Voluntary drive-dependent changes in vastus lateralis motor unit firing rates during a sustained isometric contraction at 50% of maximum knee extension force

Ruiter, C. J., Elzinga, M. J. H., Verdijk, P. W. L., van Mechelen, W. and Haan, A. (2004) Voluntary drive-dependent changes in vastus lateralis motor unit firing rates during a sustained isometric contraction at 50% of maximum knee extension force. Pflügers Archiv: European Journal of Physiology, 447 4: 377-464. doi:10.1007/s00424-003-1206-9


Author Ruiter, C. J.
Elzinga, M. J. H.
Verdijk, P. W. L.
van Mechelen, W.
Haan, A.
Title Voluntary drive-dependent changes in vastus lateralis motor unit firing rates during a sustained isometric contraction at 50% of maximum knee extension force
Journal name Pflügers Archiv: European Journal of Physiology   Check publisher's open access policy
ISSN 0031-6768
1432-2013
Publication date 2004-01-01
Sub-type Article (original research)
DOI 10.1007/s00424-003-1206-9
Open Access Status
Volume 447
Issue 4
Start page 377
End page 464
Total pages 8
Place of publication Heidelberg & Berlin
Publisher Springer
Language eng
Subject 1117 Public Health and Health Services
Formatted abstract
The purpose of the present study was to relate the expected inter-subject variability in voluntary drive of the knee extensor muscles during a sustained isometric contraction to the changes in firing rates of single motor units.

Voluntary activation, as established with superimposed electrical stimulation was high (range: 91–99%, n=8) during a short maximal contraction, but was lower (range: 69–100%) in most subjects at the point of force failure during a sustained (49.1±10.1 s) fatiguing contraction at 50% of maximum force. On a different experimental day the firing behaviour of 27 single motor units was recorded with wire electrodes in the vastus lateralis muscle, 24 of which could be monitored from the time of recruitment to the point of force failure (53.6±9.8 s). Motor unit firing behaviour differed considerably among subjects.

During the second half of the sustained, fatiguing contraction the changes in firing rate firing rate variability of early recruited units ranged from –10% to +100% and from –50% to +160% respectively among subjects. There were significant positive linear relations between voluntary activation, on the one hand, and rectified surface electromyogram (rsEMG, r=0.82), the changes in motor unit firing rate (r=0.49) and firing rate variability (r=0.50) towards the point of force failure on the other.

The present data suggest that differences in voluntary drive that appear among subjects during fatigue may be an important determinant of motor unit firing behaviour.
Keyword Voluntary activation
Motor unit EMG
Fatigue
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Unknown
Additional Notes Received: 20 August 2003 Revised: 2 October 2003 Accepted: 22 October 2003 Published online: 22 November 2003

Document type: Journal Article
Sub-type: Article (original research)
Collections: Excellence in Research Australia (ERA) - Collection
School of Human Movement and Nutrition Sciences Publications
 
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