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<p>Aging is associated with neuromuscular decline, but how sex modulates motor unit adaptations across adulthood remains unclear. This study examined age- and sex-related differences in motor unit firing behavior in young (YG), middle-aged (MA), and older (OLD) adults by integrating high-density surface EMG decomposition with assessments of muscle morphology and daily physical activity. Linear mixed-effects models revealed significant effects of age and sex on mean firing rate: females showed higher rates than males at 30% maximal voluntary contraction (MVC) in YG and MA groups, but not in OLD, and no sex differences were observed at 50% MVC. Firing-rate variability was consistently higher in females. During force-increasing contractions, OLD adults showed reduced motor unit discharge modulation; in early-recruited units, reductions were significant in OLD females relative to both YG and MA females, while males showed reductions across both early- and late-recruited units. Males exhibited greater muscle thickness, cross-sectional area, and maximal torque, and daily physical activity was lower in OLD participants. These findings indicate that neuromuscular aging is associated with reduced discharge-rate modulation and a convergence of motor unit behavior between sexes in older age. Physical activity may contribute, underscoring the importance of sex-sensitive strategies to preserve neuromuscular function.</p>

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Motor unit behavior adaptations across lifespan: sex differences in young, middle-aged and old adults

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年6月29日

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  • Marco Carbonaro,
  • Marta Boccardo,
  • Clarissa M. Brusco,
  • Andrea M. Pilotto,
  • Rebecca Re,
  • Fulvio Lauretani,
  • Simone Porcelli,
  • Martino V. Franchi,
  • Alberto Botter

摘要

Aging is associated with neuromuscular decline, but how sex modulates motor unit adaptations across adulthood remains unclear. This study examined age- and sex-related differences in motor unit firing behavior in young (YG), middle-aged (MA), and older (OLD) adults by integrating high-density surface EMG decomposition with assessments of muscle morphology and daily physical activity. Linear mixed-effects models revealed significant effects of age and sex on mean firing rate: females showed higher rates than males at 30% maximal voluntary contraction (MVC) in YG and MA groups, but not in OLD, and no sex differences were observed at 50% MVC. Firing-rate variability was consistently higher in females. During force-increasing contractions, OLD adults showed reduced motor unit discharge modulation; in early-recruited units, reductions were significant in OLD females relative to both YG and MA females, while males showed reductions across both early- and late-recruited units. Males exhibited greater muscle thickness, cross-sectional area, and maximal torque, and daily physical activity was lower in OLD participants. These findings indicate that neuromuscular aging is associated with reduced discharge-rate modulation and a convergence of motor unit behavior between sexes in older age. Physical activity may contribute, underscoring the importance of sex-sensitive strategies to preserve neuromuscular function.