title: Effects of ageing on single muscle fibre contractile function following short-term immobilisation.
abstract: Very little attention has been given to the combined effects of healthy ageing and short-term disuse on the contractile function of human single muscle fibres. Therefore, the present study investigated the effects of 2 weeks of lower limb cast immobilisation (i.e. disuse) on selected contractile properties of single muscle fibres (n = 378) from vastus lateralis of nine young (24 ± 1 years) and eight old (67 ± 2 years) healthy men with comparable levels of physical activity. Prior to immobilisation, MHC IIa fibres produced higher maximum Ca(2+)-activated force (approx. 32%) and specific force (approx. 33%) and had lower Ca(2+) sensitivity than MHC I fibres (P < 0.05), with no differences between young and old. After immobilisation, the decline in single fibre force (MHC I: young 21% and old 22%; MHC IIa: young 22% and old 30%; P < 0.05) as well as specific force (MHC I: young 14% and old 13%; MHC IIa: young 18% and old 25%; P < 0.05) was more pronounced in MHC IIa fibres compared to MHC I fibres (P < 0.05), with no differences between young and old. Notably, there was a selective decrease in Ca(2+) sensitivity in MHC IIa fibres of young (P < 0.05) and in MHC I fibres of old individuals (P < 0.05), respectively. In conclusion, 2 weeks of lower limb immobilisation caused greater impairments in single muscle fibre force and specific force in MHC IIa than MHC I fibres independently of age. In contrast, immobilisation-induced changes in Ca(2+) sensitivity that were dependent on age and MHC isoform.
authors.affiliation: Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, Campusvej 55, Odense M, Denmark. lhvid@health.sdu.dk
authors.forename: Lars G
authors.initials: LG
authors.lastname: Hvid
authors.forename: Niels
authors.initials: N
authors.lastname: Ortenblad
authors.forename: Per
authors.initials: P
authors.lastname: Aagaard
authors.forename: Michael
authors.initials: M
authors.lastname: Kjaer
authors.forename: Charlotte
authors.initials: C
authors.lastname: Suetta
mesh_terms: D000368:Aged; D000375:Aging / Q000378:metabolism* / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D005805:Genes, MHC Class I; D005802:Genes, MHC Class II; D006801:Humans; D007103:Immobilization / Q000379:methods; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000378:metabolism / Q000502:physiology*; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000378:metabolism / Q000502:physiology; D020033:Protein Isoforms; D012680:Sensitivity and Specificity; D055815:Young Adult
chemical_list: D020033:Protein Isoforms; D002118:Calcium