Effects of Short-Term Aerobic Exercise on Single Muscle Fibers of Older Women
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Sarcopenia, or loss of muscle mass with aging, affects about 45% of elderly humans (age 60 and older) in the United States. Previous studies showed that strength training and long-term aerobic programs help combat muscle loss, indicating that the best way to prevent or treat sarcopenia is with exercise. The purpose of this study was to characterize the influence of a shortterm (12 week) aerobic exercise training program on cellular composition and size of muscle fibers in older women (60-80 yrs). We biopsied the vastus lateralis muscle of nine older women before and after 12 weeks of aerobic training. We the~ determined the change in composition of five myosin heavy chain (MHC) isoforms using SDS-PAGE and the change in diameter of MHC I and MHC lIa fibers using computer imaging. MHC I fibers increased by 180/0, whereas MHC lIa fibers decreased by 17% from pre- to post-aerobic training. Diameters of MHC I and MHC lIa fibers did not change. Therefore, we showed that short-term aerobic exercise can change muscle fiber composition but not fiber size. We also confirmed that muscle fiber changes can be induced in older women and that starting and maintaining an aerobic training program is useful for both the prevention and treatment of sarcopenia.