Maximal power and EMG of lower limbs after 21 days spaceflight in one astronaut.

Long term space flights affect negatively muscle structure and function (Grigoriev end Egorov, 1901, 1902; Edgerton and Roy, 1994; Jaweed, 1994; Nicogossian, 1994a; Antonutto et al., 1995, Edgerton and Roy, 1997), essentially because of the long-term exposure to microgravity. Indeed, we have previously shown that the average power developed during a very short (approximately 0.25 s) maximal effort of the lower limbs, such as a vertical jump off both feet ("maximal explosive power", MEP) was reduced to 67% of pre-flight values after one month in microgravity (one subject) and to 45% after six months (three subjects). The reductions of MEP was larger than the concomitant decrease of muscle mass (9 to 13%, Zange et al., 1997). This suggests that a substantial fraction of the decrease of maximal power is due to the deterioration of the motor control, brough about by the absence of gravity. The aim of the present study was to investigate further the effects of microgram on maximal muscular power assessing also the EMG activities of 3 heads of the quadriceps femoris muscle, which contributes the major share of MEP.