A Sex Comparison Of The Physical And Physiological Demands Of United States Marine Corps Recruit Training

United States Marine Corps (USMC) recruit training is a 13-week preparatory period for military service. PURPOSE: to monitor USMC recruits throughout training to comparatively assess workload, sleep, stress, and performance responses in men and women. METHODS: 278 recruits (M = 180 & W = 98; Age = 19 ± 2y) were monitored and tested. Workload, sleep, and stress assessments occurred at weeks 2, 7/8, and 11 of training. Workload (energy expenditure per kg body mass [EE], distance [DIS], steps) and sleep (continuity & duration) were tracked over 72-hour periods using wearable accelerometry and heart rate devices. Stress was determined through salivary cortisol. Performance testing (vertical jump [CMJ] and isometric mid-thigh pull [IMTP]), occurred at weeks 2 and 11. Linear mixed models were used to test for sex, time, and sex-by-time interactions (α < 0.05). RESULTS: Recruits covered 13.0 ± 2.7 km/day, expended 3,762 ± 765 calories/day, and slept 6.2 ± 1.1 hours/night. Sex-by-time interactions were found for DIS, steps, sleep duration, cortisol, and CMJ performance (P < 0.05). Planned contrasts revealed men covered more DIS than women at week 7/8 (P < 0.001). Women experienced greater steps at week 11 (P = 0.004). Women experienced no change in sleep duration (P > 0.05), while men increased sleep duration from week 2 to week 7/8 (P = 0.03). Women experienced greater sleep duration at week 2 (P = 0.03) and week 11 (P = 0.02). Women exhibited higher cortisol levels at week 2 (P < 0.001) and week 11 (P < 0.001). Women experienced declines in cortisol at week 7 compared to week 2 (P < 0.001). Men experienced no changes in cortisol response (P > 0.05). Both sexes experienced declines in CMJ from week 2 to 11 (P > 0.001). Sex main effects were observed for EE, DIS, CMJ, and IMTP (P < 0.05) with men experiencing greater overall workloads and producing greater strength and power metrics. Sex main effects were found for sleep continuity and cortisol (P < 0.05), for which men experienced lower values. Time main effects were observed for EE, DIS, steps, cortisol, CMJ, and IMTP (P < 0.05). CONCLUSION: The greatest physical demands incurred earlier in the training cycle. Despite declining workloads, stress was maintained throughout training which may have implications for adaptation and performance. Average sleep duration fell notably below recommendations. United States Marine Corps AWD00003104 M95494-20-C-0021