Exercise Training Mitigates Multi-System Deconditioning during Bed Rest

Introduction This study investigated the safety and effectiveness of a new integrated aerobic and resistance exercise training prescription (SPRINT) using two different sets of exercise equipment: a suite of large ISS-like exercise equipment similar to what is found on the International Space Station (ISS) and a single device with aerobic and resistance exercise capability in the spaceflight analog of bed rest (BR). Methods: Subjects (n=34) completed 70 days of 6° head down tilt BR: 9 were randomized to remain sedentary (CONT), 9 to exercise training using traditional equipment (EX), 8 to exercise using traditional equipment and low dose testosterone supplementation (ExT), and 8 to exercise using a combined resistance and aerobic flywheel device (FLY). Peak aerobic capacity (VO2peak), ventilatory threshold (VT), cardiac morphology and function (echocardiography), muscle mass (magnetic resonance imaging (MRI)) and strength/power (isokinetic, leg press, and vertical jump), and bone health (bone mineral density (BMD), blood and urine bone markers) were assessed before and after bed rest. Results The SPRINT protocol mitigated bed rest-induced muscle and cardiac deconditioning regardless of the exercise device used. Molecular markers of bone did not change in CONT or EX groups. VO2peak was maintained from pre to post bed rest in all exercise groups similarly whereas significant declines were observed in CONT (~10%). Significant interaction effects between CONT and all EX groups were observed for muscle performance including leg press total work, isokinetic upper and lower leg strength, vertical jump power and maximal jump height as well as muscle size. Conclusions This is the first trial to evaluate multi-system deconditioning and the role of an integrated exercise countermeasure. These findings have important implications for the design and implementation of exercise-based countermeasures on future long duration spaceflight missions. Correspondence: Lori Ploutz-Snyder, School of Kinesiology, University of Michigan, Ann Arbor, MI. 4170 Observatory Lodge, 1402 Washington Heights, Ann Arbor, MI 48109-2013. (734) 764-5210. lorips@umich.edu Funding: This study was supported by a research grant from NASA Human Research Program and the National Space Biomedical Research Institute (NSBRI) Conflicts of Interest: The authors declare no conflicts of interest. Accepted for Publication: 5 February 2018 © 2018 American College of Sports Medicine

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