Association Between Hormone Variability and Anaerobic Performance in Recreationally Active Women: An Exploratory Study Using Mixed-Effect Location Scale Models

Abstract Ramey, KT, Unrein, CL, Yang, C-H, and Hirsch, KR. Association between hormone variability and anaerobic performance in recreationally active women: An exploratory study using mixed-effect location scale models. J Strength Cond Res XX(X): 000–000, 2026—This study explored the application of mixed-effects location scale modeling (MELS) to examine how daily variability in urinary estrogen (E), progesterone (PdG), and their ratio (E:P) relates to repeated sprint performance (peak power [PP], average power [AP], power drop [PD], and fatigue index [FI]) across low and high hormone phases in healthy, recreationally active eumenorrheic ( n = 8) women and hormonal contraceptive users (intrauterine device = 6; oral contraception = 10; age: 24.7 ± 4.2 years; height: 165.5 ± 6.5 cm; body mass: 63.0 ± 6.7 kg). Subjects completed 30.4 ± 10.7 days of at-home urine hormone testing for E (ng⋅ml −1 ), PdG (µg⋅ml −1 ), and calculate E:P ratio. A repeated sprint test (10 × [6 seconds sprint: 30 seconds rest]) on a cycle ergometer was completed during both the low and high hormone phases to evaluate sprint performance. Fatigue index (%) was recorded, and PP (W), AP (W), and PD (W) were averaged across sprints. Associations between E, P, and E:P with FI, PP, AP, and PD were examined using separate MELS models. Paired t-tests assessed phase differences, and Pearson correlations evaluated relationships between day-of-testing hormone levels and performance. Day-of-testing E ( p < 0.001), PdG ( p < 0.001), PP ( p = 0.047), and AP ( p = 0.016) were significantly higher in the high hormone phase, and PdG correlated positively with PD ( r = 0.574, p = 0.003). Greater individual E variability was associated with lower PP (Low: Estimate = −48.47, p = 0.004; High: Estimate = −50.18, p = 0.009) and AP (Low: Estimate = −46.75, p = 0.005; High: Estimate = −42.04, p = 0.024), remaining significant after controlling for percent body fat and lean mass ( p = 0.008–0.022). These findings suggest hormonal instability may meaningfully influence anaerobic performance. This study introduces novel methodology and statistical framework that captures dynamic hormonal changes across the menstrual cycle and can be used to evaluate hormonal influence on female physiology and performance variability.