title: Two weeks of one-leg immobilization decreases skeletal muscle respiratory capacity equally in young and elderly men.
abstract: Physical inactivity affects human skeletal muscle mitochondrial oxidative capacity but the influence of aging combined with physical inactivity is not known. This study investigates the effect of two weeks of immobilization followed by six weeks of supervised cycle training on muscle oxidative capacity in 17 young (23±1years) and 15 elderly (68±1years) healthy men. We applied high-resolution respirometry in permeabilized fibers from muscle biopsies at inclusion after immobilization and training. Furthermore, protein content of mitochondrial complexes I-V, mitochondrial heat shock protein 70 (mtHSP70) and voltage dependent anion channel (VDAC) were measured in skeletal muscle by Western blotting. The elderly men had lower content of complexes I-V and mtHSP70 but similar respiratory capacity and content of VDAC compared to the young. In both groups the respiratory capacity and protein content of VDAC, mtHSP70 and complexes I, II, IV and V decreased with immobilization and increased with retraining. Moreover, there was no overall difference in the response between the groups. When the intrinsic mitochondrial capacity was evaluated by normalizing respiration to citrate synthase activity, the respiratory differences with immobilization and training disappeared. In conclusion, aging is not associated with a decrease in muscle respiratory capacity in spite of lower complexes I-V and mtHSP70 protein content. Furthermore, immobilization decreased and aerobic training increased the respiratory capacity and protein contents of complexes I-V, mtHSP70 and VDAC similarly in the two groups. This suggests that inactivity and training alter mitochondrial biogenesis equally in young and elderly men.
authors.affiliation: Xlab, Center for Healthy Aging, Department of Biomedical Sciences, Faculty of Health Sciences, University of Copenhagen, DK-2200 Copenhagen, Denmark. Electronic address: mgram@sund.ku.dk.
authors.forename: Martin
authors.initials: M
authors.lastname: Gram
authors.affiliation: Xlab, Center for Healthy Aging, Department of Biomedical Sciences, Faculty of Health Sciences, University of Copenhagen, DK-2200 Copenhagen, Denmark. Electronic address: avhansen@sund.ku.dk.
authors.forename: Andreas
authors.initials: A
authors.lastname: Vigelsø
authors.affiliation: Xlab, Center for Healthy Aging, Department of Biomedical Sciences, Faculty of Health Sciences, University of Copenhagen, DK-2200 Copenhagen, Denmark; Department of Cardiovascular Medicine, Hokkaido University Graduate School of Medicine, Sapporo, Japan. Electronic address: t-yokota@med.hokudai.ac.jp.
authors.forename: Takashi
authors.initials: T
authors.lastname: Yokota
authors.affiliation: Xlab, Center for Healthy Aging, Department of Biomedical Sciences, Faculty of Health Sciences, University of Copenhagen, DK-2200 Copenhagen, Denmark. Electronic address: cnh@sund.ku.dk.
authors.forename: Christina Neigaard
authors.initials: CN
authors.lastname: Hansen
authors.affiliation: Xlab, Center for Healthy Aging, Department of Biomedical Sciences, Faculty of Health Sciences, University of Copenhagen, DK-2200 Copenhagen, Denmark. Electronic address: jhelge@sund.ku.dk.
authors.forename: Jørn Wulff
authors.initials: JW
authors.lastname: Helge
authors.affiliation: Xlab, Center for Healthy Aging, Department of Biomedical Sciences, Faculty of Health Sciences, University of Copenhagen, DK-2200 Copenhagen, Denmark. Electronic address: martin.hey.mogensen@gmail.com.
authors.forename: Martin
authors.initials: M
authors.lastname: Hey-Mogensen
authors.affiliation: Xlab, Center for Healthy Aging, Department of Biomedical Sciences, Faculty of Health Sciences, University of Copenhagen, DK-2200 Copenhagen, Denmark. Electronic address: fdela@sund.ku.dk.
authors.forename: Flemming
authors.initials: F
authors.lastname: Dela
mesh_terms: D000367:Age Factors; D000368:Aged; D000375:Aging / Q000378:metabolism*; D001642:Bicycling; D015415:Biomarkers / Q000378:metabolism; D001706:Biopsy; D019069:Cell Respiration; D002950:Citrate (si)-Synthase / Q000378:metabolism; D003718:Denmark; D045222:Electron Transport Chain Complex Proteins / Q000378:metabolism; D004734:Energy Metabolism; D015444:Exercise; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D007103:Immobilization / Q000379:methods*; D035002:Lower Extremity; D008931:Mitochondria, Muscle / Q000378:metabolism*; D063269:Mitochondrial Turnover; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000378:metabolism*; D013997:Time Factors; D050994:Voltage-Dependent Anion Channels / Q000378:metabolism; D055815:Young Adult
chemical_list: D015415:Biomarkers; D045222:Electron Transport Chain Complex Proteins; D018840:HSP70 Heat-Shock Proteins; D050994:Voltage-Dependent Anion Channels; D002950:Citrate (si)-Synthase
keywords: Aging; Disuse; Immobilization; Mitochondrial biogenesis; Muscle oxidative capacity