Injury Incidence Fluctuates Across The Menstrual Cycle In Female Athletes

Fluctuations in female reproductive hormones might influence the incidence of athletic injuries across the menstrual cycle, potentially due to effects on joint laxity and muscle function. Yet, limited research has explored the association between menstrual phases and athletic injury incidence using prospective cohort studies. PURPOSE: This study aimed to determine the incidence rates of athletic injuries during the follicular (FP), ovulatory (OP), and luteal (LP) phases of eumenorrheic menstrual cycles among Japanese female athletes. METHODS: A total of 317 collegiate or semi-professional Japanese female athletes were followed prospectively for an average of 8.5 months. Athletes self-recorded their menstrual cycles via a smartphone application. The timing of luteinizing hormone (LH) surge was predicted based on each menstrual cycle length recorded. The day of the predicted LH surge and the subsequent two days were designated as the OP, with periods before and after OP as FP and LP, respectively. Medical staff of the teams recorded time-loss injuries and exposure, defined as days that an athlete participated in practice or games. Incidence rates for each phase of eumenorrheic cycles were calculated, presented with 95% confidence intervals (CI), and expressed as the number of injuries per 1000 athlete-days (AD). RESULTS: The 317 participating athletes had an average age of 21.5 at the start of the study period and played soccer, volleyball, softball, handball, basketball, or field hockey. A total of 112 time-loss injuries were recorded. The number of injuries that occurred during eumenorrheic cycles was 91, and injuries oligomenorrheic/amenorrheic periods totaled 21. Out of 91 injuries during eumenorrheic cycles, 49 occurred in FP, 15 in OP, and 27 in LP. The amounts of exposure were 15034 AD in FP, 3213 AD in OP, and 13373 AD in LP. Incidence rates were 3.26 (95%CI = 2.41-4.31) for FP, 4.67 (95%CI = 2.61-7.70) for OP, and 2.02 (95%CI = 1.33-2.94) for LP. The injury rate ratio for OP compared to LP was 2.31 (95%CI = 1.23-4.35), which was statistically significant as the 95%CI did not include 1.00. CONCLUSION: Athletic injury risk varies throughout the eumenorrheic menstrual cycle, with the highest incidence during the OP and the lowest in the LP. Notably, the injury risk was 2.31 times higher during the OP than the LP.