The Experts below are selected from a list of 3351 Experts worldwide ranked by ideXlab platform
Simon C Gandevia - One of the best experts on this subject based on the ideXlab platform.
-
the origin of activity in the biceps brachii muscle during voluntary contractions of the contralateral Elbow Flexor muscles
Experimental Brain Research, 2006Co-Authors: Inge Zijdewind, Jane E Butler, Simon C Gandevia, Janet L TaylorAbstract: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” contractions). Subjects (n = 9) performed maximal voluntary contractions (MVCs) with their right Elbow-Flexor muscles followed by submaximal contractions with their left Elbow Flexors. Electromyographic activity (EMG) during the submaximal contractions was matched to the associated EMG in the left biceps brachii during the right MVC. During contractions, TMS was delivered to the motor cortex of the right or left hemisphere and excitatory motor evoked potentials (MEPs) and inhibitory (silent period) responses recorded from left biceps. Changes at a spinal level were investigated using cervicomedullary stimulation to activate corticospinal paths (n = 5). Stimulation of the right hemisphere produced silent periods of comparable duration in associated and voluntary contractions (218 vs 217 ms, respectively), whereas left hemisphere stimulation caused a depression of EMG but no EMG silence in either contraction. Despite matched EMG, MEPs elicited by right hemisphere stimulation were ∼1.5–2.5 times larger during associated compared to voluntary contractions (P < 0.005). Similar inhibition of the associated and matched voluntary activity during the silent period suggests that associated activity comes from the contralateral hemisphere and that motor areas in this (right) hemisphere are activated concomitantly with the motor areas in the left hemisphere. Comparison of the MEPs and subcortically evoked potentials implies that cortical excitability was greater in associated contractions than in the matched voluntary efforts.
-
the origin of activity in the biceps brachii muscle during voluntary contractions of the contralateral Elbow Flexor muscles
Experimental Brain Research, 2006Co-Authors: Inge Zijdewind, Jane E Butler, Simon C Gandevia, Janet L TaylorAbstract: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" contractions). Subjects (n = 9) performed maximal voluntary contractions (MVCs) with their right Elbow-Flexor muscles followed by submaximal contractions with their left Elbow Flexors. Electromyographic activity (EMG) during the submaximal contractions was matched to the associated EMG in the left biceps brachii during the right MVC. During contractions, TMS was delivered to the motor cortex of the right or left hemisphere and excitatory motor evoked potentials (MEPs) and inhibitory (silent period) responses recorded from left biceps. Changes at a spinal level were investigated using cervicomedullary stimulation to activate corticospinal paths (n = 5). Stimulation of the right hemisphere produced silent periods of comparable duration in associated and voluntary contractions (218 vs 217 ms, respectively), whereas left hemisphere stimulation caused a depression of EMG but no EMG silence in either contraction. Despite matched EMG, MEPs elicited by right hemisphere stimulation were approximately 1.5-2.5 times larger during associated compared to voluntary contractions (P < 0.005). Similar inhibition of the associated and matched voluntary activity during the silent period suggests that associated activity comes from the contralateral hemisphere and that motor areas in this (right) hemisphere are activated concomitantly with the motor areas in the left hemisphere. Comparison of the MEPs and subcortically evoked potentials implies that cortical excitability was greater in associated contractions than in the matched voluntary efforts.
-
maximal force voluntary activation and muscle soreness after eccentric damage to human Elbow Flexor muscles
The Journal of Physiology, 2005Co-Authors: O. Prasartwuth, Janet L Taylor, Simon C GandeviaAbstract: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 approximately 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 motor cortex or at a spinal level.
-
prediction of voluntary activation strength and endurance of Elbow Flexors in postpolio patients
Muscle & Nerve, 2004Co-Authors: G M Allen, James W Middleton, Pesi Katrak, Stephen R Lord, Simon C GandeviaAbstract:To examine the long-term effects of polio, maximal voluntary strength and voluntary activation of Elbow Flexor muscles of 177 patients from a postpolio clinic were investigated using twitch interpolation. Muscle endurance was studied in 142 patients during 45 min of submaximal exercise, and predictors of impaired muscle performance were investigated. Twenty-nine of 177 patients (16.4%) had impaired voluntary drive to their Elbow Flexor muscles, but only 16 (9.0%) had markedly reduced Elbow Flexor strength, despite 74 (41.8%) reporting they were initially affected in their tested limb and 172 (97.2%) patients reporting new generalized symptoms. Seven patients had impaired muscle endurance in the tests of strength and voluntary drive. During the submaximal exercise, 16 patients (11.3%) had impaired peripheral muscle endurance with normal voluntary activation. These results confirm a low incidence of impaired upper-limb muscle performance in postpolio patients, despite many patients having subjective symptoms consistent with postpolio syndrome. There was an increased relative risk for impaired muscle function in those patients with a subjective decrease in strength in the tested limb, a recent decline in activities of daily living in their tested limb, and who used orthotic devices in their tested limb. Monitoring of function in prior-polio patients with impaired muscle performance may be useful, particularly when combined with investigation of other potential contributory factors to the functional impairment.
-
voluntary activation of human Elbow Flexor muscles during maximal concentric contractions
The Journal of Physiology, 1998Co-Authors: Simon C Gandevia, Robert D Herbert, J B LeeperAbstract:1. To measure voluntary activation of human Elbow Flexor muscles during maximal concentric contractions, the twitch interpolation method was modified to enable detection of torque increments evoked by single stimuli during contractions of up to 300 deg s-1. Subjects flexed the Elbow to rotate a loaded beam 'as fast as possible' (load typically 23-58 N m) from 70 deg below to 70 deg above the horizontal. Electrical stimuli were delivered to biceps brachii when the beam passed through the horizontal. Voluntary activation was estimated from the amplitude of the interpolated twitch, which was expressed as a percentage of the twitch produced by relaxed muscles shortening at the same velocity. 2. In eleven subjects, the level of voluntary activation during repeated maximal concentric contractions (median 99.4%) did not differ significantly from that during maximal isometric contractions (98.0%). Voluntary activation during maximal contractions did not depend on shortening velocity and was the same when tested at two angles 30 deg apart. 3. To induce fatigue, five subjects repeatedly lifted and lowered a heavy load at about 30 deg s-1, and continued for ten to twelve contractions after they needed assistance to continue lifting. All maintained the capacity to attain maximal levels of activation. 4. It is concluded that voluntary drive to Elbow Flexor muscles during maximal concentric contractions is usually maximal or near-maximal, and that this level of drive can be maintained during development of peripheral fatigue.
Roger M Enoka - One of the best experts on this subject based on the ideXlab platform.
-
influence of neural adjustments and muscle oxygenation on task failure during sustained isometric contractions with Elbow Flexor muscles
Experimental Physiology, 2012Co-Authors: Cedric Booghs, Roger M Enoka, Stephane Baudry, Jacques DuchateauAbstract:This study investigated the adjustments in muscle activation and oxygenation in biceps and triceps brachii during two tasks sustained to failure at 20 and 60% of the maximal voluntary contraction (MVC) force. The tasks required participants either to push against a rigid restraint (force task) or to support an inertial load (position task) with the Elbow Flexor muscles. The surface EMG was recorded for biceps brachii, brachioradialis, triceps brachii and trapezius superior muscles. Muscle oxygenation of biceps and triceps brachii was measured by near-infrared spectroscopy. The position task was briefer (404 ± 159 s) than the force task (533 ± 194 s) when performed at 20% MVC (P= 0.011), but endurance time did not differ at 60% MVC (54 ± 19 versus 64 ± 16 s, respectively; P= 0.13). Biceps brachii oxygenation decreased slightly (by ∼7%) during tasks performed at 20% MVC, whereas it dropped (−40%) for tasks sustained at 60% MVC. However, the decrease in muscle oxygenation was not a significant predictor of time to failure at the two target forces, although its contribution to muscle fatigue cannot be completely ruled out at 60% MVC. In contrast, time to failure was predicted by the increase in EMG of biceps brachii for both tasks at 20% MVC, and EMG of brachioradialis and trapezius for both tasks at 60% MVC. These results suggest that neural adjustments rather than muscle oxygenation limited the time to failure for the force and position tasks at low and high target forces.
-
muscle activity and time to task failure differ with load compliance and target force for Elbow Flexor muscles
Journal of Applied Physiology, 2011Co-Authors: Thorsten Rudroff, Jamie N Justice, Matthew R Holmes, Stephen D Matthews, Roger M EnokaAbstract:The primary purpose of this study was to determine the influence of load compliance on time to failure during sustained isometric contractions performed with the Elbow Flexor muscles at four submax...
-
muscle activity and time to task failure differ with load compliance and target force for Elbow Flexor muscles
Journal of Applied Physiology, 2011Co-Authors: Thorsten Rudroff, Jamie N Justice, Matthew R Holmes, Stephen D Matthews, Roger M EnokaAbstract:The primary purpose of this study was to determine the influence of load compliance on time to failure during sustained isometric contractions performed with the Elbow Flexor muscles at four submaximal target forces. Subjects pulled against a rigid restraint during the force task and maintained a constant Elbow angle, while supporting an equivalent inertial load during the position task. Each task was sustained for as long as possible. Twenty-one healthy adults (23 ± 6 yr; 11 men) participated in the study. The maximal voluntary contraction (MVC) force was similar (P = 0.95) before the subjects performed the force and position tasks at each of the four target forces: 20, 30, 45, and 60% of MVC force. The time to task failure was longer for the force tasks (576 ± 80 and 325 ± 70 s) than for the position tasks (299 ± 77 and 168 ± 35 s) at target forces of 20 and 30% (P 0.19). The briefer times to failure for the position task at the lower forces were accompanied by greater rates of increase in Elbow Flexor muscle activity, mean arterial pressure, heart rate, and rating of perceived exertion. There was no difference in the estimates of external mechanical work at any target force. The dominant mechanisms limiting time to failure of sustained isometric contractions with the Elbow Flexor muscles appear to change at target forces between 30 and 45% MVC, with load compliance being a significant factor at lower forces only.
-
pronation supination torque and associated electromyographic activity varies during a sustained Elbow Flexor contraction but does not influence the time to task failure
Muscle & Nerve, 2009Co-Authors: Didier Staudenmann, Thorsten Rudroff, Roger M EnokaAbstract:In this study we measured the pronation-supination torque, flexion force, and electromyographic activity in Elbow Flexor muscles during an isometric contraction in which a submaximal Elbow flexion force was kept constant for as long as possible. Ten subjects performed the contraction at 20% of maximal voluntary contraction (MVC) torque until failure. Electro- myographic (EMG) activity of the long and short heads of biceps brachii, brachialis, brachioradialis, and triceps brachii was recorded with surface and intramuscular electrodes. The mean time to failure was 8.2 6.2 min. The fluctuations in flexion force and pronation-supination torque were correlated (r range 0.68 - 0.92), and subjects exhibited a range of pronation-torque profiles that were not associated with the time to failure. Knowing the influence of concurrent actions about the pronation-supination axis during a submaximal fatiguing contraction with the Elbow Flexor muscles has impli- cations for the design of workstations in ergonomic settings and in the prescription of activities for rehabilitation programs. Muscle Nerve 40: 231-239, 2009
-
a spinal pathway between synergists can modulate activity in human Elbow Flexor muscles
Experimental Brain Research, 2008Co-Authors: Zachary A Riley, Benjamin K Barry, Michael A Pascoe, Roger M EnokaAbstract:Electrical stimulation of the brachioradialis branch of the radial nerve has been shown to inhibit the discharge of voluntarily activated motor units in biceps brachii during weak contractions with the Elbow Flexor muscles. The purpose of the present study was to characterise the inhibitory reflex by comparing its strength in the short and long heads of the biceps brachii and examining the influence of forearm position on the strength of the reflex. Spike-triggered stimulation was used to assess the influence of radial nerve stimulation on the discharge of single motor units in the biceps brachii of 15 subjects. Stimulation of the radial nerve prolonged the interspike interval (P < 0.001) of motor units in the long (n = 31, 4.8 ± 5.6 ms) and short heads (n = 26, 8.1 ± 12.3 ms) of biceps brachii with no difference between the two heads (P = 0.11). The strength of inhibition varied with forearm position for motor units in both heads (n = 18, P < 0.05). The amount of inhibition was greatest in pronation (7.9 ± 8.9 ms), intermediate in neutral (5.8 ± 7.1 ms), and least in supination (2.8 ± 3.4 ms). These findings indicate that the inhibition evoked by afferent feedback from brachioradialis to low-threshold motor units (mean force 3–5% MVC) in biceps brachii varied with forearm posture yet was similar for the two heads of biceps brachii. This reflex pathway provides a mechanism to adjust the activation of biceps brachii with changes in forearm position, and represents a spinal basis for a muscle synergy in humans.
Janet L Taylor - One of the best experts on this subject based on the ideXlab platform.
-
the origin of activity in the biceps brachii muscle during voluntary contractions of the contralateral Elbow Flexor muscles
Experimental Brain Research, 2006Co-Authors: Inge Zijdewind, Jane E Butler, Simon C Gandevia, Janet L TaylorAbstract: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” contractions). Subjects (n = 9) performed maximal voluntary contractions (MVCs) with their right Elbow-Flexor muscles followed by submaximal contractions with their left Elbow Flexors. Electromyographic activity (EMG) during the submaximal contractions was matched to the associated EMG in the left biceps brachii during the right MVC. During contractions, TMS was delivered to the motor cortex of the right or left hemisphere and excitatory motor evoked potentials (MEPs) and inhibitory (silent period) responses recorded from left biceps. Changes at a spinal level were investigated using cervicomedullary stimulation to activate corticospinal paths (n = 5). Stimulation of the right hemisphere produced silent periods of comparable duration in associated and voluntary contractions (218 vs 217 ms, respectively), whereas left hemisphere stimulation caused a depression of EMG but no EMG silence in either contraction. Despite matched EMG, MEPs elicited by right hemisphere stimulation were ∼1.5–2.5 times larger during associated compared to voluntary contractions (P < 0.005). Similar inhibition of the associated and matched voluntary activity during the silent period suggests that associated activity comes from the contralateral hemisphere and that motor areas in this (right) hemisphere are activated concomitantly with the motor areas in the left hemisphere. Comparison of the MEPs and subcortically evoked potentials implies that cortical excitability was greater in associated contractions than in the matched voluntary efforts.
-
the origin of activity in the biceps brachii muscle during voluntary contractions of the contralateral Elbow Flexor muscles
Experimental Brain Research, 2006Co-Authors: Inge Zijdewind, Jane E Butler, Simon C Gandevia, Janet L TaylorAbstract: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" contractions). Subjects (n = 9) performed maximal voluntary contractions (MVCs) with their right Elbow-Flexor muscles followed by submaximal contractions with their left Elbow Flexors. Electromyographic activity (EMG) during the submaximal contractions was matched to the associated EMG in the left biceps brachii during the right MVC. During contractions, TMS was delivered to the motor cortex of the right or left hemisphere and excitatory motor evoked potentials (MEPs) and inhibitory (silent period) responses recorded from left biceps. Changes at a spinal level were investigated using cervicomedullary stimulation to activate corticospinal paths (n = 5). Stimulation of the right hemisphere produced silent periods of comparable duration in associated and voluntary contractions (218 vs 217 ms, respectively), whereas left hemisphere stimulation caused a depression of EMG but no EMG silence in either contraction. Despite matched EMG, MEPs elicited by right hemisphere stimulation were approximately 1.5-2.5 times larger during associated compared to voluntary contractions (P < 0.005). Similar inhibition of the associated and matched voluntary activity during the silent period suggests that associated activity comes from the contralateral hemisphere and that motor areas in this (right) hemisphere are activated concomitantly with the motor areas in the left hemisphere. Comparison of the MEPs and subcortically evoked potentials implies that cortical excitability was greater in associated contractions than in the matched voluntary efforts.
-
Maximal force, voluntary activation and muscle soreness after eccentric damage to human Elbow Flexor muscles
The Journal of Physiology, 2005Co-Authors: O. Prasartwuth, Janet L TaylorAbstract:Eccentric exercise lengthens muscle during contraction and damages its muscle fibres. A prolonged reduction in force occurs in animal (e.g. Faulkner et al. 1993; Friden, 2002) and human studies (e.g. Newham et al. 1983, 1987; Howell et al. 1993). Eccentric exercise also leads to muscle soreness and tenderness. Because this develops over many hours and is maximal one to two days after the exercise, it is commonly termed delayed-onset muscle soreness (e.g. Schwane et al. 1983; Ebbeling & Clarkson, 1989; Jones et al. 1989; Clarkson et al. 1992; Cleak & Eston, 1992). This muscle pain is believed to reflect activity in group III and IV muscle afferents (O'Connor & Cook, 1999), although a contribution from muscle spindle afferents has been postulated (Weerakkody et al. 2003). The reduction in maximal force is thought to be secondary to sarcomere ‘popping’ and disorganization (Morgan, 1990), as well as damage to components of the excitation–contraction coupling process (e.g. Warren et al. 1993; Balnave et al. 1997). Under some circumstances sarcolemmal function is affected (Yeung et al. 2003). These peripheral mechanisms have been reviewed (Proske & Morgan, 2001; Warren et al. 2001; Clarkson & Hubal, 2002; Lieber et al. 2002). With some forms of exercise, impaired voluntary activation or an inadequate drive to muscle fibres occurs, and such a mechanism could contribute to the prolonged reduction in voluntary force after eccentric exercise (for review see Gandevia, 2001). If interpolation of a stimulus to the motor nerve in a maximal voluntary contraction evokes a twitch-like increment in force, then voluntary activation of the muscle is less than complete. During muscle fatigue produced by sustained or intermittent maximal isometric contractions (e.g. Gandevia et al. 1996; Taylor et al. 2000), and submaximal isometric contractions (e.g. Lloyd et al. 1991; Loscher et al. 1996; Norregaard et al. 1997), interpolated stimuli reveal impaired voluntary activation. In theory, this deficit may reflect net inhibition of motoneurones due to afferent activity, but there may also be a failure to generate sufficient output from the motor cortex (e.g. Gandevia et al. 1996; Herbert & Gandevia, 1996). Under appropriate conditions, transcranial magnetic stimulation of the motor cortex generates superimposed force increments which decline linearly with increasing levels of background voluntary force. This relationship can be used to estimate reliably the size of a ‘resting’ twitch of the Elbow Flexors, and to assess the amount of extra output available from the motor cortex to increase force (Todd et al. 2003, 2004). After eccentric muscle damage, voluntary activation (and hence muscle force) may be reduced as a result of muscle pain and tenderness. Saxton & Donnelly (1996) used a type of twitch interpolation with nerve stimulation during isometric contraction of the Elbow Flexors in the days after eccentric exercise. They found inconsistent changes in the force added by tetanic stimulation. Using motor cortical stimulation to evoke force increments Loscher & Nordlund (2002) found some impairment of voluntary activation immediately after eccentric exercise, but this recovered within 5 min. Twitch interpolation using nerve stimulation after eccentric exercise of the Elbow Flexors also revealed an immediate reduction in voluntary activation (Michaut et al. 2002). In the latter two studies it was not possible to separate an acute effect of muscle fatigue from a longer-term effect related to muscle damage. Hence, in the present study we aimed to damage the Elbow Flexor muscles with fatiguing eccentric exercise and generate muscle soreness, and then to follow recovery of maximal voluntary force and voluntary activation over a week. We measured voluntary activation in brief maximal contractions throughout recovery using conventional twitch interpolation with motor nerve stimulation (e.g. Merton, 1954; Herbert & Gandevia, 1996), and we also measured voluntary activation using a new method based on motor cortical stimulation (Todd et al. 2003, 2004). These two types of stimulation provide different information about the limits to voluntary drive to the muscles. However, during fatigue, both forms of stimulation reveal impairments of voluntary activation. This indicates that some of the impairment is due to inadequate cortical output. In the current study, we hypothesized that any impairment in voluntary activation to the muscle would be maximal when muscle soreness peaked, as muscle pain has been reported to reduce cortical excitability (Le Pera et al. 2001). Furthermore, we expected impairment to be evident with both forms of stimulation.
-
maximal force voluntary activation and muscle soreness after eccentric damage to human Elbow Flexor muscles
The Journal of Physiology, 2005Co-Authors: O. Prasartwuth, Janet L Taylor, Simon C GandeviaAbstract: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 approximately 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 motor cortex or at a spinal level.
O. Prasartwuth - One of the best experts on this subject based on the ideXlab platform.
-
Maximal force, voluntary activation and muscle soreness after eccentric damage to human Elbow Flexor muscles
The Journal of Physiology, 2005Co-Authors: O. Prasartwuth, Janet L TaylorAbstract:Eccentric exercise lengthens muscle during contraction and damages its muscle fibres. A prolonged reduction in force occurs in animal (e.g. Faulkner et al. 1993; Friden, 2002) and human studies (e.g. Newham et al. 1983, 1987; Howell et al. 1993). Eccentric exercise also leads to muscle soreness and tenderness. Because this develops over many hours and is maximal one to two days after the exercise, it is commonly termed delayed-onset muscle soreness (e.g. Schwane et al. 1983; Ebbeling & Clarkson, 1989; Jones et al. 1989; Clarkson et al. 1992; Cleak & Eston, 1992). This muscle pain is believed to reflect activity in group III and IV muscle afferents (O'Connor & Cook, 1999), although a contribution from muscle spindle afferents has been postulated (Weerakkody et al. 2003). The reduction in maximal force is thought to be secondary to sarcomere ‘popping’ and disorganization (Morgan, 1990), as well as damage to components of the excitation–contraction coupling process (e.g. Warren et al. 1993; Balnave et al. 1997). Under some circumstances sarcolemmal function is affected (Yeung et al. 2003). These peripheral mechanisms have been reviewed (Proske & Morgan, 2001; Warren et al. 2001; Clarkson & Hubal, 2002; Lieber et al. 2002). With some forms of exercise, impaired voluntary activation or an inadequate drive to muscle fibres occurs, and such a mechanism could contribute to the prolonged reduction in voluntary force after eccentric exercise (for review see Gandevia, 2001). If interpolation of a stimulus to the motor nerve in a maximal voluntary contraction evokes a twitch-like increment in force, then voluntary activation of the muscle is less than complete. During muscle fatigue produced by sustained or intermittent maximal isometric contractions (e.g. Gandevia et al. 1996; Taylor et al. 2000), and submaximal isometric contractions (e.g. Lloyd et al. 1991; Loscher et al. 1996; Norregaard et al. 1997), interpolated stimuli reveal impaired voluntary activation. In theory, this deficit may reflect net inhibition of motoneurones due to afferent activity, but there may also be a failure to generate sufficient output from the motor cortex (e.g. Gandevia et al. 1996; Herbert & Gandevia, 1996). Under appropriate conditions, transcranial magnetic stimulation of the motor cortex generates superimposed force increments which decline linearly with increasing levels of background voluntary force. This relationship can be used to estimate reliably the size of a ‘resting’ twitch of the Elbow Flexors, and to assess the amount of extra output available from the motor cortex to increase force (Todd et al. 2003, 2004). After eccentric muscle damage, voluntary activation (and hence muscle force) may be reduced as a result of muscle pain and tenderness. Saxton & Donnelly (1996) used a type of twitch interpolation with nerve stimulation during isometric contraction of the Elbow Flexors in the days after eccentric exercise. They found inconsistent changes in the force added by tetanic stimulation. Using motor cortical stimulation to evoke force increments Loscher & Nordlund (2002) found some impairment of voluntary activation immediately after eccentric exercise, but this recovered within 5 min. Twitch interpolation using nerve stimulation after eccentric exercise of the Elbow Flexors also revealed an immediate reduction in voluntary activation (Michaut et al. 2002). In the latter two studies it was not possible to separate an acute effect of muscle fatigue from a longer-term effect related to muscle damage. Hence, in the present study we aimed to damage the Elbow Flexor muscles with fatiguing eccentric exercise and generate muscle soreness, and then to follow recovery of maximal voluntary force and voluntary activation over a week. We measured voluntary activation in brief maximal contractions throughout recovery using conventional twitch interpolation with motor nerve stimulation (e.g. Merton, 1954; Herbert & Gandevia, 1996), and we also measured voluntary activation using a new method based on motor cortical stimulation (Todd et al. 2003, 2004). These two types of stimulation provide different information about the limits to voluntary drive to the muscles. However, during fatigue, both forms of stimulation reveal impairments of voluntary activation. This indicates that some of the impairment is due to inadequate cortical output. In the current study, we hypothesized that any impairment in voluntary activation to the muscle would be maximal when muscle soreness peaked, as muscle pain has been reported to reduce cortical excitability (Le Pera et al. 2001). Furthermore, we expected impairment to be evident with both forms of stimulation.
-
maximal force voluntary activation and muscle soreness after eccentric damage to human Elbow Flexor muscles
The Journal of Physiology, 2005Co-Authors: O. Prasartwuth, Janet L Taylor, Simon C GandeviaAbstract: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 approximately 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 motor cortex or at a spinal level.
M. Pousson - One of the best experts on this subject based on the ideXlab platform.
-
effects of eccentric training on torque angular velocity power characteristics of Elbow Flexor muscles in older women
Experimental Gerontology, 2004Co-Authors: D. Valour, M Rouji, M. PoussonAbstract:Abstract The purpose of this study was to investigate the potential of eccentric training to improve Elbow Flexor muscle power in elderly subjects. Fourteen older female volunteers (age range 60–78 years) were randomly assigned into either a training group (TG) or a control group (CG). For the TG, the 21-session 7-week eccentric training program consisted of 5×6 eccentric muscle actions at 60–100% of concentric three maximal repetitions. Before and after training, maximal Elbow flexions were performed against increasing inertia. Maximal isokinetic Elbow flexions at four angular velocities (eccentric actions, −60° s−1, −30° rad s−1; concentric actions, 30, 60° s−1) and maximal isometric actions were also performed. Maximal power (Pmax) and an index of maximal shortening velocity (VImax) were determined. For all action conditions, the myoelectric activities of the biceps and the triceps brachii muscles were recorded and quantified as a root mean square (RMS) value. In the TG, maximal torque developed under isometric, isokinetic and inertial conditions increased significantly after training (ranging from 11 to 19%). Pmax and VImax also increased significantly (31.3 and 25.9%, respectively). These parameters remained unchanged in the CG. The RMS activity of the biceps and triceps muscles was not affected by eccentric training for all action conditions excepting the eccentric condition at −30° s−1 where the RMS activity of the biceps increased significantly. The gains in maximal torque, Pmax and VImax observed after training would result more from intramuscular modifications than from changes in muscular activity, except for eccentric condition at −30° s−1 where the torque gains could also be partly explained by a reduction in inhibition of the motor unit pool.
-
the influence of ageing on the force velocity power characteristics of human Elbow Flexor muscles
Experimental Gerontology, 2003Co-Authors: D. Valour, Julien Ochala, Y Ballay, M. PoussonAbstract:Abstract The purpose of this study was to quantify the effects of ageing on the maximal power ( P max ) of the Elbow Flexor muscles and to determine the impact of velocity on the loss of power in older people. Sixteen elderly subjects (7 men and 9 women, age range 61–78 years) and 17 young subjects (11 men and 6 women, age range 18–27 years) participated in this study. Maximal Elbow flexions were performed against increasing inertia. The maximal force ( F max ), maximal shortening velocity ( V max ), P max , dynamic constants ( a , b and a / F max ), optimal force ( F opt ), optimal velocity ( V opt ) and V opt / V max were determined from Hill's equation. Myoelectrical activity (EMG) of the biceps and triceps muscles was quantified as an root mean square (RMS) value. F max , V max , P max , F opt , and V opt were significantly lower in elderly than in young subjects (28, 31, 45, 24 and 28% lower, respectively; p a / F max and V opt / V max were not different between the two age groups. In women, the greater decrease in P max appears to be more dependent on V opt than F opt . In addition, V max decreased with age in women but not in men. The absence of significant differences between age groups in normalised RMS values indicates that P max and V max loss with increasing age could result more from changes in the properties of contractile element than from changes in muscular activity.
-
Compliance changes of the series elastic component of Elbow Flexor muscles with age in humans
Pflügers Archiv: European Journal of Physiology, 2003Co-Authors: D. Valour, M. PoussonAbstract:The purpose of this study was to determine the compliance of the series elastic component (SEC) of the Elbow Flexor muscles in young (n=13, mean age 21.5±2.5 years) and elderly (n=15, mean age 67.4±4.7 years) subjects. SEC compliance was determined using a quick-release method. Under isometric conditions, myoelectrical activity (EMG) of biceps and triceps muscles was quantified by the root mean square (RMS) value. The compliance index (CI) was defined as the slope of the regression of ln(NC) on ln(NF), where NC and NF are normalised compliance and force respectively. Maximal isometric force and neuromuscular efficiency (torque/RMS) were significantly greater in the young than in the elderly. Antagonist (triceps) co-activation was similar for both groups. The CI after quick-release movements was significantly greater in the young than in the elderly. These results suggest that the SEC compliance of the Elbow Flexors muscles decreases with age. This decrease in global compliance could be induced by changes both in the active and passive portions of the SEC. These findings may be of functional significance for everyday muscular activity in older people.