Assessing sex differences in grit and anabolic hormones during US Army Ranger Training

Psychological grit has displayed positive associations between resilience and successful completion of military training; however, it is unclear if and how grit changes in response to chronic physiological stress. Links between anabolic hormones and high levels of performance in military training have also been well-established. The Army Ranger Training Course (RTC) is a 61d course with three distinct phases of various environmental conditions (P1: basic field; P2: mountains; and P3: swamp) imposing significant physiological and psychological stress. Until 2015, RTC was only open to males, making this a unique opportunity to assess if sex differences exist with a self-reported measure of grit over a stressful training environment; and if changes in grit over time are associated with changes in anabolic biomarkers. We hypothesized that male and female RTC Soldiers would exhibit similar decreases in grit scores associated with decreases in dehydroepiandrosterone-sulfate, DHEA-s; testosterone, T; and insulin-like growth factor, IGF-1, throughout RTC. Data were collected at the start of RTC (Baseline [P0]) and immediately following culminating field training exercises at the end of each RTC phase (P1-3). Grit was assessed using a validated self-report scale (GRIT-S); venous blood samples were collected for hormone assessment (DHEA-s, µg/dL; T, ng/mL; and IGF1, ng/mL). Neither hormonal contraceptive use nor menstrual cycle phase were controlled for in female participants. Linear mixed models (LMMs) were used to assess changes in grit scores and changes in hormones from P0 to P1-3. Linear regression models were used to estimate the associations between grit scores and hormones cross-sectionally at P0 to P1-3. LMMs with an interaction term between grit score and hormone level were used to compare grit score and hormones over time. All models were adjusted for sex and age. Thirty-five participants (9F, 25.9 y; 26M, 25.2 y) completed all phases of RTC. BaselineGRIT-S scores did not differ by sex (mean ± SD: 3.9 ± 0.4 F; 4.0 ± 0.3 M) and did not change significantly over time; no group-level differences were observed in GRIT-S changes over time relative to P0. Overall, T decreased across all timepoints ((Δ [95% CI]) P1 -1.2 [-1.7, -0.7]; P2 -1.3 [-1.8, -0.9]; P3 -0.5 [-1.0, -0.1]) compared to P0 ( p ≤0.03) and IGF-1 decreased for all timepoints (P1 -91.9 [-105.4, -78.5]; P2 -85.2 [-98.8, -71.6]; P3 -104.7 [-118.3, -91.1]) compared to P0 ( p <0.001). There were no sex differences in the changes from P0 to P1-3 for DHEA-s or IGF1. Male T displayed larger decreases from P0 compared to females at P1 (-1.2 [-1.7, -0.6] and -0.1 [-0.2, 0.01], respectively; p =0.02) and at P2 (-1.3 [-1.7, -0.6] and -0.1 [-0.2, -.02], respectively; p =0.01). Females showed decreases in T between P0 and P3 (-0.1 [-0.2, -0.02]; p =0.01). Overall, grit scores were not associated with biomarkers at any time point. Findings suggest that despite fluctuations in hormonal status from extended periods of physiological stress, both sexes displayed high levels of grit throughout RTC. Overall, no sex difference was detected in grit, DHEA-s, or IGF1 over time from baseline to P1-3. Future research should investigate additional psychological traits that may affect Soldiers’ ability to adapt to a multi-stressor environment over a prolonged period. Military Operational Medical Research Program/MRDC This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.