title: Effects of aging on muscle mechanical function and muscle fiber morphology during short-term immobilization and subsequent retraining.
abstract: Very little attention has been given to the combined effects of aging and disuse as separate factors causing deterioration in muscle mechanical function. Thus the purpose of this study was to investigate the effects of 2 wk of immobilization followed by 4 wk of retraining on knee extensor muscle mechanical function (e.g., maximal strength and rapid force capacity) and muscle fiber morphology in 9 old (OM: 67.3 ± 1.3 yr) and 11 young healthy men (YM: 24.4 ± 0.5 yr) with comparable levels of physical activity. Following immobilization, OM demonstrated markedly larger decreases in rapid force capacity (i.e., rate of force development, impulse) than YM (∼ 20-37 vs. ∼ 13-16%; P < 0.05). In contrast, muscle fiber area decreased in YM for type I, IIA, and IIx fibers (∼ 15-30%; P < 0.05), whereas only type IIa area decreased in OM (13.2%; P < 0.05). Subsequent retraining fully restored muscle mechanical function and muscle fiber area in YM, whereas OM showed an attenuated recovery in muscle fiber area and rapid force capacity (tendency). Changes in maximal isometric and dynamic muscle strength were similar between OM and YM. In conclusion, the present data reveal that OM may be more susceptible to the deleterious effects of short-term muscle disuse on muscle fiber size and rapid force capacity than YM. Furthermore, OM seems to require longer time to recover and regain rapid muscle force capacity, which may lead to a larger risk of falling in aged individuals after periods of short-term disuse.
authors.affiliation: Institute of Sports Medicine, Bispebjerg Hospital and Center of Healthy Aging, Faculty of Health Science, University of Copenhagen, Copenhagen, Denmark. lhvid@health.sdu.dk
authors.forename: Lars
authors.initials: L
authors.lastname: Hvid
authors.forename: Per
authors.initials: P
authors.lastname: Aagaard
authors.forename: Lene
authors.initials: L
authors.lastname: Justesen
authors.forename: Monika L
authors.initials: ML
authors.lastname: Bayer
authors.forename: Jesper L
authors.initials: JL
authors.lastname: Andersen
authors.forename: Niels
authors.initials: N
authors.lastname: Ørtenblad
authors.forename: Michael
authors.initials: M
authors.lastname: Kjaer
authors.forename: Charlotte
authors.initials: C
authors.lastname: Suetta
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000375:Aging; D001696:Biomechanical Phenomena; D001706:Biopsy; D006801:Humans; D007103:Immobilization; D007537:Isometric Contraction; D007719:Knee Joint / Q000503:physiopathology; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000473:pathology*; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000473:pathology* / Q000503:physiopathology*; D016059:Range of Motion, Articular; D020127:Recovery of Function; D013997:Time Factors; D019415:Torque; D055815:Young Adult