scholarly journals Velocity of the muscle tendon unit is sex-dependent and not altered with acute static stretch

2018 ◽  
Vol 43 (3) ◽  
pp. 227-232 ◽  
Author(s):  
Carey L. Simpson ◽  
Rowan R. Smart ◽  
Dylan E.E. Melady ◽  
Jennifer M. Jakobi
Keyword(s):  
Plantar Flexion ◽  
Voluntary Contraction ◽  
Voluntary Activation ◽  
Plantar Flexors ◽  
Shortening Velocity ◽  
Static Stretch ◽  
Twitch Interpolation ◽  
Tendon Lengthening ◽  
The Individual ◽  
The Relationship

Contraction velocity of a muscle tendon unit (MTU) is dependent upon the interrelationship between fascicles shortening and the tendon lengthening. Altering the mechanical properties of these tissues through a perturbation such as static stretching slows force generation. Females, who have inherently greater compliance compared with males, have slower velocity of MTU components. The addition of a static stretch might further exacerbate this sex difference. The purpose of this study was to investigate the velocity of fascicle shortening and tendon lengthening in males and females during isometric maximal voluntary contraction (MVC) of the plantar flexors prior to and following an acute static stretch. The MTU was imaged with ultrasound and voluntary activation tested with twitch interpolation for the 5-s plantar flexion MVC, which proceeded and followed an acute stretch. For the 3-min stretch the ankle was passively rotated to maximal dorsi-flexion. The males were stronger (128.71 ± 7.88 Nm) than the females (89.92 ± 4.70 Nm) but voluntary activation did not differ. Tendon lengthening velocity (p = 0.001) and fascicle shortening velocity (p = 0.01) were faster in males than females. Tendon velocity was positively and significantly correlated with fascicle velocity, (r2 = 0.307, p = 0.02). Although sex was significant as a predictor (p = 0.05) time was not independently significant. Thus, stretch did not alter this relationship in either sex (p = 0.6). The velocity of the individual components of the MTU is slower in females when compared with males; however, acute stretch does not alter the relationship between these components in males or females.

scholarly journals Sex differences in central and peripheral fatigue induced by sustained isometric ankle plantar flexion

2021 ◽  
Author(s):  
Donguk Jo ◽  
Miriam Goubran ◽  
Martin Bilodeau
Keyword(s):  
Sex Differences ◽  
Plantar Flexion ◽  
Recovery Period ◽  
Isometric Exercise ◽  
Voluntary Contraction ◽  
Voluntary Activation ◽  
Peripheral Fatigue ◽  
Plantar Flexors ◽  
Maximal Voluntary Isometric Contraction ◽  
Males And Females

The main aim of this study was to determine sex differences in central and peripheral fatigue produced by a sustained isometric exercise of ankle plantar flexors in healthy young adults. Ten males and fourteen females performed a sustained isometric ankle exercise until task failure. Maximal voluntary isometric contraction torque (plantarflexion), voluntary activation level (using the twitch interpolation technique), and twitch contractile properties (twitch peak torque, twitch half relaxation time, and low frequency fatigue index) were measured before, immediately after, and throughout a recovery period (1, 2, 5, and 10 min) following the exercise protocol in order to characterize neuromuscular fatigue. Fatigue had a significant effect (p £ 0.05) on all dependent variables. Other than for the maximal voluntary contraction torque, where males showed a greater fatigue-related decrease than females, males and females showed generally similar changes with fatigue. Altogether, our findings indicate no major differences in central or peripheral fatigue mechanisms between males and females to explain a somewhat greater fatigability in males.

Mechanical and electromyographic analysis of reciprocal inhibition at the human ankle joint

1995 ◽  
Vol 74 (2) ◽  
pp. 849-855 ◽  
Author(s):  
T. Sinkjaer ◽  
J. Nielsen ◽  
E. Toft
Keyword(s):  
Ankle Joint ◽  
Stretch Reflex ◽  
Plantar Flexion ◽  
Joint Stiffness ◽  
Common Peroneal Nerve ◽  
Reciprocal Inhibition ◽  
Mechanical Effect ◽  
Voluntary Contraction ◽  
Plantar Flexors ◽  
Before And After

1. The purpose of the present study is to investigate how reciprocal inhibition influences the mechanical and electromyographic (EMG) properties of the ankle plantar flexors in humans during a voluntary contraction. 2. At different levels of maintained plantar flexion contractions ranging from 0 to 20 Nm, the size of the soleus EMG stretch reflex and the ankle joint stiffness (ration between the torque increment and the amplitude of the stretch) were measured in response to an imposed dorsiflexion. At matched plantar flexion contraction levels, stretch responses were compared before and after reversible block of the common peroneal nerve (CPN). Stretch responses were also measured during an attempted voluntary fictive dorsiflexion after CPN block. 3. In the preactivated soleus muscles, the phasic EMG response to stretch consisted of two peaks labeled M1 and M2. After CPN block, the M1 short-latency stretch reflex on average increased by 25 +/- 5.7%, mean +/- SD (P < 0.001), and the M2 stretch reflex increased on average by 29 +/- 13.0% (P = 0.002). 4. The total stiffness of the ankle joint during a stretch is the sum of the nonreflex and the reflex mediated stiffness. The total stiffness after CPN block increased on average by 13 +/- 2.7% (P = 0.002) and the estimated reflex stiffness by 33 +/- 6.5% (P < 0.001). 5. When the subjects were asked to make a strong dorsiflexion after CPN block, the soleus stretch reflex was depressed to the extent that the reflex mediated mechanical effect around the ankle joint was abolished.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of neuromuscular adjustments associated with sustained isometric contractions of four different muscle groups

2013 ◽  
Vol 114 (10) ◽  
pp. 1426-1434 ◽  
Author(s):  
Daria Neyroud ◽  
Jennifer Rüttimann ◽  
Anne F. Mannion ◽  
Guillaume Y. Millet ◽  
Nicola A. Maffiuletti ◽  
...  
Keyword(s):  
Muscle Fatigue ◽  
Upper Limb ◽  
Voluntary Contraction ◽  
Voluntary Activation ◽  
Knee Extensors ◽  
Elbow Flexors ◽  
Plantar Flexors ◽  
Task Failure ◽  
Before And After ◽  
Muscle Groups

The extent and characteristics of muscle fatigue of different muscle groups when subjected to a similar fatiguing task may differ. Thirteen healthy young men performed sustained contractions at 50% maximal voluntary contraction (MVC) force until task failure, with four different muscle groups, over two sessions. Per session, one upper limb and one lower limb muscle group were tested (knee extensors and thumb adductor, or plantar and elbow flexors). Changes in voluntary activation level and contractile properties were derived from doublet responses evoked during and after MVCs before and after exercise. Time to task failure differed ( P < 0.05) between muscle groups (220 ± 64 s for plantar flexors, 114 ± 27 s for thumb adductor, 77 ± 25 s for knee extensors, and 72 ± 14 s for elbow flexors). MVC force loss immediately after voluntary task failure was similar (−30 ± 11% for plantar flexors, −37 ± 13% for thumb adductor, −34 ± 15% for knee extensors, and −40 ± 12% for elbow flexors, P > 0.05). Voluntary activation was decreased for plantar flexors only (from 95 ± 5% to 82 ± 9%, P < 0.05). Potentiated evoked doublet amplitude was more depressed for upper limb muscles (−59.3 ± 14.7% for elbow flexors and −60.1 ± 24.1% for thumb adductor, P < 0.05) than for knee extensors (−28 ± 15%, P < 0.05); no reduction was found in plantar flexors (−7 ± 12%, P > 0.05). In conclusion, despite different times to task failure when sustaining an isometric contraction at 50% MVC force for as long as possible, diverse muscle groups present similar loss of MVC force after task failure. Thus the extent of muscle fatigue is not affected by time to task failure, whereas this latter determines the etiology of fatigue.

Twitch Interpolation in Human Muscles: Mechanisms and Implications for Measurement of Voluntary Activation

1999 ◽  
Vol 82 (5) ◽  
pp. 2271-2283 ◽  
Author(s):  
R. D. Herbert ◽  
S. C. Gandevia
Keyword(s):  
Time Course ◽  
Full Range ◽  
Electrical Stimulus ◽  
Voluntary Contraction ◽  
Voluntary Activation ◽  
Time To Peak ◽  
Motoneuron Pool ◽  
Twitch Interpolation ◽  
Muscle Nerve ◽  
Force Drop

An electrical stimulus delivered to a muscle nerve during a maximal voluntary contraction usually produces a twitchlike increment in force. The amplitude of this “interpolated twitch” is widely used to measure voluntary “activation” of muscles. In the present study, a computer model of the human adductor pollicis motoneuron pool was used to investigate factors that affect the interpolated twitch. Antidromic occlusion of naturally occurring orthodromic potentials was modeled, but reflex effects of the stimulus were not. In simulations, antidromic collisions occurred with probabilities of between ∼16% (in early recruited motoneurons) and nearly 100% (in late recruited motoneurons). The model closely predicted experimental data on the amplitude and time course of the rising phase of interpolated twitches over the full range of voluntary forces, except that the amplitude of interpolated twitches was slightly overestimated at intermediate contraction intensities. Small interpolated twitches (4.7% of the resting twitch) were evident in simulated maximal voluntary contractions, but were nearly completely occluded when mean peak firing rate was increased to ∼60 Hz. Simulated interpolated twitches did not show the marked force drop that follows the peak of the twitch, and when antidromic collisions were excluded from the model interpolated twitch amplitude was slightly increased and time-to-peak force was prolonged. These findings suggest that both antidromic and reflex effects reduce the amplitude of the interpolated twitch and contribute to the force drop that follows the twitch. The amplitude of the interpolated twitch was related to “excitation” of the motoneuron pool in a nonlinear way, so that at near-maximal contraction intensities (>90% maximal voluntary force) increases in excitation produced only small changes in interpolated twitch amplitude. Thus twitch interpolation may not provide a sensitive measure of motoneuronal excitation at near-maximal forces. Increases in the amplitude of interpolated twitches such as have been observed in fatigue and various pathologies may reflect large reductions in excitation of the motoneuron pool.

Effects of caffeine on neuromuscular function

1999 ◽  
Vol 87 (2) ◽  
pp. 801-808 ◽  
Author(s):  
J. M. Kalmar ◽  
E. Cafarelli
Keyword(s):  
Repeated Measures ◽  
Isometric Force ◽  
Neuromuscular Function ◽  
Voluntary Contraction ◽  
Voluntary Activation ◽  
Knee Extensors ◽  
Double Blind ◽  
Twitch Interpolation ◽  
Motor Unit Firing ◽  
The Right

This double-blind, repeated-measures study examined the effects of caffeine on neuromuscular function. Eleven male volunteers [22.3 ± 2.4 (SD) yr] came to the laboratory for control, placebo, and caffeine (6 mg/kg dose) trials. Each trial consisted of 10 × 1-ms stimulation of the tibial nerve to elicit maximal H reflexes of the soleus, four attempts at a maximal voluntary contraction (MVC) of the right knee extensors, six brief submaximal contractions, and a 50% MVC held to fatigue. Isometric force and surface electromyographic signals were recorded continuously. The degree of maximal voluntary activation was assessed with the twitch-interpolation technique. Single-unit recordings were made with tungsten microelectrodes during the submaximal contractions. Voluntary activation at MVC increased by 3.50 ± 1.01 (SE) % ( P < 0.01), but there was no change in H-reflex amplitude, suggesting that caffeine increases maximal voluntary activation at a supraspinal level. Neither the force-EMG relationship nor motor unit firing rates were altered by caffeine. Subjects were able to hold a 50% MVC for an average of 66.1 s in the absence of caffeine. Time to fatigue (Tlim) increased by 25.80 ± 16.06% after caffeine administration ( P < 0.05). There was no significant change in Tlim from pretest to posttest in the control or placebo trials. The increase in Tlim was associated with an attenuated decline in twitch amplitude, which would suggest that the mechanism is, at least in part, peripheral.

Dependence of Muscle Torque of Ankle Plantar and Dorsal Flexors on Different Ankle Angles

2018 ◽  
Vol 1 (80) ◽  
Author(s):  
Rima Solianik ◽  
Vaida Aleknavičiūtė ◽  
Zita Andrijauskaitė ◽  
Algimantas Putramentas ◽  
Gintarė Dargevičiūtė ◽  
...  
Keyword(s):  
Electrical Stimulation ◽  
Maximal Voluntary Contraction ◽  
Plantar Flexion ◽  
Muscle Length ◽  
Voluntary Contraction ◽  
Calf Muscle ◽  
Muscle Torque ◽  
Ankle Angle ◽  
O 15 ◽  
The Relationship

Research background and hypothesis. There is much research information about the relationship between the knee joint angle and the quadriceps muscle torque (Mohamed et al., 2002), but still we lack evidence about the relationship between ankle angle and calf muscle torque. Research aim. The purpose of this research was to establish the dependence of maximal voluntary contraction (MVC) and electrical stimulation (ES)-evoked torque and calf muscle electrical activity (EMG) on different ankle plantar and dorsal fl exion angles. We hypothesized that the calf muscle MVC and ES-evoked torque as well as muscle EMG amplitude would increase with increasing muscle length (i. . increasing ankle angle).Research methods. The subjects in the research were ten non-trained men. Calf plantar and dorsal fl exors muscle ES and MVC torque were tested at eight different ankle angles (–25 o ; –15 o ; –5 o ; 0 o ; 15 o ; 25 o ; 35 o ; 45 o ) which were chosen in randomized sequence. The tibialis anterior, soleus, gastrocnemius lateralis and medialis muscle EMG were measured during muscle MVC.Research results. The results showed that the highest ES-evoked and MVC developed torque of plantar fl exion muscles was at –25° ankle angle (149.1 ± 31.6 N·m and 207.8 ± 38.1 N·m, respectively), while the highest dorsal fl exion MVC muscle torque was at 25° ankle angle (47.2 ± 8.1 N·m). However, dorsal fl exion muscle MVC torque increased with the muscle length only until 25° ankle angle. Discussion and conclusions. Plantar flexion muscle electrical stimulation evoked and plantar / dorsal fl exion muscle maximal voluntary contraction torques are highest at that ankle angle where muscle length is the longest.Keywords: maximal voluntary contraction, electrical stimulation, EMG.

Power loss is greater in old men than young men during fast plantar flexion contractions

2010 ◽  
Vol 109 (5) ◽  
pp. 1441-1447 ◽  
Author(s):  
Brian H. Dalton ◽  
Geoffrey A. Power ◽  
Anthony A. Vandervoort ◽  
Charles L. Rice
Keyword(s):  
Peak Power ◽  
Contractile Function ◽  
Plantar Flexion ◽  
Constant Load ◽  
Triceps Surae ◽  
Voluntary Activation ◽  
Maximal Velocity ◽  
Shortening Velocity ◽  
Maximal Voluntary Isometric Contraction ◽  
Old Men

It is unclear during human aging whether healthy older adults (>70 yr old) experience greater, lesser, or the same fatigability compared with younger adults. The reported disparate findings may be related to the task-dependent nature of fatigue and the limited number of studies exploring nonisometric contractile function and aging. The purpose here was to determine the effects of fast shortening contractions on the fatigability of the triceps surae in 10 young (∼24 yr old) and 10 old (∼78 yr old) men using isometric and dynamic measures. Participants performed 50 maximal velocity-dependent plantar flexions at a constant load of 20% maximal voluntary isometric contraction (MVC). Isometric twitch properties and MVCs were tested at baseline and during and following the fatigue task. Voluntary activation was similar between the old and young (∼98%) and was unaltered with fatigue. The old had 26% lower ( P < 0.01) isometric MVC torque and 18% slower ( P < 0.01) maximal shortening velocity than the young. Hence, peak power was 38% lower in the old ( P < 0.01). At task termination, MVC torque was maintained in the old ( P = 0.15) but decreased by 21% in the young ( P < 0.01). Twitch half-relaxation time was lengthened in the old at task termination by 26% ( P < 0.01) but unchanged in the young ( P = 0.10). Peak power was reduced by 24% and 17% at task termination in the old and young, respectively ( P < 0.01). Despite a better maintenance in isometric MVC torque production, the weaker and slower contracting triceps surae of the old was more fatigable than the young during fast dynamic efforts with an unconstrained velocity.

Voluntary activation failure contributes more to plantar flexor weakness than antagonist coactivation and muscle atrophy in chronic stroke survivors

2010 ◽  
Vol 109 (5) ◽  
pp. 1337-1346 ◽  
Author(s):  
Cliff S. Klein ◽  
Dina Brooks ◽  
Denyse Richardson ◽  
William E. McIlroy ◽  
Mark T. Bayley
Keyword(s):  
Muscle Atrophy ◽  
Muscle Activation ◽  
Voluntary Contraction ◽  
Chronic Stroke ◽  
Voluntary Activation ◽  
Stroke Survivors ◽  
Plantar Flexor ◽  
Plantar Flexors ◽  
Emg Amplitude ◽  
Magnetic Resonance Imaging Mri

The contributions of nervous system muscle activation and muscle atrophy to poststroke weakness have not been evaluated together in the same subject. Maximal voluntary contraction (MVC) torque, voluntary activation (twitch interpolation), and electromyographic (EMG) amplitude were determined bilaterally in the plantar flexors of seven chronic stroke survivors (40–63 yr, 24–51 mo poststroke). Volumes of the plantar flexor muscles were determined bilaterally with magnetic resonance imaging (MRI). The mean (±SD) contralesional (paretic) MVC torque was less than one-half of the ipsilesional leg: 56.7 ± 57.4 vs. 147 ± 35.7 Nm ( P = 0.006). Contralesional voluntary activation was only 48 ± 36.9%, but was near complete in the ipsilesional leg, 97 ± 1.9% ( P = 0.01). The contralesional MVC EMG amplitude (normalized to the maximum M-wave peak-to-peak amplitude) of the gastrocnemii and soleus were 36.0 ± 28.5 and 36.0 ± 31.0% of the ipsilesional leg. Tibialis anterior (TA) EMG coactivation was not different between the contralesional (23.2 ± 24.0% of TA MVC EMG) and ipsilesional side (12.3 ± 5.7%) ( P = 0.24). However, TA EMG coactivation was excessive (71%) in one subject and accounted for ∼8% of her weakness based on the estimated antagonist torque. Relative (%ipsilesional leg) plantar flexor and gastrocnemii volumes were 88 ± 6% ( P = 0.004) and 76 ± 15% ( P = 0.01), respectively. Interlimb volume differences of the soleus, deep plantar flexors, and peronei were not significant. Preferred walking speed (0.83 ± 0.33 m/s) was related to the contralesional MVC torque ( r2 = 0.57, P = 0.05, N = 7), but the two subjects with the greatest weakness walked faster than three others. Our findings suggest that plantar flexor weakness in mobile chronic stroke survivors reflects mostly voluntary activation failure, with smaller contributions from antagonist activity and atrophy.

Plantar flexor activation capacity and H reflex in older adults: adaptations to strength training

2002 ◽  
Vol 92 (6) ◽  
pp. 2292-2302 ◽  
Author(s):  
G. Scaglioni ◽  
A. Ferri ◽  
A. E. Minetti ◽  
A. Martin ◽  
J. Van Hoecke ◽  
...  
Keyword(s):  
Maximum Voluntary Contraction ◽  
Voluntary Contraction ◽  
Weight Lifting ◽  
Voluntary Activation ◽  
Plantar Flexor ◽  
Plantar Flexors ◽  
H Index ◽  
Hoffman Reflex ◽  
Younger Men ◽  
Reflex Arc

The purpose of this study was to investigate whether the voluntary neural drive and the excitability of the reflex arc could be modulated by training, even in old age. To this aim, the effects of a 16-wk strengthening program on plantar flexor voluntary activation (VA) and on the maximum Hoffman reflex (Hmax)-to-maximum M wave (Mmax) ratio were investigated in 14 elderly men (65–80 yr). After training, isometric maximum voluntary contraction (MVC) increased by 18% ( P < 0.05) and weight-lifting ability by 24% ( P < 0.001). Twitch contraction time decreased by 8% ( P < 0.01), but no changes in half relaxation time and in peak twitch torque were observed. The VA, assessed by twitch interpolation, increased from 95 to 98% ( P < 0.05). Pretraining VA, also evaluated from the expected MVC for total twitch occlusion, was 7% higher ( P < 0.01) than MVC. This discrepancy persisted after training. The interpolated twitch torque-voluntary torque relationship was fitted by a nonlinear model and was found to deviate from linearity for torque levels >65% MVC. Compared with younger men (24–35 yr), the Hmax- to Mmax ratio and nerve conduction velocity (H index) of the older group were significantly lower (42%, P < 0.05; and 29%, P < 0.001, respectively) and were not modulated by training. In conclusion, older men seem to preserve a high VA of plantar flexors. However, the impaired functionality of the reflex pathway with aging and the lack of modulation with exercise suggest that the decrease in the Hmax- to Mmaxratio and H index may be related to degenerative phenomena.

scholarly journals Sensitivity of 24-h EMG duration and intensity in the human vastus lateralis muscle to threshold changes

2010 ◽  
Vol 108 (3) ◽  
pp. 655-661 ◽  
Author(s):  
Cliff S. Klein ◽  
Lillian B. Peterson ◽  
Sean Ferrell ◽  
Christine K. Thomas
Keyword(s):  
Vastus Lateralis ◽  
Voluntary Contraction ◽  
Voluntary Activation ◽  
Vastus Lateralis Muscle ◽  
Twitch Interpolation ◽  
Before And After ◽  
Compound Action Potentials ◽  
Small Change ◽  
Electromyographic Signals ◽  
Compound Action

Few studies have quantified lower limb muscle activity over 24 h using electromyographic signals (EMG). None have described the changes in EMG duration and intensity when data are analyzed with different thresholds. Continuous bilateral EMG recordings were made from vastus lateralis (VL) in 10 subjects (20–48 yr) for 24 h. Before and after this recording, voluntary quadriceps forces and VL EMG at 25%, 50%, 75%, and 100% of the maximal voluntary contraction (MVC), percentage voluntary activation (twitch interpolation), and compound action potentials (M-waves) were recorded. Offline, the 24-h EMG integrals (IEMG, 10-ms time constant) were normalized to the MVC IEMG. Total EMG duration and mean IEMG ranged from 1–3 h and 3.2–12.1% MVC, respectively, when the data were analyzed using the baseline (+3 SD) as threshold. When analysis was done with progressively higher thresholds, from baseline up to 4% MVC, the total EMG duration declined curvilinearly. In some cases the decline in duration was 50–60% for a 1% MVC threshold increment. The mean 24-h IEMG increased by 1.5–2% MVC for each 1% MVC threshold increment. Hence, a small change in the analysis threshold may result in large changes in 24-h EMG duration but moderate changes in mean IEMG. Our findings suggest that VL was active for a short amount of time and at low intensities over 24 h.

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