Disuse-Induced Muscle Loss and Rehabilitation: The National Aeronautics and Space Administration Bed Rest Study.

OBJECTIVES: The time course and magnitude of atrophic remodeling and the effects of an acute rehabilitation program on muscle atrophy are unclear. We sought to characterize bed rest-induced leg muscle atrophy and evaluate the safety and efficacy of an acute rehabilitation program. DESIGN: Prespecified analysis of a randomized controlled trial. SETTING: Single-center urban hospital. PATIENTS: Adults (24-55 yr) randomized to 70 days of sedentary bed rest. INTERVENTIONS: The 11-day post-bed rest rehabilitation program consisted of low intensity exercise and progressed to increased aerobic exercise duration, plyometric exercises, and higher intensity resistance exercise. MEASUREMENTS AND MAIN RESULTS: Upper (rectus femoris, vastus lateralis, quadriceps, hamstrings, adductors) and lower leg (medial gastrocnemius, lateral gastrocnemius, and soleus) MRI scans were obtained once before, nine times during, and three times after bed rest to assess muscle cross-sectional area. The magnitude and rate of muscle atrophy and recovery were determined for each muscle. Nine participants completed 70 days of sedentary bed rest and an 11-day rehabilitation program. A total of 11,588 muscle cross-sectional area images were quantified. Across all muscles except the rectus femoris (no change), there was a linear decline during bed rest, with the highest atrophic rate occurring in the soleus (-0.33%/d). Following rehabilitation, there was rapid recovery in all muscles; however, the quadriceps (-3.74 cm2; 95% CI, -7.36 to -0.12; p = 0.04), hamstrings (-2.30 cm2; 95% CI, -4.07 to -0.54; p = 0.01), medial gastrocnemius (-0.62 cm2; 95% CI, -1.10 to -0.14; p = 0.01), and soleus (-1.85 cm2; 95% CI, -2.90 to -0.81; p < 0.01) remained significantly lower than baseline. CONCLUSIONS: Bed rest results in upper and lower leg muscle atrophy in a linear pattern, and an 11-day rehabilitation program was safe and effective in initiating a rapid trajectory of muscle recovery. These findings provide important information regarding the design and refinement of rehabilitation programs following bed rest.

Exercise Training Mitigates Multisystem 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 International Space Station-like exercise equipment similar to what is found on the International Space Station and a single device with aerobic and resistance exercise capability in the spaceflight analog of bed rest (BR). METHODS: Subjects (n = 34) completed 70 d 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. Peak aerobic capacity, ventilatory threshold, cardiac morphology and function (echocardiography), muscle mass (magnetic resonance imaging) and strength/power (isokinetic, leg press, and vertical jump), and bone health (bone mineral density, blood and urine bone markers) were assessed before and after BR. RESULTS: The SPRINT protocol mitigated BR-induced muscle and cardiac deconditioning regardless of the exercise device used. Molecular markers of bone did not change in the CONT or EX groups. Peak aerobic capacity was maintained from pre- to post-BR in all exercise groups similarly, whereas significant declines were observed in the CONT group (~10%). Significant interaction effects between the CONT group 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 multisystem 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.

Integrated resistance and aerobic exercise protects fitness during bed rest.

INTRODUCTION: The current exercise countermeasures have not fully protected astronauts' preflight aerobic and muscular fitness levels during International Space Station (ISS) missions, prompting a need to optimize the exercise prescription to improve or maintain astronauts' ability to perform critical tasks and eventually extend the duration of missions. PURPOSE: To test the hypothesis that an integrated resistance and aerobic exercise prescription performed with exercise equipment similar to that on the ISS can be tolerated and maintain cardiovascular and muscular fitness during 14 d of exposure to a model of microgravity. METHODS: Subjects (n = 9) participated in 14-21 d of pre-bed rest training and familiarization, 14 d of bed rest + iRAT exercise, and 7 d of ambulatory recovery. Peak aerobic capacity (V˙O2peak), ventilatory threshold (VT), and isokinetic and leg press tests were performed before and after bed rest to evaluate cardiovascular and muscle functions. Muscle cross-sectional area (CSA) was determined before, during, and after bed rest using magnetic resonance imaging (MRI). RESULTS: Improvements from before to after bed rest were observed in V˙O2peak (2.8 ± 0.2 to 3.2 ± 0.2 L·min(-1)), VT (1.9 ± 0.2 to 2.1 ± 0.2 L·min(-1)), leg muscle power (1582 ± 317 to 1740 ± 359 W), and muscle CSA of the grouped vastus lateralis, vastus intermedius, and vastus medialis muscles (67.5 ± 8.4 to 68.9 ± 8.3 cm). Muscle strength and total CSA of the upper and lower legs were not different from before to after bed rest. CONCLUSIONS: This is the first report of exercise being completely effective for the prevention of cardiovascular and skeletal muscle deconditioning during strict bed rest using exercise equipment similar to that on the ISS. This was accomplished with high subject compliance.