Changes in the action potential and contractile properties of skeletal muscle in human's with repetitive stimulation after long-term dry immersion.

Abstract

This paper compares the effects of 7-day dry immersion and intermittent muscle contraction on electrical and mechanical failure during muscle fatigue in the human triceps surae muscle electrically stimulated at 50 impulses.s-1 via its motor nerve. Intermittent contractions of 60-s duration were separated by 1-s intervals for identical duration of tension development. The 60-s intermittent contractions decreased tetanic force to 57% (P < 0.05) of initial values, but force reduction was not significantly different in the two fatigue tests: the fatigue index was 36.2 (SEM 5.4)% versus 38.6 (SEM 2.8)%, respectively (P > 0.05). Whilst identical force reduction was present in the two fatigue tests, it would appear that concomitant electrical failure was considerably different. This electromechanical dissociation would suggest that a slowing of conduction along nerve and muscle membranes did not explain the observed mechanical failure. It is suggested that intracellular processes played major role in contractile failure during intermittent contractions after muscle disuse.