EFFECTS OF MICROGRAVITY ON MUSCLE POWER: SOME POSSIBLE COUNTERMEASURES

P.E. di Prampero, G. Antonutto
Dept. of Biomedical Sciences, University of Udine, via Gervasutta 48, I-33100 Udine (Italy)

The average power developed during a very short (~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 (µg) (one subject) and to 45 % after six months (three subjects). In the same subjects, the power developed during 6 to 7 s of maximal cycling at a pedal frequency of 1 Hz (MCP) was reduced to a lesser extent than MEP: about 75 % of pre-flight values, regardless of flight duration (Antonutto et al., 1999). The reductions of both MEP and MCP were larger than the concomitant decrease of muscle mass: 9 to 13 %, regardless of flight duration (Zange et al., 1997). This suggests that: i) a substantial fraction of the decrease of maximal power is due to the deterioration of the motor co-ordination, brought about by the absence of gravity and ii) the deterioration is larger for efforts requiring fast and balanced contractions of agonist and antagonist muscles. This large fall of maximal muscular power was not prevented by the 2 hours aerobic exercise training daily performed by the astronauts during space flight. We therefore propose that explosive exercise training be added to the daily schedule (di Prampero and Antonutto, 1996). We also describe a system aimed at reducing cardiovascular deconditioning due to µg. Gravity is simulated by the centrifugal acceleration generated by the motion of two counter rotating bicycles ridden by the astronauts on the inner wall of a cylindrical space module and coupled by a differential gearing (Antonutto et al., 1991). Tests performed on a human centrifuge have shown that the discomfort deriving from the rotating environment is reasonably low and well tolerated.

Key words: maximal muscular power; microgravity; cardiovascular deconditioning; artificial gravity

References:
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Zange J., Müller K., Schuber M., Wackerhage H., Hoffmann H., Günther R.W., Adam G., Neuerburg J.M., Sinitsyn V.E., Bacharev A.O., Belichenko O.I. (1997), Int. J. Sports Med., Suppl. 4: S308-S309.