Single-muscle fiber contractile properties in lifelong aerobic exercising women

Abstract

The purpose of this study was to examine the effects of lifelong aerobic exercise on single-muscle fiber performance in trained women (LLE; n = 7, 72 ± 2 yr) by comparing them to old healthy nonexercisers (OH; n = 10, 75 ± 1 yr) and young exercisers (YE; n = 10, 25 ± 1 yr). On average, LLE had exercised ~5 days/wk for ~7 h/wk over the past 48 ± 2 yr. Each subject had a vastus lateralis muscle biopsy to examine myosin heavy chain (MHC) I and IIa single-muscle fiber size and function (strength, speed, power). MHC I fiber size was similar across all three cohorts (YE = 5,178 ± 157, LLE = 4,983 ± 184, OH = 4,902 ± 159 µm2). MHC IIa fiber size decreased ( P < 0.05) 36% with aging (YE = 4,719 ± 164 vs. OH = 3,031 ± 153 µm2), with LLE showing a similar 31% reduction (3,253 ± 189 µm2). LLE had 17% more powerful ( P < 0.05) MHC I fibers and offset the 18% decline in MHC IIa fiber power observed with aging ( P < 0.05). The LLE contractile power was driven by greater strength (+11%, P = 0.056) in MHC I fibers and elevated contractile speed (+12%, P < 0.05) in MHC IIa fibers. These data indicate that lifelong exercise did not benefit MHC I or IIa muscle fiber size. However, LLE had contractile function adaptations that enhanced MHC I fiber power and preserved MHC IIa fiber power through different contractile mechanisms (strength vs. speed). The single-muscle fiber contractile properties observed with lifelong aerobic exercise are unique and provide new insights into aging skeletal muscle plasticity in women at the myocellular level. NEW & NOTEWORTHY This is the first investigation to examine the effects of lifelong exercise on single-muscle fiber physiology in women. Nearly 50 yr of moderate to vigorous aerobic exercise training resulted in enhanced slow-twitch fiber power primarily by increasing force production, whereas fast-twitch fiber power was preserved primarily by increasing contractile speed. These unique muscle fiber power profiles helped offset the effects of fast-twitch fiber atrophy and highlight the benefits of lifelong aerobic exercise for myocellular health.

Influence of sex on the age‐related adaptations of neuromuscular function and motor unit properties in elite masters athletes

“…Understandably, MAs are not entirely resistant to the effects of age and notable declines have been observed within older competitive athletes in overall performance (Lazarus & Harridge, 2017;Bagley et al 2019). Data at the single fibre level are less clear, suggesting older athletes have preserved contractile properties in the vastus lateralis, yet of type II fibres only (Power et al 2016b;Gries et al 2019). Moreover, as individual fibre power normalised to size appears to improve with age (Grosicki et al 2016), the neural input to muscle warrants greater research interest.…”

“…2016 b ; Gries et al . 2019). Moreover, as individual fibre power normalised to size appears to improve with age (Grosicki et al .…”

Aging with rhythmicity. Is it possible? Physical exercise as a pacemaker

“…The same group of researchers analyzed women with an average age of 72 who trained in the last 48 years and found that lifelong training did not benefit type MHC I and IIa muscle fiber size but promoted adaptations of the contractile function that increased the strength of type I fibers and preserved the energy of type IIa fibers through different contractile mechanisms [ 109 ]. In addition, a greater intensity of training throughout life provided increased protection against the infiltration of adipose tissue in muscle [ 110 ].…”

On the mechanisms underlying attenuated redox responses to exercise in older individuals: A hypothesis

“…One example situation from which more information may be obtained is study of Masters Athletes in whom muscle function may be well preserved into older age [ 112 ]. Such subjects still show an underlying age-related loss of muscle mass and function, but this extent of the loss appears reduced by the regular exercise [ 113 ].…”