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1 Physiology, University of Adelaide, Adelaide, South Australia, Australia
2 Australia; Physiology, Monash University, Melbourne, Victoria, Australia
3 Physiology, Monash University, Melbourne, Victoria, Australia
* To whom correspondence should be addressed. E-mail: john.semmler{at}adelaide.edu.au.
The purpose of this study was to determine the effect of eccentric exercise on the ability to exert steady submaximal forces with muscles that cross the elbow joint. Eight subjects performed two tasks requiring isometric contraction of the right elbow flexors: a maximum voluntary contraction (MVC) and a constant-force task at 4 submaximal target forces (5, 20, 35, 50% MVC) while electromyography (EMG) was recorded from elbow flexor and extensor muscles. These tasks were performed before, after, and 24-hrs after a period of eccentric (fatigue and muscle damage) or concentric exercise (fatigue only). MVC force declined after eccentric exercise (45% decline) and remained depressed 24-hrs later (24%), whereas the reduced force after concentric exercise (22%) fully recovered the following day. EMG amplitude during the submaximal contractions increased in all elbow flexor muscles after eccentric exercise, with the greatest change in the biceps brachii at low forces (3-4x larger at 5% and 20% MVC) and in the brachialis muscle at moderate forces (2x larger at 35% and 50% MVC). Eccentric exercise resulted in a two-fold increase in coactivation of the triceps brachii muscle during all submaximal contractions. Force fluctuations were larger after eccentric exercise, particularly at low forces (3-4x larger at 5% MVC, 2x larger at 50% MVC), with a two-fold increase in physiological tremor at 8-12 Hz. These data indicate that eccentric exercise results in impaired motor control and altered neural drive to elbow flexor muscles, particularly at low forces, suggesting altered motor unit activation after eccentric exercise.
This article has been cited by other articles:
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  T. J. Dartnall, N. C. Rogasch, M. A. Nordstrom, and J. G. Semmler Eccentric Muscle Damage Has Variable Effects on Motor Unit Recruitment Thresholds and Discharge Patterns in Elbow Flexor Muscles J Neurophysiol, July 1, 2009; 102(1): 413 - 423. [Abstract] [Full Text] [PDF]
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 J. M. Dundon, J. Cirillo, and J. G. Semmler Low-frequency fatigue and neuromuscular performance after exercise-induced damage to elbow flexor muscles J Appl Physiol, October 1, 2008; 105(4): 1146 - 1155. [Abstract] [Full Text] [PDF]
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T. S. Turner, K. J. Tucker, N. C. Rogasch, and J. G. Semmler Impaired neuromuscular function during isometric, shortening, and lengthening contractions after exercise-induced damage to elbow flexor muscles J Appl Physiol, August 1, 2008; 105(2): 502 - 509. [Abstract] [Full Text] [PDF]
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T. J. Dartnall, M. A. Nordstrom, and J. G. Semmler Motor Unit Synchronization Is Increased in Biceps Brachii After Exercise-Induced Damage to Elbow Flexor Muscles J Neurophysiol, February 1, 2008; 99(2): 1008 - 1019. [Abstract] [Full Text] [PDF]
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