Menstrual Cycle Phase-Dependent Lower Extremity Loading Patterns in Adolescent Female Athletes: Implications for Anterior Cruciate Ligament Injury Risk.

Background: Physically active females experience substantially higher anterior cruciate ligament injury rates than males, and postmenarche adolescent females commonly demonstrate high-risk mechanics. However, whether mechanics fluctuate across the menstrual cycle remains poorly understood in adolescent female athletes. The aim of this study was to examine differences in lower extremity kinematics and kinetics across two menstrual cycle phases (menstruation and mid-luteal) in postmenarchal adolescent female athletes during a dynamic change-of-direction task. It was hypothesized that biomechanical contributors to dynamic knee valgus would differ between phases. Methods: A controlled laboratory study was conducted. Thirty healthy postmenarchal adolescent female athletes (aged 13-17 years) were tested during menstruation (verified by self-reported active bleeding) and mid-luteal phase (scheduled via calendar-based day counting). Kinematics and kinetics were collected using 3-dimensional motion capture and force plates while participants performed a 45° run-cut task. Peak pelvis, hip, and knee angles and hip and knee moments were extracted during the loading phase for each limb. Linear mixed-effects models tested effects of phase and limb dominance ( Results: Participants were aged 15.6 ± 0.9 years, had a height of 168.8 ± 6.2 cm, and weighed 61.2 ± 7.0 kg, and a majority played soccer (70.0%). Compared with menstruation, the mid-luteal phase demonstrated greater peak anterior pelvic tilt ( Conclusions: Biomechanical contributors linked to dynamic knee valgus differed by menstrual cycle phase in adolescent female athletes during a change-of-direction task. Menstruation was associated with greater coronal- and transverse-plane hip and knee loading, whereas mid-luteal phase was associated with reduced knee flexion and greater pelvic instability. Cycle-synced injury prevention strategies that are individualized and evidence-based may enhance lower extremity stability when knee control appears most challenged. However, while cycle-synced training may not be feasible in all settings, awareness of phase-related vulnerability may inform screening and load management. Key Concepts: (1)Menstrual cycle phase may contribute to variability in lower extremity biomechanics during change-of-direction tasks in adolescent female athletes.(2)Biomechanical risk factors associated with dynamic knee valgus may differ between menstruation and mid-luteal phases.(3)Consideration of menstrual cycle phase may improve interpretation of biomechanical screening and performance testing.(4)Individualized injury prevention strategies may benefit from awareness of phase-related biomechanical changes. Level of Evidence: III.