Submaximal-exercise-induced impairment of human muscle to develop and maintain force at low frequencies of electrical stimulation.
The aim of this study was to test the hypothesis that low intensity exercise-induced low frequency fatigue is caused by failure of excitation-contraction coupling. Changes in knee extension torque at 5, 10, 15, 20 and 50 Hz electrical stimulation of quadriceps muscle in ten healthy, young, male subjects were recorded during 20-min voluntary exercise followed by 60-min recovery. In seven of the ten subjects, changes in torque during 3 min of 10-Hz stimulation were recorded 2 min and 20 min after 20 min voluntary exercise. Exercise was performed at 30% of maximal voluntary contraction with a contraction plus relaxation period of 6 plus 4 s. Torque at 5, 10, 15, 20 and 50-Hz stimulation at the end of exercise was reduced to mean 91.0 (SEM 5.4)%, 68.7 (SEM 5.4)%, 67.2 (SEM 3.9)%, 66.5 (SEM 4.5)% and 74.7 (SEM 4.3)% of control values, respectively. During the first 30 s of the 3 min 10-Hz stimulation, torque was reduced in exercised muscle and increased in nonfatigued muscle. The reduction in torque was more marked 20 min after exercise than after 2 min. In conclusion, the pattern of depression and recovery of muscle force observed was in agreement with the hypothesis that the main cause of low intensity exercise-induced low frequency fatigue is an impairment of excitation-contraction coupling.
Ratkevicius
A
A
Department of Physiology and Biochemistry, Lithuanian Institute of Physical Education, Kaunas.
Skurvydas
A
A
Lexell
J
J
D000328:Adult; D004558:Electric Stimulation; D015444:Exercise / Q000502:physiology*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D009126:Muscle Relaxation / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*