Hormonal contraceptive use, neuromuscular performance, and musculoskeletal health during military training.

Despite data showing half of active-duty servicewomen use hormonal contraception, its impact on physical performance during military training remains unclear. This study examined differences in general and military-specific physical performance and bone health changes based on hormonal contraceptive use. One hundred eighty-five female Marine Officer Candidates (MOCs) were grouped by self-reported menstrual/hormonal contraceptive status. Questionnaires, countermovement jumps (CMJ), isometric mid-thigh pull, physical fitness tests (PFT), peripheral Quantitative Computed Tomography (4%, 38%, and 66% tibia length), and bone biomarkers were assessed at the start and end of the 10-week program. A combat fitness test (CFT) was completed during training. Mixed ANOVAs (group*time) assessed training responses. Among 104 MOCs not using hormonal contraception (Non-Users; age = 25[IQR; 22, 27], BMI = 23.98 ± 1.98) and 81 MOCs using hormonal contraception (Users; age = 24[IQR; 22,26], BMI = 23.97 ± 2.19), Users showed no change in CMJ reactive strength index, while Non-Users decreased (interaction p = 0.042; Non-Users Δ = -0.03, p < 0.001). CMJ jump height was lower in Users than Non-Users (mean difference = -0.02 m, p = 0.031). CMJ performance decreased overall (all p < 0.001); braking and propulsive metrics increased (p ≤ 0.005). PFT total points improved (Δ = 6.05 points; p < 0.001); total volumetric bone mineral density increased (4% site, Δ = 1.37 ± 0.62 mg/cm3; p = 0.029), cortical density decreased (38% site: Δ = -3.04 ± 1.45 mg/cm3, p = 0.038, 66% site: Δ = -2.91 ± 1.35 mg/cm3, p = 0.033); bone formation markers (P1NP: Δ = 9.40 ± 1.91 µg/L; OC Δ = 3.42 ± 0.74 ng/mL; both p < 0.001) increased. CFT scores were similar between groups (p ≥ 0.304). Among Non-Users, self-reported menstrual cycle irregularity increased. Users demonstrated minor differences in neuromuscular performance/fatigue, but small in effect. Hormonal contraception use was not meaningfully associated with military outcomes.