Piasecki Jessica, Guo Yuxiao, Jones Eleanor J, Phillips Bethan E, Stashuk Daniel W, Atherton Philip J, Piasecki Mathew
Musculoskeletal Physiology Research Group, Sport, Health and Performance Enhancement Research Centre, Nottingham Trent University, Nottingham, UK.
Centre of Metabolism, Ageing and 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.
Sports Med Open. 2023 Oct 24;9(1):97. doi: 10.1186/s40798-023-00639-8.
Estrogen and progesterone are the primary female sex hormones and have net excitatory and inhibitory effects, respectively, on neuronal function. Fluctuating concentrations across the menstrual cycle has led to several lines of research in relation to neuromuscular function and performance; however evidence from animal and cell culture models has yet to be demonstrated in human motor units coupled with quantification of circulating hormones. Intramuscular electromyography was used to record motor unit potentials and corresponding motor unit potential trains from the vastus lateralis of nine eumenorrheic females during the early follicular, ovulation and mid luteal phases of the menstrual cycle, alongside assessments of neuromuscular performance. Multi-level regression models were applied to explore effects of time and of contraction level. Statistical significance was accepted as p < 0.05.
Knee extensor maximum voluntary contraction, jump power, force steadiness, and balance did not differ across the menstrual phases (all p > 0.4). Firing rate of low threshold motor units (10% maximum voluntary contraction) was lower during the ovulation and mid luteal phases (β = - 0.82 Hz, p < 0.001), with no difference in motor unit potentials analysed from 25% maximum voluntary contraction contractions. Motor unit potentials were more complex during ovulation and mid luteal phase (p < 0.03), with no change in neuromuscular junction transmission instability (p > 0.3).
Assessments of neuromuscular performance did not differ across the menstrual cycle. The suppression of low threshold motor unit firing rate during periods of increased progesterone may suggest a potential inhibitory effect and an alteration of recruitment strategy; however this had no discernible effect on performance. These findings highlight contraction level-dependent modulation of vastus lateralis motor unit function over the eumenorrheic cycle, occurring independently of measures of performance.
雌激素和孕酮是主要的女性性激素，分别对神经元功能具有净兴奋和抑制作用。月经周期中激素浓度的波动引发了多项关于神经肌肉功能和表现的研究；然而，动物和细胞培养模型的证据尚未在结合循环激素定量的人体运动单位中得到证实。在月经周期的卵泡早期、排卵期和黄体中期，使用肌内肌电图记录了9名月经周期正常女性股外侧肌的运动单位电位及相应的运动单位电位序列，并同时评估了神经肌肉表现。应用多级回归模型来探究时间和收缩水平的影响。统计学显著性以p < 0.05为标准。
在月经各阶段，膝关节伸展最大自主收缩、跳跃功率、力量稳定性和平衡能力均无差异（所有p > 0.4）。低阈值运动单位（最大自主收缩的10%）的放电频率在排卵期和黄体中期较低（β = -0.82 Hz，p < 0.001），而从最大自主收缩25%的收缩中分析的运动单位电位无差异。在排卵期和黄体中期，运动单位电位更为复杂（p < 0.03），神经肌肉接头传递不稳定性无变化（p > 0.3）。
在月经周期中，神经肌肉表现的评估无差异。孕酮升高期间低阈值运动单位放电频率的抑制可能表明存在潜在的抑制作用和募集策略的改变；然而，这对表现没有明显影响。这些发现突出了在月经周期正常的情况下，股外侧肌运动单位功能的收缩水平依赖性调节，且这种调节独立于表现指标。
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