Role of excitation-contraction coupling in muscle fatigue.
The force produced by muscles declines during prolonged activity and this decline arises largely from processes within the muscle. At a cellular level the reduced force could be caused by: (a) reduced intracellular calcium release during activity; (b) reduced sensitivity of the myofilaments to calcium; or (c) reduced maximal force development. Experiments involving intracellular calcium measurements in isolated single fibres show that all 3 of the above contribute to the decline of force during fatigue. Metabolic changes associated with fatigue are probably involved in each of the 3 factors. Thus the accumulation of phosphate and protons which occur during fatigue cause a reduction in calcium sensitivity and a decline in maximal force. The cause of the reduced intracellular calcium during contractions in fatigue is less clear. During prolonged tetani the conduction of the action potential in the T-tubules appears to fail leading to reduced intracellular calcium in the central part of the muscle fibre. However, during repeated tetani there is a uniform decline of intracellular calcium across the fibre and this remains one of the least understood processes which contribute to fatigue.
Allen
D G
DG
Department of Physiology, University of Sydney, Australia.
Westerblad
H
H
Lee
J A
JA
Lännergren
J
J
D000200:Action Potentials / Q000502:physiology; D000249:Adenosine Monophosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000502:physiology; D005221:Fatigue / Q000378:metabolism / Q000503:physiopathology*; D006801:Humans; D007291:Inosine Monophosphate / Q000378:metabolism; D051379:Mice; D009119:Muscle Contraction / Q000502:physiology*; D013035:Spasm / Q000378:metabolism
D015220:Calcium Channels; D007291:Inosine Monophosphate; D000249:Adenosine Monophosphate; D000255:Adenosine Triphosphate; D002118:Calcium