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.

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.

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.

Nonlinear behavior of muscle reflexes at the human ankle joint

1995 ◽  
Vol 73 (1) ◽  
pp. 65-72 ◽  
Author(s):  
R. B. Stein ◽  
R. E. Kearney
Keyword(s):  
Ankle Joint ◽  
Stretch Reflex ◽  
Maximum Voluntary Contraction ◽  
Voluntary Contraction ◽  
Voluntary Activation ◽  
Random Perturbations ◽  
Hydraulic Actuator ◽  
Voluntary Activity ◽  
Highly Nonlinear ◽  
Human Ankle

1. Pulse inputs (similar to tendon jerks) were applied to the human ankle joint with the use of a hydraulic actuator. Inputs of only 1-2 degrees could elicit large responses (> 20% of maximum voluntary contraction). The magnitude of the response depended nonlinearly on a number of factors: the amplitude, direction, and duration of the pulse; the angle of the ankle; and the level of voluntary activation of the ankle muscles. 2. Pulses that flexed or extended the ankle could both produce reflex torques in the same direction (extensor torque). Although an extension of the ankle did not itself produce a response, it could affect the response to a subsequent flexion for up to 1 s. 3. The influence of random perturbations on the stretch reflex at the ankle was assessed. Responses to pulse displacements alone and to pulses superimposed on random perturbations were compared at the same level of voluntary activity. Reflex responses decreased in a graded manner with increasing amplitude or bandwidth of the random perturbations. 4. These results demonstrate that stretch reflexes can generate substantial torques, but in a highly nonlinear manner. In particular, passive joint movements markedly alter stretch reflex gain, and these changes must be considered in interpreting the functional significance of reflex actions.

In vivo physiological cross-sectional area and specific force are reduced in the gastrocnemius of elderly men

2005 ◽  
Vol 99 (3) ◽  
pp. 1050-1055 ◽  
Author(s):  
Christopher I. Morse ◽  
Jeanette M. Thom ◽  
Neil D. Reeves ◽  
Karen M. Birch ◽  
Marco V. Narici
Keyword(s):  
Achilles Tendon ◽  
Voluntary Contraction ◽  
Pennation Angle ◽  
Specific Force ◽  
Plantar Flexor ◽  
Moment Arm ◽  
Plantar Flexors ◽  
Elderly Men ◽  
Cross Sectional

Sarcopenia and muscle weakness are well-known consequences of aging. The aim of the present study was to ascertain whether a decrease in fascicle force (Ff) could be accounted for entirely by muscle atrophy. In vivo physiological cross-sectional area (PCSA) and specific force (Ff/PCSA) of the lateral head of the gastrocnemius (GL) muscle were assessed in a group of elderly men [EM, aged 73.8 yr (SD 3.5), height 173.4 cm (SD 4.4), weight 78.4 kg (SD 8.3); means (SD)] and for comparison in a group of young men [YM, aged 25.3 yr (SD 4.4), height 176.4 cm (SD 7.7), weight 79.1 kg (SD 11.9)]. GL muscle volume (Vol) and Achilles tendon moment arm length were evaluated using magnetic resonance imaging. Pennation angle and fiber fascicle length (Lf) were measured using B-mode ultrasonography during isometric maximum voluntary contraction of the plantar flexors. PCSA was estimated as Vol/Lf. GL Ff was calculated by dividing Achilles tendon force by the cosine of θ, during the interpolation of a supramaximal doublet, and accounting for antagonist activation level (assessed using EMG), Achilles tendon moment arm length, and the relative PCSA of the GL within the plantar flexor group. Voluntary activation of the plantar flexors was lower in the EM than in the YM (86 vs. 98%, respectively, P < 0.05). Compared with the YM, plantar flexor maximal voluntary contraction torque and Ff of the EM were lower by 47 and 40%, respectively ( P < 0.01). Both Vol and PCSA were smaller in the EM by 28% ( P < 0.01) and 16% ( P < 0.05), respectively. Also, pennation angle was 12% smaller in the EM, whereas there was no significant difference in Lf between the YM and EM. After accounting for differences in agonists and antagonists activation, the Ff/PCSA of the EM was 30% lower than that of the YM ( P < 0.01). These findings demonstrate that the loss of muscle strength with aging may be explained not only by a reduction in voluntary drive to the muscle, but mostly by a decrease in intrinsic muscle force. This phenomenon may possibly be due to a reduction in single-fiber specific tension.

scholarly journals Maximum Voluntary Activation in Nonfatigued and Fatigued Muscle of Young and Elderly Individuals

2001 ◽  
Vol 81 (5) ◽  
pp. 1102-1109 ◽  
Author(s):  
Scott K Stackhouse ◽  
Jennifer E Stevens ◽  
Samuel CK Lee ◽  
Karen M Pearce ◽  
Lynn Snyder-Mackler ◽  
...  
Keyword(s):  
Maximum Voluntary Contraction ◽  
Quadriceps Femoris ◽  
Voluntary Contraction ◽  
Voluntary Activation ◽  
Elderly Subjects ◽  
Central Activation ◽  
Quadriceps Femoris Muscle ◽  
Age Related ◽  
Young Subjects ◽  
Femoris Muscle

Abstract Background and Purpose. Researchers studying central activation of muscles in elderly subjects (≥65 years of age) have investigated activation in only the nonfatigued state. This study examined the ability of young and elderly people to activate their quadriceps femoris muscles voluntarily under both fatigued and nonfatigued conditions to determine the effect of central activation failure on age-related loss of force. Subjects and Methods. Twenty young subjects (11 men, 9 women; mean age=22.67 years, SD=4.14, range=18–32 years) and 17 elderly subjects (8 men, 9 women; mean age=71.5 years, SD=5.85, range=65–84 years) participated in this study. Subjects were seated on a dynamometer and stabilized. Central activation was quantified, based on the change in force produced by a 100-Hz, 12-pulse electrical train that was delivered during a 3- to 5-second isometric maximum voluntary contraction (MVC) of the quadriceps femoris muscle. Next, subjects performed 25 MVCs (a 5-second contraction with 2 seconds of rest) to fatigue the muscle. During the last MVC, central activation was measured again. Results. In the nonfatigued state, elderly subjects had lower central activation than younger subjects. In the fatigued state, this difference became larger. Discussion and Conclusion. Central activation of the quadriceps femoris muscle in elderly subjects was reduced in both the fatigued and nonfatigued states when compared with young subjects. Some part of age-related weakness, therefore, may be attributed to failure of central activation in both the fatigued and nonfatigued states.

scholarly journals Motor planning perturbation: muscle activation and reaction time

2018 ◽  
Vol 120 (4) ◽  
pp. 2059-2065
Author(s):  
Stefan Delmas ◽  
Agostina Casamento-Moran ◽  
Seoung Hoon Park ◽  
Basma Yacoubi ◽  
Evangelos A. Christou
Keyword(s):  
Reaction Time ◽  
Muscle Activity ◽  
Muscle Activation ◽  
Maximum Voluntary Contraction ◽  
Motor Planning ◽  
Reaction Time Task ◽  
Voluntary Contraction ◽  
Voluntary Activation ◽  
Time Interval ◽  
Voluntary Activity

Reaction time (RT) is the time interval between the appearance of a stimulus and initiation of a motor response. Within RT, two processes occur, selection of motor goals and motor planning. An unresolved question is whether perturbation to the motor planning component of RT slows the response and alters the voluntary activation of muscle. The purpose of this study was to determine how the modulation of muscle activity during an RT response changes with motor plan perturbation. Twenty-four young adults (20.5 ±1.1 yr, 13 women) performed 15 trials of an isometric RT task with ankle dorsiflexion using a sinusoidal anticipatory strategy (10–20% maximum voluntary contraction). We compared the processing part of the RT and modulation of muscle activity from 10 to 60 Hz of the tibialis anterior (primary agonist) when the stimulus appeared at the trough or at the peak of the sinusoidal task. We found that RT ( P = 0.003) was longer when the stimulus occurred at the peak compared with the trough. During the time of the reaction, the electromyography (EMG) power from 10 to 35 Hz was less at the peak than the trough ( P = 0.019), whereas the EMG power from 35 to 60 Hz was similar between the peak and trough ( P = 0.92). These results suggest that perturbation to motor planning lengthens the processing part of RT and alters the voluntary activation of the muscle by decreasing the relative amount of power from 10 to 35 Hz. NEW & NOTEWORTHY We aimed to determine whether perturbation to motor planning would alter the speed and muscle activity of the response. We compared trials when a stimulus appeared at the peak or trough of an oscillatory reaction time task. When the stimulus occurred at the trough, participants responded faster, with greater force, and less EMG power from 10-35 Hz. We provide evidence that motor planning perturbation slows the response and alters the voluntary activity of the muscle.

Adaptations in the activation of human skeletal muscle induced by short-term isometric resistance training

2007 ◽  
Vol 103 (1) ◽  
pp. 402-411 ◽  
Author(s):  
Christopher Del Balso ◽  
E. Cafarelli
Keyword(s):  
Resistance Training ◽  
Muscle Activation ◽  
Voluntary Contraction ◽  
Spinal Reflex ◽  
Voluntary Activation ◽  
Control Group ◽  
Hoffman Reflex ◽  
V Wave ◽  
Spinal Excitability ◽  
Rate Of Activation

This study employed longitudinal measures of evoked spinal reflex responses (Hoffman reflex, V wave) to investigate changes in the activation of muscle and to determine if there are “linked” neural adaptations in the motor pathway following isometric resistance training. Twenty healthy, sedentary males were randomly assigned to either the trained ( n = 10) or control group ( n = 10). The training protocol consisted of 12 sessions of isometric resistance training of the plantar flexor muscles over a 4-wk period. All subjects were tested prior to and after the 4-wk period. To estimate changes in spinal excitability, soleus Hoffman (H) reflex and M wave recruitment curves were produced at rest and during submaximal contractions. Recruitment curves were analyzed using the slope method (Hslp/Mslp). Modulation of efferent neural drive was assessed through evoked V wave responses (V/Mmax) at 50, 75, and 100% maximal voluntary contraction (MVC). After 4 weeks, MVC torque increased 20.0 ± 13.9% (mean ± SD) in the trained group. The increase in MVC was accompanied by significant increases in the rate of torque development (42.5 ± 13.3%), the soleus surface electromyogram (60.7 ± 30.8%), voluntary activation (2.8 ± 0.1%), and the rate of activation (48.7 ± 24.3%). Hslp/Mslp was not altered by training; however, V/Mmax increased 57.3 ± 34.2% during MVC. These results suggest that increases in MVC observed in the first few days of isometric resistance training can be accounted for by an increase in the rate of activation at the onset of muscle contraction. Augmentation of muscle activation may be due to increased volitional drive from supraspinal centers.

scholarly journals Effect of Elbow Flexion Angle on Cortical Voluntary Activation of the Non-Impaired Biceps: A 3 Days Repeated Sessions Study

2020 ◽  
Author(s):  
Thibault Roumengous ◽  
Paul A. Howell ◽  
Carrie L. Peterson
Keyword(s):  
Cortical Neurons ◽  
Maximum Voluntary Contraction ◽  
Motor Evoked Potential ◽  
Elbow Flexion ◽  
Voluntary Contraction ◽  
Voluntary Activation ◽  
Elbow Angle ◽  
Flexion Extension ◽  
Minimal Stimulation ◽  
Stimulation Of

ABSTRACTMeasurement of cortical voluntary activation (VA) with transcranial magnetic stimulation (TMS) is limited by technical challenges. One challenge is the difficulty in preferential stimulation of cortical neurons projecting to the target muscle and minimal stimulation of cortical neurons projecting to antagonists. Thus, the motor evoked potential (MEP) response to TMS in the target muscle compared to its primary antagonist may be an important parameter in the assessment of cortical VA. Modulating isometric elbow angle alters the magnitude of MEPs at rest. The purpose of this study was to evaluate the effect of isometric elbow flexion-extension angle on: 1) the ratio of biceps MEP relative to the triceps MEP amplitude across a range of voluntary efforts, and 2) cortical VA. Ten non-impaired participants completed three sessions wherein VA was determined using TMS at 45°, 90° and 120° of isometric elbow flexion, and peripheral electrical stimulation at 90° of elbow flexion. The biceps/triceps MEP ratio was greater in the more flexed elbow angle (120° flexion) compared to 90° during contractions of 50% and 75% of maximum voluntary contraction. Cortical VA assessed in the more extended elbow angle (45° flexion) was lower relative to 90° elbow flexion; this effect was dependent on the biceps/triceps MEP ratio. Cortical VA was sensitive to small changes in the linearity of the voluntary torque and superimposed twitch relationship, regardless of the elbow angle. Peripheral and cortical VA measures at 90° of elbow flexion were repeatable across three days. In conclusion, although the biceps/triceps MEP ratio was increased at a more flexed elbow angle relative to 90°, there was not a corresponding difference in cortical VA. Thus, increasing the MEP ratio via elbow angle did not affect estimation of cortical VA.

scholarly journals Effects of whole-body vibrations on neuromuscular fatigue: a study with sets of different durations

PeerJ ◽  
2020 ◽  
Vol 8 ◽  
pp. e10388
Author(s):  
Miloš Kalc ◽  
Ramona Ritzmann ◽  
Vojko Strojnik
Keyword(s):  
High Frequency ◽  
Maximum Voluntary Contraction ◽  
Peak Torque ◽  
Voluntary Contraction ◽  
Neuromuscular Fatigue ◽  
Voluntary Activation ◽  
Whole Body ◽  
Peripheral Fatigue ◽  
Single Twitch ◽  
Whole Body Vibrations

Background Whole body vibrations have been used as an exercise modality or as a tool to study neuromuscular integration. There is increasing evidence that longer WBV exposures (up to 10 minutes) induce an acute impairment in neuromuscular function. However, the magnitude and origin of WBV induced fatigue is poorly understood. Purpose The study aimed to investigate the magnitude and origin of neuromuscular fatigue induced by half-squat long-exposure whole-body vibration intervention (WBV) with sets of different duration and compare it to non-vibration (SHAM) conditions. Methods Ten young, recreationally trained adults participated in six fatiguing trials, each consisting of maintaining a squatting position for several sets of the duration of 30, 60 or 180 seconds. The static squatting was superimposed with vibrations (WBV30, WBV60, WBV180) or without vibrations (SHAM30, SHAM60, SHAM180) for a total exercise exposure of 9-minutes in each trial. Maximum voluntary contraction (MVC), level of voluntary activation (%VA), low- (T20) and high-frequency (T100) doublets, low-to-high-frequency fatigue ratio (T20/100) and single twitch peak torque (TWPT) were assessed before, immediately after, then 15 and 30 minutes after each fatiguing protocol. Result Inferential statistics using RM ANOVA and post hoc tests revealed statistically significant declines from baseline values in MVC, T20, T100, T20/100 and TWPT in all trials, but not in %VA. No significant differences were found between WBV and SHAM conditions. Conclusion Our findings suggest that the origin of fatigue induced by WBV is not significantly different compared to control conditions without vibrations. The lack of significant differences in %VA and the significant decline in other assessed parameters suggest that fatiguing protocols used in this study induced peripheral fatigue of a similar magnitude in all trials.

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.

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