Back to Search
Start Over
Changes in force, surface and motor unit EMG during post-exercise development of low frequency fatigue in vastus lateralis muscle.
- Source :
-
European journal of applied physiology [Eur J Appl Physiol] 2005 Aug; Vol. 94 (5-6), pp. 659-69. Date of Electronic Publication: 2005 May 11. - Publication Year :
- 2005
-
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.
- Subjects :
- Adaptation, Physiological physiology
Adult
Electric Stimulation
Exercise Test
Female
Humans
Male
Muscle Contraction
Muscle, Skeletal innervation
Stress, Mechanical
Electromyography methods
Isometric Contraction physiology
Knee physiology
Motor Neurons physiology
Muscle Fatigue physiology
Muscle, Skeletal physiology
Physical Endurance physiology
Subjects
Details
- Language :
- English
- ISSN :
- 1439-6319
- Volume :
- 94
- Issue :
- 5-6
- Database :
- MEDLINE
- Journal :
- European journal of applied physiology
- Publication Type :
- Academic Journal
- Accession number :
- 15887021
- Full Text :
- https://doi.org/10.1007/s00421-005-1356-x