Physical inactivity promotes contractile dysfunction at the whole tissue, cellular and molecular levels in older adults (1102.29)

Abstract

Age‐related deficits in skeletal muscle function are likely potentiated by corresponding reductions in volitional physical activity. Our objective was to investigate the effects of chronic muscle disuse by comparing structural and functional properties of skeletal muscle between healthy older adults with limited physical mobility secondary to knee osteoarthritis (Disuse; n=16) and healthy, recreationally‐active older adults (Controls; n=15). Knee extensor strength and cellular and molecular contractile characteristics were assessed from vastus lateralis muscle biopsies. Isometric and isokinetic knee extensor strength were reduced (34‐43%; p<0.01 for all) with disuse, as was single fiber force production in MHC I (18%; p 0.1 for all). Myosin‐actin cross‐bridge kinetic parameters were reduced in MHC I with disuse, as evidenced by prolonged actin‐myosin attachment time (+20%; p <0.01), but not in MHC IIA or IIA/X fibers. A strong trend towards more (+23%; p = 0.06) strongly‐bound cross‐bridges was observed in MHC I fibers with disuse. Considering similar MHC I tension between groups, these data suggest intrinsic impairments in molecular level force production/transmission with disuse. In summary, although cellular level deficits in force production are explained by atrophy, molecular level changes, which are independent of fiber size, may contribute to impaired whole muscle performance observed with chronic muscle disuse.Grant Funding Source: Supported by NIH AG033547