Influence of simulated microgravity on human skeletal muscle architecture and function.

Ten male volunteers underwent a period of prolonged bed rest. Four subjects performed exercise countermeasures 2-3 times per week, while 6 subjects received no countermeasures. After bed rest plantarflexor force declined significantly (P < 0.001) in both exercise (-42%) and control (-55%) groups. The internal architecture of the gastrocnemius medialis (GM) muscle was significantly altered. This was associated with a reduction in fascicle shortening during isometric contraction. Exercise countermeasures partially mitigated the loss of muscle force and function following 90 days of bed rest.