IMPACT OF RESISTANCE EXERCISE DURING BED REST ON SKELETAL-MUSCLE SARCOPENIA AND MYOSIN ISOFORM DISTRIBUTION

Because resistance exercise (REx) and bed-rest unloading (BRU) are ass ociated with opposing adaptations, our purpose was to test the efficac y of REx against the effects of 14 days of BRU on the knee-extensor mu scle group. Sixteen healthy men were randomly assigned to no exercise (NoEx; n = 8) or REx (n = 8). REx performed five sets of leg press exe rcise with 80-85% of one repetition maximum (1 RM) every other day dur ing BRU. Muscle samples were removed from the vastus lateralis muscle by percutaneous needle biopsy. Myofiber distribution was determined im munohistochemically with three monoclonal antibodies against myosin he avy chain (MHC) isoforms (I, IIa, IIx). MHC distribution was further a ssessed by quantitative gel electrophoresis. Dynamic 1-RM leg press an d unilateral maximum voluntary isometric contraction (MVC) were determ ined. Maximal neural activation (root mean squared electromyogram) and rate of torque development (RTD) were measured during MVC. Reductions (P < 0.05) in type I (15%) and type II (17%) myofiber cross-sectional areas were found in NoEx but not in REx. Electrophoresis revealed no changes in MHC isoform distribution. The percentage of type IIx myofib ers decreased (P < 0.05) in REx from 9 to 2% and did not change in NoE x. 1 RM was reduced (P < 0.05) by 9% in NoEx but was unchanged in REx. MVC fell by 15 and 13% in NoEx and REx, respectively. The agonist-to- antagonist root mean squared electromyogram ratio decreased (P < 0.05) 19% in REx. RTD slowed (P < 0.05) by 54% in NoEx only. Results indica te that REx prevented BRU-induced myofiber atrophy and also maintained training-specific strength. Unlike spaceflight, BRU did not induce sh ifts in myosin phenotype. The reported benefits of REx may prove usefu l in prescribing exercise for astronauts in microgravity.