isometric contraction training for three months in two stages. Patients were all followed up for 1. 5 years. The axial pain VAS and the attack rate after 3 months, 6 months, 1 years and 1. 5 years of the two groups were re-corded and analyzed. Results After followed up for 3 months, 6 months, 1 year, 1. 5 years, the difference of axial pain VAS and the attack rate between the two groups had significant difference(P<0. 05). Conclusions Neck mus-cle isometric contraction training in early stage can promote the recovery of axial symptoms postoperative of laminopla-ty, is an effective method to prevent and treat axial pain after cervical laminoplasty, it should be widely applied in clinical practice.

  6. MUSCLE ACTIVATION DURING LOW-INTENSITY MUSCLE CONTRACTIONS WITH VARYING LEVELS OF EXTERNAL LIMB COMPRESSION

    Directory of Open Access Journals (Sweden)

    Tomohiro Yasuda

    2008-12-01

    Full Text Available The purpose was to investigate muscle activation during low- intensity muscle contractions with various levels of external limb compression to reduce muscle perfusion/outflow. A series of unilateral elbow flexion muscle contractions (30 repetitive contractions followed by 3 sets x 15 contractions was performed at 20% of 1RM with varying levels of external compression (0 (without compression, 98, 121, and 147 mmHg external compression around the upper arm. Electromyography (EMG signals were recorded from surface electrodes placed on the biceps brachii muscle and analyzed for integrated EMG (iEMG. Maximal voluntary isometric contraction (MVC decreased similarly during the control (0 mmHg and 98 mmHg external compression bout (~18%; the decline in MVC with 121 and 147 mmHg external compression was significantly greater (~37%. Muscle activation increased progressively throughout the contraction bout with each level of external compression, but iEMG was significantly greater during 147 mmHg external compression. In conclusion, low-intensity muscle contractions performed with external compression of 147 mmHg appears to alter muscle perfusion/outflow leading to increased muscle activation without decrements in work performed during the contraction bout

  7. Computation and Evaluation of Features of Surface Electromyogram to Identify the Force of Muscle Contraction and Muscle Fatigue

    Directory of Open Access Journals (Sweden)

    Sridhar P. Arjunan

    2014-01-01

    Full Text Available The relationship between force of muscle contraction and muscle fatigue with six different features of surface electromyogram (sEMG was determined by conducting experiments on thirty-five volunteers. The participants performed isometric contractions at 50%, 75%, and 100% of their maximum voluntary contraction (MVC. Six features were considered in this study: normalised spectral index (NSM5, median frequency, root mean square, waveform length, normalised root mean square (NRMS, and increase in synchronization (IIS index. Analysis of variance (ANOVA and linear regression analysis were performed to determine the significance of the feature with respect to the three factors: muscle force, muscle fatigue, and subject. The results show that IIS index of sEMG had the highest correlation with muscle fatigue and the relationship was statistically significant (P0.05.

  8. Isometric thermogenesis at rest and during movement: a neglected variable in energy expenditure and obesity predisposition.

    Science.gov (United States)

    Dulloo, A G; Miles-Chan, J L; Montani, J-P; Schutz, Y

    2017-02-01

    Isometric thermogenesis as applied to human energy expenditure refers to heat production resulting from increased muscle tension. While most physical activities consist of both dynamic and static (isometric) muscle actions, the isometric component is very often essential for the optimal performance of dynamic work given its role in coordinating posture during standing, walking and most physical activities of everyday life. Over the past 75 years, there has been sporadic interest into the relevance of isometric work to thermoregulatory thermogenesis and to adaptive thermogenesis pertaining to body-weight regulation. This has been in relation to (i) a role for skeletal muscle minor tremor or microvibration - nowadays referred to as 'resting muscle mechanical activity' - in maintaining body temperature in response to mild cooling; (ii) a role for slowed skeletal muscle isometric contraction-relaxation cycle as a mechanism for energy conservation in response to caloric restriction and weight loss and (iii) a role for spontaneous physical activity (which is contributed importantly by isometric work for posture maintenance and fidgeting behaviours) in adaptive thermogenesis pertaining to weight regulation. This paper reviews the evidence underlying these proposed roles for isometric work in adaptive thermogenesis and highlights the contention that variability in this neglected component of energy expenditure could contribute to human predisposition to obesity.

  9. Muscle force generation and force control of finger movements in children with spastic hemiplegia during isometric tasks.

    NARCIS (Netherlands)

    Smits-Engelsman, B.C.M.; Rameckers, E.A.A.; Duysens, J.E.J.

    2005-01-01

    Force control ability was investigated in 10 males and 10 females, between 5 and 15 years old with spastic hemiplegia (mild and moderate hand dysfunction), and an aged-matched control group (eight males, 12 females). An isometric force production task at five different levels of maximum voluntary co

  10. Effect of combined variation of force amplitude and rate of force development on the modulation characteristics of muscle activation during rapid isometric aiming force production.

    Science.gov (United States)

    Park, Jin-Hoon; Stelmach, George E

    2006-01-01

    Studies of rapid target-directed limb movements have suggested that various control schemes can be defined by the modulation pattern of the muscle activity. The present study was aimed to address the question regarding the extent to which a simultaneous control of force amplitude, and rate of force development influences the modulation characteristics of muscle activation associated with producing rapid isometric aiming forces at the elbow joint. The subjects were instructed to produce rapid isometric force pulses to three different force amplitudes (15, 35, and 55% of their maximal voluntary contractions) under systematically varied force-rate conditions ranging from a fast and accurate force-rate to the fastest force-rate possible. The results showed that larger force amplitudes were achieved by increasing the rate of force development (d F/d t) while the time to peak force remained relatively constant. The magnitude of the electromyographic (EMG) burst systematically increased as a function of force amplitude at all force-rate conditions. The primary finding was that the characteristic of the EMG burst duration associated with different force amplitudes showed a significant difference among force-rate conditions. Under a fast and accurate force-rate condition, the duration of the agonist burst increased linearly with force amplitude. A gradual transition into a fixed duration of the agonist burst then was observed over the remaining three force-rate requirements. With increasingly faster force-rates, there were no changes in the agonist burst duration over three force amplitudes. These results indicate that the combined variations in force amplitude and force-rate examined relative to the most rapid force-rate influence the control patterns for the muscle activation during the fast isometric force production. Changes in the EMG modulation patterns observed are likely due to the constraints imposed by muscle contractile properties.

  11. Beta-range EEG-EMG coherence with isometric compensation for increasing modulated low-level forces.

    Science.gov (United States)

    Chakarov, Vihren; Naranjo, José Raúl; Schulte-Mönting, Jürgen; Omlor, Wolfgang; Huethe, Frank; Kristeva, Rumyana

    2009-08-01

    Corticomuscular synchronization has been shown to occur in beta (15-30 Hz) and gamma range (30-45 Hz) during isometric compensation of static and dynamic (periodically modulated) low-level forces, respectively. However, it is still unknown to what extent these synchronization processes in beta and gamma range are modified with increasing modulated force. We addressed this question by investigating the corticomuscular coherence (CMC) between the electroencephalogram (EEG) and electromyogram (EMG) from the first dorsal interosseus muscle (FDI) as well as the cortical and muscular spectral power during a visuomotor task where different levels of a dynamic (modulated) force were used. Seven healthy right-handed female subjects compensated dynamic forces at 8, 16, and 24% of the maximal voluntary contraction (MVC) isometrically with their right index finger. Under the three conditions investigated, we found a broad-band CMC comprising both beta and gamma range and peaking at approximately 22 Hz within the beta band. This broad-band coherence increased linearly with higher force level. A separate analysis of the gamma range CMC did not show significant modulation of the CMC by the force levels. EEG and EMG spectral power did not show any significant difference among the three force conditions. Our results favor the view that the function of beta range CMC is not specific for low-level static forces only. The sensorimotor system may resort to stronger and also broader beta-range CMC to generate stable corticospinal interaction during increased force level, as well as when compensating for dynamic modulated forces. This finding re-enforces the importance of the beta-range EEG-EMG coherence in sensorimotor integration.

  12. Fiber-type susceptibility to eccentric contraction-induced damage of hindlimb-unloaded rat AL muscles

    Science.gov (United States)

    Vijayan, K.; Thompson, J. L.; Norenberg, K. M.; Fitts, R. H.; Riley, D. A.

    2001-01-01

    Slow oxidative (SO) fibers of the adductor longus (AL) were predominantly damaged during voluntary reloading of hindlimb unloaded (HU) rats and appeared explainable by preferential SO fiber recruitment. The present study assessed damage after eliminating the variable of voluntary recruitment by tetanically activating all fibers in situ through the motor nerve while applying eccentric (lengthening) or isometric contractions. Muscles were aldehyde fixed and resin embedded, and semithin sections were cut. Sarcomere lesions were quantified in toluidine blue-stained sections. Fibers were typed in serial sections immunostained with antifast myosin and antitotal myosin (which highlights slow fibers). Both isometric and eccentric paradigms caused fatigue. Lesions occurred only in eccentrically contracted control and HU muscles. Fatigue did not cause lesions. HU increased damage because lesioned- fiber percentages within fiber types and lesion sizes were greater than control. Fast oxidative glycolytic (FOG) fibers were predominantly damaged. In no case did damaged SO fibers predominate. Thus, when FOG, SO, and hybrid fibers are actively lengthened in chronically unloaded muscle, FOG fibers are intrinsically more susceptible to damage than SO fibers. Damaged hybrid-fiber proportions ranged between these extremes.

  13. Complex myograph allows the examination of complex muscle contractions for the assessment of muscle force, shortening, velocity, and work in vivo

    Directory of Open Access Journals (Sweden)

    Ruhschulte Hainer

    2008-07-01

    Full Text Available Abstract Background The devices used for in vivo examination of muscle contractions assess only pure force contractions and the so-called isokinetic contractions. In isokinetic experiments, the extremity and its muscle are artificially moved with constant velocity by the measuring device, while a tetanic contraction is induced in the muscle, either by electrical stimulation or by maximal voluntary activation. With these systems, experiments cannot be performed at pre-defined, constant muscle length, single contractions cannot be evaluated individually and the separate examination of the isometric and the isotonic components of single contractions is not possible. Methods The myograph presented in our study has two newly developed technical units, i.e. a. a counterforce unit which can load the muscle with an adjustable, but constant force and b. a length-adjusting unit which allows for both the stretching and the contraction length to be infinitely adjustable independently of one another. The two units support the examination of complex types of contraction and store the counterforce and length-adjusting settings, so that these conditions may be accurately reapplied in later sessions. Results The measurement examples presented show that the muscle can be brought to every possible pre-stretching length and that single isotonic or complex isometric-isotonic contractions may be performed at every length. The applied forces act during different phases of contraction, resulting into different pre- and after-loads that can be kept constant – uninfluenced by the contraction. Maximal values for force, shortening, velocity and work may be obtained for individual muscles. This offers the possibility to obtain information on the muscle status and to monitor its changes under non-invasive measurement conditions. Conclusion With the Complex Myograph, the whole spectrum of a muscle's mechanical characteristics may be assessed.

  14. The rate of force development obtained at early contraction phase is not influenced by active static stretching.

    Science.gov (United States)

    Morais de Oliveira, André L; Greco, Camila Coelho; Molina, Renato; Denadai, Benedito S

    2012-08-01

    The objective of this study was to investigate the influence of active static stretching on the maximal isometric muscle strength (maximal voluntary contraction [MVC]) and rate of force development (RFD) determined within time intervals of 30, 50, 100, and 200 milliseconds relative to the onset of muscle contraction. Fifteen men (aged 21.3 ± 2.4 years) were submitted on different days to the following tests: (a) familiarization session to the isokinetic dynamometer; (b) 2 maximal isometric contractions for knee extensors in the isokinetic dynamometer to determine MVC and RFD (control); and (c) 2 active static stretching exercises for the dominant leg extensors (10 × 30 seconds for each exercise with a 20-second rest interval between bouts). After stretching, the isokinetic test was repeated (poststretching). Conditions 2 and 3 were performed in random order. The RFD was considered as the mean slope of the moment-time curve at time intervals of 0-30, 0-50, 0-100; 0-150; and 0200 milliseconds relative to the onset of muscle contraction. The MVC was reduced after stretching (285 ± 59 vs. 271 ± 56 N · m, p 0.05). However, the RFD measured at intervals of 0-150 and 0-200 milliseconds was significantly lower after stretching (p < 0.01). It can be concluded that explosive muscular actions of a very short duration (<100 milliseconds) seem less affected by active static stretching when compared with actions using maximal muscle strength.

  15. The influence of the type of contraction on the masseter muscle EMG power spectrum.

    Science.gov (United States)

    Nadeau, S; Bilodeau, M; Delisle, A; Chmielewski, W; Arsenault, A B; Gravel, D

    1993-01-01

    Different behaviours of the EMG power spectrum across increasing force levels have been reported for the masseter muscle. A factor that could explain these different behaviours may be the type of contraction used, as was recently shown for certain upper limb muscles(5). The purpose of this study was to compare, between two types of isometric contractions, the behaviour of EMG power spectrum statistics (median frequency (MF) and mean power frequency (MPF)) obtained across increasing force levels. Ten women exerted, while biting in the intercuspal position, three 5 s ramp contractions that increased linearly from 0 to 100% of the maximal voluntary contraction (MVC). They also completed three step contractions (constant EMG amplitude) at each of the following levels: 20, 40, 60 and 80% MVC. EMG signals from the masseter muscle were recorded with miniature surface electrodes. The RMS, as well as the MPF and MF of the power spectrum were calculated at 20, 40, 60 and 80% MVC for each type of contraction. As expected, the RMS values showed similar increases with increasing levels of effort for both types of contractions. Different behaviours for both MPF (contraction(∗)force interaction, ANOVA, P0.05) across increasing levels of effort were found between the two types of contraction. The use of step contractions gave rise to a decrease of both MPF and MF with increasing force, while the use of ramp contractions gave rise to an increase in both statistics up to at least 40% MVC followed by a decrease at higher force levels. These findings suggest that the type of contraction used does influence the behaviour of the spectral statistics across increasing force levels and that this could explain the differences obtained in previous studies for the masseter muscle. Copyright © 1993. Published by Elsevier Ltd.

  16. Isometric cervical extension strength of recreational and experienced cyclists.

    Science.gov (United States)

    Jacobs, K; Nichols, J; Holmes, B; Buono, M

    1995-06-01

    The effect for cyclists of the typical forward sitting position on neck strength and its possible relationship to neck pain have not been examined. The purpose of this study was to measure the peak isometric cervical extension strength (PICES) of both recreational and experienced road cyclists and to compare these values to those of noncyclists. Subjects, 45 men between the ages of 18 and 40, were tested for voluntary PICES through a 126 degrees range of motion on a MedX cervical extension machine. No significant differences were found between the three groups in PICES at any angle. When expressed relative to body weight, significant differences in PICES were found at 126 degrees between the control group and the recreational cyclist group (p cycling, rather than from muscle weakness.

  17. Interaction of Rate of Force Development and Duration of Rate in Isometric Force.

    Science.gov (United States)

    Siegel, Donald

    A study attempted to determine whether force and duration parameters are programmed in an interactive or independent fashion prior to executing ballistic type isometric contractions of graded intensities. Four adult females each performed 360 trials of producing ballistic type forces representing 25, 40, 55, and 75 percent of their maximal…

  18. In vitro comparison of isometric and stop-test contractility parameters for the urinary bladder

    NARCIS (Netherlands)

    R. van Mastrigt (Ron); J.J. Glerum (Jacobus)

    1985-01-01

    textabstractContractility parameters in the urinary bladder can be calculated from isometric contractions (no extra patient load as compared to routine cystometry) or from stop-tests (more accurate, simpler analysis). A stop-test involves a voluntarily interrupted micturition with pressure and flow

  19. Cardiovascular responses to voluntary and nonvoluntary static exercise in humans.

    Science.gov (United States)

    Friedman, D B; Peel, C; Mitchell, J H

    1992-11-01

    We have measured the cardiovascular responses during voluntary and nonvoluntary (electrically induced) one-leg static exercise in humans. Eight normal subjects were studied at rest and during 5 min of static leg extension at 20% of maximal voluntary contraction performed voluntarily and nonvoluntarily in random order. Heart rate (HR), mean arterial pressure (MAP), and cardiac output (CO) were determined, and peripheral vascular resistance (PVR) and stroke volume (SV) were calculated. HR increased from approximately 65 +/- 3 beats/min at rest to 80 +/- 4 and 78 +/- 6 beats/min (P voluntary and nonvoluntary contractions, respectively. CO increased from 5.1 +/- 0.7 to 6.0 +/- 0.8 and 6.2 +/- 0.8 l/min (P voluntary and nonvoluntary contractions, respectively. PVR and SV did not change significantly during voluntary or nonvoluntary contractions. Thus the cardiovascular responses were not different between voluntary and electrically induced contractions. These results suggest that the increases in CO, HR, SV, MAP, and PVR during 5 min of static contractions can be elicited without any contribution from a central neural mechanism (central command). However, central command could still have an important role during voluntary static exercise.

  20. Characteristics of the Motor Units during Sternocleidomastoid Isometric Flexion among Patients with Mechanical Neck Disorder and Asymptomatic Individuals

    Science.gov (United States)

    Yang, Chia-Chi; Su, Fong-Chin; Yang, Po-Ching; Lin, Hwai-Ting

    2016-01-01

    Mechanical neck disorder is a widespread and non-neurological musculoskeletal condition resulting from modern lifestyles. Presently, the fundamental electrophysiological properties of the motor units of the sternocleidomastoid muscles and the characteristics of the short-term synchronization of the motor unit in patients with neck pain are ambiguous. This study therefore aims to clarify the fundamental electrophysiological properties of the motor units of the sternocleidomastoid muscles in patients with mechanical neck disorder and in asymptomatic individuals. We further investigated whether alterations in the degree of motor unit short-term synchronization occur. The surface electrophysiological signals of the bilateral sternal heads of the sternocleidomastoid muscles of twelve patients with mechanical neck disorder and asymptomatic individuals were detected at 25% of the maximum voluntary contraction during cervical isometric flexion and then decomposed into individual motor unit action potential trains. We found that the patients with mechanical neck disorder showed significantly higher initial and mean firing rates of the sternocleidomastoid muscles and displayed substantially lower motor unit short-term synchronization values compared with the asymptomatic subjects. Consequently, these convincing findings support the assertion that patients with mechanical neck disorder display altered neuromuscular control strategies, such as the reinforcement of motor unit recruitment firing rates in the sternocleidomastoid muscles. The motor units of these patients also revealed neural recruitment strategies with relatively poor efficiency when executing the required motor tasks. PMID:27941995

  1. Cross-talk in mechanomyographic signals from the forearm muscles during sub-maximal to maximal isometric grip force.

    Directory of Open Access Journals (Sweden)

    Md Anamul Islam

    Full Text Available PURPOSE: This study aimed: i to examine the relationship between the magnitude of cross-talk in mechanomyographic (MMG signals generated by the extensor digitorum (ED, extensor carpi ulnaris (ECU, and flexor carpi ulnaris (FCU muscles with the sub-maximal to maximal isometric grip force, and with the anthropometric parameters of the forearm, and ii to quantify the distribution of the cross-talk in the MMG signal to determine if it appears due to the signal component of intramuscular pressure waves produced by the muscle fibers geometrical changes or due to the limb tremor. METHODS: Twenty, right-handed healthy men (mean ± SD: age  = 26.7±3.83 y; height  = 174.47±6.3 cm; mass  = 72.79±14.36 kg performed isometric muscle actions in 20% increment from 20% to 100% of the maximum voluntary isometric contraction (MVIC. During each muscle action, MMG signals generated by each muscle were detected using three separate accelerometers. The peak cross-correlations were used to quantify the cross-talk between two muscles. RESULTS: The magnitude of cross-talk in the MMG signals among the muscle groups ranged from, R2(x, y = 2.45-62.28%. Linear regression analysis showed that the magnitude of cross-talk increased linearly (r2 = 0.857-0.90 with the levels of grip force for all the muscle groups. The amount of cross-talk showed weak positive and negative correlations (r2 = 0.016-0.216 with the circumference and length of the forearm respectively, between the muscles at 100% MVIC. The cross-talk values significantly differed among the MMG signals due to: limb tremor (MMGTF, slow firing motor unit fibers (MMGSF and fast firing motor unit fibers (MMGFF between the muscles at 100% MVIC (p<0.05, η2 = 0.47-0.80. SIGNIFICANCE: The results of this study may be used to improve our understanding of the mechanics of the forearm muscles during different levels of the grip force.

  2. 股四头肌等长收缩练习治疗膝骨性关节炎的病例对照研究%Case-control study on isometric quadriceps femoris contraction exercises for the treatment of knee osteoarthritis

    Institute of Scientific and Technical Information of China (English)

    何本祥; 檀亚军; 夏万荣; 魏微

    2012-01-01

    目的:探讨股四头肌等长收缩练习治疗膝骨性关节炎的临床疗效,并建立膝骨性关节炎运动处方.方法:2008年1月至2010年9月采用股四头肌等长收缩练习治疗膝骨性关节炎120例,其中男39例,女81例;年龄40~85岁,平均62.50岁;病程1个月~30年.按就诊先后顺序分为2组,治疗组60例,男21例,女39例;年龄40~85岁,平均(62.27±8.99)岁;病程2个月~30年,给予玻璃酸钠关节腔注射加股四头肌等长收缩练习治疗.对照组60例,男18例,女42例;年龄41~80岁,平均(62.72±8.34)岁;病程个1个月~30年,给予常规玻璃酸钠关节腔注射治疗.分别观察2组膝关节疼痛、功能及积液等指标,比较其临床疗效.结果:120例均获随访,时间1~3年,平均18个月.参照JOA判定标准:治疗组治愈12例,显效33例,有效14例,无效1例;对照组治愈7例,显效14例,有效31例,无效8例,治疗组疗效优于对照组.治疗组累计复发7膝(1年内复发3膝,1年后复发4膝),对照组累计复发31膝(1年内复发13膝,1年后复发18膝),治疗组复发病例少于对照组.结论:股四头肌等长收缩练习在治疗膝骨性关节炎中具有明显的缓解症状、改善关节功能、增强关节稳定性及减缓关节退变进程的作用,远期临床疗效较好.%Objective:To evaluate clinical effecto oi knee osleoarthritis with the treatment of the isometric quadriceps femoris contraction exercises,which aims at establishing the exercise prescription of knee osteoarthrilis,and promoting its clinical application. Methods:From January 2008 to September 2010,120 patients with knee osleoarthrilis were divided into two groups according to visiting sequence .including 39 males and 81 females,ranging in age from 40 to 85 years,with an average of 62.50 years,the disease course ranged from 1 month to 30 years. There were 60 patients in the therapeutic group, including 21 males and 39 females,ranging in age from 40 to 85 years

  3. Whey protein hydrolysate augments tendon and muscle hypertrophy independent of resistance exercise contraction mode.

    Science.gov (United States)

    Farup, J; Rahbek, S K; Vendelbo, M H; Matzon, A; Hindhede, J; Bejder, A; Ringgard, S; Vissing, K

    2014-10-01

    In a comparative study, we investigated the effects of maximal eccentric or concentric resistance training combined with whey protein or placebo on muscle and tendon hypertrophy. 22 subjects were allocated into either a high-leucine whey protein hydrolysate + carbohydrate group (WHD) or a carbohydrate group (PLA). Subjects completed 12 weeks maximal knee extensor training with one leg using eccentric contractions and the other using concentric contractions. Before and after training cross-sectional area (CSA) of m. quadriceps and patellar tendon CSA was quantified with magnetic resonance imaging and a isometric strength test was used to assess maximal voluntary contraction (MVC) and rate of force development (RFD). Quadriceps CSA increased by 7.3 ± 1.0% (P contraction mode. MVC and RFD increased by 15.6 ± 3.5% (P contraction mode effects. In conclusion, high-leucine whey protein hydrolysate augments muscle and tendon hypertrophy following 12 weeks of resistance training - irrespective of contraction mode. © 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  4. Low-frequency fatigue at maximal and submaximal muscle contractions

    Directory of Open Access Journals (Sweden)

    R.R. Baptista

    2009-04-01

    Full Text Available Skeletal muscle force production following repetitive contractions is preferentially reduced when muscle is evaluated with low-frequency stimulation. This selective impairment in force generation is called low-frequency fatigue (LFF and could be dependent on the contraction type. The purpose of this study was to compare LFF after concentric and eccentric maximal and submaximal contractions of knee extensor muscles. Ten healthy male subjects (age: 23.6 ± 4.2 years; weight: 73.8 ± 7.7 kg; height: 1.79 ± 0.05 m executed maximal voluntary contractions that were measured before a fatigue test (pre-exercise, immediately after (after-exercise and after 1 h of recovery (after-recovery. The fatigue test consisted of 60 maximal (100% or submaximal (40% dynamic concentric or eccentric knee extensions at an angular velocity of 60°/s. The isometric torque produced by low- (20 Hz and high- (100 Hz frequency stimulation was also measured at these times and the 20:100 Hz ratio was calculated to assess LFF. One-way ANOVA for repeated measures followed by the Newman-Keuls post hoc test was used to determine significant (P < 0.05 differences. LFF was evident after-recovery in all trials except following submaximal eccentric contractions. LFF was not evident after-exercise, regardless of exercise intensity or contraction type. Our results suggest that low-frequency fatigue was evident after submaximal concentric but not submaximal eccentric contractions and was more pronounced after 1-h of recovery.

  5. Voluntary Environmental Governance Arrangements

    NARCIS (Netherlands)

    van der Heijden, J.

    2012-01-01

    Voluntary environmental governance arrangements have focal attention in studies on environmental policy, regulation and governance. The four major debates in the contemporary literature on voluntary environmental governance arrangements are studied. The literature falls short of sufficiently

  6. Voluntary Environmental Governance Arrangements

    NARCIS (Netherlands)

    van der Heijden, J.

    2012-01-01

    Voluntary environmental governance arrangements have focal attention in studies on environmental policy, regulation and governance. The four major debates in the contemporary literature on voluntary environmental governance arrangements are studied. The literature falls short of sufficiently specify

  7. Voluntary Service System (VSS)

    Data.gov (United States)

    Department of Veterans Affairs — Voluntary Service System (VSS) is a national-level application which replaced the site-based Voluntary Timekeeping System (VTK). VTK was used for many years at the...

  8. Higher Neuromuscular Manifestations of Fatigue in Dynamic than Isometric Pull-Up Tasks in Rock Climbers.

    Science.gov (United States)

    Boccia, Gennaro; Pizzigalli, Luisa; Formicola, Donato; Ivaldi, Marco; Rainoldi, Alberto

    2015-09-29

    Neuromuscular assessment of rock climbers has been mainly focused on forearm muscles in the literature. We aimed to extend the body of knowledge investigating on two other upper limb muscles during sport-specific activities in nine male rock climbers. We assessed neuromuscular manifestations of fatigue recording surface electromyographic signals from brachioradialis and teres major muscles, using multi-channel electrode arrays. Participants performed two tasks until volitional exhaustion: a sequence of dynamic pull-ups and an isometric contraction sustaining the body at half-way of a pull-up (with the elbows flexed at 90°). The tasks were performed in randomized order with 10 minutes of rest in between. The normalized rate of change of muscle fiber conduction velocity was calculated as the index of fatigue. The time-to-task failure was significantly shorter in the dynamic (31 ±10 s) than isometric contraction (59 ±19 s). The rate of decrease of muscle fiber conduction velocity was found steeper in the dynamic than isometric task both in brachioradialis (isometric: -0.2 ±0.1%/s; dynamic: -1.2 ±0.6%/s) and teres major muscles (isometric: -0.4±0.3%/s; dynamic: -1.8±0.7%/s). The main finding was that a sequence of dynamic pull-ups lead to higher fatigue than sustaining the body weight in an isometric condition at half-way of a pull-up. Furthermore, we confirmed the possibility to properly record physiological CV estimates from two muscles, which had never been studied before in rock climbing, in highly dynamic contractions.

  9. Effectiveness of joint mobilization and rehab training of isometric contraction on professional athletes'wrist triangular fibrocartilage complex injury%关节松动术结合耐力性康复训练治疗运动员腕三角软骨复合体损伤的有效性分析

    Institute of Scientific and Technical Information of China (English)

    徐青

    2015-01-01

    Objective:To analyze the effectiveness of joint mobilization and endurance of rehabilitation training on athletes'triangular fibro cartilage complex (TFCC ) injuries and explore an effective method that can speed up the treatment for TFCC.Methods:According to the principle of random,we divided 48 cases of athletes with TFCC into two groups,each group having 24 cases.The control group received conservative therapy in general and then got Bracers fixed;the observation group also received conservative therapy in general,and then got joint mobilization and rehabilitation of isometric endurance contraction without Bracers fixed. The two groups were treated for 6 weeks.Then,the Visual Analogue Score (VAS)and index of grip strength are used to analyze them.Results:There were significant differences between observation group and the control group.The effect of the observation group was significantly better than that of the control group.Conclusion:Based on the conventional conservative therapy,we can significantly improve the curative effect of athlete's TFCC injury with joint mobilization and isometric endurance of rehabilitation training and promote the recovery of the TFCC injury,whose effect is better than the fixed treatment.%目的:应用关节松动术结合耐力性康复训练治疗职业运动员三角纤维软骨复合体损伤的有效性进行分析,探讨一种加快三角纤维软骨复合体损伤的有效治疗方法。方法:48例三角纤维软骨复合体损伤的职业运动员按照随机分组的原则分为观察组和对照组两组,各24例。对照组给予常规的保守疗法,并佩戴护腕固定;观察组在常规疗法的基础上采用关节松动术配合等长耐力收缩性康复训练疗法治疗。两组患者治疗时间均为6周。然后采用视觉模拟评分(VAS )、握力指数等指标对两组患者的疗效进行比较分析。结果:观察组疗效明显优于对照组,呈显著性差异。结论:在

  10. Age-related changes in motor unit firing pattern of vastus lateralis muscle during low-moderate contraction.

    Science.gov (United States)

    Watanabe, Kohei; Holobar, Aleš; Kouzaki, Motoki; Ogawa, Madoka; Akima, Hiroshi; Moritani, Toshio

    2016-06-01

    Age-related changes in motor unit activation properties remain unclear for locomotor muscles such as quadriceps muscles, although these muscles are preferentially atrophied with aging and play important roles in daily living movements. The present study investigated and compared detailed motor unit firing characteristics for the vastus lateralis muscle during isometric contraction at low to moderate force levels in the elderly and young. Fourteen healthy elderly men and 15 healthy young men performed isometric ramp-up contraction to 70 % of the maximal voluntary contractions (MVC) during knee extension. Multichannel surface electromyograms were recorded from the vastus lateralis muscle using a two-dimensional grid of 64 electrodes and decomposed with the convolution kernel compensation technique to extract individual motor units. Motor unit firing rates in the young were significantly higher (~+29.7 %) than in the elderly (p  0.05). Firing rates at 60 % of the MVC force level for the motor units recruited at MVC were significantly correlated with MVC force in the elderly (r = 0.885, p  0.05). These results suggest that the motor unit firing rate in the vastus lateralis muscle is affected by aging and muscle strength in the elderly and/or age-related strength loss is related to motor unit firing/recruitment properties.

  11. Motor unit firing rates of the gastrocnemii during maximal brief steady-state contractions in humans.

    Science.gov (United States)

    Graham, Mitchell T; Rice, Charles L; Dalton, Brian H

    2016-02-01

    The human triceps surae (soleus, medial (MG) and lateral (LG) gastrocnemii) is complex and important for posture and gait. The soleus exhibits markedly lower motor unit firing rates (MUFRs; ∼16Hz) during maximal voluntary isometric contraction (MVC) than other limb muscles, but this information is unknown for the MG and LG. During multiple visits, subjects performed a series of 5-7, ∼7-s plantar flexor MVCs with tungsten microelectrodes inserted into the MG and LG. During a separate testing session, another group of subjects performed submaximal isometric contractions at 25%, 50%, and 75% MVC with inserted fine-wires in the MG, LG and soleus. Maximum steady-state MUFRs for MG and LG (∼23Hz) were not different, but faster than prior reports for the soleus. No differences between the three triceps surae components were detected for 25% or 50% MVC, but at 75% MVC, the MG MUFRs were 31% greater than soleus. The triceps surae exhibit similar torque modulation strategies at 75% MVC) the gastrocnemii rely on faster rates to generate maximal torque than the soleus. Therefore, the MG and LG exhibit a larger range of MUFR capacities.

  12. Effects of amplitude and phase-duration modification on electrically induced contraction force and discomfort.

    Science.gov (United States)

    Springer, Shmuel; Shapiro, Maxim

    2017-08-09

    Neuromuscular electrical stimulation (NMES) is commonly used in rehabilitation. However, the optimal combination of phase-duration and amplitude for enhancing motor output is not yet resolved. To test the effects of increasing phase-duration and amplitude on isometric knee extension force and discomfort, while controlling the effects of electrode-skin resistance and body mass index (BMI). Twenty-one healthy volunteers participated in the study. Stimulation was set at 250 μsec phase-duration and 45 Hz to evoke 10% of maximal voluntary isometric contraction of the quadriceps. Electrode-skin resistance was measured. Then, electrically induced contraction (EIC) forces and discomfort level were measured under four conditions: Moderate (25%) or substantial increase (50%) from baseline amplitude with constant phase-duration and moderate (25%) or substantial increase (50%) in phase-duration with amplitude constant. Compared with baseline, EIC force was significantly higher in all intensification conditions, while discomfort was significantly greater in all conditions except for moderate increase in phase-duration (p= 0.44). Amplitude intensification produced significantly higher force and greater discomfort than phase-duration. Electrode-skin resistance and BMI were not significant covariates. Greater force is elicited by increasing amplitude than by similar increase in phase-duration; however, the associated discomfort is also higher. Clinicians may use phase-duration while conditioning for NMES.

  13. The dynamics of quasi-isometric foliations

    CERN Document Server

    Hammerlindl, Andy

    2011-01-01

    If the stable, center, and unstable foliations of a partially hyperbolic system are quasi-isometric, the system has Global Product Structure. This result also applies to Anosov systems and to other invariant splittings. If a partially hyperbolic system on a manifold with abelian fundamental group has quasi-isometric stable and unstable foliations, the center foliation is without holonomy. If, further, the system has Global Product Structure, then all center leaves are homeomorphic.

  14. Effect of generalized joint hypermobility on knee function and muscle activation in children and adults

    DEFF Research Database (Denmark)

    Jensen, Bente Rona; Olesen, Annesofie T.; Pedersen, Mogens Theisen

    2013-01-01

    were evaluated in 39 children and 36 adults during isometric knee extension and flexion. Subjects performed isometric maximum contractions, submaximal contractions at 25% maximum voluntary contraction (MVC), and explosive contractions. Results: Agonist activation was reduced, and coactivation ratio...

  15. Isometric exercise and chronic heart failure

    Directory of Open Access Journals (Sweden)

    Efthimia Zerva

    2013-07-01

    Full Text Available The resistance exercise is an important part of all rehabilitation programs in patients with chronic heart failure. Among several kinds of resistance exercises, the one mainly applied is isotonic exercise, whereas, in the contrary, isometric is not heavily used although it affects the daily lives of patients who, trying to look after themselves (moving, walking, lifting objects, twitch in an isometric way their peripheral muscles due to reduced cardiovascular endurance. Purpose: The purpose of the present review was to present the data available so far for isometric exercise in cardiovascular patients and to examine the importance of applying this kind of exercise in rehabilitation programs in the context of, firstly, evaluation, and secondly therapeutic intervention. Material - Methods: The methodology followed included searching inquiries and reviews from international databases (Pubmed, Medline, Scopus on the effects of isometric exercise in patients with chronic heart failure. The progress and development of the studies are of particular importance to this work and, to this end, the literature refers to the entire range of time in the last three decades, from 1985 to 2012 according the key words noted. Results: In rehabilitation programs for patients with chronic heart failure, resistance exercise if applied in an isotonic way helps improve hemodynamic and functional parameters. In contrast, resistance exercise applied in an isometric way requires further investigation because most findings are related to hemodynamic disturbances. The data which is encouraging for isometric exercise programs are few and, therefore, it cannot be directly recommended as a proper way to exercise. Conclusions: Isometric exercise has an important place in the evaluation of patients with chronic heart failure, and limits should be "placed" in its application as a therapeutic tool to prevent complications.

  16. Motor unit activity in biceps brachii of left-handed humans during sustained contractions with two load types.

    Science.gov (United States)

    Gould, Jeffrey R; Cleland, Brice T; Mani, Diba; Amiridis, Ioannis G; Enoka, Roger M

    2016-09-01

    The purpose of the study was to compare the discharge characteristics of single motor units during sustained isometric contractions that required either force or position control in left-handed individuals. The target force for the two sustained contractions (24.9 ± 10.5% maximal force) was identical for each biceps brachii motor unit (n = 32) and set at 4.7 ± 2.0% of maximal voluntary contraction (MVC) force above its recruitment threshold (range: 0.5-41.2% MVC force). The contractions were not sustained to task failure, but the duration (range: 60-330 s) was identical for each motor unit and the decline in MVC force immediately after the sustained contractions was similar for the two tasks (force: 11.1% ± 13.7%; position: 11.6% ± 9.9%). Despite a greater increase in the rating of perceived exertion during the position task (task × time interaction, P contractions requiring either force or position control.

  17. In-vivo Strain Measurement for Surgically Repaired Achilles Tendon under Isometric Contraction Using Real-time Ultrasound Imaging%实时超声测量用于等长收缩条件下修复跟腱应变的研究

    Institute of Scientific and Technical Information of China (English)

    郑永平; 陈艳玲; 吴嘉豪; 丁赛君; 李添捷; 李曾慧平

    2011-01-01

    tendon during isometric contractions. Six male subjects with age ranging from 28 to 51 years old were recruited and their level of rupture was 2 to 7 cm from the insertion of Achilles tendon. They were tested 12.8 ± 1.3 weeks after operation. Their healthy legs were used as control. In addition, three healthy male subjecLs were recruited to test the differences of the tendon strain between the dominant and non-dominant legs. Ultrasound images were obtained along the Achilles tendon at the level of rupture site in-vivo under isometric contraction using Cybex 6000, which also recorded the torque of gastrocnemius-soleus complex similtaneously. Ankle-foot-orthosis (AFO) custom-made for each foot was used to secure the consistent alignment between the ultrasound imaging plane and the tendon. The strain of the selected part of the tendon during the contractian was extracted from the ultrasound images. The ultrasound measurement was validated usinng an in vitro experiment with porcine Achilles tendons together with an optical imaging technique. We found that the strain at the repaired site after rupture was 14.8%± 12.6%, which was significantly (p = 0.017) smaller than that of the tendon at the contralateral healthy side, which was 23.7% ± 12.7%. Future Btudies can focus on the strain distribution along the tendon and how the distribution changes during the healing process. This research may provide information for therapista to select optimized exercise plan for patients during their rehabilitation process after the repair of Achiles tendon.

  18. Hand-grip isometric strength in judo

    Directory of Open Access Journals (Sweden)

    Juan G Bonitch-Góngora

    2014-02-01

    Full Text Available The grip is an important technical and tactical aspect through which the judokas dominate the adversary, hindering the application of appropriate techniques and favoring their own attack. The judokas must have high levels of isometric force and endurance to this type of force on the gripping muscles of the forearms, as one of the key aspects for success. This article reviews the grip muscular strength and endurance profiles of judokas of different groups (gender, age and competitive level. In general, the peak isometric strength of elite judokas has not changed in the last 40 years and is similar to that reached by non-elite judokas or even registered in large populations. This indicate that the evaluation of the isometric hand grip endurance may be a more relevant parameter than the peak isometric force in judokas, as during the bouts the grip must be maintained for relatively long periods of time and the maximum force cannot be maintained for long. However there are few studies on the ability to resist successive isometric handgrip stress in judokas.

  19. Interaction of poststroke voluntary effort and functional neuromuscular electrical stimulation.

    Science.gov (United States)

    Makowski, Nathaniel; Knutson, Jayme; Chae, John; Crago, Patrick

    2013-01-01

    Functional electrical stimulation (FES) may be able to augment functional arm and hand movement after stroke. Poststroke neuroprostheses that incorporate voluntary effort and FES to produce the desired movement must consider how forces generated by voluntary effort and FES combine, even in the same muscle, in order to provide an appropriate level of stimulation to elicit the desired assistive force. The goal of this study was to determine whether the force produced by voluntary effort and FES add together independently of effort or whether the increment in force depends on the level of voluntary effort. Isometric force matching tasks were performed under different combinations of voluntary effort and FES. Participants reached a steady level of force, and while attempting to maintain a constant effort level, FES was applied to augment the force. Results indicate that the increment in force produced by FES decreases as the level of initial voluntary effort increases. Potential mechanisms causing the change in force output are proposed, but the relative contribution of each mechanism is unknown.

  20. Motor Variability during Sustained Contractions Increases with Cognitive Demand in Older Adults.

    Science.gov (United States)

    Vanden Noven, Marnie L; Pereira, Hugo M; Yoon, Tejin; Stevens, Alyssa A; Nielson, Kristy A; Hunter, Sandra K

    2014-01-01

    To expose cortical involvement in age-related changes in motor performance, we compared steadiness (force fluctuations) and fatigability of submaximal isometric contractions with the ankle dorsiflexor muscles in older and young adults and with varying levels of cognitive demand imposed. Sixteen young (20.4 ± 2.1 year: 8 men, 9 women) and 17 older adults (68.8 ± 4.4 years: 9 men, 8 women) attended three sessions and performed a 40 s isometric contraction at 5% maximal voluntary contraction (MVC) force followed by an isometric contraction at 30% MVC until task failure. The cognitive demand required during the submaximal contractions in each session differed as follows: (1) high-cognitive demand session where difficult mental math was imposed (counting backward by 13 from a 4-digit number); (2) low-cognitive demand session which involved simple mental math (counting backward by 1); and (3) control session with no mental math. Anxiety was elevated during the high-cognitive demand session compared with other sessions for both age groups but more so for the older adults than young adults (p  Older adults had larger force fluctuations than young adults during: (1) the 5% MVC task as cognitive demand increased (p  = 0.007), and (2) the fatiguing contraction for all sessions (p  = 0.002). Time to task failure did not differ between sessions or age groups (p  > 0.05), but the variability between sessions (standard deviation of three sessions) was greater for older adults than young (2.02 ± 1.05 vs. 1.25 ± 0.51 min, p  cognitive demand was imposed, and may be related to modulation of synergist and antagonist muscles and an altered neural strategy with age originating from central sources. These data have significant implications for cognitively demanding low-force motor tasks that are relevant to functional and ergonomic in an aging workforce.

  1. Low-intensity eccentric contractions attenuate muscle damage induced by subsequent maximal eccentric exercise of the knee extensors in the elderly.

    Science.gov (United States)

    Chen, Trevor C; Tseng, Wei-Chin; Huang, Guan-Ling; Chen, Hsin-Lian; Tseng, Kou-Wei; Nosaka, Kazunori

    2013-04-01

    This study investigated whether low-intensity eccentric contractions of the knee extensors would attenuate the magnitude of muscle damage induced by maximal eccentric exercise of the same muscle performed 7 days later using elderly individuals. Healthy older men (66.4 ± 4.6 years) were assigned to control or experimental (Exp) group (n = 13 per group). The control group performed six sets of ten maximal eccentric contractions (MaxECC) of the knee extensors of non-dominant leg. The Exp group performed six sets of ten low-intensity eccentric contractions of the knee extensors on a leg extension machine by lowering a weight of 10 % maximal voluntary isometric knee extension strength (10 %ECC) 7 days prior to MaxECC. Changes in maximal voluntary isokinetic concentric torque (MVC-CON), angle at peak torque, range of motion (ROM), upper thigh circumference, muscle soreness, plasma creatine kinase activity and myoglobin (Mb) concentration and B-mode ultrasound echo-intensity before and for 5 days after MaxECC were compared between groups by a mixed factor ANOVA. No significant changes in any variables were observed following 10 %ECC. Following MaxECC, all variables changed significantly, and changes in all variables except for angle at peak torque were significantly different between groups. MVC-CON and ROM decreased smaller and recovered faster (P eccentric contractions was effective for attenuating muscle damage induced by subsequent MaxECC of the knee extensors for elderly individuals.

  2. Roughly isometric minimal immersions into Riemannian manifolds

    DEFF Research Database (Denmark)

    Markvorsen, Steen

    A given metric (length-) space $X$ (whether compact or not) is roughly isometric to any one of its Kanai graphs $G$, which in turn can be {\\em{geometrized}} by considering each edge of $G$ as a 1-dimensional manifold with an associated metric $g$ giving the 'correct' length of the edge. In this t......A given metric (length-) space $X$ (whether compact or not) is roughly isometric to any one of its Kanai graphs $G$, which in turn can be {\\em{geometrized}} by considering each edge of $G$ as a 1-dimensional manifold with an associated metric $g$ giving the 'correct' length of the edge....... In this talk we will mainly be concerned with {\\em{minimal}} isometric immersions of such geometrized approximations $(G, g)$ of $X$ into Riemannian manifolds $N$ with bounded curvature. When such an immersion exists, we will call it an $X$-web in $N$. Such webs admit a natural 'geometric' extension...

  3. Isometric Isomorphisms in Proper CQ*-algebras

    Institute of Scientific and Technical Information of China (English)

    Choonkil PARK; Jong Su AN

    2009-01-01

    In this paper,we prove the Hyers-Ulam-Rassias stability of isometric homomorphisms in proper CQ*-algebras for the following Cauchy-Jensen additive mapping:2f(x1+x2/2+y)=f(x1)+f(x2)+2f(y).The concept of Hyers-Ulam-Rassias stability originated from the Th.M.Rassias' stability theorem that appeared in the paper: On the stability of the linear mapping in Banach spaces,Proc.Amer.Math.Soc.,72 (1978),297-300.This is applied to investigate isometric isomorphisms between proper CQ*-algebras.

  4. Fatigue-induced dissociation between rate of force development and maximal force across repeated rapid contractions.

    Science.gov (United States)

    Boccia, Gennaro; Dardanello, Davide; Tarperi, Cantor; Festa, Luca; La Torre, Antonio; Pellegrini, Barbara; Schena, Federico; Rainoldi, Alberto

    2017-08-01

    We examined whether the presence of fatigue induced by prolonged running influenced the time courses of force generating capacities throughout a series of intermittent rapid contractions. Thirteen male amateur runners performed a set of 15 intermittent isometric rapid contractions of the knee extensor muscles, (3s/5s on/off) the day before (PRE) and immediately after (POST) a half marathon. The maximal voluntary contraction force, rate of force development (RFDpeak), and their ratio (relative RFDpeak) were calculated. At POST, considering the first (out of 15) repetition, the maximal force and RFDpeak decreased (p<0.0001) at the same extent (by 22±6% and 24±22%, respectively), resulting in unchanged relative RFDpeak (p=0.6). Conversely, the decline of RFDpeak throughout the repetitions was more pronounced at POST (p=0.02), thus the decline of relative RFDpeak was more pronounced (p=0.007) at POST (-25±13%) than at PRE (-3±13%). The main finding of this study was that the fatigue induced by a half-marathon caused a more pronounced impairment of rapid compared to maximal force in the subsequent intermittent protocol. Thus, the fatigue-induced impairment in rapid muscle contractions may have a greater effect on repeated, rather than on single, attempts of maximal force production. Copyright © 2017 Elsevier B.V. All rights reserved.

  5. Electromechanical delay components during skeletal muscle contraction and relaxation in patients with myotonic dystrophy type 1.

    Science.gov (United States)

    Esposito, Fabio; Cè, Emiliano; Rampichini, Susanna; Limonta, Eloisa; Venturelli, Massimo; Monti, Elena; Bet, Luciano; Fossati, Barbara; Meola, Giovanni

    2016-01-01

    The electromechanical delay during muscle contraction and relaxation can be partitioned into mainly electrochemical and mainly mechanical components by an EMG, mechanomyographic, and force combined approach. Component duration and measurement reliability were investigated during contraction and relaxation in a group of patients with myotonic dystrophy type 1 (DM1, n = 13) and in healthy controls (n = 13). EMG, mechanomyogram, and force were recorded in DM1 and in age- and body-matched controls from tibialis anterior (distal muscle) and vastus lateralis (proximal muscle) muscles during maximum voluntary and electrically-evoked isometric contractions. The electrochemical and mechanical components of the electromechanical delay during muscle contraction and relaxation were calculated off-line. Maximum strength was significantly lower in DM1 than in controls under both experimental conditions. All electrochemical and mechanical components were significantly longer in DM1 in both muscles. Measurement reliability was very high in both DM1 and controls. The high reliability of the measurements and the differences between DM1 patients and controls suggest that the EMG, mechanomyographic, and force combined approach could be utilized as a valid tool to assess the level of neuromuscular dysfunction in this pathology, and to follow the efficacy of pharmacological or non-pharmacological interventions.

  6. Clinical significance of isometric bite force versus electrical activity in temporal and masseter muscles

    DEFF Research Database (Denmark)

    Bakke, Merete; Michler, L; Han, K

    1989-01-01

    Bite force and activity in temporal and masseter muscles during biting and chewing were recorded in 19 control subjects and 23 subjects with symptoms and signs of functional disorders of the craniomandibular system. The entire group comprised 13 men and 29 women, 14-63 yr of age. Maximal unilater...... of mandibular elevator strength as a whole, but inadequate to disclose asymmetric conditions. During isometric contraction, relative strength of electromyographic activity fairly accurately imaged the output of mechanical activity....

  7. Within- and between-session reliability of the maximal voluntary knee extension torque and activation.

    Science.gov (United States)

    Park, Jihong; Hopkins, J Ty

    2013-01-01

    A ratio between the torque generated by maximal voluntary isometric contraction (MVIC) and exogenous electrical stimulus, central activation ratio (CAR), has been widely used to assess quadriceps function. To date, no data exist regarding between-session reliability of this measurement. Thirteen neurologically sound volunteers underwent three testing sessions (three trials per session) with 48 hours between-session. Subjects performed MVICs of the quadriceps with the knee locked at 90° flexion and the hip at 85°. Once the MVIC reached a plateau, an electrical stimulation from superimposed burst technique (SIB: 125 V with peak output current 450 mA) was manually delivered and transmitted directly to the quadriceps via stimulating electrodes. CAR was calculated by using the following equation: CAR = MVIC torque/MVIC + SIB torque. Intraclass correlation coefficients (ICC) were calculated within- (ICC((2,1))) and between-session (ICC((2,k))) for MVIC torques and CAR values. Our data show that quadriceps MVIC and CAR are very reliable both within- (ICC((2,1)) = 0.99 for MVIC; 0.94 for CAR) and between-measurement sessions (ICC((2,k)) = 0.92 for MVIC; 0.86 for CAR) in healthy young adults. For clinical research, more data of the patients with pathological conditions are required to ensure reproducibility of calculation of CAR.

  8. The use of isometric exercise as a means of evaluating the parasympathetic contribution to the tachycardia induced by dynamic exercise in normal man.

    Science.gov (United States)

    Gallo, L; Maciel, B C; Marin-Neto, J A; Martins, L E; Lima-Filho, E C; Manço, J C

    1988-07-01

    Fourteen normal subjects were submitted to isometric exercise (IE), dynamic exercise (DE) and a combination of the two (IE + DE). The main purpose of the present study was to use IE as a means of evaluating the mechanism of the heart rate (HR) increase induced by DE. To this end, the magnitude of the IE (handgrip) was standardized so as to cause an elevation of HR almost exclusively by vagal withdrawal: IE was performed using a dynamometer strain-gauge system with a linear response at 75% of maximum voluntary contraction (MVC) for 10 s, repeated at 1 min intervals. The change in HR evoked by IE under control conditions was compared with that evoked during DE, and during the corresponding recovery period. DE was performed by the legs, with the subject in the seated position for 4 min, at workloads of 55 and 105 watts, separated by a rest period. In the combined protocol, IE was performed at the beginning of DE, as well as at 1, 2 and 3 min during DE, and at 0, 1, 2, 3 and 5 min during recovery period. The following results were obtained: (1) IE associated with DE always induced smaller increase in heart rate than IE alone, and this effect was more marked at 105 than at 55 W; this finding suggested a workload-dependent vagal withdrawal at the very beginning of DE that was sustained until the end of effort.(ABSTRACT TRUNCATED AT 250 WORDS)

  9. On isometric extension problem between two unit spheres

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    In this paper we introduce the isometric extension problem of isometric mappings between two unit spheres. Some important results of the related problems are outlined and the recent progress is mentioned.

  10. On isometric extension problem between two unit spheres

    Institute of Scientific and Technical Information of China (English)

    Ding GuangGui

    2009-01-01

    In this paper we introduce the isometric extension problem of isometric mappings between two unit spheres.Some important results of the related problems are outlined and the recent progress is mentioned.

  11. Neural control of lengthening contractions.

    Science.gov (United States)

    Duchateau, Jacques; Enoka, Roger M

    2016-01-01

    A number of studies over the last few decades have established that the control strategy employed by the nervous system during lengthening (eccentric) differs from those used during shortening (concentric) and isometric contractions. The purpose of this review is to summarize current knowledge on the neural control of lengthening contractions. After a brief discussion of methodological issues that can confound the comparison between lengthening and shortening actions, the review provides evidence that untrained individuals are usually unable to fully activate their muscles during a maximal lengthening contraction and that motor unit activity during submaximal lengthening actions differs from that during shortening actions. Contrary to common knowledge, however, more recent studies have found that the recruitment order of motor units is similar during submaximal shortening and lengthening contractions, but that discharge rate is systematically lower during lengthening actions. Subsequently, the review examines the mechanisms responsible for the specific control of maximal and submaximal lengthening contractions as reported by recent studies on the modulation of cortical and spinal excitability. As similar modulation has been observed regardless of contraction intensity, it appears that spinal and corticospinal excitability are reduced during lengthening compared with shortening and isometric contractions. Nonetheless, the modulation observed during lengthening contractions is mainly attributable to inhibition at the spinal level.

  12. Short-interval intracortical inhibition is not affected by varying visual feedback in an isometric task in biceps brachii muscle

    Directory of Open Access Journals (Sweden)

    Timo eRantalainen

    2013-03-01

    Full Text Available Short-interval intracortical inhibition (SICI of the primary motor cortex (M1 appears to play a significant role in skill acquisition. Consequently, it is of interest to find out which factors cause modulation of SICI. Purpose: To establish if visual feedback and force requirements influence SICI. Methods: SICI was assessed from 10 healthy adults (5 males and 5 females aged between 21 and 35 years in three submaximal isometric elbow flexion torque levels (5%, 20% and 40% of maximal voluntary contraction [MVC] and with two tasks differing in terms of visual feedback. Single-pulse and paired-pulse motor evoked potentials (MEPs, supramaximal M-wave and background surface electromyogram (sEMG were recorded from the biceps brachii muscle. Results: Repeated measures MANOVA was used for statistical analyses. Background sEMG did not differ between tasks (F = 0.4, P = 0.68 nor was task × torque level interaction observed (F = 1.2, P = 0.32, whereas background sEMG increased with increasing torque levels (P = 0.001. SICI did not differ between tasks (F = 0.9, P = 0.43 and no task × torque level interaction was observed (F = 2.3, P = 0.08. However, less SICI was observed at 40% MVC compared to the 5% and 20% MVC torque levels (P = 0.01 to 0.001. Conclusion: SICI was not altered by performing the same task with differing visual feedback. However, SICI decreased with increasing submaximal torque providing further evidence that SICI is one mechanism of modulating cortical excitability and plays a role in force gradation.

  13. Study of CNC Grinding Machining Method About Isometric Polygon Profile

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The formed principle and CNC grinding machining method of isometric polygonal profile are studied deeply and systematically. Equation about section curve of isometric polygon profile is set up by means of geometric principle. With the use of differential geometry theory, the curve is proved to be with geometric feature of convex curve. It is referred to as Isometric Polygonal Curve (IPC), because that is a kind of convex curve on which the distance between any parallel tangent lines is equal. Isometric Poly...

  14. Peripheral Vascular Resistance Impairment during Isometric Physical Exercise in Normotensive Offspring of Hypertensive Parents

    Directory of Open Access Journals (Sweden)

    Natália Portela

    Full Text Available Abstract Background: A family history of hypertension is associated with vascular and autonomic abnormalities, as well as an impaired neurohemodynamic response to exercise. Objective: To test the hypothesis that normotensive individuals with a family history of hypertension present an impaired peripheral vascular resistance response to exercise. Methods: The study included 37 normotensive volunteers of both sexes who were sedentary, eutrophic, and nonsmokers, comprising 23 with (FH+; 24 ± 3 years and 14 without (FH-; 27 ± 5 years a family history of hypertension. Blood pressure, heart rate (DIXTAL®, forearm blood flow (Hokanson®, and peripheral vascular resistance were simultaneously measured for 3 minutes during rest and, subsequently, for 3 minutes during an isometric exercise at 30% of maximal voluntary contraction (Jamar®. Results: At rest, the FH+ and FH- groups present similar mean blood pressure (83 ± 7 versus 83 ± 5 mmHg, p = 0.96, heart rate (69 ± 8 bpm versus 66 ± 7 bpm, p = 0.18, forearm blood flow (3 ± 1 mL/min/100 mL versus 2.7 ± 1 mL/min/100 mL, p = 0.16, and peripheral vascular resistance (30 ± 9 units versus 34±9 units, p = 0.21, respectively. Both groups showed a significant and similar increase in mean blood pressure (∆ = 15 ± 7 mmHg versus 14 ± 7 mmHg, p = 0.86, heart rate (∆ = 12 ± 8 bpm versus 13 ± 7 bpm, p = 0.86, and forearm blood flow (∆ = 0.8 ± 1.2 mL/min/100 mL versus 1.4 ± 1.1 mL/min/100 mL, p = 0.25, respectively, during exercise. However, individuals in the FH+ group showed no reduction in peripheral vascular resistance during exercise, which was observed in the FH- group (∆ = -0.4 ± 8.6 units versus -7.2 ± 6.3 units, p = 0.03. Conclusion: Normotensive individuals with a family history of hypertension present an impaired peripheral vascular resistance response to exercise.

  15. Effects of effort and EMG levels on short-latency stretch reflex modulation after varying background muscle contractions.

    Science.gov (United States)

    Ogiso, K; McBride, J M; Finni, T; Komi, P V

    2005-08-01

    It is known that the short-latency stretch reflex (SLSR) is modulated by the background muscle activity when it is elicited at matched torque levels. This study was designed to examine the effects of muscle contraction types before a stretch perturbation on SLSR in the human soleus muscle (SOL) when SLSR was elicited at the same levels of effort and at matched electromyographic (EMG) activity levels. A mechanical stretch perturbation was applied to the calf muscles when the ankle joint reached a ninety degree tibio-tarsal joint angle after the muscles performed an isometric (pre-ISO), shortening (pre-SHO) and lengthening contraction (pre-LEN). Subjects were seated on an ankle ergometer chair and developed 0%, 10%, 20%, 30%, 40%, 50%, 60% and 70% ankle joint torque (AJT) of maximum voluntary isometric plantar flexion contraction at 80 degrees in pre-SHO, at 90 degrees in pre-ISO and at 100 degrees in pre-LEN. After that, isometric or dynamic contractions started, and the subjects were asked to maintain effort levels as, needed, to maintain the target torque levels until the end of the stretch. They relaxed their muscles fully after the stretch. This chain of processes was consecutively repeated 10 times. EMG signals obtained from SOL were averaged after they were high-pass filtered and full-wave rectified. Some major findings resulted: (1) there were no differences in SLSR area in the active muscle between pre-ISO and pre-SHO, whereas its waveform was steeper in pre-ISO than in pre-SHO. (2) SLSR p-to-p amplitude and waveform were larger and steeper in the active muscle than in the relaxed one in all conditions, whereas they were independent of the effort levels once the muscle was activated. This led to steady SLSR modulation in response to the background muscle contraction in the active muscle regardless of whether the SLSR was elicited at matched AJT or EMG activity levels. These findings suggest that SLSR is closely related to the muscle spindle sensitivity

  16. Electromagnetic field anomalies above an isometric depression

    Science.gov (United States)

    Golubtsova, N. S.

    1981-12-01

    The paper examines the three-dimensional simulation of the electromagnetic field above an isometric depression with conducting deposits. The model makes it possible to study the development of electromagnetic anomalies over such a depression and to make qualitative as well as quantitative assessments of the dependence of electromagnetic anomalies on field frequency, the dimensions of geoelectric inhomogeneities, and the specific resistance of the foundation of the depression. The present approach can be used in geoelectric and magnetotelluric studies of electromagnetic anomalies.

  17. The influence of athletic status on maximal and rapid isometric torque characteristics and postural balance performance in Division I female soccer athletes and non-athlete controls.

    Science.gov (United States)

    Palmer, Ty B; Hawkey, Matt J; Thiele, Ryan M; Conchola, Eric C; Adams, Bailey M; Akehi, Kazuma; Smith, Doug B; Thompson, Brennan J

    2015-07-01

    The purpose of this study was to examine the effectiveness of maximal and rapid isometric torque characteristics of the hip extensor muscles and postural balance performance to discriminate between female collegiate soccer athletes and non-athlete controls. Ten athletes (mean ± SE: age = 19·20 ± 0·36 year; mass = 62·23 ± 3·12 kg; height = 162·43 ± 1·70 cm) and 10 non-athletes (age = 20·30 ± 0·40 year; mass = 69·64 ± 3·20 kg; height = 163·22 ± 2·10 cm) performed two isometric maximal voluntary contractions (MVCs) of the hip extensor muscles. Peak torque (PT) and absolute and relative rate of torque development (RTD) at early (0-50 ms) and late (100-200 ms) phases of muscle contraction were examined during each MVC. Postural balance was assessed using a commercially designed balance testing device, which provides a measurement of static stability based on sway index (SI). Results indicated that absolute and relative RTD at 0-50 ms (RTD50 and RTD50norm) were greater (P = 0·007 and 0·026), and postural SI was lower (P = 0·022) in the athletes compared with the non-athletes. However, no differences (P = 0·375-0·709) were observed for PT nor absolute and relative RTD at 100-200 ms (RTD100-200 and RTD100-200norm). Significant relationships were also observed between RTD50 and RTD50norm and SI (r = -0·559 and -0·521; P = 0·010 and 0·019). These findings suggest that early rapid torque characteristics of the hip extensor muscles and postural balance performance may be sensitive and effective measures for discriminating between college-aged athletes and non-athletes. Coaches and practitioners may use these findings as performance evaluation tools to help in identifying athletes with both superior early rapid torque and balance performance abilities, which may possibly be an indicator of overall athletic potential.

  18. Effects of a compression garment on shoulder external rotation force outputs during isotonic contractions.

    Science.gov (United States)

    Tsuruike, Masaaki; Ellenbecker, Todd S

    2013-02-01

    The use of compression garments (CGs) has been advocated for performance enhancement and recovery in athletes. The effect of a CG on humeral rotation motor control has not been previously tested. The purpose of this study was to examine the isotonic contraction of external rotation (ER) of the glenohumeral joint at different force outputs to determine the effect of wearing a long sleeve CG on muscular performance. Twelve male college tennis players and 12 male college soccer players were tested for ER of the dominant shoulder during both concentric and eccentric isotonic contractions. The subjects performed 5 consecutive repetitions of both concentric and eccentric ER at 20-30% and 40-50% of maximum voluntary isometric contraction (MVIC) intensities. All subjects were tested with and without CG as well as with and without ongoing visual feedback information (OVFI). The order of CG wearing and the presence of OVFI were randomly assigned across all subjects. The results indicated a significant 3-way interaction between CG wearing and OVFI across 2 loads. Specifically, significantly different mean value of the completion time was found between OVFI and no-OVFI without CG wearing at 40-50% of MVIC, whereas no difference in the completion time was found with and without OVFI with CG wearing. Taken together, with CG wearing, athletes may have ER at 40-50% of MVIC more readily maintained by peripheral feedback without visuomotor control imposed on force outputs as compared without CG wearing.

  19. Do additional inputs change maximal voluntary motor unit firing rates after spinal cord injury?

    Science.gov (United States)

    Zijdewind, Inge; Gant, Katie; Bakels, Rob; Thomas, Christine K

    2012-01-01

    Motor unit firing frequencies are low during maximal voluntary contractions (MVCs) of human thenar muscles impaired by cervical spinal cord injury (SCI). This study aimed to examine whether thenar motor unit firing frequencies increase when driven by both maximal voluntary drive and other concurrent inputs compared with an MVC alone. Motor unit firing rates, force, and surface electromyographic activity (EMG) were compared across 2 contractions: (a) MVC alone and (b) MVC combined with another input (combination contraction). Other inputs (conditions) included vibration, heat, or cold applied to the anterior surface of the forearm, electrical stimulation delivered to the anterior surface of the middle finger, a muscle spasm, or a voluntary contraction of the contralateral thenar muscles against resistance. The maximal firing frequency (n = 68 units), force, and electromyographic activity (n = 92 contraction pairs) were all significantly higher during the combined contractions compared with MVCs alone. There was a 3-way interaction between contraction, condition, and subject for maximal motor unit firing rates, force, and EMG. Thus, combined contraction responses were different for conditions across subjects. Some conditions (eg, a muscle spasm) resulted in more effective and more frequent responses (increases in unit firing frequency, force, EMG in >50% contractions) than others. Recruitment of new units also occurred in combined contractions. Motoneurons are still responsive to additional afferent inputs from various sources when rate modulation from voluntary drive is limited by SCI. Individuals with SCI may be able to combine inputs to control functional tasks they cannot perform with voluntary drive alone.

  20. The influence of unilateral contraction of hand muscles on the contralateral corticomuscular coherence during bimanual motor tasks.

    Science.gov (United States)

    Zheng, Yang; Gao, Lin; Wang, Gang; Wang, Yingtuo; Yang, Zi; Wang, Xiuyue; Li, Tianqi; Dang, Chuan; Zhu, Ruohan; Wang, Jue

    2016-05-01

    The mechanisms behind how muscle contractions in one hand influence corticomuscular coherence in the opposite hand are still undetermined. Twenty-two subjects were recruited to finish bimanual and unimanual motor tasks. In the unimanual tasks, subjects performed precision grip using their right hand with visual feedback of exerted forces. The bimanual tasks involved simultaneous finger abduction of their left hand with visual feedback and precision grip of their right hand. They were divided into four conditions according to the two contraction levels of the left-hand muscles and whether visual feedback existed for the right hand. Measures of coherence and power spectrum were calculated from EEG and EMG data and statistically analyzed to identify changes in corticomuscular coupling and oscillatory activity. Results showed that compared with the unimanual task, a significant increase in the mean corticomuscular coherence of the right hand was found when left-hand muscles contracted at 5% of the maximal isometric voluntary contraction (MVC). No significant changes were found when the contraction level was 50% of the MVC. Furthermore, both the increase of muscle contraction levels and the elimination of visual feedback for right hand can significantly decrease the corticomuscular coupling in right hand during bimanual tasks. In summary, the involvement of moderate left-hand muscle contractions resulted in an increase tendency of corticomuscular coherence in right hand while strong left-hand muscle contractions eliminated it. We speculated that the perturbation of activities in one corticospinal tract resulted from the movement of the opposite hand can enhance the corticomuscular coupling when attention distraction is limited. Copyright © 2016 Elsevier Ltd. All rights reserved.

  1. On the effect of thermal agents in the response of the brachial biceps at different contraction levels.

    Science.gov (United States)

    Garcia, Larissa Martins; Soares, Alcimar Barbosa; Simieli, Camila; Boratino, Alessandra Vairo Peres; Guirro, Rinaldo Roberto de Jesus

    2014-12-01

    The objective of this study was to assess electromyographic features of the brachial biceps muscle after the application of cryotherapy and short-wave diathermy. Sixty healthy volunteers participated in the study and were equally divided into three groups: cryotherapy - application of ice packs for 30 min; short-wave diathermy for 20 min; and control. The thermal agents were applied to the anterior and posterior regions of the non-dominant arm. The electromyographic (EMG) signal from the brachial biceps was recorded before and after the application of thermal agents during flexion of the elbow joint at 25%, 50%, 75% of a maximum voluntary isometric contraction defined at least two days before the actual experiments (MVICbl). The volunteers also were asked to execute a free MVIC before and after the application of the thermal agents (MVIC free). A linear regression model with mixed effects (random and fixed) was used. Intra-group analysis showed a reduction in root mean square (RMS) at MVIC free, with no change in the median frequency of the EMG signal at any contraction level for the short-wave diathermy group. An increase on RMS values and a decrease on median frequencies were found after the application of cryotherapy for all contraction levels. The results imply that cryotherapy plays an important role on changing neuromuscular responses at various levels of muscle contraction. Therapists should be aware of that and carefully consider its use prior to activities in which neuromuscular precision is required.

  2. Quadriceps femoris electromyogram during concentric, isometric and eccentric phases of fatiguing dynamic knee extensions.

    Science.gov (United States)

    Pincivero, Danny M; Gandhi, Varsha; Timmons, Mark K; Coelho, Alan J

    2006-01-01

    The objective of this study was to examine the superficial quadriceps femoris (QF) muscle electromyogram (EMG) during fatiguing knee extensions. Thirty young adults were evaluated for their one-repetition maximum (1RM) during a seated, right-leg, inertial knee extension. All subjects then completed a single set of repeated knee extensions at 50% 1RM, to failure. Subjects performed a knee extension (concentric phase), held the weight with the knee extended for 2s (isometric phase), and lowered the weight in a controlled manner (eccentric phase). Raw EMG of the vastus medialis (VM), vastus lateralis (VL) and rectus femoris (RF) muscles were full-wave rectified, integrated and normalized to the 1RM EMG, for each respective phase and repetition. The EMG median frequency (f(med)) was computed during the isometric phase. An increase in QF muscle EMG was observed during the concentric phase across the exercise duration. VL EMG was greater than the VM and RF muscles during the isometric phase, in which no significant changes occurred in any of the muscles across the exercise duration. A significant decrease in EMG across the exercise duration was observed during the eccentric phase, with the VL EMG greater than the VM and RF muscles. A greater decrease in VL and RF muscle f(med) during the isometric phase, than the VM muscle, was observed with no gender differences. The findings demonstrated differential recruitment of the superficial QF muscle, depending on the contraction mode during dynamic knee extension exercise, where VL muscle dominance appears to manifest across the concentric-isometric-eccentric transition.

  3. Fourier and wavelet spectral analysis of EMG signals in isometric and dynamic maximal effort exercise.

    Science.gov (United States)

    Dantas, José L; Camata, Thiago V; Brunetto, Maria A C; Moraes, Antonio C; Abrão, Taufik; Altimari, Leandro R

    2010-01-01

    Frequency domain analyses of changes in electromyographic (EMG) signals over time are frequently used to assess muscle fatigue. Fourier based approaches are typically used in these analyses, yet Fourier analysis assumes signal stationarity, which is unlikely during dynamic contractions. Wavelet based methods of signal analysis do not assume stationarity and may be more appropriate for joint time-frequency domain analysis. The purpose of this study was to compare Short-Time Fourier Transform (STFT) and Continuous Wavelet Transform (CWT) in assessing muscle fatigue in isometric and dynamic exercise. The results of this study indicate that CWT and STFT analyses give similar fatigue estimates (slope of median frequency) in isometric and dynamic exercise (P>0.05). However, the results of the variance was lower for both types of exercise in CWT compared to STFT (P signal analysis using STFT. Thus, the stationarity assumption may not be the sole factor responsible for affecting the Fourier based estimates.

  4. Rethinking voluntary euthanasia.

    Science.gov (United States)

    Stoyles, Byron J; Costreie, Sorin

    2013-12-01

    Our goal in this article is to explicate the way, and the extent to which, euthanasia can be voluntary from both the perspective of the patient and the perspective of the health care providers involved in the patient's care. More significantly, we aim to challenge the way in which those engaged in ongoing philosophical debates regarding the morality of euthanasia draw distinctions between voluntary, involuntary, and nonvoluntary euthanasia on the grounds that drawing the distinctions in the traditional manner (1) fails to reflect what is important from the patient's perspective and (2) fails to reflect the significance of health care providers' interests, including their autonomy and integrity.

  5. Accuracy of predicting maximal quadriceps force from submaximal effort contractions after anterior cruciate ligament injury.

    Science.gov (United States)

    Farquhar, Sara J; Chmielewski, Terese L; Snyder-Mackler, Lynn

    2005-10-01

    Weakness and failure of voluntary activation of the quadriceps femoris muscles often occur after anterior cruciate ligament (ACL) rupture. Side-to-side strength comparisons are used as a measure of progress, and are inaccurate if the quadriceps has activation failure. Burst superimposition testing is commonly used to assess quadriceps strength and activation during a maximal volitional isometric contraction (MVIC), using the central activation ratio (CAR) calculation. A recently developed mathematical model predicts the MVIC from submaximal efforts. The purpose of this study was to compare the CAR calculation to the mathematical model. We hypothesized that the model would be a more accurate predictor of strength than the CAR calculation when voluntary activation failure is present. Data from the involved and uninvolved quadriceps muscles of 100 consecutive subjects with complete, isolated ACL rupture were retrospectively evaluated. Subjects who required multiple trials to produce an MVIC with full activation (true MVIC) were used to compare the CAR calculation, the mathematical model, and this true MVIC. Subjects unable to produce a true MVIC with multiple trials were used to compare the mathematical model to the CAR calculation. Results demonstrate that both methods reliably and accurately estimate the quadriceps weakness associated with ACL rupture. We recommend use of the CAR calculation to provide estimations of true quadriceps strength to facilitate clinical decisions about progress in rehabilitation after ACL rupture.

  6. Power spectral analysis of surface electromyography (EMG) at matched contraction levels of the first dorsal interosseous muscle in stroke survivors.

    Science.gov (United States)

    Li, Xiaoyan; Shin, Henry; Zhou, Ping; Niu, Xun; Liu, Jie; Rymer, William Zev

    2014-05-01

    The objective of this study was to help assess complex neural and muscular changes induced by stroke using power spectral analysis of surface electromyogram (EMG) signals. Fourteen stroke subjects participated in the study. They were instructed to perform isometric voluntary contractions by abducting the index finger. Surface EMG signals were collected from the paretic and contralateral first dorsal interosseous (FDI) muscles with forces ranging from 30% to 70% maximum voluntary contraction (MVC) of the paretic muscle. Power spectral analysis was performed to characterize features of the surface EMG in paretic and contralateral muscles at matched forces. A Linear Mixed Model was applied to identify the spectral changes in the hemiparetic muscle and to examine the relation between spectral parameters and contraction levels. Regression analysis was performed to examine the correlations between spectral characteristics and clinical features. Differences in power spectrum distribution patterns were observed in paretic muscles when compared with their contralateral pairs. Nine subjects showed increased mean power frequency (MPF) in the contralateral side (>15 Hz). No evident spectrum difference was observed in 3 subjects. Only 2 subjects had higher MPF in the paretic muscle than the contralateral muscle. Pooling all subjects' data, there was a significant reduction of MPF in the paretic muscle compared with the contralateral muscle (paretic: 168.7 ± 7.6 Hz, contralateral: 186.1 ± 8.7 Hz, mean ± standard error, F=36.56, ppower spectrum did not confirm a significant correlation between the MPF and contraction force in either hand (F=0.7, p>0.5). There was no correlation between spectrum difference and Fugl-Meyer or Chedoke scores, or ratio of paretic and contralateral MVC (p>0.2). There appears to be complex muscular and neural processes at work post stroke that may impact the surface EMG power spectrum. The majority of the tested stroke subjects had lower MPF in the

  7. Voluntary Public Unemployment Insurance

    DEFF Research Database (Denmark)

    O. Parsons, Donald; Tranæs, Torben; Bie Lilleør, Helene

    Denmark has drawn much attention for its active labor market policies, but is almost unique in offering a voluntary public unemployment insurance program requiring a significant premium payment. A safety net program – a less generous, means-tested social assistance plan – completes the system...

  8. Expression of the bilateral deficit during reflexively evoked contractions.

    Science.gov (United States)

    Khodiguian, N; Cornwell, A; Lares, E; DiCaprio, P A; Hawkins, S A

    2003-01-01

    During maximal contractions, the sum of forces exerted by homonymous muscles unilaterally is typically larger than the sum of forces exerted by the same muscles bilaterally. This phenomenon is known as the bilateral deficit (BLD), and it is suggested that this deficit is due to neural inhibition. It remains unclear, however, whether such inhibition is mediated by supraspinal mechanisms or by reflex pathways at the level of spinal cord. To further study the origin of likely neural influences, we tested for the presence of BLD under the condition of reflexive force generation. Force output and integrated electromyogram (iEMG) (quadriceps femoris) were measured in 17 male participants after initiation of the myotatic patellar reflex under unilateral and bilateral conditions. A significant BLD of 9.26 +/- 1.19 (P = 0.004) and 16.76 +/- 4.69% (P = 0.001) was found for force and iEMG, respectively. However, because similar findings were not evident during maximal isometric knee extensions, it is difficult to predict the contribution of a spinal mechanism to the BLD under the condition of maximal voluntary activation.

  9. Rigidity of contractions on Hilbert spaces

    CERN Document Server

    Eisner, Tanja

    2009-01-01

    We study the asymptotic behaviour of contractive operators and strongly continuous semigroups on separable Hilbert spaces using the notion of rigidity. In particular, we show that a "typical" contraction $T$ contains the unit circle times the identity operator in the strong limit set of its powers, while $T^{n_j}$ converges weakly to zero along a sequence $\\{n_j\\}$ with density one. The continuous analogue is presented for isometric ang unitary $C_0$-(semi)groups.

  10. Isometric Reflection Vectors and Characterizations of Hilbert Spaces

    Directory of Open Access Journals (Sweden)

    Donghai Ji

    2014-01-01

    Full Text Available A known characterization of Hilbert spaces via isometric reflection vectors is based on the following implication: if the set of isometric reflection vectors in the unit sphere SX of a Banach space X has nonempty interior in SX, then X is a Hilbert space. Applying a recent result based on well-known theorem of Kronecker from number theory, we improve this by substantial reduction of the set of isometric reflection vectors needed in the hypothesis.

  11. Cervical Resistance Training: Effects on Isometric and Dynamic Strength

    Science.gov (United States)

    2006-11-01

    skinfold thicknesses . San Diego, CA: Naval Health Research Center; 1984. Report No: 84–39. 3. Coakwell MR, Bloswick DS, Moser R Jr. High-risk head and...Strength, Dynamic Strength, and Neck Circumference Isometric strength values are displayed in Table I. For isometric strength-flexion, the 2 2 ANOVA...Also, a main effect was observed TABLE I. RESISTANCE TRAINING VS. CONTROL GROUPS: ISOMETRIC STRENGTH (LB). RT Group (n 5) C Group (n 5) FLX EXT

  12. Do Additional Inputs Change Maximal Voluntary Motor Unit Firing Rates After Spinal Cord Injury?

    NARCIS (Netherlands)

    Zijdewind, Inge; Gant, Katie; Bakels, Rob; Thomas, Christine K.

    Background. Motor unit firing frequencies are low during maximal voluntary contractions (MVCs) of human thenar muscles impaired by cervical spinal cord injury (SCI). Objective. This study aimed to examine whether thenar motor unit firing frequencies increase when driven by both maximal voluntary

  13. Do Additional Inputs Change Maximal Voluntary Motor Unit Firing Rates After Spinal Cord Injury?

    NARCIS (Netherlands)

    Zijdewind, Inge; Gant, Katie; Bakels, Rob; Thomas, Christine K.

    2012-01-01

    Background. Motor unit firing frequencies are low during maximal voluntary contractions (MVCs) of human thenar muscles impaired by cervical spinal cord injury (SCI). Objective. This study aimed to examine whether thenar motor unit firing frequencies increase when driven by both maximal voluntary dri

  14. Relations Between Lower Body Isometric Muscle Force Characteristics and Start Performance in Elite Male Sprint Swimmers

    Directory of Open Access Journals (Sweden)

    Igor Beretić

    2013-12-01

    Full Text Available The aim of the present study was twofold. The first aim was to examine the influence of absolute and relative lower body muscle force on kinematic component which determine the start performance. The second aim was to create multiregressional model which could use as a tool for swimming coaches with the purpose to start performance control and improvement. Twenty seven high-level trained male competitive swimmers all members of the Serbian National Youth and Senior Swimming Team (Age = 21.1 ± 4.3 yrs., Height = 1. 89 ± 0.10 m, Weight = 81.6 ± 8.4 kg, 50m freestyle - long course = 24.36 ± 0.86 s performed two trials of standing leg extensors isometric muscle force testing and three swimming start trials corresponding to 10m distance. The average start time significantly correlated with variables of leg extensors maximum voluntary force (Fmax, r = -0.559, p = 0.002, leg extensors relative muscle voluntary force (Frel, r = -0.727, p < 0.001, leg extensors specific rate of force development (RFD50%, r = -0.338, p = 0.047 and leg extensors relative value of specific rate of force development (RFD50%rel, r = -0.402, p = 0.040. Regression equation for t10m prediction was defined by following variables: maximum voluntary isometric force of leg extensors muscles at absolute and relative level (Fmax and Frel, as well as a specific rate of force development of the same muscle groups (RFD50% and RFD50%rel at absolute and relative level too with 74.4% of explained variance. Contractile abilities indicators of the leg extensors muscles included consideration: Fmax, RFD50%, Frel and RFD50%rel showed significant correlation with swimming start times on 10m. Additionally, the results suggest that swimmers, who possess greater isometric maximum force and specific rate of force development at absolute and relative levels, tend to be able to swim faster on initial 10m swim start perforamnce.

  15. Calcium transients in skeletal muscle fibres under isometric conditions and during and after a quick stretch.

    Science.gov (United States)

    Haugen, P

    1991-12-01

    The transient change in the sarcoplasmic concentration of Ca2+ was measured in intact fibres isolated from the anterior tibial muscle of the frog Litoria moorei. The fibres had been injected with the calcium-sensitive dye arsenazo III and the change of the calcium concentration was calculated from the changes in light absorbance at 570, 600 and 720 nm wavelengths. Absorbance and force were measured under three different conditions: (1) during a normal isometric twitch, (2) when a quick ramp-and-hold stretch had been applied to the fibre during onset of the contraction, and (3) when the fibre was allowed to contract isometrically at a length corresponding to the final length of the stretch. A method was devised to neutralize most of the movement artefacts encountered in such measurements. While the quick stretch caused substantial increase in the level and the duration of the contractile force such as originally described in whole muscle by A. V. Hill, the calcium transients appeared basically unaffected. It thus seems that the mechanism behind the phenomenon of the force enhancement lies at a step in the excitation-contraction coupling subsequent to the calcium release. From the present results, however, it is not clear whether the phenomenon is caused by an increase in the level of activation of the calcium-dependent regulatory system, or whether it is to be found in the acto-myosin interaction itself. The latter alternative would be consistent with the stiffness measurements published earlier.

  16. Influence of Isometric Exercise Training on Quadriceps Muscle Architecture and Strength in Obese Subjects with Knee Osteoarthritis

    Directory of Open Access Journals (Sweden)

    Waleed S Mahmoud

    2017-03-01

    Full Text Available Obese individuals have reduced quadriceps muscle strength relative to body mass that may increase the rate of progression of knee osteoarthritis (OA. The purpose of this study was to evaluate the effects of isometric exercise training on quadriceps muscle architecture and strength in obese subjects with knee osteoarthritis. Methods: Fortyfour obese male subjects aged 40–65 years diagnosed with knee osteoarthritis were randomly assigned into group A (n=32 and group B (n=12. Group A subjects performed a 12-week isometric exercise program. Group B subjects did not participate in any exercise program and maintained their ordinary activities for the same period. Both groups received the same conventional physical therapy program including hot packs and therapeutic ultrasonic. Muscle thickness, pennation angles and fascicle length of the vastus lateralis (VL muscle of the affected knee were measured at rest by B-mode ultrasonography. Maximal voluntary isometric knee extension torque (MVIC of the affected knee was measured using an isokinetic dynamometer. Knee pain and function were evaluated using visual analogue pain scale (VAS and Western Ontario and McMaster Universities Arthritis Index (WOMAC. All variables were evaluated before and the end of the intervention period for both groups. Results: at the end of the program, group A subjects showed significant improvements compared with group B subjects regarding MVIC and muscle architecture parameters (p<0.05. Also, there was significant improvement in post-test VAS and WOMAC scores in group A subjects compared to group B subjects (p<0.05. Conclusion: A 12-week quadriceps isometric training program improves knee pain and quadriceps muscle strength and architecture in obese subjects with knee OA. These results indicate that isometric training should be regarded as a proper exercise intervention for obese patients with knee OA.

  17. Standardized voluntary force measurement in a lower extremity rehabilitation robot

    Directory of Open Access Journals (Sweden)

    Bolliger Marc

    2008-10-01

    Full Text Available Abstract Background Isometric force measurements in the lower extremity are widely used in rehabilitation of subjects with neurological movement disorders (NMD because walking ability has been shown to be related to muscle strength. Therefore muscle strength measurements can be used to monitor and control the effects of training programs. A new method to assess isometric muscle force was implemented in the driven gait orthosis (DGO Lokomat. To evaluate the capabilities of this new measurement method, inter- and intra-rater reliability were assessed. Methods Reliability was assessed in subjects with and without NMD. Subjects were tested twice on the same day by two different therapists to test inter-rater reliability and on two separate days by the same therapist to test intra-rater reliability. Results Results showed fair to good reliability for the new measurement method to assess isometric muscle force of lower extremities. In subjects without NMD, intraclass correlation coefficients (ICC for inter-rater reliability ranged from 0.72 to 0.97 and intra-rater reliability from 0.71 to 0.90. In subjects with NMD, ICC ranged from 0.66 to 0.97 for inter-rater and from 0.50 to 0.96 for intra-rater reliability. Conclusion Inter- and intra- rater reliability of an assessment method for measuring maximal voluntary isometric muscle force of lower extremities was demonstrated. We suggest that this method is a valuable tool for documentation and controlling of the rehabilitation process in patients using a DGO.

  18. Reduced muscle lengthening during eccentric contractions as a mechanism underpinning the repeated-bout effect.

    Science.gov (United States)

    Lau, Wing Yin; Blazevich, Anthony J; Newton, Michael J; Wu, Sam Shi Xuan; Nosaka, Kazunori

    2015-05-15

    This study investigated biceps brachii distal myotendinous junction (MTJ) displacement during maximal eccentric elbow flexor contractions to test the hypothesis that muscle length change would be smaller (less MTJ displacement) during the second than the first exercise bout. Ten untrained men performed two eccentric exercise bouts (ECC1 and ECC2) with the same arm consisting of 10 sets of six maximal isokinetic (60°/s) eccentric elbow flexor contractions separated by 4 wk. Biceps brachii distal MTJ displacement was assessed using B-mode ultrasonography, and changes in the displacement (muscle length change) from the start to the end of each contraction during each set and over 10 sets were compared between bouts by two-way repeated-measures ANOVA. Several indirect muscle damage markers were also measured and compared between bouts by two-way repeated-measures ANOVA. The magnitude of MTJ displacement (average of six contractions) increased from set 1 (8.2 ± 4.7 mm) to set 10 (16.4 ± 4.7 mm) during ECC1 (P < 0.05), but no significant changes over sets were evident during ECC2 (set 1: 8.5 ± 4.0 mm; set 10: 9.3 ± 3.1 mm). Changes in maximal voluntary isometric contraction strength, range of motion, muscle thickness, ultrasound echo intensity, serum creatine kinase activity, and muscle soreness (visual analog scale) were smaller (P < 0.05) following ECC2 than ECC1, showing less damage in the repeated bout. These results indicate that the magnitude of muscle lengthening was less during the second than the first eccentric exercise bout, which appears to be a mechanism underpinning the repeated-bout effect. Copyright © 2015 the American Physiological Society.

  19. Motor unit rate coding is severely impaired during forceful and fast muscular contractions in individuals post stroke.

    Science.gov (United States)

    Chou, Li-Wei; Palmer, Jacqueline A; Binder-Macleod, Stuart; Knight, Christopher A

    2013-06-01

    Information regarding how motor units are controlled to produce forces in individuals with stroke and the mechanisms behind muscle weakness and movement slowness can potentially inform rehabilitation strategies. The purpose of this study was to describe the rate coding mechanism in individuals poststroke during both constant (n = 8) and rapid (n = 4) force production tasks. Isometric ankle dorsiflexion force, motor unit action potentials, and surface electromyography were recorded from the paretic and nonparetic tibialis anterior. In the paretic limb, strength was 38% less and the rate of force development was 63% slower. Linear regression was used to describe and compare the relationships between motor unit and electromyogram (EMG) measures and force. During constant force contractions up to 80% maximal voluntary contraction (MVC), rate coding was compressed and discharge rates were lower in the paretic limb. During rapid muscle contractions up to 90% MVC, the first interspike interval was prolonged and the rate of EMG rise was less in the paretic limb. Future rehabilitation strategies for individuals with stroke could focus on regaining these specific aspects of motor unit rate coding and neuromuscular activation.

  20. On the generalized resolvents of isometric operators with gaps

    CERN Document Server

    Zagorodnyuk, Sergey M

    2012-01-01

    In this paper we obtain some slight correction and generalization of the results of Ryabtseva on the generalized resolvents for isometric operators with a gap in their spectrum. Also, analogs of some McKelvey's results and a short proof of Inin's formula for the generalized resolvents of an isometric operator are obtained.

  1. Supplementary motor area and other cortical areas in organization of voluntary movements in man

    DEFF Research Database (Denmark)

    Roland, P E; Larsen, B; Lassen, N A

    1980-01-01

    in the contralateral primary motor area. In addition, there were more modest rCBF increases in the contralateral sensory hand area, the convexity part of the premotor area, and bilaterally in the inferior frontal region. 4. Repetitive fast flexions of the same finger or a sustained isometric muscular contraction raise...

  2. The influence of familiarization sessions on the stability of ramp and ballistic isometric torque in older adults.

    Science.gov (United States)

    Wallerstein, Lilian F; Barroso, Renato; Tricoli, Valmor; Mello, Marco T; Ugrinowitsch, Carlos

    2010-10-01

    Ramp isometric contractions determine peak torque (PT) and neuromuscular activation (NA), and ballistic contractions can be used to evaluate rate of torque development (RTD) and electrical mechanical delay (EMD). The purposes of this study were to assess the number of sessions required to stabilize ramp and ballistic PT and to compare PT and NA between contractions in older adults. Thirty-five older men and women (age 63.7 ± 3.7 yr, body mass 64.3 ± 10.7 kg, height 159.2 ± 6.6 cm) performed 4 sessions of unilateral ramp and ballistic isometric knee extension, 48 hr apart. PT significantly increased (main time effect p < .05) from the first to the third session, with no further improvements thereafter. There was a trend toward higher PT in ballistic than in ramp contractions. No difference between contraction types on EMG values was observed. Therefore, the authors suggest that 3 familiarization sessions be performed to correctly assess PT. In addition, PT, NA, RTD, and EMD can be assessed with ballistic contraction in older adults.

  3. Voluntary agreements as instruments for international environmental policy; Frivillege avtaler som internasjonalt miljoepolitisk verkemiddel

    Energy Technology Data Exchange (ETDEWEB)

    Torvanger, Asbjoern

    1997-12-31

    According to this report, voluntary agreements have a potential as instruments for environmental policy. Such agreements can be national or international. Through an international voluntary agreement the authorities in one country may make contracts with factories in another country about emission reductions against some kind of compensation. A supranational organisation of voluntary agreements may ensure equal environmental political conditions for factories in different countries and be a useful means for the regulation of environmental problems of regional or global extent. It is most realistic to establish a supranational system of voluntary agreements in a group of countries that have already institutionalized their relations, such as the European Union. 14 refs., 1 table

  4. Ultrasound evaluation of muscle thickness changes in the external oblique, internal oblique, and transversus abdominis muscles considering the influence of posture and muscle contraction.

    Science.gov (United States)

    Sugaya, Tomoaki; Abe, Yota; Sakamoto, Masaaki

    2014-09-01

    [Purpose] The aim of this study was to investigate muscle thickness changes in the external oblique (EO), internal oblique (IO), and transversus abdominis (TrA) muscles between the neutral position and trunk rotation, under a state of rest without voluntary contractions, and isometric contractions to both sides with resistance of 50% of the maximum trunk rotation strength. [Subjects] The subjects of this study were 21 healthy young men. [Methods] Muscle thickness changes in the EO, IO, and TrA in each position and state were evaluated by ultrasound. The range of motion at maximum trunk rotation and the maximum strength of trunk rotation were measured using a hand-held dynamometer. [Results] In the neutral position and at 50% trunk rotation to the right side, the thicknesses of the IO and TrA significantly increased with resistance. In both states, the thicknesses of the IO and TrA significantly increased at 50% trunk rotation to the right side. [Conclusion] The muscular contractions of the IO and TrA were stronger during ipsilateral rotation than in the neutral position and with resistance than at rest. Moreover, the muscular contraction was strongest in the resistive state during ipsilateral rotation.

  5. Homogeneity of fascicle architecture following repeated contractions in the human gastrocnemius medialis.

    Science.gov (United States)

    Thomas, Neil M; Dewhurst, Susan; Bampouras, Theodoros M

    2015-12-01

    This investigation sought to determine the effects of fatigue on fascicle architecture across the length of the human gastrocnemius medialis (GM). With institutional ethical approval, fifteen healthy males performed repeated isometric plantar flexion maximal voluntary contractions (MVC) until peak force fell 30% below baseline. Brightness-mode ultrasound was used to determine fascicle length and pennation angle at rest and during MVC prior to and following the fatiguing contractions. The results show a significant increase in fascicle length during MVC in the distal (2.8 mm, 8.1%) middle, (4.9 mm, 14.1%), and proximal (5.2 mm, 14.7%) regions post-fatigue compared to pre-fatigue (p MVC in the distal (3.3°, 8.8%), middle (3.9°, 9.4%), and proximal (2.9°, 6.9%) regions post-fatigue compared to pre-fatigue (p < 0.05). These changes, however, were not region specific. These are the first results to show that fascicle shortening within the GM remains homogeneous following fatigue, suggesting that the fascicles were fatigued in a similar pattern throughout the muscle. The significant reduction of fascicle shortening may reflect an additional strategy to maintain an optimal force output in fatigued conditions, although future work is needed to confirm this notion.

  6. Severe COPD Alters Muscle Fiber Conduction Velocity During Knee Extensors Fatiguing Contraction.

    Science.gov (United States)

    Boccia, Gennaro; Coratella, Giuseppe; Dardanello, Davide; Rinaldo, Nicoletta; Lanza, Massimo; Schena, Federico; Rainoldi, Alberto

    2016-10-01

    The aim of this study was to assess the changes in muscle fiber conduction velocity (CV), as a sign of fatigue during knee extensor contraction in patients with chronic obstructive pulmonary disease (COPD) as compared with healthy controls. Eleven male patients (5 with severe and 6 with moderate COPD; age 67 ± 5 years) and 11 age-matched healthy male controls (age 65 ± 4 years) volunteered for the study. CV was obtained by multichannel surface electromyography (EMG) from the vastus lateralis (VL) and medialis (VM) of the quadriceps muscle during isometric, 30-second duration knee extension at 70% of maximal voluntary contraction. The decline in CV in both the VL and VM was steeper in the severe COPD patients than in healthy controls (for VL: severe COPD vs. controls -0.45 ± 0.07%/s; p < 0.001, and for VM: severe COPD vs. controls -0.54 ± 0.09%/s, p < 0.001). No difference in CV decline was found between the moderate COPD patients and the healthy controls. These findings suggest that severe COPD may impair muscle functions, leading to greater muscular fatigue, as expressed by CV changes. The results may be due to a greater involvement of anaerobic metabolism and a shift towards fatigable type II fibers in the muscle composition of the severe COPD patients.

  7. Bed rest attenuates sympathetic and pressor responses to isometric exercise in antigravity leg muscles in humans.

    Science.gov (United States)

    Kamiya, Atsunori; Michikami, Daisaku; Shiozawa, Tomoki; Iwase, Satoshi; Hayano, Junichiro; Kawada, Toru; Sunagawa, Kenji; Mano, Tadaaki

    2004-05-01

    Although spaceflight and bed rest are known to cause muscular atrophy in the antigravity muscles of the legs, the changes in sympathetic and cardiovascular responses to exercises using the atrophied muscles remain unknown. We hypothesized that bed rest would augment sympathetic responses to isometric exercise using antigravity leg muscles in humans. Ten healthy male volunteers were subjected to 14-day 6 degrees head-down bed rest. Before and after bed rest, they performed isometric exercises using leg (plantar flexion) and forearm (handgrip) muscles, followed by 2-min postexercise muscle ischemia (PEMI) that continues to stimulate the muscle metaboreflex. These exercises were sustained to fatigue. We measured muscle sympathetic nerve activity (MSNA) in the contralateral resting leg by microneurography. In both pre- and post-bed-rest exercise tests, exercise intensities were set at 30 and 70% of the maximum voluntary force measured before bed rest. Bed rest attenuated the increase in MSNA in response to fatiguing plantar flexion by approximately 70% at both exercise intensities (both P antigravity leg muscles.

  8. Contractively complemented subspaces of pre-symmetric spaces

    CERN Document Server

    Neal, Matthew

    2008-01-01

    In 1965, Ron Douglas proved that if $X$ is a closed subspace of an $L^1$-space and $X$ is isometric to another $L^1$-space, then $X$ is the range of a contractive projection on the containing $L^1$-space. In 1977 Arazy-Friedman showed that if a subspace $X$ of $C_1$ is isometric to another $C_1$-space (possibly finite dimensional), then there is a contractive projection of $C_1$ onto $X$. In 1993 Kirchberg proved that if a subspace $X$ of the predual of a von Neumann algebra $M$ is isometric to the predual of another von Neumann algebra, then there is a contractive projection of the predual of $M$ onto $X$. We widen significantly the scope of these results by showing that if a subspace $X$ of the predual of a $JBW^*$-triple $A$ is isometric to the predual of another $JBW^*$-triple $B$, then there is a contractive projection on the predual of $A$ with range $X$, as long as $B$ does not have a direct summand which is isometric to a space of the form $L^\\infty(\\Omega,H)$, where $H$ is a Hilbert space of dimensio...

  9. Prediction of isometric motor tasks and effort levels based on high-density EMG in patients with incomplete spinal cord injury

    Science.gov (United States)

    Jordanić, Mislav; Rojas-Martínez, Mónica; Mañanas, Miguel Angel; Francesc Alonso, Joan

    2016-08-01

    Objective. The development of modern assistive and rehabilitation devices requires reliable and easy-to-use methods to extract neural information for control of devices. Group-specific pattern recognition identifiers are influenced by inter-subject variability. Based on high-density EMG (HD-EMG) maps, our research group has already shown that inter-subject muscle activation patterns exist in a population of healthy subjects. The aim of this paper is to analyze muscle activation patterns associated with four tasks (flexion/extension of the elbow, and supination/pronation of the forearm) at three different effort levels in a group of patients with incomplete Spinal Cord Injury (iSCI). Approach. Muscle activation patterns were evaluated by the automatic identification of these four isometric tasks along with the identification of levels of voluntary contractions. Two types of classifiers were considered in the identification: linear discriminant analysis and support vector machine. Main results. Results show that performance of classification increases when combining features extracted from intensity and spatial information of HD-EMG maps (accuracy = 97.5%). Moreover, when compared to a population with injuries at different levels, a lower variability between activation maps was obtained within a group of patients with similar injury suggesting stronger task-specific and effort-level-specific co-activation patterns, which enable better prediction results. Significance. Despite the challenge of identifying both the four tasks and the three effort levels in patients with iSCI, promising results were obtained which support the use of HD-EMG features for providing useful information regarding motion and force intention.

  10. Maximal isometric strength of the cervical musculature in 100 healthy volunteers

    DEFF Research Database (Denmark)

    Jordan, A; Mehlsen, J; Bülow, P M

    1999-01-01

    A descriptive study involving maximal isometric strength measurements of the cervical musculature.......A descriptive study involving maximal isometric strength measurements of the cervical musculature....

  11. ANALYSIS OF INTENTION TO CONTINUE SERVICES AMONG RECRUITED VOLUNTARY SOLDIERS

    Directory of Open Access Journals (Sweden)

    Kuo-Wei Lin

    2012-01-01

    Full Text Available In order to attract more promising young people to join the military and enhance combat capability, Taiwan’s Department of Defense is transforming the nation’s military service system from a draft system, which has been in effect for more than sixty years, to an all-volunteer military force system. The government hopes that the new system not only can recruit promising voluntary soldiers, but that they also continue their military service after the contract expires in order to ensure stability in recruitment sources. This study explores the intention of voluntary soldiers to continue their military service. This study’s questionnaire encompasses five dimensions: Participation motivation, organization commitment, career planning, personality traits and departure tendency. The questionnaires were issued to 350 voluntary soldiers to explore if they intend to continue their service after their contract expires, with a total of 314 effective questionnaires that were recovered and analyzed. The results find that about half of the voluntary soldiers indicate that they do not plan on staying and continuing their service after contract expiration, which will result in understaffing in the military. In order to stabilize the prescribed number of soldiers, the existing recruiting policy and military management system should be re-adjusted.

  12. EVALUATION OF BILATERAL ASYMMETRY OF CONCENTRIC AND ISOMETRIC KNEE EXTENSION- FLEXION STRENGTH IN MALE FENCERS

    Directory of Open Access Journals (Sweden)

    Yusuf ŞAHİN

    2016-08-01

    Full Text Available Fencing is an Olympic combat sport in which two athletes fight through their weapons such as epee, foil and sabre. During the competition, athletes hold the weapon with their dominant arm and stay in defense or attack positions by stepping forward, behind or right/left with dominant leg in front. Depending upon chronic applications structural and/or functional asymmetries between dominant and non-dominant extremities are shown with cross-sectional area and performance measurements. The aim of this study was to compare dominant and non-dominant knee flexion-extension strength values of epee fencers. The study was conducted on nine athletes whose age average was 18,1± 1,4 years. Strength measurements of dominant and non-dominant knees were carried out by using concentric and isometric modules of isokinetic dynamometers (Cybex II. Angular velocities were determined as 240- 180- 120- 60⁰/s and 5 repetitions were done at each velocity. The highest value was accepted as the maximal strength. Isometric contraction was carried out at 60⁰ knee joint angle (when full extension is accepted as 0⁰ during 5 seconds. Ratios of Hamstrings/ Quadriceps were calculated with ratios of strength of flexor and extensor muscles at every angular velocity. Results were analyzed with independent sample t-test and data were given as ±SEM. Strength values of dominant leg were found statistically significantly higher than those of non-dominant leg in 240⁰/s, 180⁰/s, 120⁰/s extension movement and isometric contraction (p<0.05. When examining flexion movement, it was recorded that strength of dominant leg was higher than that of non-dominant leg at 240⁰/s velocity and during isometric contraction (p<0.05. There was no meaningful difference in H/ Q ratios between dominant and non dominant legs (p<0.05. These findings suggest that, there is an important difference in terms of dominant and non-dominant leg strength in high level fencers, though ratio of H/Q is

  13. Sweating responses to isometric hand-grip exercise and forearm muscle metaboreflex in prepubertal children and elderly.

    Science.gov (United States)

    Amano, Tatsuro; Kai, Seiko; Nakajima, Michi; Ichinose-Kuwahara, Tomoko; Gerrett, Nicola; Kondo, Narihiko; Inoue, Yoshimitsu

    2017-02-01

    What is the central question of this study? Non-thermal factors (e.g. muscle metaboreflex) contribute to the sweating response during exercise. Although it is well recognized that the sweating responses caused by core temperature elevation in prepubertal children and the elderly are attenuated compared with young adults, it is unknown whether non-thermal sweating is also attenuated in these populations. What is the main finding and its importance? The non-thermal sweating response during isometric hand-grip exercise and isolated muscle metaboreflex were attenuated in prepubertal children compared with young adults in a non-uniform manner over the body, but only during the muscle metaboreflex in the elderly. This may explain the maturation- and ageing-related decline of sweating during exercise. The purpose of the present study was to investigate sweating responses to isometric hand-grip (IH) exercise and muscle metaboreflex in prepubertal children and the elderly. In hot conditions (ambient temperature, 35°C; relative humidity, 45%), 13 healthy young adults, 10 prepubertal children and 10 elderly subjects (aged 20.4 ± 1.2, 11.4 ± 0.5 and 63.5 ± 3.1 years, respectively) repeated a three hand-grip exercise protocol that consisted of 1 min IH exercise at 15, 30 or 45% of maximal voluntary contraction (MVC) followed by 2 min postexercise forearm occlusion. Local sweat rates (SRs) on the forehead, chest, forearm, thigh and palm were continuously measured (ventilated capsule method). The forehead SR in prepubertal children during IH exercise at 45% MVC was significantly lower than that of young adults (0.26 ± 0.22 and 0.08 ± 0.15 mg cm(-2)  min(-1) for young adults and children, respectively; P elderly at any exercise intensities. The SR on the chest (0.22 ± 0.22 and -0.01 ± 0.05 mg cm(-2)  min(-1) for young adults and children, respectively), forearm (0.14 ± 0.12 and 0.03 ± 0.04 mg cm(-2)  min(-1) ) and thigh (0.13 ± 0.10 and 0

  14. Isometric and eccentric force generation assessment of skeletal muscles isolated from murine models of muscular dystrophies.

    Science.gov (United States)

    Moorwood, Catherine; Liu, Min; Tian, Zuozhen; Barton, Elisabeth R

    2013-01-31

    Critical to the evaluation of potential therapeutics for muscular disease are sensitive and reproducible physiological assessments of muscle function. Because many pre-clinical trials rely on mouse models for these diseases, isolated muscle function has become one of the standards for Go/NoGo decisions in moving drug candidates forward into patients. We will demonstrate the preparation of the extensor digitorum longus (EDL) and diaphragm muscles for functional testing, which are the predominant muscles utilized for these studies. The EDL muscle geometry is ideal for isolated muscle preparations, with two easily accessible tendons, and a small size that can be supported by superfusion in a bath. The diaphragm exhibits profound progressive pathology in dystrophic animals, and can serve as a platform for evaluating many potential therapies countering fibrosis, and promoting myofiber stability. Protocols for routine testing, including isometric and eccentric contractions, will be shown. Isometric force provides assessment of strength, and eccentric contractions help to evaluate sarcolemma stability, which is disrupted in many types of muscular dystrophies. Comparisons of the expected results between muscles from wildtype and dystrophic muscles will also be provided. These measures can complement morphological and biochemical measurements of tissue homeostasis, as well as whole animal assessments of muscle function.

  15. Notes on affine isometric actions of discrete groups

    CERN Document Server

    Neretin, Yu A

    1997-01-01

    Consider a lattice $\\Gamma$ in a group $G = SL_2(\\R), SO(1,n), SU(1,n)$, $SL_2(\\Q_p)$. We discuss actions of $\\Gamma$ by affine isometric transformations of Hilbert spaces. We show that for irreducible affine isometric action of $G$ its restriction to $\\Gamma$ is irreducible. We prove the existence of canonical irreducible affine isometric actions of $\\Gamma$ associated to actions of $\\Gamma$ on $\\R$- trees. Using such actions we construct irreducible representations of semigroup of probabilistic measures on diffeomorphisms of Riemann surfaces enumerated by the points of Thurston compactification of Teichmüller (Teichmuller) space.

  16. 41 CFR 105-68.640 - May a settlement include a voluntary exclusion?

    Science.gov (United States)

    2010-07-01

    ... 41 Public Contracts and Property Management 3 2010-07-01 2010-07-01 false May a settlement include a voluntary exclusion? 105-68.640 Section 105-68.640 Public Contracts and Property Management Federal Property Management Regulations System (Continued) GENERAL SERVICES ADMINISTRATION...

  17. Voluntary Simplicity: A Lifestyle Option.

    Science.gov (United States)

    Pestle, Ruth E.

    This guide provides practical ideas for incorporating the concept of voluntary simplicity into home economics classes. Discussed in the first chapter are the need to study voluntary simplicity, its potential contributions to home economics, and techniques and a questionnaire for measuring student attitudes toward the concept. The remaining…

  18. Operant Variability and Voluntary Action

    Science.gov (United States)

    Neuringer, Allen; Jensen, Greg

    2010-01-01

    A behavior-based theory identified 2 characteristics of voluntary acts. The first, extensively explored in operant-conditioning experiments, is that voluntary responses produce the reinforcers that control them. This bidirectional relationship--in which reinforcer depends on response and response on reinforcer--demonstrates the functional nature…

  19. Resposta da frequência cardíaca durante o exercício isométrico de pacientes submetidos à reabilitação cardíaca fase III Heart rate responses during isometric exercises in patients undergoing a phase III cardiac rehabilitation program

    Directory of Open Access Journals (Sweden)

    Poliana H. Leite

    2010-10-01

    Full Text Available CONTEXTUALIZAÇÃO: A magnitude das respostas cardiovasculares depende dos componentes estático e dinâmico bem como da duração e intensidade da contração realizada. OBJETIVO: Avaliar as respostas da frequência cardíaca (FC frente a diferentes percentuais de contração isométrica em 12 pacientes (63±11,6 anos; média±dp com doença da artéria coronária e/ou fatores de risco para ela, participantes de um programa de reabilitação cardíaca fase III. MÉTODOS: A variação da frequência cardíaca (ΔFC foi avaliada durante as contrações voluntárias máximas (CVM; 5" e 10" de duração e submáximas (CVSM; 30 e 60% da CVM-5, até exaustão muscular de preensão palmar, utilizando-se um dinamômetro (hand grip. Adicionalmente, o RMSSD dos iR-R em ms (índice representante da modulação vagal cardíaca foi calculado em repouso (pré-contração nos últimos 30 segundos da CVSM e na recuperação (pós-contração. RESULTADOS: A ΔFC apresentou maiores valores em CVM-10 vs CVM-5 (17±5,5 vs 12±4,2 bpm, p0,05. RMSSD de repouso reduziu-se (pBACKGROUND: The magnitude of cardiovascular responses is dependent on the static and dynamic components as well as the duration and intensity of the contraction performed. OBJECTIVE: To evaluate the heart rate responses to different percentages of isometric contractions in 12 patients (63±11.6 years with coronary artery disease and/or risk factors for coronary artery disease that were participating in a phase III cardiac rehabilitation program. METHODS: Heart rate variation (ΔHR was evaluated during maximum (MVC, five and ten seconds in duration and submaximal (SMVC, 30 and 60% of MVC-5, until muscle exhaustion voluntary contraction, using a handgrip dynamometer. Additionally, the representative index of cardiac vagal modulation (RMSSD index was calculated at rest (pre-contraction, at the final 30 seconds of SMVC and during recovery (post-contraction. RESULTS: ΔHR showed higher values in MVC-10

  20. Toward voluntary parenthood.

    Science.gov (United States)

    Scarr, S

    2000-06-01

    David Lykken's proposal to license married parents for child rearing, and to deny the same opportunity to single and inept parents, springs from his deep concern for millions of youngsters cruelly subjected to abusive and neglectful rearing circumstances. Children from such inadequate homes grow up to have high rates of school failure, criminality, and drug addiction. The problem is clear, but Lykken's remedies of mandated marriage and parental licensure are unacceptable in U.S. society, where our reproductive rights are fortunately protected by our Constitution. As a devoted proponent of reproductive rights, I propose a legally and morally acceptable proposal to the same end. Increasing women's effective control of reproduction and moving toward entirely voluntary parenthood will accomplish the same goals without compromising our civil liberties.

  1. Premature Contractions

    Science.gov (United States)

    ... Peripheral Artery Disease Venous Thromboembolism Aortic Aneurysm More Premature Contractions - PACs and PVCs Updated:Dec 15,2016 ... You felt this more-forceful beat. Types of premature contractions Premature atrial contractions (PACs) start in the ...

  2. Assessing voluntary muscle activation with the twitch interpolation technique.

    Science.gov (United States)

    Shield, Anthony; Zhou, Shi

    2004-01-01

    The twitch interpolation technique is commonly employed to assess the completeness of skeletal muscle activation during voluntary contractions. Early applications of twitch interpolation suggested that healthy human subjects could fully activate most of the skeletal muscles to which the technique had been applied. More recently, however, highly sensitive twitch interpolation has revealed that even healthy adults routinely fail to fully activate a number of skeletal muscles despite apparently maximal effort. Unfortunately, some disagreement exists as to how the results of twitch interpolation should be employed to quantify voluntary activation. The negative linear relationship between evoked twitch force and voluntary force that has been observed by some researchers implies that voluntary activation can be quantified by scaling a single interpolated twitch to a control twitch evoked in relaxed muscle. Observations of non-linear evoked-voluntary force relationships have lead to the suggestion that the single interpolated twitch ratio can not accurately estimate voluntary activation. Instead, it has been proposed that muscle activation is better determined by extrapolating the relationship between evoked and voluntary force to provide an estimate of true maximum force. However, criticism of the single interpolated twitch ratio typically fails to take into account the reasons for the non-linearity of the evoked-voluntary force relationship. When these reasons are examined, it appears that most are even more challenging to the validity of extrapolation than they are to the linear equation. Furthermore, several factors that contribute to the observed non-linearity can be minimised or even eliminated with appropriate experimental technique. The detection of small activation deficits requires high resolution measurement of force and careful consideration of numerous experimental details such as the site of stimulation, stimulation intensity and the number of interpolated

  3. A modified isometric test to evaluate blood pressure control with ...

    African Journals Online (AJOL)

    be measured during effort to evaluate hypertension ... achieved by a variety of medications. However, appro- ... aspirin, and 5 were non-insulin-dependent diabetics. Isometric ... Blood pressure was then measured at baseline (no treat- ment) ...

  4. Minimum-distortion isometric shape correspondence using EM algorithm.

    Science.gov (United States)

    Sahillioğlu, Yusuf; Yemez, Yücel

    2012-11-01

    We present a purely isometric method that establishes 3D correspondence between two (nearly) isometric shapes. Our method evenly samples high-curvature vertices from the given mesh representations, and then seeks an injective mapping from one vertex set to the other that minimizes the isometric distortion. We formulate the problem of shape correspondence as combinatorial optimization over the domain of all possible mappings, which then reduces in a probabilistic setting to a log-likelihood maximization problem that we solve via the Expectation-Maximization (EM) algorithm. The EM algorithm is initialized in the spectral domain by transforming the sampled vertices via classical Multidimensional Scaling (MDS). Minimization of the isometric distortion, and hence maximization of the log-likelihood function, is then achieved in the original 3D euclidean space, for each iteration of the EM algorithm, in two steps: by first using bipartite perfect matching, and then a greedy optimization algorithm. The optimal mapping obtained at convergence can be one-to-one or many-to-one upon choice. We demonstrate the performance of our method on various isometric (or nearly isometric) pairs of shapes for some of which the ground-truth correspondence is available.

  5. Decreasing systolic blood pressure with isometric muscle training: a CAT

    Directory of Open Access Journals (Sweden)

    Alexis Espinoza Salinas

    2014-09-01

    Full Text Available INTRODUCTION Hypertension is a major risk factor for cardiovascular diseases such as coronary heart disease or heart failure. One of the interventions for the management of this disorder is isometric muscle training on upper and lower limbs. PURPOSE To prove the validity and applicability of results regarding the effectiveness of isometric training in hypertensive subjects. We also attempt to answer the following question: what is the effectiveness of isometric muscle training on the decrease of systolic blood pressure in hypertensive patients? METHODS Critical appraisal of the systematic review and meta-analysis “Isometric exercise training for blood pressure management”. RESULTS Isometric training reduces systolic blood pressure in normotensive and medicated hypertensive subjects, with a standardized mean difference of 6.77 mm Hg (95% confidence interval: 7.93-5.62. CONCLUSION It is reasonable to recommend isometric muscle training with the aim of lowering systolic blood pressure, considering the impact of the results of the articles analyzed and the applicability of this type of training.

  6. Intramuscular fiber conduction velocity, isometric force and explosive performance.

    Science.gov (United States)

    Methenitis, Spyridon; Terzis, Gerasimos; Zaras, Nikolaos; Stasinaki, Angeliki-Nikoletta; Karandreas, Nikolaos

    2016-06-01

    Conduction of electrical signals along the surface of muscle fibers is acknowledged as an essential neuromuscular component which is linked with muscle force production. However, it remains unclear whether muscle fiber conduction velocity (MFCV) is also linked with explosive performance. The aim of the present study was to investigate the relationship between vastus lateralis MFCV and countermovement jumping performance, the rate of force development and maximum isometric force. Fifteen moderately-trained young females performed countermovement jumps as well as an isometric leg press test in order to determine the rate of force development and maximum isometric force. Vastus lateralis MFCV was measured with intramuscular microelectrodes at rest on a different occasion. Maximum MFCV was significantly correlated with maximum isometric force (r = 0.66, p rate of force development at 100 ms, 150 ms, 200 ms, and 250 ms (r = 0.85, r = 0.89, r = 0.91, r = 0.92, respectively, p rate of force development than with maximum isometric leg press force. Lower, but significant correlations were found between mean MFCV and countermovement jump power (r = 0.65, p rate of force development than with isometric force, perhaps because conduction velocity is higher in the larger and fastest muscle fibers which are recognized to contribute to explosive actions.

  7. Percent voluntary inactivation and peak force predictions with the interpolated twitch technique in individuals with high ability of voluntary activation.

    Science.gov (United States)

    Herda, Trent J; Walter, Ashley A; Costa, Pablo B; Ryan, Eric D; Hoge, Katherine M; Stout, Jeffrey R; Cramer, Joel T

    2011-10-01

    The purpose of this study was to examine the sensitivity and peak force prediction capability of the interpolated twitch technique (ITT) performed during submaximal and maximal voluntary contractions (MVCs) in subjects with the ability to maximally activate their plantar flexors. Twelve subjects performed two MVCs and nine submaximal contractions with the ITT method to calculate percent voluntary inactivation (%VI). Additionally, two MVCs were performed without the ITT. Polynomial models (linear, quadratic and cubic) were applied to the 10-90% VI and 40-90% VI versus force relationships to predict force. Peak force from the ITT MVC was 6.7% less than peak force from the MVC without the ITT. Fifty-eight percent of the 10-90% VI versus force relationships were best fit with nonlinear models; however, all 40-90% VI versus force relationships were best fit with linear models. Regardless of the polynomial model or the contraction intensities used to predict force, all models underestimated the actual force from 22% to 28%. There was low sensitivity of the ITT method at high contraction intensities and the predicted force from polynomial models significantly underestimated the actual force. Caution is warranted when interpreting the % VI at high contraction intensities and predicted peak force from submaximal contractions.

  8. Mechanical loading of knee articular cartilage induced by muscle contraction can be assessed by measuring electrical potentials at the surface of the knee.

    Science.gov (United States)

    Zhu, Lin; Buschmann, Michael D; Savard, Pierre

    2016-02-01

    Electroarthrography (EAG) consists of recording electrical potentials on the knee surface that originate from streaming potentials within articular cartilage while the joint is undergoing compressive loading. The aim was to investigate how the contraction of specific leg muscles affects the contact force of the knee joint and, in turn, the EAG values. For six normal subjects, voluntary isometric muscle contractions were repeatedly conducted to activate four leg muscle groups while the subject was lying on his back. Two EAG signals were recorded on the medial and lateral sides of the knee, as well as four EMG signals (gastrocnemius, hamstring, quadriceps, tensor fascia latae), and the signal from a force plate fixed against the foot according to the direction of the force. The EAG and force signals were very well correlated: the median of the correlation coefficients between an EAG signal and the corresponding force signal during each loading cycle was 0.91, and 86% of the correlation coefficients were statistically significant (pmuscle contraction was possible for the gastrocnemius and hamstring, but not always for the quadriceps and tensor fascia latae. Using the clinical loading protocol which consists of a one-legged stance, the quadriceps and hamstring EMGs showed minimal activity; loading cycles with increased EAG amplitude were associated with higher EMG activity from the gastrocnemius, which is involved in antero-posterior balance. These results document the role of the EAG as a "sensor" of the knee contact force and contribute to the development of clinical loading protocols with improved reproducibility.

  9. Age effect on fatigue-induced limb acceleration as a consequence of high-level sustained submaximal contraction.

    Science.gov (United States)

    Huang, Chien-Ting; Huang, Chien-Chun; Young, Ming-Shing; Hwang, Ing-Shiou

    2007-08-01

    In reference to electromyographic measurement, the study was conducted to reassess differences in the behavior of fatigue-related neuromuscular function between young and elderly humans with limb acceleration (LA). Fourteen young and fourteen elderly subjects performed sustained index abduction at 75% of their maximal voluntary contractions (MVC) until task failure. Measures of neuromuscular function, including temporal/spectral features of muscle activity of the first dorsal interosseous (FDI) and LA of the index and hand, were monitored. The results showed a manifest fatigue-induced increase in LA of the index in the elderly group, but not in the young group. In contrast, only the young group developed a significant increase in amplitude of the electromyography (EMG) until task failure. Spectral analyses of LA in the index reflected marked age-dependent reorganization following muscle fatigue, with a greater reduction of relative spectral amplitude of LA in the range of 20-40 Hz, but a lesser reduction in coherence between EMG and LA in the elderly group. In line with fatigue-associated restructuring of LA, the mechanical coupling of the metacarpophalangeal joint was more severely undermined in the elderly group than in the young group. The present study manifested an age-related difference in the relative contributions of neural versus mechanical factors to muscle fatigue. Subsequent to a high-level sustained submaximal isometric contraction, a predominant mechanical failure of the musculotendon complex in the elderly was featured with LA, whereas EMG measurement characterized prevailing impairment of neuromuscular propagation in the young.

  10. Analyzing voluntary medical incident reports.

    Science.gov (United States)

    Gong, Yang; Richardson, James; Zhijian, Luan; Alafaireet, Patricia; Yoo, Illhoi

    2008-11-06

    Voluntary medical incident reports lacking consistency and accuracy impede the ultimate use of the reports for patient safety research. To improve this, two coders examined harm score usage in a voluntary medical incident reporting system where the harm scores were selected from a predefined list by different reporters. The two coders inter-rater agreement percent was 82%. The major categories and reviewed harm score jointly demonstrate that this process is critical and necessary in preparing the voluntary reports for further content and semantics analysis.

  11. Simultaneous Knee Extensor Muscle Action Induces an Increase in Voluntary Force Generation of Plantar Flexor Muscles.

    Science.gov (United States)

    Suzuki, Takahito; Shioda, Kohei; Kinugasa, Ryuta; Fukashiro, Senshi

    2017-02-01

    Suzuki, T, Shioda, K, Kinugasa, R, and Fukashiro, S. Simultaneous knee extensor muscle action induces an increase in voluntary force generation of plantar flexor muscles. J Strength Cond Res 31(2): 365-371, 2017-Maximum activation of the plantar flexor muscles is required for various sporting activities that involve simultaneous plantar flexion and knee extension. During a multi-joint movement, activation of the plantar flexor muscles is affected by the activity of the knee extensor muscles. We hypothesized that coactivation of the plantar flexor muscles and knee extensor muscles would result in a higher plantar flexion torque. To test this hypothesis, 8 male volunteers performed maximum voluntary isometric action of the plantar flexor muscles with and without isometric action of the knee extensor muscles. Surface electromyographic data were collected from 8 muscles of the right lower limb. Voluntary activation of the triceps surae muscles, evaluated using the interpolated twitch technique, significantly increased by 6.4 percentage points with intentional knee extensor action (p = 0.0491). This finding is in line with a significant increase in the average rectified value of the electromyographic activity of the vastus lateralis, fibularis longus, and soleus muscles (p = 0.013, 0.010, and 0.045, respectively). The resultant plantar flexion torque also significantly increased by 11.5% of the predetermined maximum (p = 0.031). These results suggest that higher plantar flexor activation coupled with knee extensor activation facilitates force generation during a multi-joint task.

  12. Low-intensity eccentric contractions of the knee extensors and flexors protect against muscle damage.

    Science.gov (United States)

    Lin, Min-Ju; Chen, Trevor Chung-Ching; Chen, Hsin-Lian; Wu, Bo-Han; Nosaka, Kazunori

    2015-10-01

    This study investigated the magnitude and duration of the protective effect of low-intensity eccentric contractions (LowEC) against damage induced by maximal eccentric contractions (MaxEC) of the knee flexors (KF) and extensors (KE). Young men were assigned to 8 experimental groups and 2 control groups (n = 13/group); the experimental groups performed LowEC of KF or KE 2 days (2d), 1 week (1wk), 2 weeks (2wk), or 3 weeks (3wk) before MaxEC, while the control groups performed MaxEC of KF or KE without LowEC. The 2d, 1wk, 2wk, and 3wk groups performed 30 LowEC of KF or 60 LowEC of KE with a load of 10% of maximal voluntary isometric contraction strength on a resistance-training machine, and all groups performed 30 MaxEC of KF or 60 MaxEC of KE on an isokinetic dynamometer. Several muscle damage markers were measured from before to 2 days after exercise (LowEC) or from before to 5 days after exercise (MaxEC). No significant changes in any variables were evident after LowEC. The changes in all variables after MaxEC were smaller (P < 0.05) for the 2d and 1wk groups (e.g., peak creatine kinase activity: 1002 ± 501 IU/L; peak muscle soreness: 13 ± 5 mm) than for the control group (peak creatine kinase activity: 3005 ± 983 IU/L; peak muscle soreness 28 ± 6 mm) for both KE and KF. There were no significant differences between the 2d and 1wk groups or among the 2wk, 3wk, and control groups. These results show that LowEC provided 30%-66% protection against damage induced by MaxEC of KF and KE, and the protective effect lasted 1 week.

  13. Muscular contraction mode differently affects autonomic control during heart rate matched exercise.

    Science.gov (United States)

    Weippert, Matthias; Behrens, Martin; Gonschorek, Ray; Bruhn, Sven; Behrens, Kristin

    2015-01-01

    The precise contributions of afferent feedback to cardiovascular and respiratory responses to exercise are still unclear. The aim of this crossover study was to assess whether and how autonomic cardiovascular and respiratory control differed in response to dynamic (DYN) and isometric contractions (ISO) at a similar, low heart rate (HR) level. Therefore, 22 healthy males (26.7 ± 3.6 yrs) performed two kinds of voluntary exercises at similar HR: ISO and DYN of the right quadriceps femoris muscle. Although HR was eqivalent (82 ± 8 bpm for DYN and ISO, respectively), rating of exertion, blood pressures, and rate pressure product were higher, whereas breathing frequency, minute ventilation, oxygen uptake and carbon dioxide output were significantly lower during ISO. Tidal volume, end-tidal partial pressures of O2 and CO2, respiratory exchange ratio and capillary blood lactate concentration were comparable between both contraction modes. Heart rate variability (HRV) indicators, SDNN, HF-Power and LF-Power, representing both vagal and sympathetic influences, were significantly higher during ISO. Sample entropy, a non-linear measure of HRV was also significantly affected by contraction mode. It can be concluded that, despite the same net effect on HR, the quality of cardiovascular control during low intensity exercise is significantly different between DYN and ISO. HRV analysis indicated a sympatho-vagal coactivation during ISO. Whether mechanoreceptor feedback alone, a change in central command, or the interaction of both mechanisms is the main contributor of the distinct autonomic responses to the different exercise modes remains to be elucidated.

  14. Muscular Contraction Mode Differently Affects Autonomic Control During Heart Rate Matched Exercise

    Directory of Open Access Journals (Sweden)

    Matthias eWeippert

    2015-05-01

    Full Text Available The precise contributions of afferent feedback to cardiovascular and respiratory responses to exercise are still unclear. Aim of this crossover study was to assess whether and how autonomic cardiovascular and respiratory control differed in response to dynamic (DYN and isometric contractions (ISO at a similar, low heart rate (HR level. Therefore, 22 healthy males (26.7 ± 3.6 yrs performed two kinds of voluntary exercises at similar HR: ISO and DYN of the right quadriceps femoris muscle. Although HR was eqivalent (82 ± 8 bpm for DYN and ISO, respectively, rating of exertion, blood pressures, and rate pressure product were higher, whereas breathing frequency, minute ventilation, oxygen uptake and carbon dioxide output were significantly lower during ISO. Tidal volume, end-tidal partial pressures of O2 and CO2, respiratory exchange ratio and capillary blood lactate concentration were comparable between both contraction modes. Heart rate variability (HRV indicators, SDNN, HF-Power and LF-Power, representing both vagal and sympathetic influences, were significantly higher during ISO. Sample entropy, a nonlinear measure of HRV was also significantly affected by contraction mode. It can be concluded that, despite the same net effect on HR, the quality of cardiovascular control during low intensity exercise is significantly different between DYN and ISO. HRV analysis indicated a sympatho-vagal coactivation during ISO. Whether mechanoreceptor feedback alone, a change in central command, or the interaction of both mechanisms is the main contributor of the distinct autonomic responses to the different exercise modes remains to be elucidated.

  15. The Notion of Voluntary Unemployment.

    Science.gov (United States)

    Standing, Guy

    1981-01-01

    Considers the distinction between voluntary and involuntary unemployment by analyzing six behavioral characteristics attributed to groups of workers suspected of indulging in the former, and the labor market mechanisms supposedly encouraging them. (Author/CT)

  16. Surface electromyogram analysis of the direction of isometric torque generation by the first dorsal interosseous muscle

    Science.gov (United States)

    Zhou, Ping; Suresh, Nina L.; Zev Rymer, William

    2011-06-01

    The objective of this study was to determine whether a novel technique using high density surface electromyogram (EMG) recordings can be used to detect the directional dependence of muscle activity in a multifunctional muscle, the first dorsal interosseous (FDI). We used surface EMG recordings with a two-dimensional electrode array to search for inhomogeneous FDI activation patterns with changing torque direction at the metacarpophalangeal joint, the locus of action of the FDI muscle. The interference EMG distribution across the whole FDI muscle was recorded during isometric contraction at the same force magnitude in five different directions in the index finger abduction-flexion plane. The electrode array EMG activity was characterized by contour plots, interpolating the EMG amplitude between electrode sites. Across all subjects the amplitude of the flexion EMG was consistently lower than that of the abduction EMG at the given force. Pattern recognition methods were used to discriminate the isometric muscle contraction tasks with a linear discriminant analysis classifier, based on the extraction of two different feature sets of the surface EMG signal: the time domain (TD) feature set and a combination of autoregressive coefficients and the root mean square amplitude (AR+RMS) as a feature set. We found that high accuracies were obtained in the classification of different directions of the FDI muscle isometric contraction. With a monopolar electrode configuration, the average overall classification accuracy from nine subjects was 94.1 ± 2.3% for the TD feature set and 95.8 ± 1.5% for the AR+RMS feature set. Spatial filtering of the signal with bipolar electrode configuration improved the average overall classification accuracy to 96.7 ± 2.7% for the TD feature set and 98.1 ± 1.6% for the AR+RMS feature set. The distinct EMG contour plots and the high classification accuracies obtained from this study confirm distinct interference EMG pattern distributions as a

  17. Perbandingan Tekanan Darah Sebelum dan Sewaktu Melakukan Handgrip Isometric Exercise pada Mahasiswa Angkatan 2011 Fakultas Kedokteran Universitas Andalas

    Directory of Open Access Journals (Sweden)

    M.Yoga Sefia Nurindra

    2016-08-01

    Full Text Available AbstrakHipertensi dapat menyebabkan gangguan jantung yang serius sampai kematian. Handgrip isometric exercise adalah latihan yang melibatkan kontraksi otot lengan bawah dan tangan dengan melakukan cengkraman menggunakan handgrip dynamometer. Tujuan penelitian ini adalah mengetahui perubahan tekanan darah sewaktu melakukan handgrip isometric exercise. Penelitian ini merupakan penelitian eksperimental dengan menggunakan desain randomized crossover study yang melibatkan 24 orang subjek laki-laki dengan usia 20,7 ± 0,6 tahun dan BMI 21,8 ± 2,1 Kg/m2. Hasil penelitian menunjukkan peningkatan tekanan darah baik sistolik maupun diastolik yang signifikan sewaktu melakukan handgrip isometric exercise. Tekanan darah sistolik dari 115,2 ± 5,0 mmHg menjadi 135,0± 6,5 mmHg (p<0,05 dan diastolik 76,3± 5,0 mmHg menjadi 98,3 ± 8,7 mmHg (p<0,05. Pada kontrol terlihat penurunan tekanan darah sistolik yang signifikan dari 113,8 ± 6,1 mmHg menjadi 111,5 ± 7,1 mmHg (p<0,05 dan diastolik penurunan tidak signifikan dari 75,0 ± 5,9 mmHg menjadi 72,9 ± 6,2 mmHg (p>0,05.  Pada penelitian ini disimpulkan bahwa tekanan darah meningkat sewaktu handgrip isometric exercise.Kata kunci: hipertensi, handgrip isometric exercise, tekanan darah AbstractHypertension can cause a serious heart problem and mortality. Handgrip isometric exercise is an activity involving contraction of forearm and hand muscle of one arm by pressing handgrip dynamometer. The objective  of  this study was to investigated blood pressure during handgrip isometric exercise. This research was an experimental study with randomized crossover design that involved 24 male subjects, age of 20,7 ± 0,6 years old and BMI 21,8 ± 2,1 Kg/m2. The results demonstrated significant increases in systolic and diastolic blood pressure during handgrip isometric exercise. Systolic blood pressure significantly increased from 115,2 ± 5,0 mmHg to 135,0 ± 6,5 mmHg (p<0,05 and diastolic from 76,3 ± 5,0

  18. 等长收缩运动促进急性冠状动脉闭塞时侧支血流募集%Facilitating coronary collateral recruitment by isometric exercise during acute coronary occlusion

    Institute of Scientific and Technical Information of China (English)

    陆晓; 林松; 励建安

    2012-01-01

    Objective To determine whether isometric handgrip exercise can increase collateral flow to the ischemic myocardium in acute coronary occlusion patients with coronary artery disease (CAD).Methods Sixty-five patients with one-vessel CAD were randomly assigned to either an isometric exercise (IME) group or no-exercise (NE) group.Patients in the IME group performed isometric handgrip exercises (50% of the maximum voluntary contraction) during 1 min of coronary balloon occlusion.Patients in the NE group remained sedentary during the procedure.The collateral flow index (CFI),heart rare (HR),systolic blood pressure (SBP) and diastolic blood pressure (DBP) were determined prior to and at the end of 1 min of coronary occlusion.Results In the IME group the average CFI improved significantly more during the occlusion than in the NE group.The differences in HR,SBP and DBP were also significantly grcatcr in the CFI group than in the NE group controls.Conclusion Isometric exercise can induce significantly increased coronary collateral flow in CAD patients during acute vessel occlusion.%目的 观察等长收缩运动对冠心病患者急性冠状动脉闭塞时缺血心肌侧支血流募集的影响.方法 65例单支血管病变的患者按随机数字表法分为等长收缩运动(IME)组和对照组,其中IME组33例,对照组32例.所有患者在经皮冠状动脉介入治疗(PCI)术中病变血管接受1 min的冠脉球囊阻塞,IME组患者在球囊阻塞同时行等长握拳收缩(50%最大自主收缩力),而对照组不做任何运动.所有患者均在球囊阻塞前及阻塞终未时测定侧支血流指数(CFI)、心率(HR)、收缩压(SBP)和舒张压(DBP).结果 IME组冠脉血管阻塞终未时与冠脉阻塞前的CFI差值(0.04±0.05)较对照组的CFI差值(0.01 ±0.03)显著增加,且2组比较,差异有统计学意义(P <0.01);IME组的HR、SBP和DBP治疗后与治疗前的差值分别为(7.84±8.20)次/min、(3.25 ±7.17) mmHg和(5.88±6.40)mmHg,而

  19. EFFECT OF ISOMETRIC QUADRICEPS STRENGTHENING EXERCISE AT MULTIPLE ANGLES IN KNEE JOINT AMONG NORMAL ADULTS

    Directory of Open Access Journals (Sweden)

    JibiPaul

    2014-04-01

    Full Text Available Introduction: Strengthening exercises have been routinely used in persons with orthopaedic problems and athletes to increase force production or minimize muscle imbalance and joint injuries.Many studies have reported that isometric contractions can rapidly increases strength in quadriceps muscle. Objective: Objective of the study was to find out the effect of isometric strengthening exercise on strength of quadriceps at 45 and 90 degree of knee joint and also to compare the effect of strengthening exercise on strength of quadriceps at multiple angles of knee joint among control and experimental group. Methodology: This was a ccomparative experimental study with forty female healthy subjects from physiotherapy department of KPJ Healthcare University College, Malaysia. Convenient sampling method used to select the samples. The subjects were selected by inclusion criteria and randomly divided equally in to two with 20 subjects in each group. Isometric strengthening exercise and squatting exercise were given as intervention program for eight weeks respectively for experimental and control group. Pre and post data of quadriceps muscle strength measured were collected separately at 45 and 90 degree of knee joint using goniometry during resisted extension of knee in multi gym. Result: In experimental group Pre –Post statistical analysis found significant effect in increase of quadriceps strength at 45 and 90 degree with P<0.0001.****In control group quadriceps pre-post statistical analysis found no significant effect in increase of quadriceps strength at 45 and 90 degree with P<0.083NS and P<0.055 NS respectively. Comparative study between experimental and control groups for quadriceps strength at 90 degree of knee joint found significant effect in increase of quadriceps strength with P< 0.001.*** Comparative study between experimental and control groups for quadriceps strength at 45 degree of knee joint found significant effect in increase of

  20. Isometric exercises reduce temporal summation of pressure pain in humans

    DEFF Research Database (Denmark)

    Vægter, Henrik Bjarke; Handberg, G.; Graven-Nielsen, Thomas

    2015-01-01

    BACKGROUND: Aerobic and isometric exercises are known to decrease pain sensitivity. The effect of different types of exercise on central mechanisms such as temporal summation of pain (TSP) is less clear. This study hypothesized that both aerobic and isometric exercises would increase pressure pain...... and a non-exercise condition (experiment 1), and after low- and high-intensity bicycling and low- and high-intensity isometric arm and leg exercises with the dominant arm/leg (experiment 2). PTT and TSP were assessed before and after each exercise condition on the non-dominant arm and leg by computer......-controlled cuff algometry. TSP was assessed by visual analogue scale (VAS) scores of the pain intensity during sequential cuff-pressure stimulation at the pain tolerance intensity related to that specific time point. RESULTS: In experiment 1, bicycling, but not the non-exercise condition, slightly increased PTT...

  1. Human movement onset detection from isometric force and torque measurements: a supervised pattern recognition approach.

    Science.gov (United States)

    Soda, Paolo; Mazzoleni, Stefano; Cavallo, Giuseppe; Guglielmelli, Eugenio; Iannello, Giulio

    2010-09-01

    Recent research has successfully introduced the application of robotics and mechatronics to functional assessment and motor therapy. Measurements of movement initiation in isometric conditions are widely used in clinical rehabilitation and their importance in functional assessment has been demonstrated for specific parts of the human body. The determination of the voluntary movement initiation time, also referred to as onset time, represents a challenging issue since the time window characterizing the movement onset is of particular relevance for the understanding of recovery mechanisms after a neurological damage. Establishing it manually as well as a troublesome task may also introduce oversight errors and loss of information. The most commonly used methods for automatic onset time detection compare the raw signal, or some extracted measures such as its derivatives (i.e., velocity and acceleration) with a chosen threshold. However, they suffer from high variability and systematic errors because of the weakness of the signal, the abnormality of response profiles as well as the variability of movement initiation times among patients. In this paper, we introduce a technique to optimise onset detection according to each input signal. It is based on a classification system that enables us to establish which deterministic method provides the most accurate onset time on the basis of information directly derived from the raw signal. The approach was tested on annotated force and torque datasets. Each dataset is constituted by 768 signals acquired from eight anatomical districts in 96 patients who carried out six tasks related to common daily activities. The results show that the proposed technique improves not only on the performance achieved by each of the deterministic methods, but also on that attained by a group of clinical experts. The paper describes a classification system detecting the voluntary movement initiation time and adaptable to different signals. By

  2. Redefining RECs: Additionality in the voluntary Renewable Energy Certificate market

    Science.gov (United States)

    Gillenwater, Michael Wayne

    long-term contracts that would reduce the risk of relying on revenue the voluntary green power market. Although no simple solutions are identified, a proposal for integrating RECs into a load based cap-and-trade system is presented. Keywords: Renewable Energy Certificate (REC); Renewable Portfolio Standard (RPS); emission offset; additionality; attributes

  3. Fatigue-related firing of distal muscle nociceptors reduces voluntary activation of proximal muscles of the same limb.

    Science.gov (United States)

    Kennedy, David S; McNeil, Chris J; Gandevia, Simon C; Taylor, Janet L

    2014-02-15

    With fatiguing exercise, firing of group III/IV muscle afferents reduces voluntary activation and force of the exercised muscles. These afferents can also act across agonist/antagonist pairs, reducing voluntary activation and force in nonfatigued muscles. We hypothesized that maintained firing of group III/IV muscle afferents after a fatiguing adductor pollicis (AP) contraction would decrease voluntary activation and force of AP and ipsilateral elbow flexors. In two experiments (n = 10) we examined voluntary activation of AP and elbow flexors by measuring changes in superimposed twitches evoked by ulnar nerve stimulation and transcranial magnetic stimulation of the motor cortex, respectively. Inflation of a sphygmomanometer cuff after a 2-min AP maximal voluntary contraction (MVC) blocked circulation of the hand for 2 min and maintained firing of group III/IV muscle afferents. After a 2-min AP MVC, maximal AP voluntary activation was lower with than without ischemia (56.2 ± 17.7% vs. 76.3 ± 14.6%; mean ± SD; P muscle afferents from the hand decreased voluntary drive and force of AP. Moreover, this effect decreased voluntary drive and torque of proximal unfatigued muscles, the elbow flexors. Fatigue-sensitive group III/IV muscle nociceptors act to limit voluntary drive not only to fatigued muscles but also to unfatigued muscles within the same limb.

  4. Repeatability of corticospinal and spinal measures during lengthening and shortening contractions in the human tibialis anterior muscle.

    Directory of Open Access Journals (Sweden)

    Jamie Tallent

    Full Text Available UNLABELLED: Elements of the human central nervous system (CNS constantly oscillate. In addition, there are also methodological factors and changes in muscle mechanics during dynamic muscle contractions that threaten the stability and consistency of transcranial magnetic stimulation (TMS and perpherial nerve stimulation (PNS measures. PURPOSE: To determine the repeatability of TMS and PNS measures during lengthening and shortening muscle actions in the intact human tibialis anterior. METHODS: On three consecutive days, 20 males performed lengthening and shortening muscle actions at 15, 25, 50 and 80% of maximal voluntary contraction (MVC. The amplitude of the Motor Evoked Potentials (MEPs produced by TMS was measured at rest and during muscle contraction at 90° of ankle joint position. MEPs were normalised to Mmax determined with PNS. The corticospinal silent period was recorded at 80% MVC. Hoffman reflex (H-reflex at 10% isometric and 25% shortening and lengthening MVCs, and V-waves during MVCs were also evoked on each of the three days. RESULTS: With the exception of MEPs evoked at 80% shortening MVC, all TMS-derived measures showed good reliability (ICC = 0.81-0.94 from days 2 to 3. Confidence intervals (CI, 95% were lower between days 2 and 3 when compared to days 1 and 2. MEPs significantly increased at rest from days 1 to 2 (P = 0.016 and days 1 to 3 (P = 0.046. The H-reflex during dynamic muscle contraction was reliable across the three days (ICC = 0.76-0.84. V-waves (shortening, ICC = 0.77, lengthening ICC = 0.54 and the H-reflex at 10% isometric MVC (ICC = 0.66 was generally less reliable over the three days. CONCLUSION: Although it is well known that measures of the intact human CNS exhibit moment-to-moment fluctuations, careful experimental arrangements make it possible to obtain consistent and repeatable measurements of corticospinal and spinal excitability in the actively lengthening and shortening human

  5. Folded isometric deformations and banana-shaped seedpod

    Science.gov (United States)

    Couturier, Etienne

    2016-08-01

    Thin vegetal shells have recently been a significant source of inspiration for the design of smart materials and soft actuators. Herein is presented a novel analytical family of isometric deformations with a family of θ-folds crossing a family of parallel z-folds; it contains the isometric deformations of a banana-shaped surface inspired by a seedpod, which converts a vertical closing into either an horizontal closing or an opening depending on the location of the fold. Similarly to the seedpod, optimum shapes for opening ease are the most elongated ones.

  6. Comparing Voluntary and Mandatory Gameplay

    Directory of Open Access Journals (Sweden)

    Esther Kuindersma

    2016-09-01

    Full Text Available Gameplay is commonly considered to be a voluntary activity. Game designers generally believe that voluntary gameplay is essentially different from mandatory gameplay. Such a belief may be a challenge for serious games, as instruction is usually mandatory. The article describes the outcomes of two experiments on the impact of voluntariness on the learning effect and enjoyment of a serious game. In the first experiment freedom of choosing to play a serious game was studied, with participants who had volunteered to participate. The results suggested that, contrary to the opinion of many game designers, being required to play a serious game does not automatically take the fun out of the game. The second experiment had voluntary participants and mandatory participants, who had to participate as part of a homework assignment. The outcomes show that mandatory participants enjoyed the game as much as the voluntary participants, even if they had to play the game for a minimum required time. These studies indicate that mandatory gameplay does not reduce enjoyment and learning effect.

  7. Voluntary organisation and adult education

    Directory of Open Access Journals (Sweden)

    Konrad Elsdon

    1998-12-01

    Full Text Available The author starts by offering a definition of voluntary organisations. He then discusses their importance and role, focusing on the issue of adult education wi­ thin these organisations. He also wells upon learning and change of voluntary organisation members, making use of the results of a study he conducted together with his collaborators. One of their fin­dings has been that voluntary organisati­ons, due to their organisational targets li­ke painting, singing or caring for people in need, lead their members to learning, i.e. essentially content learning. Moreo­ver, voluntary organisations offer a fair number of opportunities for social lear­ning and change. ln spite of the fact that the respondents were mostly not aware of the outcomes of their learning and change, careful listeners conducting the interview made them understand the im­portance of the learning they had gone through. The author concludes by poin­ ting out that formal education of adults can get its inspiration in learning in voluntary organisations. On the other hand, such learning would benefit greatly from findings and methods of formal education of adults.

  8. Effect of differing intensities of fatiguing dynamic contractions on contralateral homologous muscle performance.

    Science.gov (United States)

    Kawamoto, Jon-Erik; Aboodarda, Saied Jalal; Behm, David George

    2014-12-01

    The purpose of this study was to investigate different intensities of unilateral fatiguing dynamic quadriceps contractions on non-exercised, contralateral quadriceps performance. In a randomized crossover study design with 12 recreationally trained male (1.78 ± 0.05 m, 84.5 ± 7.6 kg, 30.0 ± 8.5 yrs) participants, maximal voluntary contraction (MVC) force, force developed in the first 100 ms (F100), and electromyography of the non-exercised contralateral knee extensors were measured before and after fatiguing protocols performed by ipsilateral knee extensors. Non-exercised knee extensors' endurance was also measured post-intervention. The fatigue protocols consisted of four sets of dynamic knee extensions each to task failure with 40% and 70% MVC on separate days. Both the 40% (p = 0.009, Effect Size [ES] = 0.72) and 70% (p = 0.001, ES = 2.03) conditions exhibited 23.7% and 34.6% decreases in F100 respectively with the non-exercised contralateral knee extensors. A significant time effect (p = 0.002) demonstrated that both the 40% (and 70% (conditions exhibited 4.4% (ES = 0.29) and 7.1% (ES = 0.53) force decreases from pre- to post-intervention, respectively. However, the condition * time interaction only showed a trend (p = 0.09) with moderate (40%: ES = 0.62) to large (70%: ES = 0.82) effect sizes for decreased contralateral limb force compared with control session. The 40% (p = 0.09, ES = 0.65) and 70% (p = 0.07, ES = 0.79) protocols had a tendency to induce greater contralateral force variation during sustained submaximal isometric contraction compared with control. In conclusion, this study highlighted that unilateral lower limb fatigue induced by low intensity as well as high intensity dynamic knee extensions provided some evidence of crossover fatigue with the contralateral non-exercised limb. Key PointsThere was a pattern of crossover fatigue effects with significant impairments in F100, near significant, moderate to large magnitude decrements in MVC force

  9. On simulating sustained isometric muscle fatigue: a phenomenological model considering different fiber metabolisms.

    Science.gov (United States)

    Grasa, J; Sierra, M; Muñoz, M J; Soteras, F; Osta, R; Calvo, B; Miana-Mena, F J

    2014-11-01

    The present study shows a new computational FEM technique to simulate the evolution of the mechanical response of 3D muscle models subjected to fatigue. In an attempt to obtain very realistic models, parameters needed to adjust the mathematical formulation were obtained from in vivo experimental tests. The fatigue contractile properties of three different rat muscles (Tibialis Anterior, Extensor Digitorium Longus and Soleus) subjected to sustained maximal isometric contraction were determined. Experiments were conducted on three groups [Formula: see text] of male Wistar rats [Formula: see text] using a protocol previously developed by the authors for short tetanic contractions. The muscles were subjected to an electrical stimulus to achieve tetanic contraction during 10 s. The parameters obtained for each muscle were incorporated into a finite strain formulation for simulating active and passive behavior of muscles with different fiber metabolisms. The results show the potential of the model to predict muscle fatigue under high-frequency stimulation and the 3D distribution of mechanical variables such as stresses and strains.

  10. ISOMETRIC EXERCISE AND ITS EFFECT ON BLOOD PRESSURE AND HEART RATE, BEFORE AND AFTER TRAINING IN YOUNG HEALTHY MALES

    Directory of Open Access Journals (Sweden)

    Mohammed

    2015-05-01

    Full Text Available INTRODUCTION: Isometric exercise is a normal part of everyday activities and many occupational tasks. Preventive services are important as they give physicians an opportunity and responsibility to promote regular physical activity, reduc e high blood pressure, and help in weight control. Physical inactivity is recognized as a risk factor for coronary artery disease. Regular aerobic physical activity increases exercise capacity and plays a role in both primary and secondary prevention of ca rdiovascular disease. OBJECTIVE: To assess the effects of isometric handgrip training on Blood pressure and Heart rate in healthy young males in the age group of 18 - 22 years. MATERIALS AND METHOD : Study subjects consisted of 30 healthy adult males in the age group of 18 - 22 yrs. Age and sex matched adults who were not active in sports or in physical activities constituted the control group (n=30. Blood pressure and heart rate were recorded and eval uated after a defined protocol of handgrip sustained static (isometric contractions performed with the handgrip dynamometer at Rest and Post Exercise. BP and HR were recorded with the help of automated blood pressure monitor and power lab 8/30 series inst rument available in the Department of Physiology , Navodaya Medical college, Raichur. RESULTS: There was no change in Resting Blood pressure and Heart rate between the subject and control group before the training sessions. There was significant decrease in resting Blood pressure and Heart rate in trained subject group when compared to untrained control group after 5 weeks of training sessions. CONCLUSION : Isometric hand grip training is effective in lowering arterial pressure in normotensive subjects. Isome tric training may be an effective intervention in the prevention and treatment of hypertension

  11. Isokinetic and isometric muscle function of the knee extensors and flexors during simulated soccer activity: effect of exercise and dehydration.

    Science.gov (United States)

    Ali, Ajmol; Williams, Clyde

    2013-01-01

    This study investigated the influence of dehydration during soccer-type intermittent exercise on isokinetic and isometric muscle function. Eight soccer players performed two 90-min high-intensity intermittent shuttle-running trials without (NF) or with (FL) fluid ingestion (5 ml · kg(-1) before and 2 ml · kg(-1) every 15 min). Isokinetic and isometric strength and muscular power of knee flexors and knee extensors were measured pre-exercise, at half-time and post-exercise using isokinetic dynamometry. Sprint performance was monitored throughout the simulated-soccer exercise. Isokinetic knee strength was reduced at faster (3.13 rad · s(-1); P = 0.009) but not slower (1.05 rad · s(-1); P = 0.063) contraction speeds with exercise; however, there was no difference between FL and NF. Peak isometric strength of the knee extensors (P = 0.002) but not the knee flexors (P = 0.065) was significantly reduced with exercise with no difference between FL and NF. Average muscular power was reduced over time at both 1.05 rad · s(-1) (P = 0.01) and 3.14 rad · s(-1) (P = 0.033) but was not different between FL and NF. Mean 15-m sprint time increased with duration of exercise (P = 0.005) but was not different between FL and NF. In summary, fluid ingestion during 90 min of soccer-type exercise was unable to offset the reduction in isokinetic and isometric strength and muscular power of the knee extensors and flexors.

  12. Changes in voluntary quadriceps activation predict changes in muscle strength and gait biomechanics following knee joint effusion.

    Science.gov (United States)

    Pietrosimone, Brian; Lepley, Adam S; Murray, Amanda M; Thomas, Abbey C; Bahhur, Nael O; Schwartz, Todd A

    2014-09-01

    It has been hypothesized that arthrogenic muscle inhibition is responsible for altering physical function following knee injury. The association between the onset of arthrogenic muscle inhibition, measured using voluntary quadriceps activation, and changes in muscle strength and gait biomechanics are unknown. Outcomes were collected before and following a 60 ml experimental knee effusion in eighteen healthy participants. Voluntary quadriceps activation was the predictor variable, while the criterion variable included, maximal voluntary isometric strength, peak knee flexion angle, peak internal knee extension moment, and peak vertical ground reaction forces during the first half of stance phase upon stair descent. Percent change scores (Δ) were imputed into linear regression equations to determine associations between predictor and criterion variables. The variance in Δ voluntary quadriceps activation significantly predicted 87% the variance in the Δ strength (R(2)=0.87, Pknee flexion angle, Δ voluntary quadriceps activation predicted an additional 29% (Δ R(2)=0.29, P=0.007) of the variance in the Δ knee extension moment (R(2)=0.54, P=0.003, Δ knee extension moment=-10.79+0.74Δ knee flexion angle+1.64Δ voluntary quadriceps activation) following knee effusion. Immediate quadriceps activation deficits following joint effusion result in immediate alterations in muscle strength, knee extensor moment and vertical ground reaction force during gait. Published by Elsevier Ltd.

  13. A Multiple Degree of Freedom Lower Extremity Isometric Device to Simultaneously Quantify Hip, Knee, and Ankle Torques.

    Science.gov (United States)

    Sánchez, Natalia; Acosta, Ana Maria; Stienen, Arno H A; Dewald, Julius P A

    2015-09-01

    Characterization of the joint torque coupling strategies used in the lower extremity to generate maximal and submaximal levels of torque at either the hip, knee, or ankle is lacking. Currently, there are no available isometric devices that quantify all concurrent joint torques in the hip, knee, and ankle of a single leg during maximum voluntary torque generation. Thus, joint-torque coupling strategies in the hip, knee, and concurrent torques at ankle and/or coupling patterns at the hip and knee driven by the ankle have yet to be quantified. This manuscript describes the design, implementation, and validation of a multiple degree of freedom, lower extremity isometric device (the MultiLEIT) that accurately quantifies simultaneous torques at the hip, knee, and ankle. The system was mechanically validated and then implemented with two healthy control individuals and two post-stroke individuals to test usability and patient acceptance. Data indicated different joint torque coupling strategies used by both healthy individuals. In contrast, data showed the same torque coupling patterns in both post-stroke individuals, comparable to those described in the clinic. Successful implementation of the MultiLEIT can contribute to the understanding of the underlying mechanisms responsible for abnormal movement patterns and aid in the design of therapeutic interventions.

  14. The role of agonist and antagonist muscles in explaining isometric knee extension torque variation with hip joint angle.

    Science.gov (United States)

    Bampouras, Theodoros M; Reeves, Neil D; Baltzopoulos, Vasilios; Maganaris, Constantinos N

    2017-08-12

    The biarticular rectus femoris (RF), operating on the ascending limb of the force-length curve, produces more force at longer lengths. However, experimental studies consistently report higher knee extension torque when supine (longer RF length) compared to seated (shorter RF length). Incomplete activation in the supine position has been proposed as the reason for this discrepancy, but differences in antagonistic co-activation could also be responsible due to altered hamstrings length. We examined the role of agonist and antagonist muscles in explaining the isometric knee extension torque variation with changes in hip joint angle. Maximum voluntary isometric knee extension torque (joint MVC) was recorded in seated and supine positions from nine healthy males (30.2 ± 7.7 years). Antagonistic torque was estimated using EMG and added to the respective joint MVC (corrected MVC). Submaximal tetanic stimulation quadriceps torque was also recorded. Joint MVC was not different between supine (245 ± 71.8 Nm) and seated (241 ± 69.8 Nm) positions and neither was corrected MVC (257 ± 77.7 and 267 ± 87.0 Nm, respectively). Antagonistic torque was higher when seated (26 ± 20.4 Nm) than when supine (12 ± 7.4 Nm). Tetanic torque was higher when supine (111 ± 31.9 Nm) than when seated (99 ± 27.5 Nm). Antagonistic co-activation differences between hip positions do not account for the reduced MVC in the supine position. Rather, reduced voluntary knee extensor muscle activation in that position is the major reason for the lower MVC torque when RF is lengthened (hip extended). These findings can assist standardising muscle function assessment and improving musculoskeletal modelling applications.

  15. Near isometric biomass partitioning in forest ecosystems of China.

    Science.gov (United States)

    Hui, Dafeng; Wang, Jun; Shen, Weijun; Le, Xuan; Ganter, Philip; Ren, Hai

    2014-01-01

    Based on the isometric hypothesis, belowground plant biomass (MB) should scale isometrically with aboveground biomass (MA) and the scaling exponent should not vary with environmental factors. We tested this hypothesis using a large forest biomass database collected in China. Allometric scaling functions relating MB and MA were developed for the entire database and for different groups based on tree age, diameter at breast height, height, latitude, longitude or elevation. To investigate whether the scaling exponent is independent of these biotic and abiotic factors, we analyzed the relationship between the scaling exponent and these factors. Overall MB was significantly related to MA with a scaling exponent of 0.964. The scaling exponent of the allometric function did not vary with tree age, density, latitude, or longitude, but varied with diameter at breast height, height, and elevation. The mean of the scaling exponent over all groups was 0.986. Among 57 scaling relationships developed, 26 of the scaling exponents were not significantly different from 1. Our results generally support the isometric hypothesis. MB scaled near isometrically with MA and the scaling exponent did not vary with tree age, density, latitude, or longitude, but increased with tree size and elevation. While fitting a single allometric scaling relationship may be adequate, the estimation of MB from MA could be improved with size-specific scaling relationships.

  16. Isometric Spacelike Immersions of Space Forms in Indefinite Space Forms

    Institute of Scientific and Technical Information of China (English)

    李海中; 吴岚

    2001-01-01

    Let M be a connected n-dimensional space form spacelike isometrically immersed in a (2n -1)-dimensional indefinite space form. If M is maximal, we prove that either M is totally geodesic or M is apiece of the n-dimensional hyperbolic cylinder in the (2n - 1)-dimensional pseudo-hyperbolic space.``

  17. LINEAR ISOMETRIC NON-ANTICIPATIVE TRANSFORMATIONS OF WIENER PROCESS

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The necessary and sufficient conditions are given so that a non-anticipative transformation in Hilbert space is isometric. In terms of second order Wiener process, these conditions assure that a non-anticipative transformation of Wiener process is a Wiener process, too.

  18. Probing disorder in isometric pyrochlore and related complex oxides

    Science.gov (United States)

    Shamblin, Jacob; Feygenson, Mikhail; Neuefeind, Joerg; Tracy, Cameron L.; Zhang, Fuxiang; Finkeldei, Sarah; Bosbach, Dirk; Zhou, Haidong; Ewing, Rodney C.; Lang, Maik

    2016-05-01

    There has been an increased focus on understanding the energetics of structures with unconventional ordering (for example, correlated disorder that is heterogeneous across different length scales). In particular, compounds with the isometric pyrochlore structure, A2B2O7, can adopt a disordered, isometric fluorite-type structure, (A, B)4O7, under extreme conditions. Despite the importance of the disordering process there exists only a limited understanding of the role of local ordering on the energy landscape. We have used neutron total scattering to show that disordered fluorite (induced intrinsically by composition/stoichiometry or at far-from-equilibrium conditions produced by high-energy radiation) consists of a local orthorhombic structural unit that is repeated by a pseudo-translational symmetry, such that orthorhombic and isometric arrays coexist at different length scales. We also show that inversion in isometric spinel occurs by a similar process. This insight provides a new basis for understanding order-to-disorder transformations important for applications such as plutonium immobilization, fast ion conduction, and thermal barrier coatings.

  19. Development of isometric force and force control in children

    NARCIS (Netherlands)

    Smits-Engelsman, B.C.M.; Westenberg, Y.; Duysens, J.E.J.

    2004-01-01

    Fifty-six children between 5 and 12 years of age and 15 adults performed a task (pressing on a lever with the index finger of the preferred hand), in which a force had to be maintained constant at five levels with on-line visual feedback. Since this is a simple isometric task, the hypothesis is that

  20. Development of isometric force and force control in children.

    NARCIS (Netherlands)

    Smits-Engelsman, B.C.M.; Westenberg, Y.; Duysens, J.E.J.

    2003-01-01

    Fifty-six children between 5 and 12 years of age and 15 adults performed a task (pressing on a lever with the index finger of the preferred hand), in which a force had to be maintained constant at five levels with on-line visual feedback. Since this is a simple isometric task, the hypothesis is that

  1. Probing disorder in isometric pyrochlore and related complex oxides.

    Science.gov (United States)

    Shamblin, Jacob; Feygenson, Mikhail; Neuefeind, Joerg; Tracy, Cameron L; Zhang, Fuxiang; Finkeldei, Sarah; Bosbach, Dirk; Zhou, Haidong; Ewing, Rodney C; Lang, Maik

    2016-05-01

    There has been an increased focus on understanding the energetics of structures with unconventional ordering (for example, correlated disorder that is heterogeneous across different length scales). In particular, compounds with the isometric pyrochlore structure, A2B2O7, can adopt a disordered, isometric fluorite-type structure, (A, B)4O7, under extreme conditions. Despite the importance of the disordering process there exists only a limited understanding of the role of local ordering on the energy landscape. We have used neutron total scattering to show that disordered fluorite (induced intrinsically by composition/stoichiometry or at far-from-equilibrium conditions produced by high-energy radiation) consists of a local orthorhombic structural unit that is repeated by a pseudo-translational symmetry, such that orthorhombic and isometric arrays coexist at different length scales. We also show that inversion in isometric spinel occurs by a similar process. This insight provides a new basis for understanding order-to-disorder transformations important for applications such as plutonium immobilization, fast ion conduction, and thermal barrier coatings.

  2. ASYMPTOTICALLY ISOMETRIC COPIES OF lp (1≤p<∞) AND c0 IN BANACH SPACES

    Institute of Scientific and Technical Information of China (English)

    Chen Dongyang

    2006-01-01

    Let X be a Banach space. If there exists a quotient space of X which is asymptotically isometric to l1, then X contains complemented asymptotically isometric copies of l1. Every infinite dimensional closed subspace of l1 contains a complemented subspace of l1 which is asymptotically isometric to l1. Let X be a separable Banach space such that X* contains asymptotically isometric copies of lp (1 < p <∞). Then there exists a quotient space of X which is asymptotically isometric to lq (1/p+1/q=1). Complementedasymptotically isometric copies of c0 in K(X, Y) and W(X, Y) are discussed. Let X be a Gelfand-Phillips space. If X contains asymptotically isometric copies of c0, it has to contain complemented asymptotically isometric copies of c0.

  3. The effect of heating and cooling on time course of voluntary and electrically induced muscle force variation.

    Science.gov (United States)

    Brazaitis, Marius; Skurvydas, Albertas; Vadopalas, Kazys; Daniusevičiūtė, Laura; Senikienė, Zibuoklė

    2011-01-01

    The aim of this study was to investigate the effect of heating and cooling on time course of voluntary and electrically induced muscle force variation. Ten volunteers performed 50 maximal voluntary and electrically induced contractions of the knee extensors at an angle of 120 degrees under the control conditions and after passive lower body heating and cooling in the control, heating, and cooling experiments. Peak torque, torque variation, and half-relaxation time were assessed during the exercise. Passive lower body heating increased muscle and core temperatures, while cooling lowered muscle temperature, but did not affect core temperature. We observed significantly lower muscle fatigue during voluntary contraction compared with electrically induced contractions. Body heating (opposite to cooling) increased involuntarily induced muscle force, but caused greater electrically induced muscle fatigue. In the middle of the exercise, the coefficient of correlation for electrically induced muscle torque decreased significantly as compared with the beginning of the exercise, while during maximal voluntary contractions, this relation for torque remained significant until the end of the exercise. It was shown that time course of voluntary contraction was more stable than in electrically induced contractions.

  4. Isometric Multipliers of $L^p(G, X)$

    Indian Academy of Sciences (India)

    U B Tewari; P K Chaurasia

    2005-02-01

    Let be a locally compact group with a fixed right Haar measure and a separable Banach space. Let $L^p(G, X)$ be the space of -valued measurable functions whose norm-functions are in the usual $L^p$. A left multiplier of $L^p(G, X)$ is a bounded linear operator on $L^p(G, X)$ which commutes with all left translations. We use the characterization of isometries of $L^p(G, X)$ onto itself to characterize the isometric, invertible, left multipliers of $L^p(G, X)$ for 1 ≤ < ∞, ≠ 2, under the assumption that is not the $l^p$-direct sum of two non-zero subspaces. In fact we prove that if is an isometric left multiplier of $L^p(G, X)$ onto itself then there exists $a y \\in G$ and an isometry of onto itself such that $Tf(x) = U(R_y f)(x)$. As an application, we determine the isometric left multipliers of $L^1 \\cap L^p(G, X)$ and $L^1 \\cap C_0(G, X)$ where is non-compact and is not the $l^p$-direct sum of two non-zero subspaces. If is a locally compact abelian group and is a separable Hilbert space, we define $A^p(G, H)=\\{f\\in l^1(G, H):\\hat{f}\\in L^p(, H)\\}$ where is the dual group of . We characterize the isometric, invertible, left multipliers of $A^p(G, H)$, provided is non-compact. Finally, we use the characterization of isometries of (,) for compact to determine the isometric left multipliers of (,) provided * is strictly convex.

  5. A linear description of shortening induced changes in isometric length-force characteristics of rat muscle

    NARCIS (Netherlands)

    Meijer, K.; Grootenboer, H.J.; Koopman, H.F.J.M.; Huijing, P.A.

    1996-01-01

    Active muscle shortening reduces the isometric force potential of muscle. This observation indicates that the isometric length-force characteristics are altered during muscle shortening. Post-shortening decrease in isometric force depends on starting length, shortening amplitude and shortening veloc

  6. The effects of K+ channel blockade on eccentric and isotonic twitch and fatiguing contractions in situ

    OpenAIRE

    Michelle eMoyer; Erik evan Lunteren

    2012-01-01

    K+ channel blockers like 3,4-diaminopyridine (DAP) can double isometric muscle force. Functional movements require more complex concentric and eccentric contractions, however the effects of K+ channel blockade on these types of contractions in situ are unknown. Extensor digitorum longus (EDL) muscles were stimulated in situ with and without DAP in anesthetized rats and fatigability was addressed using a series of either concentric or eccentric contractions. During isotonic protocols (5-100...

  7. The Effects of K+ Channel Blockade on Eccentric and Isotonic Twitch and Fatiguing Contractions in situ

    OpenAIRE

    van Lunteren, Erik; Moyer, Michelle

    2012-01-01

    K+ channel blockers like 3,4-diaminopyridine (DAP) can double isometric muscle force. Functional movements require more complex concentric and eccentric contractions, however the effects of K+ channel blockade on these types of contractions in situ are unknown. Extensor digitorum longus (EDL) muscles were stimulated in situ with and without DAP in anesthetized rats and fatigability was addressed using a series of either concentric or eccentric contractions. During isotonic protocols (5–100% l...

  8. Voluntary euthanasia: a utilitarian perspective.

    Science.gov (United States)

    Singer, Peter

    2003-10-01

    Belgium legalised voluntary euthanasia in 2002, thus ending the long isolation of the Netherlands as the only country in which doctors could openly give lethal injections to patients who have requested help in dying. Meanwhile in Oregon, in the United States, doctors may prescribe drugs for terminally ill patients, who can use them to end their life--if they are able to swallow and digest them. But despite President Bush's oft-repeated statements that his philosophy is to 'trust individuals to make the right decisions' and his opposition to 'distant bureaucracies', his administration is doing its best to prevent Oregonians acting in accordance with a law that its voters have twice ratified. The situation regarding voluntary euthanasia around the world is therefore very much in flux. This essay reviews ethical arguments regarding voluntary euthanasia and physician-assisted suicide from a utilitarian perspective. I shall begin by asking why it is normally wrong to kill an innocent person, and whether these reasons apply to aiding a person who, when rational and competent, asks to be killed or given the means to commit suicide. Then I shall consider more specific utilitarian arguments for and against permitting voluntary euthanasia.

  9. Social Cohesion and Voluntary Associations

    Science.gov (United States)

    Heuser, Brian L.

    2005-01-01

    Voluntary organizations exert great influence over how social norms and ethical codes are guided into action. As such, they have a significant impact on societal levels of social cohesion. Although social capital involves generalized trust becoming manifest as spontaneous sociability, social cohesion is determined by how that sociability is…

  10. Voluntary Incentive Early Retirement Programs.

    Science.gov (United States)

    Research Dialogues, 1988

    1988-01-01

    Arrangements in educational institutions for voluntary early retirement programs are discussed. Retirement at any age can be a profound and stressful lifetime change; and it can also represent a welcome transition into newly satisfying and rewarding opportunities. The focus is on: mandatory retirement (exceptions and the new meaning of "early");…

  11. Voluntary disclosure: Evidence from UK

    NARCIS (Netherlands)

    N.S. Zourarakis (Nicolaos)

    2009-01-01

    textabstractThis paper investigates the voluntary disclosure of Intellectual Capital (IC) of British firms and provides some evidence on an unexplored area of the literature; that of the association of Corporate Governance (CG) with IC disclosure. Inconsistent with expectations, the results show tha

  12. Administrative contracts

    Directory of Open Access Journals (Sweden)

    Vukićević-Petković Milica

    2015-01-01

    Full Text Available Administrative contracts are a special type of contract where usually one of the contracting parties is a public law body and which is concluded for the performance of public service and the realization of a public interest. They go a long way since its inception to its eventual final acceptance of all the legal systems. One of the enduring characteristics of this type of contract is their disquised or unnoticed existence. This is why only monitoring their development may lead to a complete understanding of the importance and essence of this institution as well as the need for its complete legal regulation.

  13. Electrical contracting

    CERN Document Server

    Neidle, Michael

    2013-01-01

    Electrical Contracting, Second Edition is a nine-chapter text guide for the greater efficiency in planning and completing installations for the design, installation and control of electrical contracts. This book starts with a general overview of the efficient cabling and techniques that must be employed for safe wiring design, as well as the cost estimation of the complete electrical contract. The subsequent chapters are devoted to other electrical contracting requirements, including electronic motor control, lighting, and electricity tariffs. A chapter focuses on the IEE Wiring Regulations an

  14. Voluntary sterilization in Serbia: Unmet need?

    OpenAIRE

    Rašević Mirjana M.

    2002-01-01

    Is voluntary sterilization as a birth control method accepted in Serbia? This is certainly a question that is being imposed for research, regardless of the fact that voluntary sterilization is neither accessible nor promoted. Most importantly because there is no understanding in the social nor political sphere for legalization of voluntary sterilization as a form of birth control, apart from the clear necessity for this, first, step. They are: the recognition that voluntary sterilization is a...

  15. One single bout of low-intensity isometric handgrip exercise reduces blood pressure in healthy pre- and hypertensive individuals.

    Science.gov (United States)

    van Assche, Tim; Buys, Roselien; de Jaeger, Mats; Coeckelberghs, Ellen; Cornelissen, Véronique A

    2017-04-01

    The aim of this study was to investigate the acute effect of one single session of isometric handgrip exercise (IHG) on blood pressure (BP) during daily life activities in healthy adults. Fifteen healthy adults with pre- or stage 1 hypertension (10 men; mean age 48±7.1 years) completed two experimental sessions in random order: one control (rest for 15 minutes) and one low intensity IHG session (4×2 minutes sustained contractions at 30% of maximal volutional contraction interspersed with 1-minute rest intervals). Blood pressure was recorded before each intervention and following the intervention BP was recorded for one hour in the office and thereafter for 6 hours during their daily activities by means of an ambulatory BP device. Physical activity (number of steps and total energy expenditure) was assessed by means of a SenseWear mini device. Systolic BP was higher the first minute after the isometric handgrip exercise but quickly returned to baseline levels after 15 minutes in the office. Over the 7-hour period, systolic blood pressure was significantly lower (-5.4±7.3 vs. +0.23±6.9; Pblood pressure after IHG compared to control (P=0.09). Physical activity behavior was similar on both days (P>0.05). This study demonstrates that one single bout of IHG can result in an overall reduction in BP during daily activities. More research is needed to confirm these findings and to explain possible mechanisms responsible for these observed changes.

  16. 22 CFR 513.210 - Voluntary exclusion.

    Science.gov (United States)

    2010-04-01

    ... 22 Foreign Relations 2 2010-04-01 2010-04-01 true Voluntary exclusion. 513.210 Section 513.210... GOVERNMENTWIDE REQUIREMENTS FOR DRUG-FREE WORKPLACE (GRANTS) Effect of Action § 513.210 Voluntary exclusion. Persons who accept voluntary exclusions under § 513.315 are excluded in accordance with the terms of...

  17. Análise da translação anterior da tíbia, pico de torque e atividade eletromiográfica do quadríceps e isquiotibiais em indivíduos com lesão do ligamento cruzado anterior em cadeia cinética aberta Analysis of anterior tibial translation, peak torque, and quadriceps and hamstrings coactivation in individuals with anterior cruciate ligament injuries performing isometric open kinetic chain exercises

    Directory of Open Access Journals (Sweden)

    Rodrigo Antunes de Vasconcelos

    2007-01-01

    hamstrings EMG activity, passive and active ATT and isometric peak torque respectively during three maximum isometric voluntary contractions at 30 degrees of knee flexion. The results demonstrated that the passive and active ATT is significant greater in knees with acl rupture compared with the contralateral knees, dominant and non dominant knees of the control group. However the active ATT values were greater than the passive ATT. There is no statistic significant differences between groups concerning quadriceps and hamstring EMG activity and in the peak torque produced during the motor task requested. The results of this study demonstrated that individuals with acl rupture had similar behavior compared with normal knees in relation to isometric peak torque and motor control despite the different arthrokinematics of the tibiofemural joint observed in injured knees.

  18. Direct measurement of Vorticella contraction force by micropipette deflection.

    Science.gov (United States)

    France, Danielle; Tejada, Jonathan; Matsudaira, Paul

    2017-02-01

    The ciliated protozoan Vorticella convallaria is noted for its exceptionally fast adenosine triphosphate-independent cellular contraction, but direct measurements of contractile force have proven difficult given the length scale, speed, and forces involved. We used high-speed video microscopy to image live Vorticella stalled in midcontraction by deflection of an attached micropipette. Stall forces correlate with both distance contracted and the resting stalk length. Estimated isometric forces range from 95 to 177 nanonewtons (nN), or 1.12 nN·μm(-1) of the stalk. Maximum velocity and work are also proportional to distance contracted. These parameters constrain proposed biochemical/physical models of the contractile mechanism.

  19. Fuzzy contractibility

    OpenAIRE

    GÜNER, Erdal

    2007-01-01

    Abstract. In this paper, .rstly some fundamental concepts are included re- lating to fuzzy topological spaces. Secondly, the fuzzy connected set is intro- duced. Finally, de.ning fuzzy contractible space, it is shown that X is a fuzzy contractible space if and only if X is fuzzy homotopic equivalent with a fuzzy single-point space.

  20. Resistance Exercise with concurrent whole body vibration preserves isometric knee extension strength during 8 weeks of horizontal bed rest

    Science.gov (United States)

    Mulder, E. R.; Stegeman, D. F.; Gerrits, K.; Rittweger, J.; Felsenberg, D.; de Haan, A.

    2005-08-01

    Changes in the quadriceps femoris (QF) muscle with respect to anatomical cross sectional area (CSA), neural activation level and isometric maximal voluntary torque (MVT) were determined in 18 healthy men subjected to 8 weeks of horizontal bed rest (BR) with (n = 9) and without (Ctrl; n = 9) 6 days/week resistance exercise concurrent with whole body vibration (RVE). For Ctrl, mean QF CSA decreased linearly over time to a reduction of 14.3 ± 4.9% at the end of BR. For RVE, exercise during BR significantly mitigated this reduction (3.9 ± 4.4%). Prior to and seven times during BR, MVT values were obtained together with neural activation levels, the latter by means of a superimposed stimulation technique. MVT was maintained for RVE during BR, whereas for Ctrl, MVT was significantly reduced by 14.2 ± 8.1% after 8 weeks. In contrast to previous reports, the maximal voluntary activation remained unaltered for both groups throughout the study. For Ctrl, the absence of a change in neural activation might be related to the repeated testing during the bed rest, which had presumably resulted in a habituation to the task. When both groups were pooled, a significant positive correlation (R= 0.62; P < 0.01) was observed between changes in CSA and changes in MVT.

  1. Reaganomics: Its Impact on the Voluntary Not-for-Profit Sector.

    Science.gov (United States)

    Demone, Harold W., Jr.; Gibelman, Margaret

    1984-01-01

    Uses several data sources to analyze the effects of reduced funding for human services on the voluntary sector in relation to services offered, use of professional personnel, reliance on service contracts, financing patterns, compensatory responses, and use of volunteers. Comments on the future status of volunteerism. (JAC)

  2. Increase in rate of force development with skin cooling during isometric knee extension.

    Science.gov (United States)

    Shimose, Ryota; Ushigome, Nobuyuki; Tadano, Chigaya; Sugawara, Hitoshi; Yona, Masae; Matsunaga, Atsuhiko; Muro, Masuo

    2014-12-01

    Rate of force development (RFD) plays an important role when performing rapid and forceful movements. Cold-induced afferent input with transient skin cooling (SC) can modulate neural drive. However, the relationship between RFD and SC is unknown. The purpose of this study was to investigate whether SC increases RFD during isometric knee extension. Fifteen young healthy men (25 ± 8 yrs old) contracted their quadriceps muscle as fast and forcefully as possible with or without SC. Skin cooling was administered to the front of the thigh. Torque and electromyographic activity were measured simultaneously. Peak torque was not affected by SC. Skin cooling induced a significant increase in RFD at the phase 0-30 and 0-50 ms. The root mean square of the electromyography of vastus medialis, rectus femoris and vastus lateralis at the phases 0-30-50-100 ms increased significantly or tended to increase with SC. These results suggest that SC may increase neural drive and improve RFD in the very early phases of contraction.

  3. Peripheral Vascular Resistance Impairment during Isometric Physical Exercise in Normotensive Offspring of Hypertensive Parents.

    Science.gov (United States)

    Portela, Natália; Amaral, Josária Ferraz; Mira, Pedro Augusto de Carvalho; Souza, Livia Victorino de; Martinez, Daniel Godoy; Laterza, Mateus Camaroti

    2017-07-10

    A family history of hypertension is associated with vascular and autonomic abnormalities, as well as an impaired neurohemodynamic response to exercise. To test the hypothesis that normotensive individuals with a family history of hypertension present an impaired peripheral vascular resistance response to exercise. The study included 37 normotensive volunteers of both sexes who were sedentary, eutrophic, and nonsmokers, comprising 23 with (FH+; 24 ± 3 years) and 14 without (FH-; 27 ± 5 years) a family history of hypertension. Blood pressure, heart rate (DIXTAL®), forearm blood flow (Hokanson®), and peripheral vascular resistance were simultaneously measured for 3 minutes during rest and, subsequently, for 3 minutes during an isometric exercise at 30% of maximal voluntary contraction (Jamar®). At rest, the FH+ and FH- groups present similar mean blood pressure (83 ± 7 versus 83 ± 5 mmHg, p = 0.96), heart rate (69 ± 8 bpm versus 66 ± 7 bpm, p = 0.18), forearm blood flow (3 ± 1 mL/min/100 mL versus 2.7 ± 1 mL/min/100 mL, p = 0.16), and peripheral vascular resistance (30 ± 9 units versus 34±9 units, p = 0.21), respectively. Both groups showed a significant and similar increase in mean blood pressure (∆ = 15 ± 7 mmHg versus 14 ± 7 mmHg, p = 0.86), heart rate (∆ = 12 ± 8 bpm versus 13 ± 7 bpm, p = 0.86), and forearm blood flow (∆ = 0.8 ± 1.2 mL/min/100 mL versus 1.4 ± 1.1 mL/min/100 mL, p = 0.25), respectively, during exercise. However, individuals in the FH+ group showed no reduction in peripheral vascular resistance during exercise, which was observed in the FH- group (∆ = -0.4 ± 8.6 units versus -7.2 ± 6.3 units, p = 0.03). Normotensive individuals with a family history of hypertension present an impaired peripheral vascular resistance response to exercise. O histórico familiar para hipertensão arterial está relacionado a anormalidades vasculares e autonômicas, bem como disfunções no comportamento neuro-hemodinâmico durante o exerc

  4. Decreased muscle GLUT-4 and contraction-induced glucose transport after eccentric contractions

    DEFF Research Database (Denmark)

    Kristiansen, S; Asp, Svend; Richter, Erik

    1996-01-01

    Eccentric exercise causes muscle damage and decreased muscle glycogen and glucose transporter isoform (GLUT-4) protein content. We investigated whether the contraction-induced increase in skeletal muscle glucose transport and muscle performance is affected by prior eccentric contractions. The calf...... than in CT rats. In the GW and GR muscle, prior eccentric exercise decreased contraction-induced stimulation of glucose transport compared with CT, ST, and CC rats despite no difference in tension development and oxygen uptake among the groups. There was no change in total GLUT-4 content and glucose...... muscles from rats were stimulated for eccentric (EC) or concentric (CC) contractions or were passively stretched (ST). Muscles from unstimulated control (CT) rats were also studied. Two days later, all rats had their isolated hindlimbs perfused either at rest or during 15 min of isometric muscle...

  5. Tendon vibration during submaximal isometric strength and postural tasks.

    Science.gov (United States)

    Spiliopoulou, S I; Amiridis, I G; Hatzitaki, V; Patikas, D; Kellis, E

    2012-11-01

    To establish the effect of tendon vibration (TV) on steady submaximal strength and static balance control, 29 women performed isometric plantarflexions at 10, 20, 30 and 50% of MVC and postural tasks of increasing difficulty (Normal Quiet Stance, NQS, Sharpened Tandem Stance and One Leg Stance) with vibrators (80 Hz) applied to the Achilles tendon. Both tasks were performed under four conditions (10 s each): eyes open, eyes closed, eyes closed with TV, eyes open with TV. During the isometric tasks, the application of TV increased the plantarflexion torque at 20 and 30% of MVC, accompanied by a greater (p vibration-induced muscle excitation and accompanying increase in motor output, probably due to excitatory Ia afferent input, was confirmed during strength and postural tasks. However, motor output attenuates when the magnitude of central drive to the ankle muscles increases.

  6. International Voluntary Renewable Energy Markets (Presentation)

    Energy Technology Data Exchange (ETDEWEB)

    Heeter, J.

    2012-06-01

    This presentation provides an overview of international voluntary renewable energy markets, with a focus on the United States and Europe. The voluntary renewable energy market is the market in which consumers and institutions purchase renewable energy to match their electricity needs on a voluntary basis. In 2010, the U.S. voluntary market was estimated at 35 terawatt-hours (TWh) compared to 300 TWh in the European market, though key differences exist. On a customer basis, Australia has historically had the largest number of customers, pricing for voluntary certificates remains low, at less than $1 megawatt-hour, though prices depend on technology.

  7. Combined isometric, concentric, and eccentric resistance exercise prevents unloading-induced muscle atrophy in rats.

    Science.gov (United States)

    Adams, G R; Haddad, F; Bodell, P W; Tran, P D; Baldwin, K M

    2007-11-01

    Previously, we reported that an isometric resistance training program that was effective in stimulating muscle hypertrophy in ambulatory rats could not completely prevent muscle atrophy during unloading (Haddad F, Adams GR, Bodell PW, Baldwin KM. J Appl Physiol 100: 433-441, 2006). These results indicated that preventing muscle atrophy does not appear to be simply a function of providing an anabolic stimulus. The present study was undertaken to determine if resistance training, with increased volume (3-s contractions) and incorporating both static and dynamic components, would be effective in preventing unloading-induced muscle atrophy. Rats were exposed to 5 days of muscle unloading via tail suspension. During that time one leg received electrically stimulated resistance exercise (RE) that included an isometric, concentric, and eccentric phase. The results of this study indicate that this combined-mode RE provided an anabolic stimulus sufficient to maintain the mass and myofibril content of the trained but not the contralateral medial gastrocnemius (MG) muscle. Relative to the contralateral MG, the RE stimulus increased the amount of total RNA (indicative of translational capacity) as well as the mRNA for several anabolic/myogenic markers such as insulin-like growth factor-I, myogenin, myoferlin, and procollagen III-alpha-1 and decreased that of myostatin, a negative regulator of muscle size. The combined-mode RE protocol also increased the activity of anabolic signaling intermediates such as p70S6 kinase. These results indicate that a combination of static- and dynamic-mode RE of sufficient volume provides an effective stimulus to stimulate anabolic/myogenic mechanisms to counter the initial stages of unloading-induced muscle atrophy.

  8. The influence of isometric preload on power expressed during bench press in strength-trained men.

    Science.gov (United States)

    Bartolomei, Sandro; Fukuda, David H; Hoffman, Jay R; Stout, Jeffrey R; Merni, Franco

    2017-03-01

    The purpose of this study was to compare the power expressed during the bench press exercise in resistance-trained men following different pre-activation conditions. Twenty-two trained men (age 24.1 ± 1.7 years, height 178.6 ± 6.1 cm, body mass 81.1 ± 10.6 kg) completed a maximal effort bench press (1-RM) test (100.0 kg ± 8.1 kg). In a subsequent assessment, each participant performed concentric bench press movements with loads of 20%, 30%, 40% and 50% of their 1-RM preceded by either a concentric contraction (CC), a low isometric preload (LIP; 70% 1-RM) or a high isometric preload (HIP; 100% 1-RM) conditions. All movements were performed in a Smith machine with a settable quick-release device. Participants performed all three conditions in randomized fashion. Results indicated that power outputs during the bench press exercise following HIP were significantly (p < 0.05) greater than CC at 20% 1-RM (+9%), 30% 1-RM (+16%) and 40% 1-RM (+14%), and LIP at 20% 1-RM (+4%), 30% 1-RM (+20%) and 40% 1-RM (+15%). No differences were found between conditions at 50% 1-RM. Area under the force-power curve with HIP was greater (p < 0.05) than with CC and LIP. In conclusion, results of this study indicate that the use of a HIP (100% 1-RM) in trained participants results in significantly greater power output during the concentric phase of a multi-joint exercise when compared to standard concentric movement.

  9. Intramuscular fiber conduction velocity, isometric force and explosive performance

    OpenAIRE

    Methenitis Spyridon; Terzis Gerasimos; Zaras Nikolaos; Stasinaki Angeliki-Nikoletta; Karandreas Nikolaos

    2016-01-01

    Conduction of electrical signals along the surface of muscle fibers is acknowledged as an essential neuromuscular component which is linked with muscle force production. However, it remains unclear whether muscle fiber conduction velocity (MFCV) is also linked with explosive performance. The aim of the present study was to investigate the relationship between vastus lateralis MFCV and countermovement jumping performance, the rate of force development and maximum isometric force. Fifteen moder...

  10. Intramuscular fiber conduction velocity, isometric force and explosive performance

    OpenAIRE

    Methenitis, Spyridon; Terzis, Gerasimos; Zaras, Nikolaos; Stasinaki, Angeliki-Nikoletta; Karandreas, Nikolaos

    2016-01-01

    Abstract Conduction of electrical signals along the surface of muscle fibers is acknowledged as an essential neuromuscular component which is linked with muscle force production. However, it remains unclear whether muscle fiber conduction velocity (MFCV) is also linked with explosive performance. The aim of the present study was to investigate the relationship between vastus lateralis MFCV and countermovement jumping performance, the rate of force development and maximum isometric force. Fift...

  11. Decomposition of surface EMG signals from cyclic dynamic contractions.

    Science.gov (United States)

    De Luca, Carlo J; Chang, Shey-Sheen; Roy, Serge H; Kline, Joshua C; Nawab, S Hamid

    2015-03-15

    Over the past 3 decades, various algorithms used to decompose the electromyographic (EMG) signal into its constituent motor unit action potentials (MUAPs) have been reported. All are limited to decomposing EMG signals from isometric contraction. In this report, we describe a successful approach to decomposing the surface EMG (sEMG) signal collected from cyclic (repeated concentric and eccentric) dynamic contractions during flexion/extension of the elbow and during gait. The increased signal complexity introduced by the changing shapes of the MUAPs due to relative movement of the electrodes and the lengthening/shortening of muscle fibers was managed by an incremental approach to enhancing our established algorithm for decomposing sEMG signals obtained from isometric contractions. We used machine-learning algorithms and time-varying MUAP shape discrimination to decompose the sEMG signal from an increasingly challenging sequence of pseudostatic and dynamic contractions. The accuracy of the decomposition results was assessed by two verification methods that have been independently evaluated. The firing instances of the motor units had an accuracy of ∼90% with a MUAP train yield as high as 25. Preliminary observations from the performance of motor units during cyclic contractions indicate that during repetitive dynamic contractions, the control of motor units is governed by the same rules as those evidenced during isometric contractions. Modifications in the control properties of motoneuron firings reported by previous studies were not confirmed. Instead, our data demonstrate that the common drive and hierarchical recruitment of motor units are preserved during concentric and eccentric contractions.

  12. Isometric Contractions Are More Analgesic Than Isotonic Contractions for Patellar Tendon Pain : An In-Season Randomized Clinical Trial

    NARCIS (Netherlands)

    Rio, Ebonie; van Ark, Mathijs; Docking, Sean; Moseley, G Lorimer; Kidgell, Dawson; Gaida, Jamie E; van den Akker-Scheek, Inge; Zwerver, Johannes; Cook, Jill

    2016-01-01

    OBJECTIVE: This study aimed to compare the immediate analgesic effects of 2 resistance programs in in-season athletes with patellar tendinopathy (PT). Resistance training is noninvasive, a principle stimulus for corticospinal and neuromuscular adaptation, and may be analgesic. DESIGN: Within-season

  13. Isometric Contractions Are More Analgesic Than Isotonic Contractions for Patellar Tendon Pain : An In-Season Randomized Clinical Trial

    NARCIS (Netherlands)

    Rio, Ebonie; van Ark, Mathijs; Docking, Sean; Moseley, G. Lorimer; Kidgell, Dawson; Gaida, Jamie E.; van den Akker-Scheek, Inge; Zwerver, Johannes; Cook, Jill

    2017-01-01

    Objective: This study aimed to compare the immediate analgesic effects of 2 resistance programs in in-season athletes with patellar tendinopathy (PT). Resistance training is noninvasive, a principle stimulus for corticospinal and neuromuscular adaptation, and may be analgesic. Design: Within-season

  14. Double-leg isometric exercise training in older men

    Directory of Open Access Journals (Sweden)

    Baross AW

    2013-01-01

    Full Text Available Anthony W Baross,1 Jonathan D Wiles,2 Ian L Swaine21Sport and Exercise Science, University of Northampton, Northampton, UK; 2Sport and Exercise Science, Canterbury Christ Church University, Canterbury, Kent, UKAbstract: Double-leg isometric training has been demonstrated to reduce resting blood pressure in young men when using electromyographic activity (EMG to regulate exercise intensity. This study assessed this training method in healthy older (45–60 years. men. Initially, 35 older men performed an incremental isometric exercise test to determine the linearity of the heart rate versus percentage peak EMG (%EMGpeak and systolic blood pressure versus %EMGpeak relationship. Thereafter, 20 participants were allocated to a training or control group. The training group performed three double-leg isometric sessions per week for 8 weeks, at 85% of peak heart rate. The training resulted in a significant reduction in resting systolic (11 ± 8 mmHg, P < 0.05 and mean arterial (5 ± 7 mmHg, P < 0.05 blood pressure. There was no significant change in resting systolic blood pressure for the control group or diastolic blood pressure in either group (all P > 0.05. These findings show that this training method, used previously in young men, is also effective in reducing resting systolic and mean arterial blood pressure in older men.Keywords: electromyography, resting blood pressure, heart rate

  15. Effects of prolonged and acute muscle pain on the force control strategy during isometric contractions

    DEFF Research Database (Denmark)

    Mista, Christian Ariel; Bergin, M.; Hirata, Rogerio Pessoto;

    2016-01-01

    -10 numeric scale) in the NGF-group on day-2 whereas maximum saline-induced pain was 6.8±0.3 cm (10-cm visual analogue scale). The difference in centroid position of force direction relative to day-0 was greater in the NGF-group than controls (P

  16. System identification of evoked mechanomyogram from abductor pollicis brevis musc