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Control scheme governing concurrently active human motor units during voluntary contractions
Author(s) -
de Luca C. J.,
LeFever R. S.,
McCue M. P.,
Xenakis A. P.
Publication year - 1982
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1982.sp014294
Subject(s) - isometric exercise , motor unit , motor unit recruitment , deltoid curve , muscle contraction , motor control , muscle fatigue , electromyography , chemistry , physical medicine and rehabilitation , anatomy , neuroscience , psychology , medicine , physical therapy
1. The electrical activity of up to eight concurrently active motor units has been recorded from the human deltoid and first dorsal interosseous muscles. The resulting composite myoelectric signals have been decomposed into their constituent motor‐unit action potential trains using a recently developed technique. 2. A computer cross‐correlation analysis has been performed on motor‐unit firing rate and muscle‐force output records obtained from both constant‐force and triangular force‐varying isometric contractions performed by normal subjects, and three groups of highly trained performers (long‐distance swimmers, powerlifters and pianists). 3. The temporal relationships between firing rate activity and force output have provided evidence that the deltoid of long‐distance swimmers has a significantly higher percentage of slowly fatiguing fibres than that of normal subjects. 4. Results showed that both muscles are incapable of producing a purely isotonic contraction under isometric conditions. Small, possibly compensatory force variations at 1‐2 Hz result from a common drive to all active motoneurones in a single muscle pool. 5. Rapid force reversals during triangular, force‐varying isometric contractions appear to be accomplished through a size‐related motor‐unit control scheme. All firing rates decline prior to the force peak, but small motor units with slow‐twitch responses tend to decrease their firing rates before large, fast‐twitch motor units. This mechanism is not visually controlled, and does not depend on force rate in non‐ballistic contractions.