Background: Ageing is associated with a progressive decline in skeletal muscle mass and strength termed sarcopenia, which can influence both limb and respiratory muscles. However, established pharmacological interventions to treat sarcopenia remain limited. Lifelong caloric restriction (CR) of moderate deficits (~40%) can reduce sarcopenia in ageing rodents, but in humans extended CR periods are limited by both desire and commitment.
Objectives: To characterise the effects of an acute and mild caloric restriction intervention on limb and respiratory muscle properties in ageing mice.
Methods: Older male C57BL/6 mice (23 months; n=9) were subject to 4 weeks of caloric restriction (10-25% reduction in food intake) and were compared to ad libitum chow-fed control mice including age-matched (n=7) or young (10 months; n=7). Following euthanasia, a limb muscle (EDL) was evaluated for wet-mass and fibre cross-sectional area (via immunohistochemistry), whereas diaphragm bundles were isolated and directly stimulated in vitro across the force-frequency relationship to examine contractile function.
Results: Ageing was associated with an 18% reduction in EDL mass vs young controls (P=0.08), with calorie-restriction further decreasing wet-mass by 24% (P<0.01) and myofiber size by 14% (P=0.079) vs control younger mice. However, twitch specific force increased by 32% (P<0.01) following caloric restriction in aged mice (5.5 vs. 7.2 N/cm2).
Conclusion: Acute caloric restriction in ageing mice was associated with atrophy in the limb muscle but improved contractile function in respiratory muscle. Mild and acute caloric restriction during ageing may have divergent structural and functional effects between limb and respiratory muscles.