Document Detail

Relationships between surface-detected EMG signals and motor unit activation.
MedLine Citation:
PMID:  12218747     Owner:  NLM     Status:  MEDLINE    
INTRODUCTION: Surface-detected electromyographic (S-EMG) signals are used in exercise science to assess the extent of muscle activation, muscle fatigue, and neural activity during muscle contraction. However, the relationship has not been studied between S-EMG signal amplitude and motor unit activation at different muscle force levels. METHODS: S-EMG signals were measured from 76 healthy subjects during target force levels of 5, 10, 20, 30, and 50% of maximal voluntary contraction (MVC) of the knee extensors over 20-30 s. Mean absolute S-EMG amplitude, surface-detected motor unit action potential amplitude (S-MUAP), motor unit mean firing rate (mFR), and motor unit mean voltage, which is the product of S-MUAP amplitude and mFR, were assessed in the vastus medialis by using EMG signal-decomposition and spike-triggered averaging techniques. RESULTS: Motor unit mean voltage increased to the same degree as mean absolute S-EMG amplitude with increasing force, implying that motor unit size and firing rate explain the increase in mean absolute S-EMG amplitude with increasing force generation. In addition, mean absolute S-EMG amplitude increased linearly during the course of each 20-30 s contraction, with the slope being greater at higher force levels. A small change was observed in the shape of needle-detected motor unit action potentials during the contraction, but this change was not sufficient to explain the large change in mean absolute S-EMG amplitude during the contraction. CONCLUSION: Mean absolute S-EMG amplitude at different force levels and its changes during the course of a submaximal contraction are dependent on the number of motor units active, their size, and firing rates.
Hiromasa Suzuki; Robin A Conwit; Dan Stashuk; Lynn Santarsiero; E Jeffrey Metter
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Medicine and science in sports and exercise     Volume:  34     ISSN:  0195-9131     ISO Abbreviation:  Med Sci Sports Exerc     Publication Date:  2002 Sep 
Date Detail:
Created Date:  2002-09-09     Completed Date:  2002-12-09     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  8005433     Medline TA:  Med Sci Sports Exerc     Country:  United States    
Other Details:
Languages:  eng     Pagination:  1509-17     Citation Subset:  IM; S    
Department of Rehabilitation Medicine, Dokkyo University School of Medicine, 880 Shimotuga, Mibu, Tochigi 321-02, Japan.
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MeSH Terms
Middle Aged
Motor Neurons / physiology*
Muscle Contraction / physiology*
Muscle Fatigue
Muscle, Skeletal / physiology*
Physical Exertion / physiology
Regression Analysis

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