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

C J de Ruiter, M J H Elzinga, P W L Verdijk, W van Mechelen

Research output: Contribution to journalArticleAcademicpeer-review

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.

Original languageEnglish
Pages (from-to)436-44
Number of pages9
JournalPflügers Archiv European Journal of Physiology
Volume447
Issue number4
DOIs
Publication statusPublished - Jan 2004

Cite this

@article{1ca2eb600f324341ad0093adeb3f9fa7,
title = "Voluntary drive-dependent changes in vastus lateralis motor unit firing rates during a sustained isometric contraction at 50{\%} of maximum knee extension force",
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.",
keywords = "Action Potentials/physiology, Adult, Electric Stimulation, Electromyography, Evoked Potentials, Motor, Female, Humans, Isometric Contraction/physiology, Knee, Male, Motor Neurons/metabolism, Muscle Fatigue/physiology, Muscle, Skeletal/physiology, Thigh/anatomy & histology",
author = "{de Ruiter}, {C J} and Elzinga, {M J H} and Verdijk, {P W L} and {van Mechelen}, W",
year = "2004",
month = "1",
doi = "10.1007/s00424-003-1206-9",
language = "English",
volume = "447",
pages = "436--44",
journal = "Pfl{\"u}gers Archiv European Journal of Physiology",
issn = "0031-6768",
publisher = "Springer Verlag",
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Voluntary drive-dependent changes in vastus lateralis motor unit firing rates during a sustained isometric contraction at 50% of maximum knee extension force. / de Ruiter, C J; Elzinga, M J H; Verdijk, P W L; van Mechelen, W.

In: Pflügers Archiv European Journal of Physiology, Vol. 447, No. 4, 01.2004, p. 436-44.

Research output: Contribution to journalArticleAcademicpeer-review

TY - JOUR

T1 - Voluntary drive-dependent changes in vastus lateralis motor unit firing rates during a sustained isometric contraction at 50% of maximum knee extension force

AU - de Ruiter, C J

AU - Elzinga, M J H

AU - Verdijk, P W L

AU - van Mechelen, W

PY - 2004/1

Y1 - 2004/1

N2 - 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.

AB - 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.

KW - Action Potentials/physiology

KW - Adult

KW - Electric Stimulation

KW - Electromyography

KW - Evoked Potentials, Motor

KW - Female

KW - Humans

KW - Isometric Contraction/physiology

KW - Knee

KW - Male

KW - Motor Neurons/metabolism

KW - Muscle Fatigue/physiology

KW - Muscle, Skeletal/physiology

KW - Thigh/anatomy & histology

U2 - 10.1007/s00424-003-1206-9

DO - 10.1007/s00424-003-1206-9

M3 - Article

VL - 447

SP - 436

EP - 444

JO - Pflügers Archiv European Journal of Physiology

JF - Pflügers Archiv European Journal of Physiology

SN - 0031-6768

IS - 4

ER -