Document Detail

Frequency response of spine extensors during rapid isometric contractions: effects of muscle length and tension.
MedLine Citation:
PMID:  9779396     Owner:  NLM     Status:  MEDLINE    
During muscle contraction, electrical activity necessarily precedes force output, yet models that utilize processed electromyograms sometimes predict force as preceding EMG under rapid ballistic loading conditions. The purpose of this study was to define the frequency response transfer function of the upper and lower erector spinae musculature, at different lengths and tensions, using rectified, low pass filtered EMG. This would enable accurate estimates of force from the processed electromyogram, specifically during impulsive contractions. Abdominal and erector spinae EMG were measured in synchrony with impulsive low back moments in five men. EMG signals were rectified and low pass filtered repeatedly with cut-off frequencies from 1 to 3 Hz at 0.5 Hz increments in order to quantify the frequency response. It was found that EMG signals processed through a simple, Butterworth low pass filter could not produce the measured force output without an additional time shift. These shifts were quantified by cross-correlating EMG and force with increments of 1 ms. In order to define the transfer function of EMG to force, optimal cut-off frequencies were selected two ways: quantitatively by searching for maximum cross correlations coefficients, and qualitatively. Results indicated that the frequency response of both the upper and lower erector spinae can be modelled with a cut-off frequency between 2 and 2.5 Hz and that these values are not significantly modulated by changes in muscle length or tension.
L C Brereton; S M McGill
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Publication Detail:
Type:  Comparative Study; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology     Volume:  8     ISSN:  1050-6411     ISO Abbreviation:  J Electromyogr Kinesiol     Publication Date:  1998 Aug 
Date Detail:
Created Date:  1998-12-08     Completed Date:  1998-12-08     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  9109125     Medline TA:  J Electromyogr Kinesiol     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  227-32     Citation Subset:  IM    
Department of Kinesiology, Faculty of Applied Health Sciences, University of Waterloo, Ontario, Canada.
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MeSH Terms
Isometric Contraction / physiology*
Muscle, Skeletal / anatomy & histology,  physiology*
Reference Values
Spine / physiology*

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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