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Type: Journal article
Title: Motor Unit Synchronization is Increased in Biceps Brachii after Exercise-Induced Damage to Elbow Flexor Muscles
Author: Dartnall, T.
Nordstrom, M.
Semmler, J.
Citation: Journal of Neurophysiology, 2008; 99(2):1008-1019
Publisher: Amer Physiological Soc
Issue Date: 2008
ISSN: 0022-3077
Statement of
Tamara J. Dartnall, Michael A. Nordstrom and John G. Semmler
Abstract: The purpose of this study was to determine the effect of eccentric exercise on correlated motor unit discharge (motor unit synchronization and coherence) during low-force contractions of the human biceps brachii muscle. Eight subjects (age, 25 ± 7 yr) performed three tasks involving isometric contraction of elbow flexors while EMG (surface and intramuscular) records were obtained from biceps brachii. Tasks were 1) maximum voluntary contraction (MVC); 2) constant-force contraction at various submaximal targets; and 3) sustained discharge of pairs of concurrently active motor units for 2–5 min. These tasks were performed before, immediately after, and 24 h after fatiguing eccentric exercise. MVC force declined 46% immediately after eccentric exercise and remained depressed (31%) 24 h later, which is indicative of muscle damage. For the constant-force task, biceps brachii EMG (~100% greater) and force fluctuations (~75% greater) increased immediately after exercise, and both recovered by ~50% 24 h later. Motor unit synchronization, quantified by cross-correlation of motor unit pairs during low-force (1–26% MVC) contractions, was 30% greater immediately after (n = 105 pairs) and 24 h after exercise (n = 92 pairs) compared with before exercise (n = 99 pairs). Similarly, motor unit coherence at low (0–10 Hz) frequencies was 20% greater immediately after exercise and 34% greater 24 h later. These results indicate that the series of events leading to muscle damage from eccentric exercise alters the correlated behavior of human motor units in biceps brachii muscle for ≥24 h after the exercise.
Keywords: Elbow
Muscle, Skeletal
Motor Neurons
Brachial Plexus
Analysis of Variance
Task Performance and Analysis
Muscle Contraction
Time Factors
Biomechanical Phenomena
DOI: 10.1152/jn.00686.2007
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Physiology publications

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