Changes in motor unit characteristics after eccentric elbow flexor exercise

Morphological evidence suggests that fast‐twitch fibers are prone to disruption of their membrane structures by eccentric exercise. However, it is unclear how this is reflected in the discharge rate and action potential propagation of individual motor units, especially at high contraction levels. Hi...

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Bibliographic Details
Published in:Scandinavian journal of medicine & science in sports 2012-06, Vol.22 (3), p.418-429
Main Authors: Piitulainen, H., Holobar, A., Avela, J.
Format: Article
Language:English
Subjects:
Adult
Analysis of Variance
Biomechanical Phenomena
Elbow
Elbow - physiology
Electromyography
Exercise
Exercise - physiology
exercise-induced muscle damage
Humans
Isometric Contraction - physiology
Male
mean muscle fiber conduction velocity
Morphology
motor unit discharge rate
muscle cell membrane
Muscle Contraction - physiology
muscle fatigue
Muscle Fatigue - physiology
Muscle, Skeletal - physiology
Muscular system
Nervous system
Pain Measurement
Skin Temperature
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Summary:Morphological evidence suggests that fast‐twitch fibers are prone to disruption of their membrane structures by eccentric exercise. However, it is unclear how this is reflected in the discharge rate and action potential propagation of individual motor units, especially at high contraction levels. High‐density surface electromyograms were recorded from biceps brachii muscle and decomposed to individual motor unit action potentials at isometric contraction levels between 10% and 75% of maximal voluntary contraction (MVC) before intermittent maximal elbow flexor eccentric exercise, and two hours (2H), two days (2D) and four days (4D) post‐exercise. Maximal voluntary force decreased by 21.3±5.6% 2H and by 12.6±11.1% 2D post‐exercise. Motor unit discharge rate increased and mean muscle fiber conduction velocity decreased, at the highest isometric contraction levels only (50% and 75% of MVC) at 2H post‐exercise. These results indicate that eccentric exercise can disturb the function of motor units active at high contraction levels in the early stages after exercise, which seems to be compensated by the central nervous system with an increase in neural drive during submaximal isometric contractions.
ISSN:0905-7188
1600-0838
DOI:10.1111/j.1600-0838.2010.01228.x