Exercise in space: human skeletal muscle after 6 months aboard the International Space Station

Physiol 106: 1159 –1168, 2009. First published January 15, 2009; doi:10.1152/japplphysiol.91578.2008.—The aim of this investigation was to document the exercise program used by crewmembers (n 9; 45 2 yr) while aboard the International Space Station (ISS) for 6 mo and examine its effectiveness for preserving calf muscle characteris-tics. Before and after spaceflight, we assessed calf muscle volume (MRI), static and dynamic calf muscle performance, and muscle fiber types (gastrocnemius and soleus). While on the ISS, crewmembers had access to a running treadmill, cycle ergometer, and resistance exercise device. The exercise regimen varied among the crewmem-bers with aerobic exercise performed 5 h/wk at a moderate intensity and resistance exercise performed 3–6 days/wk incorporating multi-ple lower leg exercises. Calf muscle volume decreased (P 0.05) 13 2 % with greater (P 0.05) atrophy of the soleus (15 2%) compared with the gastrocnemius (10 2%). Peak power was 32