The effect of age and sex hormones on female neuromuscular function across the adult lifespan

Abstract

Neuromuscular ageing is characterized by neural and/or skeletal muscle degeneration that decreases maximal force and power. Female neuromuscular ageing occurs earlier in life compared to males, potentially due to sex hormone changes during the menopausal transition. We quantified neuromuscular function in 88 healthy females represented equally over each decade from 18-80 years of age and investigated the potential role of decreased ovarian hormone concentrations following menopause. Neuromuscular assessment included quadriceps maximal voluntary and evoked isometric torque and surface electromyography measurements, plus one-repetition maximum leg press. Voluntary and evoked torques and one-repetition maximum decreased non-linearly with age, with accelerated reductions starting during the fourth decade. An absence of changes in volitional recruitment of existing quadriceps motor units and Ia afferent facilitation of spinal motoneurons suggests that functional decline was largely mediated by impairment in intrinsic muscle function and/or neuromuscular transmission. Maximal muscle compound action potential amplitude decreased with increasing age for rectus femoris only, indicating increased vulnerability to neuromuscular degeneration compared to vastus lateralis and medialis. In postmenopausal females, some variance in data was explained by inter-individual differences in body composition and physical activity level, however, changes in total or free concentrations of oestrogen, progesterone and/or testosterone were correlated with all age-related decreases in neuromuscular variables. In conclusion, we demonstrate an accelerated onset of neuromuscular degeneration of muscular origin around menopause onset, which is associated with changes in sex hormone concentrations. Interventions aimed at mitigating declines in ovarian hormones and their subsequent effects on neuromuscular function postmenopause should be further explored. Key PointsO_LINeuromuscular deterioration with age is associated with poor physical function and quality of life in older adults, but female-specific trajectories and mechanisms remain unclear. C_LIO_LIThis study is the first to map neuromuscular function across each decade of the adult lifespan in 88 healthy females from 18 to 80 years old and to examine the potential role of hormonal changes after menopause C_LIO_LIWe show an accelerated reduction in neuromuscular function, primarily of muscular origin, that occurs between 40 and 50 years of age, coinciding with the onset of menopause. C_LIO_LIIn postmenopausal females, age-related reductions in neuromuscular function can be explained by differences in body composition, physical activity, and sex hormone concentrations. C_LIO_LIThese findings help us better understand the factors that contribute to the loss of neuromuscular function with age in females, enabling the identification of potential therapeutic interventions to prolong the female health span. C_LI