Effects of ageing on single muscle fibre contractile function following short-term immobilisation

Authors

  • Lars G. Hvid,

    1. Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark
    2. Institute of Sports Medicine, Bispebjerg Hospital and Centre of Healthy Aging, Faculty of Health Science, University of Copenhagen, Copenhagen, Denmark
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  • Niels Ørtenblad,

    1. Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark
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  • Per Aagaard,

    1. Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark
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  • Michael Kjaer,

    1. Institute of Sports Medicine, Bispebjerg Hospital and Centre of Healthy Aging, Faculty of Health Science, University of Copenhagen, Copenhagen, Denmark
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  • Charlotte Suetta

    1. Institute of Sports Medicine, Bispebjerg Hospital and Centre of Healthy Aging, Faculty of Health Science, University of Copenhagen, Copenhagen, Denmark
    2. Department of Clinical Physiology and Nuclear Medicine, Bispebjerg Hospital, Copenhagen, Denmark
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Lars G Hvid: Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark.  Email: lhvid@health.sdu.dk

Abstract

Non-Technical Summary  The contractile function of human single muscle fibres is of particular importance for whole muscle contractile function. Yet, whereas ageing and short-term disuse (immobilisation) separately have been shown to impair single fibre contractile function, very little attention has been given to their combined effects. We show that 2 weeks of lower limb immobilisation reduces force and specific force (force per cross-sectional area) of both slow and fast single muscle fibres and that this occurred to a similar extent in young and old individuals. In contrast, disuse led to reduced Ca2+ sensitivity in fast fibres of young and in slow fibres of old, respectively. These results help us to better understand the underlying physiological mechanisms responsible for the deleterious effects of short-term disuse on whole muscle contractile function in both young and old.

Abstract

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 Ca2+-activated force (approx. 32%) and specific force (approx. 33%) and had lower Ca2+ 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 Ca2+ 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 Ca2+ sensitivity that were dependent on age and MHC isoform.

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