Document Detail

Contraction-induced potentiation of human motor unit discharge and surface EMG activity.
MedLine Citation:
PMID:  3173048     Owner:  NLM     Status:  MEDLINE    
In quadrupeds, an electrically induced, moderate to high intensity brief muscle contraction potentiates autogenetic excitation and leads to enhanced recruitment and/or tonic firing frequency of alpha-motor neurons. To determine if similar adaptations occur in humans, single motor units (SMUs) and surface electromyographic activity (EMG) were recorded from the right biceps brachii before and immediately after a 5-s 25% or 50% maximum voluntary contraction (MVC), while subjects held a handle (0-1% MVC) attached to a force transducer or maintained a 2% MVC for 30-60 s. Of 26 SMUs recorded, 15 increased, 4 decreased, and 7 showed no change in firing frequency (mean increase: 5 imp/s, P less than 0.01). Twelve SMUs had lower recruitment force thresholds after contraction. There was no significant treatment effect for the % MVC intensity. The postcontraction surface EMG power spectrum broadened, increased in amplitude, and contained a higher frequency component than the control contraction power spectrum. Changes in recruitment and/or frequency coding were reflected in the raw EMG records. Findings agree with previous reports in animals of contraction-induced potentiation of subsequent submaximal muscle contractions. Such acute adaptations in spinal neuromuscular pathways would function to optimize force output to a submaximal range of neural input frequencies.
S Suzuki; K Kaiya; S Watanabe; R S Hutton
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Medicine and science in sports and exercise     Volume:  20     ISSN:  0195-9131     ISO Abbreviation:  Med Sci Sports Exerc     Publication Date:  1988 Aug 
Date Detail:
Created Date:  1988-11-16     Completed Date:  1988-11-16     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  8005433     Medline TA:  Med Sci Sports Exerc     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  391-5     Citation Subset:  IM; S    
Department of Physiology, Kyorin University, School of Medicine, Tokyo, Japan.
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MeSH Terms
Isometric Contraction*
Motor Endplate / physiology*
Muscle Contraction*
Neuromuscular Junction / physiology*
Recruitment, Neurophysiological
Sensory Thresholds / physiology

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