Deschenes, Mr 2000

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Journal of the Neurological Sciences 174 (2000) 9299www.elsevier.com/locate/jns

Neuromuscular disturbance outlasts other symptoms of exercise-inducedmuscle damage

a , a b a c*Michael R. Deschenes , Rhonda E. Brewer , Jill A. Bush , Raymond W. McCoy , Jeff S. Volek ,c

William J. Kraemera

Department of Kinesiology, The College of William & Mary, Williamsburg, VA 23187-8795, U SAb

Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, U SAc

The Human Performance Laboratory, Ball State University, Muncie, IN 47306, U SA

Received 26 July 1999; received in revised form 13 October 1999; accepted 22 December 1999

Abstract

This study examined the biochemical, immunological, functional, and neuromuscular responses associated with exercise-induced

muscle damage in the quadriceps of untrained men. Muscle damage and soreness was elicited with maximal concentric/eccentric muscle21

actions at 0.53 rads s . Significant (P,0.05) soreness was evident 1, 2, and 3 days following muscle insult, while plasma creatine

kinase, a marker of muscle damage, was elevated 3 and 5 days post-insult. Plasma interleukin-Ib was significantly increased within 5 min,

and remained elevated 1, 2, 5, and 7 days post-insult. Maximal isometric quadriceps function was impaired ( P,0.05) for 5 days following21

muscle challenge. Maximal isokinetic performance at 1.09 rads s was diminished (P,0.05) for 2 days post-insult; no significant21

decrements at 3.14 rads s were noted. Average electrical activation (iEMG) of the quadriceps was unaltered, but iEMG activity of the

rectus femoris where soreness was focused was significantly increased. Neuromuscular efficiency (torque/iEMG) was compromisedthroughout the 10-day post-insult period investigated. While other symptoms of exercise-induced muscle damage dissipate within 7 days,

neuromuscular perturbation persists for at least 10 days. 2000 Elsevier Science B.V. All rights reserved.

Keywords: Creatine kinase; IL-Ib; EMG; Isometric; Isokinetic; Soreness

1. Introduction and is generally indicated by elevated concentrations of

circulating macrophages, monocytes, and interleukins

Participation in unaccustomed physical exertion, par- [11,12].

ticularly that involving eccentric, or muscle lengthening, Such muscle insult is also associated with a diminution

actions typically results in muscle damage [14]. This of maximal force production and localized discomfortdamage is evidenced by ultrastructural damage, i.e. Z-line [13,14], yet these manifestations of exercise-induced mus-

streaming [5,6], and due to sarcolemmal disruption, in- cle damage exhibit disparate temporal characteristics. For

creased blood-borne levels of intramuscular proteins such example, while impaired force production is most pro-

as creatine kinase (CK), lactate dehydrogenase (LDH), and nounced within 24 h [2,13,15], peak soreness is not

myoglobin [710]. Consequent to this damage, an in- reported until 23 days following eccentric work [13].

flammatory response is mounted by the immune system Accordingly, the discomfort accompanying unfamiliar

muscular exertion is referred to as delayed onset muscle

soreness or DOMS. The precise mechanism for the

postponement of discomfort following muscle insult is*Corresponding author. Tel.: 11-757-221-2778; fax: 11-757-221-

unknown, but it has been suggested that it is related to a2761.E-mail address:[email protected] (M.R. Deschenes) local inflammatory stimulation [12,16]. That is, the release

0022-510X/00/$ see front matter 2000 Elsevier Science B.V. All rights reserved.P I I : S 0 0 2 2 - 51 0 X ( 0 0 ) 0 0 2 58 - 6

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M.R. Deschenes et al. /Journal of the Neurological Sciences 174 (2000) 9299 93

of pain substances such as bradykinin and histamine is tube via venipuncture of an antecubital vein. Whole blood

delayed after the onset of muscle injury. was centrifuged at 30003g for 15 min at 48C; plasma was

Similar to delayed soreness, the exact cause(s) of stored at2758C until analysis.

attenuated muscle strength following unaccustomed exer- The subject then performed a light (40 W), nonspecific

tion is not yet fully understood. It has been suggested that warm-up protocol on an electrically braked cycle ergome-

the decrement in force production may be due to damage ter (Excalibur Unit, Lode, Groningen, The Netherlands) for

to the contractile elements, impaired electrical activation, 5 min. One min into the warm-up, the subject was asked to

and/ or disruption of the excitationcontraction (EC) rate the level of soreness of the non-dominant thigh. If anycoupling process [17]. soreness was indicated, the subject was asked whether the

To date, the investigation of the effects of, and recovery discomfort was more pronounced in the inner, middle, or

from, exercise-induced muscle damage has mainly em- outer region of the quadriceps.

ployed an animal model [7,17,18], or in humans, a small, The subject was then situated on the isokinetic device

seldom used muscle, i.e. biceps brachii [1,2,14,19], or the with the knee aligned with its axis, to test muscle function

quadriceps following submaximal exertion [8,9,11,20]. The of the non-dominant leg. In preparation for concurrent

aim of the present study was twofold: (1) to examine the isometric testing and electromyographic (EMG) analysis,

effects of exercise-induced muscle trauma in a large, the involved knee was positioned at a 958 angle, and a one

commonly used muscle mass (quadriceps) in humans square inch area of skin over each of the three surface

following a maximal, voluntary effort, and (2) to assess the quadriceps muscles (vastus medialis, rectus femoris, vastus

impact of muscle insult on neuromuscular function over an lateralis) was shaved, abraded, and cleansed with an

extended period of time. alcohol wipe. Following the longitudinal contour of the

muscle, 2-mm-diameter electrodes filled with electrolyte

gel were secured on the skin with adhesive collars at an

interelectrode distance of 2 cm, and traced with ink. These2. Materials and methods

tracings enabled electrode placement at the same sites for

each subsequent test. EMG signals were amplified by a2.1. Subjects

factor of 1000 and passed through a bandwidth filter set at

30 and 500 Hz, along with a 60-Hz notch filter. SignalsNine healthy, untrained men (20.961.0 years,

were digitized at a sampling frequency of 1000 Hz, and174.862.0 cm, 72.366.1 kg; mean6S.E.) agreed to par-

recorded by an on-line computer system during the first 5 sticipate in the study. After receiving a verbal description of

of a 15-s maximal isometric contraction of the kneethe investigation, its potential risks, and the experimental

extensors. The EMG signal was then full wave rectified,procedures employed, the subjects provided written in-

and integrated (iEMG in mV/s). Subjects were given a 1-s

formed consent. Each subject also completed a medical ramp-up phase to achieve full muscle activation beforequestionnaire that was examined by a physician to ensureEMG and force measurements were begun.

that no contraindications to participation existed. AllFollowing completion of the 15-s isometric contraction,

experimental procedures were approved by the Committeethe electrodes were removed from the subjects leg. In

for the Protection of Human Subjects at The College ofpreparation for isokinetic testing, the subjects limb weight

William & Mary.was measured by the dynamometer so that performance

variables could be corrected for that resistance. A full

2.2. Experimental protocol range of motion was then selected by the subject that was

adhered to for isokinetic testing at each subsequent ses-

Subjects initially performed a familiarization trial on an sion.

isokinetic dynamometer (model 900-350, Biodex Co., Maximal isokinetic muscle function (peak torque, and

Shirley, NY). Since an extended prophylactic effect for total work) was then determined with five repetition sets of

muscle damage occurs following a single exertional effort alternating, concentric actions of the knee extensors andthat is specific to the musculature involved [15,19,21], flexors of the non-dominant leg at velocities of 1.05 and21

only the subjects dominant leg was exercised during the 3.14 rads s . A rest interval of 5 min occurred between

familiarization trial; the nondominant leg would be used sets, and verbal encouragement was provided during all

during actual data collection sessions. To ensure that any isokinetic, as well as isometric, testing.

potential elevations in circulating markers of muscle After collection of baseline (day 0) data was completed,

damage or inflammation were dissipated following this subjects rested for 5 min before carrying out the damage-

exercise, a 1014-day period interspersed the familiariza- inducing event. This muscle insult was presented as four

tion trial from the first data collection session [22,23]. At sets of 25 repetitions, interspersed by 3-min rest periods, of

the first test session (day 0) baseline data were collected. unilateral, alternating concentric / eccentric muscle actions21

The subjects height and weight were determined, and a of the non-dominant knee extensors at 0.53 rads s . Five

3-ml sample of blood was collected into a heparin-treated min following completion of the concentric / eccentric work

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94 M.R. Deschenes et al. /Journal of the Neurological Sciences 174 (2000) 9299

protocol, another blood sample was drawn, centrifuged, contraction divided by average iEMG during that time,

and plasma was stored at 2758C until analysis. was determined and compared among test sessions.

With the exception of the muscle damaging protocol and

the blood sample taken 5 min after that muscle challenge, 2.4. Statistical analysis

data collection, i.e. blood draw, soreness assessment,

EMG, isometric and isokinetic testing, was repeated (61 Data are reported as means6S.E. To assess changes in

h), at 24 h (day 1), 48 h (day 2), 72 h (day 3), 120 h (day each variable of interest during the experimental period,

5), 168 h (day 7), and 240 h (day 10) after collection of repeated measures one-way ANOVAs were utilized. Whenbaseline data. For 10 days prior to, and throughout the significant F-ratios were found, Fisher PLSD post-hoc

study period, subjects were instructed to avoid anti-in- analyses were conducted. In this report, only statistically

flammatory medications, maintain normal sleeping pat- significant differences from baseline values will be iden-

terns, and to refrain from unaccustomed muscular exertion. tified since deviations from, and resumptions to, pre-insult

For 68 h prior to arriving at the laboratory for testing, conditions were the focus of the study. Statistical signifi-

subjects consumed only water. cance was established at P#0.05.

2.3. Quantitation 3. Results

Subjective ratings of muscular soreness were determined The combination of concentric/ eccentric actions of the

with a 010 scale where 05no soreness, 55moderate knee extensors resulted in damage, and soreness of the

soreness, and 105extreme soreness. Plasma CK activities involved muscles. Muscle damage was indicated by in-

were measured in duplicate with a Vitros blood chemistry creased plasma CK activity at days 3 and 5. In addition,

analyzer (model DT 60 II, Johnson and Johnson Clinical significant elevations in plasma IL-Ib were detected at 5

Diagnostics, Rochester, NY). Plasma concentrations of min post-insult, as well as on days 1, 2, 5, and 7.

interleukin Ib (IL-Ib) were assessed in duplicate with Responses of these blood-borne variables are presented in

ELISA kits (Cytimmune Sciences Inc., College Park, MD). Figs. 1 and 2, respectively.

During the 15-s maximal isometric contractions of knee There was significant overall soreness of the quadriceps

extensors, peak and total torque, along with fatigue (% at 1, 2, and 3 days following muscle insult, with the

difference in torque from first to last 5 s) were calculated highest ratings occurring at day 2. When subjects were

by the Advantage software accompanying the Biodex asked to localize where pain was most acute, 74% of the

dynamometer. During isokinetic maximal actions of knee time the central region of the thigh (rectus femoris) was

extensors and flexors, peak torque and total work were identified. This was significantly greater than the inner

ascertained with the Advantage software. In addition to (vastus medialis) or outer (vastus lateralis) regions at 26%average iEMG values derived from the three surface and 12%, respectively. Soreness of the quadriceps over the

muscles of the quadriceps, iEMG data from each of those 10-day investigation is illustrated in Fig. 3.

muscles were examined individually over the experimental Performance of the quadriceps, during both isometric

period. In addition, neuromuscular efficiency, defined as and isokinetic actions was significantly diminished follow-

total torque generated during the first 5 s of the isometric ing muscle insult. During the 15-s maximal isometric

Fig. 1. Plasma activities of creatine kinase (CK). Values are means6S.E., n59. *Indicates significant difference (P,0.05) from day 0.

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evidenced no performance decrements (data not shown).

Data regarding quadriceps function are found in Table 1.

Integrated EMG data, averaged among the measured

knee extensor muscles, exhibited no significant differences

during the study. In addition to this overall iEMG value,

the electrical activation of the rectus femoris, vastus

lateralis, and vastus medialis was examined individually.

Results of these analyses revealed no significant variationin iEMG data for the vastus lateralis or vastus medialis

subsequent to the DOMS-inducing event. However, electri-

cal activation of the rectus femoris was significantly

enhanced at days 2, 3, and 10. The results of iEMG

analyses are presented in Fig. 4.

Neuromuscular efficiency (torque/ iEMG) was deter-

mined during the first 5 s of the maximal isometric

contraction of the quadriceps. This parameter demonstratedFig. 2. Plasma concentrations of interleukin Ib (IL-Ib). Values area significant diminution at each of the 10 days studiedmeans6S.E.,n59. *Indicates significant difference (P,0.05) from day 0.following the collection of baseline data at day 0. Changes

in neuromuscular efficiency during the investigation can becontraction, significant decrements in peak and total torqueobserved in Fig. 5.

produced were evident at days 1, 2, 3, and 5 compared tobaseline values at day 0. Torque generated during the first

5 s of the isometric contraction demonstrated an identical4. Discussion`pattern of disturbance. Specifically, vis-a-vis baseline data,

total force produced during the initial 5 s was less at daysThe data presented here add to a large body of evidence1, 2, 3, and 5. Interestingly, no changes in fatigue during

confirming that unaccustomed muscle exertion results in15-s isometric contractions were demonstrated throughoutmuscle damage, and a sequela of associated physiologicalthe experimental period.responses. The plasma CK elevations consequent to mus-Isokinetic data indicate that during five repetition sets at

21 cle insult noted here are similar to previous studies despite1.09 and 3.14 rads s , significant impairments in quad-the use of high intensity isokinetic resistance exercise toriceps performance were displayed only at the slower

21 elicit damage and pain in the quadriceps. While othervelocity of movement. At 1.09 rads s , peak torque wasresearchers have studied circulating levels of intramuscularsignificantly lower at day 1 compared to day 0, while total

proteins to indicate muscle damage in the knee extensors,work was significantly decreased at days 1 and 2 relative21 they typically employed submaximal efforts such as down-to baseline values. However, at 3.14 rads s , neither peak

hill running [7,8,20], cycle ergometry [5,6], or benchtorque nor total work produced by the quadriceps variedstepping [4,9] as the unaccustomed exertion. Maximalsignificantly during the investigation. Knee flexors, whicheccentric contractions have been used to investigate circu-were not subjected to damage-inducing eccentric actions,lating markers of sarcolemmal damage, however, those

studies focused on the elbow flexors [1,14,19]. Despite

differences in muscles utilized, or intensity of muscle

exertion, the temporal responses of blood-borne CK levels

noted here are consistent with those earlier studies. Spe-

cifically, elevations in CK activity are most marked 35

days following unaccustomed physical activity.

Muscle soreness manifested itself most acutely 23 daysfollowing muscle insult. The intensity of the discomfort in

the quadriceps reported by our subjects was similar to that

experienced in the elbow flexors following eccentric

contractions in previous studies [19,24]. Based upon these

and other investigations [1,4] comparing the effects of

different modes of muscle actions on soreness, it is

reasonable to assume that the eccentric component of our

exercise protocol was principally responsible for the

muscle damage and soreness evinced in our subjects.

It has been postulated [16] that the delay that occursFig. 3. Soreness of quadriceps muscles. Values are means6S.E., n59.*Indicates significant difference (P,0.05) from day 0. between muscle insult and the onset of soreness is concor-

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Table 1a

Muscle function of knee extensors

Day 0 Day 1 Day 2 Day 3 Day 5 Day 7 Day 10

Peak torque (N)21

0 rads s 219.0620.3* 179.7621.2 190.3621.2 188.1623.3 194.9622.8 203.6624.8 214.5625.0

Total torque (N)21

0 rads s 2846.96262.9* 2338.46275.7 2473.86274.0 2445.86303.4 2531.26297.6 2647.56321.2 2787.76325.2

Torque, first 5 s (N)21

0 rads s 942.1685.8* 775.2687.9 823.9685.5 823.6698.5 824.0686.1 869.6695.6 917.06110.0

Peak torque (Nm)21 D

1.09 rads s 203.3621.9 177.3614.0 191.8612.6 194.8615.0 197.6618.9 197.3618.0 200.7618.1

Total work (J)21 [

1.09 rads s 754.7674.5 653.1651.0 686.8639.2 723.0651.4 741.5658.3 734.0664.7 754.1666.5

Peak torque (Nm)21

3.14 rads s 150.8614.3 135.068.2 139.969.8 142.8612.4 148.5613.7 145.0614.1 148.0614.4

Total work (J)21

3.14 rads s 504.8653.6 470.7624.6 478.0625.4 494.9634.3 524.3638.6 500.9640.0 512.3647.7

a DValues are means6S.E.;n59. *Indicates significant difference (P,0.05) from days 1, 2, 3, and 5. Indicates significant difference (P,0.05) from day

[

1. Indicates significant difference (P,0.05) from days 1 and 2.

dant with the time necessary for the activation of the cle function included testing during isometric and iso-

inflammatory response resulting from muscle damage. Our kinetic contractions. During both modes of contraction,

plasma IL-Ib data indicate that the inflammatory response significant decreases in force production followed muscle

of the immune system was almost immediately stimulated injury. Isometric functional capacity of the quadriceps was

by muscle insult. After adjusting for plasma volume shifts measured during a 15-s maximal effort. A significant

[25], a nearly threefold increase in this cytokine was decrement in peak torque, and total torque during the 15-s

observed as early as 5 min following the series of contraction was detected 24 h following the damage-

concentric/ eccentric muscle actions. This acute response inducing protocol, and persisted through the next 4 days.

supports the role of IL-Ib as a pro-inflammatory cytokine By day 7, neither peak nor total torque produced were

that is responsible for the release of other soluble agents of significantly different from baseline values.

the immune system that more directly mediate the in- The 15-s isometric test was also used to evaluate muscle

flammatory response [26], and suggests that it may serve fatigue. Our results indicate that while the capacity of theas a particularly sensitive marker of muscle damage. affected muscle to produce force was modulated by

Unlike previous studies, the present evaluation of mus- damage, the ability to maintain force was not. Based upon

Fig. 4. Average iEMG among three surface quadriceps muscles, and iEMG for rectus femoris. Values are means6S.E., n59. *Indicates significant

difference (P,0.05) from day 0.

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210 to day 1 occurred at 0 rads s , while the least severe

21was at 3.14 rads s . Moreover, knee extensor function

(peak and total torque) remained significantly compro-

mised for 5 days post-insult during maximal contractions21 21

at 0 rads s , for 2 days (total work) at 1.09 rads s ,21

while it was never significantly affected at 3.14 rads s .

In fact, it may be that these data do not conflict with

evidence that fast-twitch fibers suffer more damage thanslow-twitch muscle. Rather, these results reasonably imply

that a relationship exists between the degree of functional

disturbance, and the capacity to generate force prior to

muscle insult. In essence, the greater the ability to produce

force, the greater the degree and duration of the loss

suffered following injury. Alternatively, it is possible that

since muscle damage was elicited with slow muscleFig. 5. Neuromuscular efficiency (torque/ average iEMG). Values are actions, the effects are most pronounced during move-means6S.E.,n59. *Indicates significant difference (P,0.05) from day 0. ments of similar velocities.

In an effort to determine potential causes of the di-

these performance data, it appears that the bioenergetics of minished muscle function observed post-insult, iEMG

the involved muscle, at least with respect to the phos- analyses of the three surface muscles of the quadriceps, i.e.

phagen pathway, remained unaffected. rectus femoris, vastus lateralis, vastus medialis, were

Isokinetic muscle performance was tested at two differ- performed. Komi and Viitasalo [30] had previously ex-21

ent velocities. As with isometric results, at 1.09 rads s amined the electrical activation of the rectus femoris and

isokinetic performance of the quadriceps, measured as vastus lateralis following unaccustomed exertion, but those

peak torque and total work during the five repetition set, authors collected iEMG data during submaximal contrac-

was significantly impaired as a result of muscle damage. tions, and for only 2 days following muscle challenge. In

However, in contrast to isometric function of the knee the present study, iEMG data were collected on each of the

extensors which was reduced through day 5 of the study, three surface muscles during maximal isometric contrac-21

peak torque at 1.09 rads s demonstrated a significant tions for 10 days following muscle insult. In analyzing the

decrement only at day 1, while total work was hindered at effects of exercise-induced damage on muscle activation,

days 1 and 2. we examined each of the three muscles individually, as

Interestingly, when knee extensor muscle performance well as the average iEMG value among the three muscles.21

was assessed at 3.14 rads s , no significant decreases in This indicator of overall activation of the quadricepspeak torque, or total work were noted. Although both remained steady over the period of investigation, sug-

slow- and fast-twitch muscle fibers are activated at this gesting that decreased muscle performance cannot be

speed, fast-twitch fibers primarily, if not exclusively, ascribed to impaired electrical excitation of the contractile

account for force production [27]. Our in vivo functional apparatus. When iEMG data for each of the three muscles

results appear to be at odds with ultrastructural evidence were considered individually, no impact of injury was

that exercise-induced muscle damage occurs mainly in apparent in either the vastus lateralis or the vastus

fast-twitch fibers [5,28]. Presumably, if damage was medialis. However, electrical activation of the rectus

specific to fast-twitch fibers in this study, functional femoris showed increases during the study period. These

diminution would be most pronounced at the velocity of results are interesting in that iEMG alterations were21

3.14 rads s , where these fibers are almost exclusively localized to the same quadriceps muscle in which soreness

responsible for force production. Yet, significant functional was most acute. This localized soreness cannot be attribu-

disturbances are restricted to the slower movement velocity ted to normal conditions of greater recruitment, since data21of 1.09 rads s where, during maximal exertion, both collected at day 0 indicate that the rectus femoris is

slow- and fast-twitch muscle fibers contribute to force activated no more than the vasti muscles during maximal

production [29]. exertion prior to muscle insult (data not shown). Unlike the

Upon closer examination, our results reveal that the vasti muscles, the rectus femoris crosses both the hip and

amount of force generated determines both the degree, and knee joints [31]. Perhaps this anatomical arrangement

the duration of the functional impairment of muscle leaves the rectus femoris more susceptible to stretch-

damaged during unaccustomed exertion. Consistent with related damage from eccentric actions, and consequently to

the forcevelocity curve, our baseline data illustrate that greater discomfort and electrical activation. The data21

peak torque of the quadriceps was greatest at 0 rads s presented here do not allow firm conclusions to be drawn21

(219.0 Nm) and lowest at 3.14 rads s (150.8 Nm). on these points.

Interestingly, the most severe drop in peak torque from day During the initial 5 s of the maximal isometric muscle

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action, measurements on muscle force production and significant alterations in electrical activation. Yet overall

electrical activation were concurrently performed. This iEMG analyses indicate that the reduction in force pro-

enabled us to examine neuromuscular efficiency, or the duction was unrelated to muscle activation which remained

capacity of the contractile elements to respond to electrical unchanged for 10 days following muscle insult. These data

stimulation of the sarcolemma. Komi and Viitasalo [30] contributed to the most striking finding of our inves-

had found that 2 days following unaccustomed exertion, a tigation: neuromuscular efficiency was significantly im-

disturbance in this relationship existed such that, relative to paired the first day following insult, and remained compro-

original efforts, a greater degree of electrical activation mised for 10 days. This prolonged disturbance is probablywas necessary to perform the same submaximal muscle related to dysfunction within the EC coupling mecha-

task. Our data extend those findings. During maximal nism; further research is needed to determine at what point

effort, significant decrements in neuromuscular efficiency subsequent to unaccustomed exertion this disorder is

were detected throughout the 10-day post-insult interval. resolved.

Initially, this finding may be explained by the significant

reduction in torque produced during the 5-s interval

documented on days 1, 2, 3, and 5, without concomitant Acknowledgements

changes in overall iEMG values. This implies that early

neuromuscular dysfunction is mainly due to damage to The authors would like to express their gratitude to the

contractile elements [5,6]. Yet, torque returned to normal subjects who generously gave their time and effort to

values by day 7, while neuromuscular alterations persisted enable the successful completion of this study. This project

through day 10. The continuation of this disturbance may was supported, in part, by a grant from the Faculty

be related to the gradual trend (P50.07) toward an Research Committee of The College of William & Mary.

increase in average iEMG activity, mainly accounted for

by the rectus femoris, during the study period. Still, an

impaired capacity of the myofilaments to respond to References

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