scholarly journals Repeated contractions alter the geometry of human skeletal muscle

2002 ◽  
Vol 93 (6) ◽  
pp. 2089-2094 ◽  
Author(s):  
Constantinos N. Maganaris ◽  
Vasilios Baltzopoulos ◽  
Anthony J. Sargeant
Keyword(s):  
Skeletal Muscle ◽  
Maximal Voluntary Contraction ◽  
Human Skeletal Muscle ◽  
Voluntary Contraction ◽  
Pennation Angle ◽  
Medial Gastrocnemius ◽  
Myotendinous Junction ◽  
Rest Interval ◽  
In Series ◽  
The Moment

The aim of this study was to investigate the effect of repeated contractions on the geometry of human skeletal muscle. Six men performed two sets ( sets Aand B) of 10 repeated isometric plantarflexion contractions at 80% of the moment generated during plantarflexion maximal voluntary contraction (MVC), with a rest interval of 15 min between sets. By use of ultrasound, the geometry of the medial gastrocnemius (MG) muscle was measured in the contractions of set A and the displacement of the MG tendon origin in the myotendinous junction was measured in the contractions of set B. In the transition from the 1st to the 10th contractions, the fascicular length at 80% of MVC decreased from 34 ± 4 (means ± SD) to 30 ± 3 mm ( P < 0.001), the pennation angle increased from 35 ± 3 to 42 ± 3° ( P < 0.001), the myotendinous junction displacement increased from 5 ± 3 to 10 ± 3 mm ( P < 0.001), and the average fascicular curvature remained constant ( P > 0.05) at ∼4.3 m−1. No changes ( P > 0.05) were found in fascicular length, pennation angle, and myotendinous junction displacement after the fifth contraction. Electrogoniometry showed that the ankle rotated by ∼6.5° during contraction, but no differences ( P > 0.05) were obtained between contractions. The present results show that repeated contractions induce tendon creep, which substantially affects the geometry of the in-series contracting muscles, thus altering their potential for force and joint moment generation.

Metabolism of Exercising and Resting Human Skeletal Muscle, in the Post-Prandial and Fasting States

1973 ◽  
Vol 44 (5) ◽  
pp. 479-491 ◽  
Author(s):  
Patricia G. B. Baker ◽  
R. F. Mottram
Keyword(s):  
Carbon Dioxide ◽  
Skeletal Muscle ◽  
Oxygen Uptake ◽  
Glucose Uptake ◽  
Maximal Voluntary Contraction ◽  
Human Skeletal Muscle ◽  
Voluntary Contraction ◽  
Contraction Force ◽  
Carbon Dioxide Output

1. Methods are described for study of metabolism of human skeletal muscle in situ, at rest and during mild sustained contraction in the fed and fasted states. 2. At rest the average oxygen uptake was 0.29 ml min−1 100 ml of muscle−1 and the carbon dioxide output was 0.22 ml. Glucose uptake was 0.49 mg min−1 100 ml of muscle−1. The respiratory quotient was 0.75, indicating that most of the glucose was being stored. 3. When subjects made hand-grips of 5% of their maximal voluntary contraction force (5% MVC) the oxygen and carbon dioxide exchanges both increased by six times while the glucose uptake increased by 70% of the resting value. 4. A 7 h fast before the observations were made severely decreased both resting and exercising glucose uptake but produced no other alteration in the metabolism of the muscle.

MRI measures of perfusion-related changes in human skeletal muscle during progressive contractions

2004 ◽  
Vol 97 (6) ◽  
pp. 2385-2394 ◽  
Author(s):  
D. M. Wigmore ◽  
B. M. Damon ◽  
D. M. Pober ◽  
J. A. Kent-Braun
Keyword(s):  
Skeletal Muscle ◽  
Blood Flow ◽  
Maximal Voluntary Contraction ◽  
Human Skeletal Muscle ◽  
Venous Occlusion ◽  
Voluntary Contraction ◽  
Arterial Blood Flow ◽  
Arterial Blood ◽  
Planar Images

Although skeletal muscle perfusion is fundamental to proper muscle function, in vivo measurements are typically limited to those of limb or arterial blood flow, rather than flow within the muscle bed itself. We present a noninvasive functional MRI (fMRI) technique for measuring perfusion-related signal intensity (SI) changes in human skeletal muscle during and after contractions and demonstrate its application to the question of occlusion during a range of contraction intensities. Eight healthy men (aged 20–31 yr) performed a series of isometric ankle dorsiflexor contractions from 10 to 100% maximal voluntary contraction. Axial gradient-echo echo-planar images (repetition time = 500 ms, echo time = 18.6 ms) were acquired continuously before, during, and following each 10-s contraction, with 4.5-min rest between contractions. Average SI in the dorsiflexor muscles was calculated for all 240 images in each contraction series. Postcontraction hyperemia for each force level was determined as peak change in SI after contraction, which was then scaled to that obtained following a 5-min cuff occlusion of the thigh (i.e., maximal hyperemia). A subset of subjects ( n = 4) performed parallel studies using venous occlusion plethysmography to measure limb blood flow. Hyperemia measured by fMRI and plethysmography demonstrated good agreement. Postcontraction hyperemia measured by fMRI scaled with contraction intensity up to ∼60% maximal voluntary contraction. fMRI provides a noninvasive means of quantifying perfusion-related changes during and following skeletal muscle contractions in humans. Temporal changes in perfusion can be observed, as can the heterogeneity of perfusion across the muscle bed.

scholarly journals Motor unit firing patterns on increasing force during force and position tasks

2021 ◽  
Author(s):  
Shun Kunugi ◽  
Ales Holobar ◽  
Tsutomu Kodera ◽  
Heishiro Toyoda ◽  
Kohei Watanabe
Keyword(s):  
Firing Rate ◽  
Motor Unit ◽  
Maximal Voluntary Contraction ◽  
Gastrocnemius Muscle ◽  
Voluntary Contraction ◽  
Medial Gastrocnemius ◽  
Firing Patterns ◽  
Motor Unit Firing ◽  
The Difference ◽  
Medial Gastrocnemius Muscle

Different neurophysiological strategies are used to perform angle adjustments during motor tasks such as car driving and force-control tasks using a fixed-rigid pedal. However, the difference in motor unit behavior in response to an increasing exerted force between tasks is unknown. This study aimed to investigate the difference in motor unit responsiveness on increasing force between force and position tasks. Twelve healthy participants performed ramp and hold contractions during ankle plantarflexion at 20 and 30% of the maximal voluntary contraction using a rigid pedal (force task) and a free pedal with an inertial load (position task). High-density surface electromyograms were recorded of the medial gastrocnemius muscle and decomposed into individual motor unit firing patterns. Ninety and 109 motor units could be tracked between different target torques in each task. The mean firing rate increased and firing rate variability decreased on 10% maximal voluntary contraction force gain during both force and position tasks. There were no significant differences in these responses between the two tasks. Our results suggest that the motor unit firing rate is similarly regulated between force and position tasks in the medial gastrocnemius muscle with an increase in the exerted force.

A three-dimensional approach to pennation angle estimation for human skeletal muscle

2014 ◽  
Vol 18 (13) ◽  
pp. 1474-1484 ◽  
Author(s):  
Dongwoon Lee ◽  
Zhi Li ◽  
Qazi Zain Sohail ◽  
Ken Jackson ◽  
Eugene Fiume ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Human Skeletal Muscle ◽  
Three Dimensional ◽  
Pennation Angle ◽  
Dimensional Approach ◽  
Angle Estimation

In vivo determination of fascicle curvature in contracting human skeletal muscles

2002 ◽  
Vol 92 (1) ◽  
pp. 129-134 ◽  
Author(s):  
Tadashi Muramatsu ◽  
Tetsuro Muraoka ◽  
Yasuo Kawakami ◽  
Akira Shibayama ◽  
Tetsuo Fukunaga
Keyword(s):  
Maximum Voluntary Contraction ◽  
Muscle Length ◽  
Muscle Thickness ◽  
Voluntary Contraction ◽  
Pennation Angle ◽  
Medial Gastrocnemius ◽  
Fascicle Length ◽  
Fascicle Curvature

Fascicle curvature of human medial gastrocnemius muscle (MG) was determined in vivo by ultrasonography during isometric contractions at three (distal, central, and proximal) locations ( n = 7) and at three ankle angles ( n = 7). The curvature significantly ( P < 0.05) increased from rest to maximum voluntary contraction (MVC) (0.4–5.2 m−1). In addition, the curvature at MVC became larger in the order dorsiflexed, neutral, plantar flexed ( P < 0.05). Thus both contraction levels and muscle length affected the curvature. Intramuscular differences in neither the curvature nor the fascicle length were found. The direction of curving was consistent along the muscle: fascicles were concave in the proximal side. Fascicle length estimated from the pennation angle and muscle thickness, under the assumption that the fascicle was straight, was underestimated by ∼6%. In addition, the curvature was significantly correlated to pennation angle and muscle thickness. These findings are particularly important for understanding the mechanical functions of human skeletal muscle in vivo.

scholarly journals Shifting gears: dynamic muscle shape changes and force-velocity behavior in the medial gastrocnemius

2017 ◽  
Vol 123 (6) ◽  
pp. 1433-1442 ◽  
Author(s):  
Taylor J. M. Dick ◽  
James M. Wakeling
Keyword(s):  
Skeletal Muscle ◽  
Muscle Activation ◽  
Mechanical Performance ◽  
Shape Change ◽  
Muscle Thickness ◽  
Pennation Angle ◽  
Medial Gastrocnemius ◽  
Force Velocity ◽  
Shape Changes

When muscles contract, they bulge in thickness or in width to maintain a (nearly) constant volume. These dynamic shape changes are tightly linked to the internal constraints placed on individual muscle fibers and play a key functional role in modulating the mechanical performance of skeletal muscle by increasing its range of operating velocities. Yet to date we have a limited understanding of the nature and functional implications of in vivo dynamic muscle shape change under submaximal conditions. This study determined how the in vivo changes in medial gastrocnemius (MG) fascicle velocity, pennation angle, muscle thickness, and subsequent muscle gearing varied as a function of force and velocity. To do this, we obtained recordings of MG tendon length, fascicle length, pennation angle, and thickness using B-mode ultrasound and muscle activation using surface electromyography during cycling at a range of cadences and loads. We found that that increases in contractile force were accompanied by reduced bulging in muscle thickness, reduced increases in pennation angle, and faster fascicle shortening. Although the force and velocity of a muscle contraction are inversely related due to the force-velocity effect, this study has shown how dynamic muscle shape changes are influenced by force and not influenced by velocity.NEW & NOTEWORTHY During movement, skeletal muscles contract and bulge in thickness or width. These shape changes play a key role in modulating the performance of skeletal muscle by increasing its range of operating velocities. Yet to date the underlying mechanisms associated with muscle shape change remain largely unexplored. This study identified muscle force, and not velocity, as the mechanistic driving factor to allow for muscle gearing to vary depending on the contractile conditions during human cycling.

Limiting mechanisms of force production after repetitive dynamic contractions in human triceps surae

2004 ◽  
Vol 96 (4) ◽  
pp. 1516-1521 ◽  
Author(s):  
M. Klass ◽  
N. Guissard ◽  
J. Duchateau
Keyword(s):  
Maximal Voluntary Contraction ◽  
Muscle Activation ◽  
Voluntary Contraction ◽  
Triceps Surae ◽  
Medial Gastrocnemius ◽  
Emg Activity ◽  
Neutral Position ◽  
M Wave ◽  
Human Triceps Surae ◽  
Fatiguing Contractions

The influence of repetitive dynamic fatiguing contractions on the neuromuscular characteristics of the human triceps surae was investigated in 10 subjects. The load was 50% of the torque produced during a maximal voluntary contraction, and the exercise ended when the ankle range of motion declined to 50% of control. The maximal torque of the triceps surae and the electromyographic (EMG) activities of the soleus and medial gastrocnemius were studied in response to voluntary and electrically induced contractions before and after the fatiguing task and after 5 min of recovery. Reflex activities were also tested by recording the Hoffmann reflex (H reflex) and tendon reflex (T reflex) in the soleus muscle. The results indicated that whereas the maximal voluntary contraction torque, tested in isometric conditions, was reduced to a greater extent ( P < 0.05) at 20° of plantar flexion (-33%) compared with the neutral position (-23%) of the ankle joint, the EMG activity of both muscles was not significantly reduced after fatigue. Muscle activation, tested by the interpolated-twitch method or the ratio of the voluntary EMG to the amplitude of the muscle action potential (M-wave), as well as the neuromuscular transmission and sarcolemmal excitation, tested by the M-wave amplitude, did not change significantly after the fatiguing exercise. Although the H and T reflexes declined slightly (10-13%; P < 0.05) after fatigue, these adjustments did not appear to have a direct deleterious effect on muscle activation. In contrast, alterations in the mechanical twitch time course and postactivation potentiation indicated that intracellular Ca2+-controlled excitation-contraction coupling processes most likely played a major role in the force decrease after dynamic fatiguing contractions performed for short duration.

scholarly journals Absence of phosphocreatine resynthesis in human calf muscle during ischaemic recovery

1993 ◽  
Vol 291 (3) ◽  
pp. 681-686 ◽  
Author(s):  
B Quistorff ◽  
L Johansen ◽  
K Sahlin
Keyword(s):  
Skeletal Muscle ◽  
Time Resolution ◽  
Isometric Contraction ◽  
Human Skeletal Muscle ◽  
Voluntary Contraction ◽  
Calf Muscle ◽  
Elevated Concentration ◽  
Anaerobic Glycolysis ◽  
Phosphocreatine Resynthesis ◽  
Human Calf

Changes in the metabolites phosphocreatine (PCr), Pi and ATP were quantified by 31P n.m.r. spectroscopy in the human calf muscle during isometric contraction and recovery under ischaemic conditions. Time resolution of the measurements was 10 s. During a 30-60 s ischaemic isometric contraction, PCr decreased linearly at a rate of 1.17%/s (relative to the resting value) at a contraction strength equivalent to 70% of the maximal voluntary contraction (MVC) and at a rate of 2.43%/s at 90% MVC. There was a corresponding increase in Pi but the concentration of ATP did not change. pH decreased linearly during contraction by 4.22 and 8.23 milli-pH units/s at 70 and 90% MVC respectively. During a subsequent 5 min interval of ischaemic recovery, PCr, Pi, ATP, phosphomonoesters and calculated free ADP, free AMP and pH retained the value they had attained by the end of contraction with no significant recovery. Thus it is concluded that anaerobic glycolysis and glycogenolysis is halted momentarily on termination of contraction and that PCr is not resynthesized during ischaemic recovery. This paradoxical arrest of glycolytic flow in spite of the very significantly elevated concentration of potent activators such as Pi and free AMP clearly indicates that parameters other than PCr, ATP, Pi, calculated pH, free ADP and free AMP regulate glycolysis and glycogenolysis of human skeletal muscle very efficiently under ischaemic conditions.

scholarly journals Time to task failure and muscle activation vary with load type for a submaximal fatiguing contraction with the lower leg

2008 ◽  
Vol 105 (2) ◽  
pp. 463-472 ◽  
Author(s):  
Sandra K. Hunter ◽  
Tejin Yoon ◽  
Joseph Farinella ◽  
Erin E. Griffith ◽  
Alexander V. Ng
Keyword(s):  
Maximal Voluntary Contraction ◽  
Muscle Activation ◽  
Lower Leg ◽  
Voluntary Contraction ◽  
Medial Gastrocnemius ◽  
Emg Activity ◽  
Time To Failure ◽  
Contraction Force ◽  
Task Failure ◽  
Position Task

The purpose was to compare the time to failure and muscle activation patterns for a sustained isometric submaximal contraction with the dorsiflexor muscles when the foot was restrained to a force transducer (force task) compared with supporting an equivalent inertial load and unrestrained (position task). Fifteen men and women (mean ± SD; 21.1 ± 1.4 yr) performed the force and position tasks at 20% maximal voluntary contraction force until task failure. Maximal voluntary contraction force performed before the force and position tasks was similar (333 ± 71 vs. 334 ± 65 N), but the time to task failure was briefer for the position task (10.0 ± 6.2 vs. 21.3 ± 17.8 min, P < 0.05). The rate of increase in agonist root-mean-square electromyogram (EMG), EMG bursting activity, rating of perceived exertion, fluctuations in motor output, mean arterial pressure, and heart rate during the fatiguing contraction was greater for the position task. EMG activity of the vastus lateralis (lower leg stabilizer) and medial gastrocnemius (antagonist) increased more rapidly during the position task, but coactivation ratios (agonist vs. antagonist) were similar during the two tasks. Thus the difference in time to failure for the two tasks with the dorsiflexor muscles involved a greater level of neural activity and rate of motor unit recruitment during the position task, but did not involve a difference in coactivation. These findings have implications for rehabilitation and ergonomics in minimizing fatigue during prolonged activation of the dorsiflexor muscles.

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