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. 185 female Marine Officer Candidates (MOCs) were grouped by self-reported menstrual/hormonal contraceptive status. Questionnaires, countermovement jumps (CMJ), isometric mid-thigh pull (IMTP), physical fitness tests (PFT), peripheral Quantitative Computed Tomography (pQCT; 4%, 38%, 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=-0.02m, 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.