Skeletal muscle function does not differ between menstrual cycle phases: A prospective cohort study across three cycles.

Fluctuations in ovarian hormones across the menstrual cycle have been proposed to influence skeletal muscle function, yet current evidence remains inconsistent. This study investigated associations between menstrual cycle phases and multidimensional outcomes of skeletal muscle function across three menstrual cycles. In this prospective cohort study repeated within-subjects measurements were performed during the early follicular, ovulatory and mid-luteal phases in physically active eumenorrheic females. Cycle phases were verified using luteinizing hormone detection and salivary hormone analysis. Outcomes included concentric and eccentric isokinetic peak torque of leg extension, muscular fatigue resistance and jump performance. Contractility was quantified by tensiomyography, and muscle stiffness was evaluated using shear wave elastography. Thirty-two participants were enrolled, and 14 completed all measurements. No significant effect of phase occurred for functional parameters or muscle stiffness. Significant effects of cycle were observed for eccentric peak torque, total work, drop jump height, reactive strength index and relaxed muscle stiffness with varying directions of change; however, no phase-dependent pattern emerged. Estradiol concentrations did not vary significantly, whereas progesterone concentrations increased significantly during the mid-luteal phase. We concluded that skeletal muscle function appeared to be largely unaffected by menstrual cycle phases. Potential phase-related effects are likely minimal under real-life conditions.