| Abstract: | Bamman, Marcas M., Mark S. F. Clarke, Daniel L. Feeback,Robert J. Talmadge, Bruce R. Stevens, Steven A. Lieberman, and MichaelC. Greenisen. Impact of resistance exercise during bed rest onskeletal muscle sarcopenia and myosin isoform distribution. J. Appl. Physiol. 84(1): 157-163, 1998. Because resistance exercise (REx) and bed-rest unloading (BRU)are associated with opposing adaptations, our purpose was to test theefficacy of REx against the effects of 14 days of BRU on theknee-extensor muscle group. Sixteen healthy men were randomly assignedto no exercise (NoEx; n = 8) or REx(n = 8). REx performed five sets ofleg press exercise with 80-85% of one repetition maximum (1 RM)every other day during BRU. Muscle samples were removed from the vastuslateralis muscle by percutaneous needle biopsy. Myofiber distributionwas determined immunohistochemically with three monoclonal antibodiesagainst myosin heavy chain (MHC) isoforms (I, IIa, IIx). MHCdistribution was further assessed by quantitative gel electrophoresis.Dynamic 1-RM leg press and unilateral maximum voluntary isometriccontraction (MVC) were determined. Maximal neural activation (root meansquared electromyogram) and rate of torque development (RTD) weremeasured during MVC. Reductions(P < 0.05) in type I (15%) and typeII (17%) myofiber cross-sectional areas were found in NoEx but not inREx. Electrophoresis revealed no changes in MHC isoform distribution. The percentage of type IIx myofibers decreased(P < 0.05) in REx from 9 to 2% anddid not change in NoEx. 1 RM was reduced(P < 0.05) by 9% in NoEx but wasunchanged in REx. MVC fell by 15 and 13% in NoEx and REx,respectively. The agonist-to-antagonist root mean squaredelectromyogram ratio decreased (P < 0.05) 19% in REx. RTD slowed (P < 0.05) by 54% in NoEx only. Results indicate that REx preventedBRU-induced myofiber atrophy and also maintained training-specificstrength. Unlike spaceflight, BRU did not induce shifts in myosinphenotype. The reported benefits of REx may prove useful in prescribingexercise for astronauts in microgravity. |
