Maximal instantaneous muscular power after prolonged bed rest in humans

• A reduction in lower limb cross-sectional area (CSA) occurs after bed rest (BR). This should lead to an equivalent reduction in maximal instantaneous muscular power (W˙p) if the body segments' lengths remain unchanged. W˙p was determined during maximal jumps off both feet on a force platform before and on days 2, 6, 10, 32, and 48 after a 42-day duration BR. CSA of thigh muscles was measured by magnetic resonance imaging before and on day 5 after BR. Before BR, W˙p was 3.63 ± 0.43 kW or 48.6 ± 3.3 W/kg. On days 2 and 6 after BR, W˙p was reduced by 23.7 ± 6.9 and 22.7 ± 5.4% ( P < 0.01), respectively. Thigh extensors CSA (CSAext) was 16.7 ± 4.7% ( P < 0.01) lower than before. When normalized per CSAext, W˙p was reduced by only 4.8 ± 4.5% ( P < 0.05). By day 48 of recovery,W˙p had returned to baseline values. Therefore, ifW˙p is appropriately normalized for CSA of the extensor muscles, the reduction in CSAext explains most of the decrease in W˙p decrease after BR. Other factors such as a deficit in neural activation or a decrease in fiber-specific tension may account for only 5% of theW˙p loss after BR.

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