Document Detail

Rank-ordered regulation of motor units.
MedLine Citation:
PMID:  8618553     Owner:  NLM     Status:  MEDLINE    
Myoelectric signals were detected from the tibialis anterior muscle of 5 subjects with a quadrifilar needle electrode while the subjects generated isometric forces that increased linearly with time (10% of maximal voluntary contraction/s) up to maximal voluntary level. Motor unit firing rates were studied as a function of force throughout the full range of muscle force output. The relationship between force and firing rate was found to contain three distinct regions. At recruitment and near maximal force levels, firing rates increased more rapidly with force than in the intermediate region. Furthermore, in the regions with rapid increases, the rate of change of firing rate was correlated to the recruitment threshold, with higher recruitment threshold motor units displaying greater rates of change. In the intermediate region, all motor units had similar rates of change of firing rate. A weak positive correlation was found between initial firing rate and recruitment threshold. Firing rates of motor units at any instant were found to be ordered according to the recruitment order: at any given time in the contraction motor units with lower recruitment thresholds had higher firing rates than units with higher recruitment thresholds. Firing rates of all motor units were observed to converge to the same value at maximal forces. Mechanisms underlying motor unit recruitment and firing rate modulation are discussed in the context of a conceptual model.
Z Erim; C J De Luca; K Mineo; T Aoki
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, Non-P.H.S.    
Journal Detail:
Title:  Muscle & nerve     Volume:  19     ISSN:  0148-639X     ISO Abbreviation:  Muscle Nerve     Publication Date:  1996 May 
Date Detail:
Created Date:  1996-06-12     Completed Date:  1996-06-12     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  7803146     Medline TA:  Muscle Nerve     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  563-73     Citation Subset:  IM    
NeuroMuscular Research Center, Boston University, MA 02215, USA.
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MeSH Terms
Action Potentials
Differential Threshold
Motor Neurons / physiology*
Muscle Contraction / physiology
Muscles / innervation
Recruitment, Neurophysiological

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