Torque potentiation and myosin light-chain phosphorylation in human muscle following a fatiguing contraction.
Indices of electrically stimulated and maximal voluntary isometric muscle torgue and the phosphate content of myosin phosphorylatable light chains (P light chains) were studied during recovery following a 60-s maximal voluntary isometric contraction (MVC) in 21 human subjects. Analysis of muscle biopsy samples revealed that immediately after the 60-s MVC there were significant decreases in ATP (-15%) and phosphocreatine (-82%), and lactate concentration increased by 17-fold. All indices of muscle torque production were reduced by the 60-s MVC, but the twitch torque and torque at 10 Hz were relatively less reduced compared with the torque at 20 and 50 Hz or a 1-s MVC. Between 3 and 6 min of recovery, twitch torque and torque at 10 Hz stimulation were significantly potentiated, reaching peak values of 125 and 134%, respectively, compared with rest. Phosphate content of the fast and two slow P light chains was significantly increased over rest levels immediately after and 4 min after the 60-s MVC. These results suggest that myosin P light-chain phosphorylation could provide a mechanism to increase human muscle torque under conditions of submaximal contractile element activation following fatigue.
Houston
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ME
Department of Kinesiology, University of Waterloo, Ont., Canada.
Grange
R W
RW
D000255:Adenosine Triphosphate / Q000378:metabolism; D000328:Adult; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D007537:Isometric Contraction; D007773:Lactates / Q000378:metabolism; D019344:Lactic Acid; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D009132:Muscles / Q000378:metabolism* / Q000502:physiology; D009218:Myosins / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism; D010725:Phosphocreatine / Q000378:metabolism; D010766:Phosphorylation; D010812:Physical Stimulation
D007773:Lactates; D010710:Phosphates; D010725:Phosphocreatine; D019344:Lactic Acid; D000255:Adenosine Triphosphate; D009218:Myosins