Association Between Menstrual Cycle Regularity, Neuromuscular Control, and Dynamic Knee Stability in Female Athletes:...

Evidence linking menstrual characteristics to knee-related functional measures in female athletes remains inconsistent, partly due to an emphasis on menstrual phase without adequate consideration of cycle regularity. This study examined associations between menstrual cycle regularity, neuromuscular activation variables, and Dynamic Postural Stability Index (DPSI) measures across standardized menstrual phases.

A longitudinal repeated-measures study was conducted among 90 female athletes (46 with regular cycles and 44 with irregular cycles). Participants were assessed during the early follicular, ovulatory, and mid-luteal phases across three consecutive menstrual cycles. DPSI was used to assess dynamic postural stability, while quadriceps activation latency and hamstring-to-quadriceps co-contraction ratio were assessed using surface electromyography. Linear mixed-effects models were used to examine group, phase, and interaction effects, adjusting for age and training volume.

Athletes with irregular cycles demonstrated higher DPSI values overall compared with athletes with regular cycles (β = +0.05, 95% CI: 0.01-0.09; p = 0.012). No significant main effect of menstrual phase was observed; however, significant group × phase interactions were identified, with the largest between-group differences occurring during the ovulatory phase. Athletes with regular cycles demonstrated shorter quadriceps activation latency and higher hamstring-to-quadriceps co-contraction ratios across phases. Menstrual cycle regularity was significantly associated with DPSI values (r = -0.38, p < 0.001).

Menstrual cycle regularity was associated with DPSI and neuromuscular activation variables across menstrual phases. These findings support the consideration of cycle regularity as a stratification variable in future studies examining knee function-related outcomes in female athletes.