title: Moderate-intensity resistance exercise alters skeletal muscle molecular and cellular structure and function in inactive older adults with knee osteoarthritis.
abstract: High-intensity resistance exercise (REX) training increases physical capacity, in part, by improving muscle cell size and function. Moderate-intensity REX, which is more feasible for many older adults with disease and/or disability, also increases physical function, but the mechanisms underlying such improvements are not understood. Therefore, we measured skeletal muscle structure and function from the molecular to the tissue level in response to 14 wk of moderate-intensity REX in physically inactive older adults with knee osteoarthritis (n= 17; 70 ± 1 yr). Although REX training increased quadriceps muscle cross-sectional area (CSA), average single-fiber CSA was unchanged because of reciprocal changes in myosin heavy chain (MHC) I and IIA fibers. Intermyofibrillar mitochondrial content increased with training because of increases in mitochondrial size in men, but not women, with no changes in subsarcolemmal mitochondria in either sex. REX increased whole muscle contractile performance similarly in men and women. In contrast, adaptations in single-muscle fiber force production per CSA (i.e., tension) and contractile velocity varied between men and women in a fiber type-dependent manner, with adaptations being explained at the molecular level by differential changes in myosin-actin cross-bridge kinetics and mechanics and single-fiber MHC protein expression. Our results are notable compared with studies of high-intensity REX because they show that the effects of moderate-intensity REX in older adults on muscle fiber size/structure and myofilament function are absent or modest. Moreover, our data highlight unique sex-specific adaptations due to differential cellular and subcellular structural and functional changes.NEW & NOTEWORTHYModerate-intensity resistance training causes sex-specific adaptations in skeletal muscle structure and function at the cellular and molecular levels in inactive older adult men and women with knee osteoarthritis. However, these responses were minimal compared with high-intensity resistance training. Thus adjuncts to moderate-intensity training need to be developed to correct underlying cellular and molecular structural and functional deficits that are at the root of impaired physical function in this mobility-limited population.
authors.affiliation: Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont.|Department of Kinesiology, University of Massachusetts, Amherst, Massachusetts.
authors.forename: Mark S
authors.initials: MS
authors.lastname: Miller
authors.affiliation: Department of Medicine, University of Vermont, Burlington, Vermont.
authors.forename: Damien M
authors.initials: DM
authors.lastname: Callahan
authors.affiliation: Department of Orthopaedics and Rehabilitation, University of Vermont, Burlington, Vermont.|Department of Rehabilitation and Movement Science, University of Vermont, Burlington, Vermont; and.
authors.forename: Timothy W
authors.initials: TW
authors.lastname: Tourville
authors.affiliation: Department of Orthopaedics and Rehabilitation, University of Vermont, Burlington, Vermont.
authors.forename: James R
authors.initials: JR
authors.lastname: Slauterbeck
authors.affiliation: Department of Medicine, University of Vermont, Burlington, Vermont.
authors.forename: Anna
authors.initials: A
authors.lastname: Kaplan
authors.affiliation: Department of Medicine, University of Vermont, Burlington, Vermont.
authors.forename: Brad R
authors.initials: BR
authors.lastname: Fiske
authors.affiliation: Department of Medicine, University of Vermont, Burlington, Vermont.
authors.forename: Patrick D
authors.initials: PD
authors.lastname: Savage
authors.affiliation: Department of Medicine, University of Vermont, Burlington, Vermont.
authors.forename: Philip A
authors.initials: PA
authors.lastname: Ades
authors.affiliation: Department of Orthopaedics and Rehabilitation, University of Vermont, Burlington, Vermont.
authors.forename: Bruce D
authors.initials: BD
authors.lastname: Beynnon
authors.affiliation: Department of Medicine, University of Vermont, Burlington, Vermont.|Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont.|Department of Orthopaedics and Rehabilitation, University of Vermont, Burlington, Vermont.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Toth
mesh_terms: D000199:Actins / Q000378:metabolism; D000222:Adaptation, Physiological / Q000502:physiology; D000375:Aging / Q000378:metabolism / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D007717:Knee / Q000503:physiopathology*; D008297:Male; D008928:Mitochondria / Q000378:metabolism / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D009210:Myofibrils / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000378:metabolism; D009218:Myosins / Q000378:metabolism; D020370:Osteoarthritis, Knee / Q000378:metabolism / Q000503:physiopathology*; D055070:Resistance Training / Q000379:methods
chemical_list: D000199:Actins; D018995:Myosin Heavy Chains; D009218:Myosins
keywords: mitochondria; myofilament; sex differences; training