Physiological and Perceptual Responses Across Menstrual Cycle Phases in Female Ultra-Endurance Athletes: A Pilot Study

Ultra-endurance places considerable physiological stress on the body, and understanding how hormonal fluctuations affect women, who take part in ultra endurance training and events, could improve both safety and performance. The aim of this pilot study was to explore physiological and perceptual responses across MC phases in trained female ultra-endurance athletes. Methods: Naturally menstruating participants (VO₂max: 51.4 +/- 5.7 mL/kg/min; ultramarathon experience: 2.6 +/- 1.1 years) were recruited. Seven completed a questionnaire on past experiences and performance perceptions related to the MC. Six underwent physiological testing in the early follicular (EFP), late follicular (LFP), and mid-luteal (MLP) phases. Assessments included resting metabolic rate (RMR), heart rate variability (HRV), and an incremental treadmill test for submaximal and maximal performance. Phase-specific questionnaires recorded perceived performance and well-being. Results: More than half of participants (57.1%) reported perceived performance decrements in the days preceding and during menstruation. However, no significant 2 differences were found in submaximal (heart rate, running economy, rate of perceived exertion) or maximal (VO₂max, peak velocity, time to exhaustion) physiological markers across MC phases. Respiratory frequency at LT1 showed a significant main effect of phase (p = 0.045), though pairwise comparisons did not reach significance. Resting variables, including HRV and RMR, or well-being markers, did not vary significantly between phases. Conclusions: Physiological performance remained stable across MC phases, though trends suggested improved ventilatory efficiency in the LFP compared to the MLP during submaximal work. Despite the small sample size, the frequent reporting of MC-related symptoms indicates the importance of personalised MC monitoring. These findings highlight the practicability of integrating both objective and perceptual measurements in ultra-endurance research and support further investigation with larger cohorts.