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Type: Journal article
Title: Eccentric Muscle Damage Has Variable Effects on Motor Unit Recruitment Thresholds and Discharge Patterns in Elbow Flexor Muscles
Author: Dartnall, T.
Rogasch, N.
Nordstrom, M.
Semmler, J.
Citation: Journal of Neurophysiology, 2009; 102(1):413-423
Publisher: Amer Physiological Soc
Issue Date: 2009
ISSN: 0022-3077
Statement of
Tamara J. Dartnall, Nigel C. Rogasch, Michael A. Nordstrom and John G. Semmler
Abstract: The purpose of this study was to determine the effect of eccentric muscle damage on recruitment threshold force and repetitive discharge properties of low-threshold motor units. Ten subjects performed four tasks involving isometric contraction of elbow flexors while electromyographic (EMG) data were recorded from human biceps brachii and brachialis muscles. Tasks were 1) maximum voluntary contraction (MVC); 2) constant-force contraction at various submaximal targets; 3) motor unit recruitment threshold task; and 4) minimum motor unit discharge rate task. These tasks were performed on three separate days before, immediately after, and 24 h after eccentric exercise of elbow flexor muscles. MVC force declined (42%) immediately after exercise and remained depressed (29%) 24 h later, indicative of muscle damage. Mean motor unit recruitment threshold for biceps brachii was 8.4+/-4.2% MVC, (n=34) before eccentric exercise, and was reduced by 41% (5.0+/-3.0% MVC, n=34) immediately after and by 39% (5.2+/-2.5% MVC, n=34) 24 h after exercise. No significant changes in motor unit recruitment threshold were observed in the brachialis muscle. However, for the minimum tonic discharge rate task, motor units in both muscles discharged 11% faster (10.8+/-2.0 vs. 9.7+/-1.7 Hz) immediately after (n=29) exercise compared with that before (n=32). The minimum discharge rate variability was greater in brachialis muscle immediately after exercise (13.8+/-3.1%) compared with that before (11.9+/-3.1%) and 24 h after exercise (11.7+/-2.4%). No significant changes in minimum discharge rate variability were observed in the biceps brachii motor units after exercise. These results indicate that muscle damage from eccentric exercise alters motor unit recruitment thresholds for >or=24 h, but the effect is not the same in the different elbow flexor muscles.
Keywords: Elbow; Muscle, Skeletal; Humans; Electromyography; Exercise; Analysis of Variance; Task Performance and Analysis; Psychomotor Performance; Evoked Potentials, Motor; Muscle Contraction; Time Factors; Adolescent; Adult; Female; Male; Recruitment, Neurophysiological; Young Adult; Biomechanical Phenomena
RMID: 0020090972
DOI: 10.1152/jn.91285.2008
Appears in Collections:Molecular and Biomedical Science publications

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