Author(s): PFLEIDERER, L., RASCHNER, C., HECKSTEDEN, A., PÖPEL, S., MAZZOLARI, R., Institution: UNIVERSITY OF INNSBRUCK, Country: AUSTRIA, Abstract-ID: 2495

INTRODUCTION:
Menstrual cycle (MC) phases are hypothesized to influence endurance performance through effects on several physiological processes. Recent evidence indicates that differences in performance-related measures between MC phases are trivial or non significant at the group level [1–3]. However, a trivial average effect does not necessarily preclude meaningful effects in individual athletes, as an athlete by phase interaction may be present [4]. Most prior studies monitored only one or two cycles, providing limited statistical power to detect such interactions. Accordingly, using a longitudinal repeated measures design across six consecutive MCs, this study aimed to assess the effect of MC phase on endurance performance in runners, evaluating both the group average effect and individual responses.
METHODS:
Twenty-three eumenorrheic, trained endurance athletes completed an incremental treadmill test, followed by two 2000-m time trials per MC (early follicular phase, midluteal phase). MC phase was estimated via menstrual tracking and verified for ovulation using luteinizing-hormone testing. Outcome measures were average 2000-m speed and rating of perceived exertion (RPE; Borg 6–20 scale), with RPE assessed immediately after each run. Between phase differences were analyzed using linear mixed effects models including participant as a random effect. The significance level was set at 𝛼 ≤ .05.
RESULTS:
Sixteen participants (age: 25.4 ± 3.1 years; maximal oxygen consumption: 56.8 ± 6.0 ml/kg/min; 2000m speed: 14.2 ± 1.2 km/h) provided performance data for at least two complete MCs and were included in the analysis. No participant withdrew or missed trials because of MC related symptoms. At the group level, the effect of MC phase was non-significant for both outcomes (2000-m speed: 0.0 [95% CI: –0.1, 0.1] km/h, p = 0.73; RPE: 0 [–1, 0] units, p = 0.70). The athlete by phase interaction accounted for a small proportion of overall variance in phase differences (2000-m speed: 8%; RPE: 24%), indicating no substantial individual responses to phase, particularly for 2000-m speed.
CONCLUSION:
The present study found no evidence of a meaningful effect of MC phase on 2000-m running performance or RPE at either the group or individual level in trained, eumenorrheic endurance athletes. These findings suggest that routine, phase-based adjustments to training or performance expectations may not be necessary for similar athletes. Limitations include MC phase estimation via tracking and luteinizing-hormone testing rather than continuous hormonal profiling, meaning atypical hormone patterns cannot be ruled out. Future studies should replicate these results with larger samples, and using direct MC phase assessment.

[1] Taylor 2024/ [2] Docter 2025/ [3] Taylor 2026/ [4] Hecksteden 2015