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1 Department of Integrative Physiology, University of Colorado, Boulder, Colorado, USA
2 Department of Health Sciences, Oita University of Nursing and Health Sciences, Oita, Japan
3 Department of Life Sciences, The University of Tokyo, Tokyo, Japan
4 School of Medicine, The University of Tokyo, Tokyo, Japan
5 Department of Sport Sciences, Waseda University, Saitama, Japan
* To whom correspondence should be addressed. E-mail: shinohara{at}colorado.edu.
The purpose of the study was to determine the effect of bedrest with or without strength training on torque fluctuations and activation strategy of the muscles. Twelve young men participated in a 20-day bedrest study. Subjects were divided into a non-training group (BRCon) and a strength-training group (BRTr). The training comprised dynamic calf-raise and leg-press exercises. Before and after bedrest, subjects performed maximal contractions and steady submaximal isometric contractions of the ankle extensor muscles and of the knee extensor muscles (2.5-10% of maximal torque). Maximal torque decreased for both the ankle extensors (9%, P < 0.05) and knee extensors (16%, P < 0.05) in BRCon, but not in BRTr. For the ankle extensors, the coefficient of variation (CV) for torque increased in both groups (p < 0.05), with a greater amount (P < 0.05) in BRCon (88%) compared with BRTr (41%). For the knee extensors, an increase in the CV for torque was observed only in BRCon (22%). The increase in the CV for torque in BRCon accompanied the greater changes in EMG amplitude of medial gastrocnemius (122%) and vastus lateralis (59%) compared with BRTr (P < 0.05). The results indicate that fluctuations in torque during submaximal contractions of the extensor muscles in the leg increase after bedrest and that strength training counteracted the decline in performance. The response varied across muscle groups. Alterations in muscle activation may lead to an increase in fluctuations in motor output after bedrest.
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