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J Appl Physiol 90: 431-435, 2001;
8750-7587/01 $5.00
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Vol. 90, Issue 2, 431-435, February 2001

Maximal instantaneous muscular power after prolonged bed rest in humans

Guido Ferretti1, Hans E. Berg2, Alberto E. Minetti3,4, Christian Moia1, Susanna Rampichini3, and Marco V. Narici3,4

1 Département de Physiologie, Centre Médical Universitaire, 1211 Genève 4, Switzerland; 2 Environmental Physiology Laboratory, Department of Physiology and Pharmacology, Karolinska Institute, S-171 77 Stockholm, Sweden; 3 Institute of Advanced Biomedical Technologies, National Research Council, 20090 Segrate, Italy; and 4 Department of Exercise and Sport Science, Manchester Metropolitan University, Alsager, Cheshire ST7 2HL, United Kingdom

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 (Wp) if the body segments' lengths remain unchanged. Wp 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, Wp was 3.63 ± 0.43 kW or 48.6 ± 3.3 W/kg. On days 2 and 6 after BR, Wp 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, Wp was reduced by only 4.8 ± 4.5% (P < 0.05). By day 48 of recovery, Wp had returned to baseline values. Therefore, if Wp is appropriately normalized for CSA of the extensor muscles, the reduction in CSAEXT explains most of the decrease in Wp 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 the Wp loss after BR.

muscle cross-sectional area; spaceflight simulation


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