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In an effort to simulate the compromised function and atrophy of lower limb muscles experienced by astronauts after spaceflight, 21 men and women age 30-56 yr were subjected to unilateral lower limb unloading for 5 wk. Whereas 10 of these subjects performed unilateral knee extensor resistance exercise (ULRE) two or three times weekly, 11 subjects (UL) refrained from training. The exercise regimen consisted of four sets of seven maximal actions, using an apparatus that offers concentric and eccentric resistance by utilizing the inertia of rotating flywheel(s). Knee extensor muscle strength was measured before and after UL and ULRE, and knee extensor and ankle plantar flexor muscle volumes were determined by means of magnetic resonance imaging. Surface electromyographic activity measured after UL inferred increased muscle use to perform a given motor task. UL induced an 8.8% decrease (P 0.05) strength. Ankle plantar flexor muscle volume of the unloaded limb decreased (P 0.05) in muscle volume or strength. The results of this study provide evidence that resistance exercise not only may offset muscle atrophy but is in fact capable of promoting marked hypertrophy of chronically unloaded muscle.
Tesch et al. (2004) studied this question.
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