Electromyographic study of the contractile and electrical properties of the human triceps surae muscle in a simulated microgravity environment

1 The effects of 7 days of simulated space flight, achieved with the technique of ‘dry’ water immersion, on human triceps surae muscle function have been investigated. 2 The maximal voluntary contraction (MVC) was reduced by 33.8 % (P < 0.01) while the electrically evoked maximal tetanic contraction force (Po) decreased by 8.2 % (P > 0.05). This suggests that most of the force loss is due to a reduction in motor drive. 3 The decrease in Po was associated with a small increase in maximal rates of tension development (7.2 %). The twitch tension (Pt) was not significantly changed and the Pt : Po ratio was decreased by 8.7 % after immersion. 4 A standard fatigue test, consisting of sixty 1 s intermittent isometric contractions (50 impulses s−1) separated by 1 s rest decreased tetanic force to approximately 60 % of initial values, but force reduction was not significantly different before and after immersion: the fatigue index was 36.2 ± 5.4 % before and 38.6 ± 2.8 % after immersion (P > 0.05). Whilst there were similar changes in mechanical output between control and disused muscles, there were differences in the pattern of electrical activity.