Guo Yuxiao, Jones Eleanor J, Smart Thomas F, Altheyab Abdulmajeed, Gamage Nishadi, Stashuk Daniel W, Piasecki Jessica, Phillips Bethan E, Atherton Philip J, Piasecki Mathew
Institute of Sports Medicine and Health, Chengdu Sport University, Chengdu, China.
Centre of Metabolism, Ageing & Physiology (COMAP), MRC-Versus Arthritis Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Nottingham Biomedical Research Centre, School of Medicine, University of Nottingham, Nottingham, UK.
J Physiol. 2025 Jan;603(1):151-165. doi: 10.1113/JP285653. Epub 2024 Jun 10.
Females typically live longer than males but, paradoxically, spend a greater number of later years in poorer health. The neuromuscular system is a critical component of the progression to frailty, and motor unit (MU) characteristics differ by sex in healthy young individuals and may adapt to ageing in a sex-specific manner due to divergent hormonal profiles. The purpose of this study was to investigate sex differences in vastus lateralis (VL) MU structure and function in early to late elderly humans. Intramuscular electromyography signals from 50 healthy older adults (M/F: 26/24) were collected from VL during standardized submaximal contractions and decomposed to quantify MU characteristics. Muscle size and neuromuscular performance were also measured. Females had higher MU firing rate (FR) than males (P = 0.025), with no difference in MU structure or neuromuscular junction transmission (NMJ) instability. All MU characteristics increased from low- to mid-level contractions (P < 0.05) without sex × level interactions. Females had smaller cross-sectional area of VL, lower strength and poorer force steadiness (P < 0.05). From early to late elderly, both sexes showed decreased neuromuscular function (P < 0.05) without sex-specific patterns. Higher VL MUFRs at normalized contraction levels previously observed in young are also apparent in old individuals, with no sex-based difference of estimates of MU structure or NMJ transmission instability. From early to late elderly, the deterioration of neuromuscular function and MU characteristics did not differ between sexes, yet function was consistently greater in males. These parallel trajectories underscore the lower initial level for older females and may offer insights into identifying critical intervention periods. KEY POINTS: Females generally exhibit an extended lifespan when compared to males, yet this is accompanied by a poorer healthspan and higher rates of frailty. In healthy young people, motor unit firing rate (MUFR) at normalized contraction intensities is widely reported to be higher in females than in age-matched males. Here we show in 50 people that older females have higher MUFR than older males with little difference in other MU parameters. The trajectory of decline from early to late elderly does not differ between sexes, yet function is consistently lower in females. These findings highlight distinguishable sex disparities in some MU characteristics and neuromuscular function, and suggest early interventions are needed for females to prevent functional deterioration to reduce the ageing health-sex paradox.
女性通常比男性寿命长，但矛盾的是，女性在晚年健康状况较差的时间却更长。神经肌肉系统是身体衰弱进程中的一个关键组成部分，在健康的年轻个体中，运动单位（MU）的特征存在性别差异，并且由于激素水平不同，可能会以性别特异性的方式适应衰老。本研究的目的是调查老年人群从早期到晚期股外侧肌（VL）运动单位的结构和功能的性别差异。在标准化次最大收缩期间，从50名健康老年人（男/女：26/24）的股外侧肌采集肌内肌电图信号，并进行分解以量化运动单位特征。同时还测量了肌肉大小和神经肌肉性能。女性的运动单位放电频率（FR）高于男性（P = 0.025），而运动单位结构或神经肌肉接头传递（NMJ）稳定性没有差异。所有运动单位特征在低到中等强度收缩时均增加（P < 0.05），且不存在性别×强度交互作用。女性的股外侧肌横截面积较小，力量较弱，力量稳定性较差（P < 0.05）。从老年早期到晚期，两性的神经肌肉功能均下降（P < 0.05），且没有性别特异性模式。在年轻人中先前观察到的标准化收缩水平下较高的股外侧肌运动单位放电频率在老年人中也很明显，运动单位结构或神经肌肉接头传递稳定性的估计没有性别差异。从老年早期到晚期，神经肌肉功能和运动单位特征的恶化在两性之间没有差异，但男性的功能始终更强。这些平行的变化趋势突出了老年女性较低的初始水平，并可能为确定关键干预时期提供见解。要点：与男性相比，女性通常寿命更长，但这伴随着更差的健康状况和更高的衰弱率。在健康的年轻人中，普遍报道在标准化收缩强度下女性的运动单位放电频率高于年龄匹配的男性。在此我们对50人进行研究发现，老年女性的运动单位放电频率高于老年男性，而其他运动单位参数差异不大。从老年早期到晚期的下降轨迹在两性之间没有差异，但女性的功能始终较低。这些发现突出了在一些运动单位特征和神经肌肉功能方面明显的性别差异，并表明女性需要早期干预以防止功能恶化，从而减少衰老健康性别悖论。
