Effects of microgravity on maximal power of lower limbs during very short efforts in humans.
The maximal power of the lower limbs was determined in four astronauts (age 37-53 yr) 1) during maximal pushes of approximately 250 ms on force platforms ["maximal explosive power" (MEP)] or 2) during all-out bouts of 6-7 s on an isokinetic cycloergometer [pedal frequency 1 Hz: maximal cycling power (MCP)]. The measurements were done before and immediately after spaceflights of 31-180 days. Before flight, peak and mean values were 3.18 +/- 0.38 and 1.5 +/- 0. 13 (SD) kW for MEP and 1.17 +/- 0.12 and 0.68 +/- 0.08 kW for MCP, respectively. After reentry, MEP was reduced to 67% after 31 days and to 45% after 180 days. MCP decreased less, attaining approximately 75% of preflight level, regardless of the flight duration. The recovery of MCP was essentially complete 2 wk after reentry, whereas that of MEP was slower, a complete recovery occurring after an estimated time close to that spent in flight. In the same subjects, the muscle mass of the lower limbs, as assessed by NMR, decreased by 9-13%, irrespective of flight duration (J. Zange, K. Müller, M. Schuber, H. Wackerhage, U. Hoffmann, R. W. G unther, G. Adam, J. M. Neuerburg, V. E. Sinitsyn, A. O. Bacharev, and O. I. Belichenko. Int. J. Sports Med. 18, Suppl. 4: S308-S309, 1997). The larger fall in maximal power, compared with that in muscle mass, suggests that a fraction of the former (especially relevant for MEP) is due to the effects of weightlessness on the motor unit recruitment pattern.
Antonutto
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Dipartimento di Scienze e Tecnologie Biomediche dell'Università di Udine, I-33100 Udine, Italy.fisioud@dstb.uniud.it
Capelli
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Girardis
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Zamparo
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di Prampero
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D000328:Adult; D000465:Algorithms; D001835:Body Weight / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006801:Humans; D007866:Leg / Q000502:physiology*; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology; D010101:Oxygen Consumption / Q000502:physiology; D013026:Space Flight; D014893:Weightlessness / Q000009:adverse effects*