Changes in force, surface and motor unit EMG during post-exercise development of low frequency fatigue in vastus lateralis muscle

de Ruiter, C. J., Elzinga, M. J. H., Verdijk, P. W. L., van Mechelen, W. and de Haan, A. (2005) Changes in force, surface and motor unit EMG during post-exercise development of low frequency fatigue in vastus lateralis muscle. European Journal of Applied Physiology, 94 5-6: 659-669. doi:10.1007/s00421-005-1356-x


Author de Ruiter, C. J.
Elzinga, M. J. H.
Verdijk, P. W. L.
van Mechelen, W.
de Haan, A.
Title Changes in force, surface and motor unit EMG during post-exercise development of low frequency fatigue in vastus lateralis muscle
Journal name European Journal of Applied Physiology   Check publisher's open access policy
ISSN 1439-6319
1439-6327
Publication date 2005-08
Sub-type Article (original research)
DOI 10.1007/s00421-005-1356-x
Volume 94
Issue 5-6
Start page 659
End page 669
Total pages 11
Place of publication Heidelberg, Germany
Publisher Springer
Language eng
Subject 1106 Human Movement and Sports Science
Abstract We investigated the effects of low frequency fatigue (LFF) on post-exercise changes in rectified surface EMG (rsEMG) and single motor unit EMG (smuEMG) in vastus lateralis muscle (n=9). On two experimental days the knee extensors were fatigued with a 60-s-isometric contraction (exercise) at 50% maximal force capacity (MFC). On the first day post-exercise (15 s, 3, 9, 15, 21 and 27 min) rsEMG and electrically-induced (surface stimulation) forces were investigated. SmuEMG was obtained on day two. During short ramp and hold (5 s) contractions at 50% MFC, motor unit discharges of the same units were followed over time. Post-exercise MFC and tetanic force (100 Hz stimulation) recovered to about 90% of the pre-exercise values, but recovery with 20 Hz stimulation was less complete: the 20–100 Hz force ratio (mean ± SD) decreased from 0.65±0.06 (pre-exercise) to 0.56±0.04 at 27 min post-exercise (P<0.05), indicative of LFF. At 50% MFC, pre-exercise rsEMG (% pre-exercise maximum) and motor unit discharge rate were 51.1±12.7% and 14.1±3.7 (pulses per second; pps) respectively, 15 s post-exercise the respective values were 61.4±15.4% (P<0.05) and 13.2±5.6 pps (P>0.05). Thereafter, rsEMG (at 50% MFC) remained stable but motor unit discharge rate significantly increased to 17.7±3.9 pps 27 min post-exercise. The recruitment threshold decreased (P<0.05) from 27.7±6.6% MFC before exercise to 25.2±6.7% 27 min post-exercise. The increase in discharge rate was significantly greater than could be expected from the decrease in recruitment threshold. Thus, post-exercise LFF was compensated by increased motor unit discharge rates which could only partly be accounted for by the small decrease in motor unit recruitment threshold
Keyword Electrical stimulation
Voluntary activation
Motor unit EMG
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Non-UQ

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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