Knee extensor and plantar flexor muscle size and function following 90 days of bed rest with or without resistance exercise
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Skeletal muscle atrophy and strength loss induced by short-term simulated spaceflight are offset or attenuated by resistance exercise (RE). This study compared the effects of plantar flexor and knee extensor RE on muscle size and function in 17 healthy men (aged 26–41years) subjected to 90 days 6° head-down-tilt bed rest with (BRE; n=8) or without (BR; n=9) RE. The RE program consisted of coupled maximal concentric and eccentric actions in the supine squat (4 sets of 7 repetitions) and calf press (4×14) every third day employing a gravity-independent flywheel ergometer (FW). Prior to, and following bed rest, muscle volume was assessed using magnetic resonance imaging. Similarly, muscle strength and power and surface electromyographic (EMG) activity were determined during maximal actions using FW or isokinetic dynamometry. In BR, knee extensor and plantar flexor muscle volume decreased (P<0.05) 18% and 29%, respectively. Torque or force and power decreased (P<0.05) 31–60% (knee extension) and 37–56% (plantar flexion) while knee extensor and plantar flexor EMG activity decreased 31–38% and 28–35%, respectively following BR. Muscle atrophy in BRE was prevented (P>0.05; knee extensors) or attenuated (−15%; plantar flexors). BRE maintained task-specific force, power and EMG activity. The decrease in non-task-specific torque was less (P<0.05) than in BR. The present data imply that the triceps surae and quadriceps muscles show different responsiveness to long-term bed rest with or without resistance exercise. The results also suggest that designing in-flight resistance exercise protocols for space travellers is complex and must extend beyond preserving muscle only.
KeywordsCountermeasures Electromyography Flywheel ergometer Magnetic resonance imaging Spaceflight
This study was supported by grants from the Swedish National Space Board (SNSB), the European Space Agency (ESA), the National Space Development Agency of Japan (NASDA), the Centre d’Etudes Spatiales (CNES) and the Swedish National Centre for Research in Sports (CIF). We thank the volunteers who endured the long-term bed rest. The technical support of Drs Marie-Pierre Bareille, Alain Maillet and Stéphane Beroud and the staff at MEDES and the Rangueil Hospital are greatly appreciated. The authors also thank Lena Norrbrand and Åsa Attling for their assistance with the image analysis.
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