Cumulative Effects of H+ and Pi on Force and Power of Skeletal Muscle Fibres from Young and Older Adults

Document Type

Article

Publication Date

1-2025

Publisher

Wiley

Source Publication

Journal of Physiology

Source ISSN

0022-3751

Original Item ID

DOI: 10.1113/JP286938

Abstract

The cellular causes of the age-related loss in power output and increased fatigability are unresolved. We previously observed that the depressive effects of hydrogen (H+) (pH 6.2) and inorganic phosphate (Pi) (30 mm) did not differ in muscle fibres from young and older men. However, the effects may have been saturated in the severe fatigue-mimicking condition, potentially masking age differences in the sensitivity of the cross-bridge to these metabolites. Thus, we compared the contractile mechanics of muscle fibres from the vastus lateralis of 13 young (20–32 years, seven women) and 12 older adults (70–90 years, six women) in conditions mimicking quiescent muscle and a range of elevated H+ (pH 6.8–6.6–6.2) and Pi (12–20–30 mm). The older adult knee extensor muscles showed hallmark signs of ageing, including 19% lower thigh lean mass, 60% lower power and a greater fatigability compared to young adult muscles. Progressively increasing concentrations of H+ and Pi in the chemically-permeabilized fibre experiments caused a linear decrease in fibre force, velocity and power; however, the effects did not differ with age or sex. Fast fibre cross-sectional area was 41% smaller in older compared to young adults, which corresponded with lower absolute power. Size-specific power was greater in fibres from older compared to young adults, indicating the age-related decline in absolute power was explained by differences in fibre size. These data suggest the age-related loss in power is determined primarily by fast fibre atrophy in men and women, but the age-related increase in fatigability cannot be explained by an increased sensitivity of the cross-bridge to H+ and Pi.

Comments

Journal of Physiology, Vol. 603, No.1 (January 2025): 187-209. DOI.

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