Female Rangers Preserve Muscle Better Than Males During Grueling 61-Day Combat Training

Understanding how the human body responds to prolonged extreme physical stress is critical for both military readiness and broader athletic performance science. Until now, little was known about whether men and women respond differently to the combined demands of sleep deprivation, high physical output, and restricted caloric intake that define elite combat training.

Researchers from the US Army Research Institute of Environmental Medicine studied 37 soldiers — 10 female and 27 male — completing the US Army Ranger Training Course, a 61-plus-day program widely regarded as one of the most physically and mentally demanding military courses in the world. Using doubly labeled water to measure total daily energy expenditure and food wrapper collection to estimate dietary intake, the team tracked energy balance and body composition via DEXA scans before training and after each of three phases.

Despite starting with lower body mass and fat-free mass but higher fat mass than males, females preserved their lean mass significantly better at every training phase. Males lost more total body weight throughout the course. By the final phase, the sex difference in fat mass had disappeared, suggesting females drew down fat stores more completely. Total daily energy expenditure was higher in males during phases one and two but converged by phase three. Females notably increased their caloric intake more between phases one and two compared to males.

The most striking finding is that the magnitude of change in energy balance did not differ by sex — meaning both groups experienced proportionally similar metabolic stress. This challenges the assumption that female soldiers face uniquely different physiological challenges in extreme training environments.

For clinicians, coaches, and military nutritionists, these results suggest that sex-specific nutrition strategies may be warranted not because women respond worse, but because their body composition trajectories differ meaningfully. Preserving lean mass in female athletes and soldiers under caloric restriction may require less intervention than previously assumed.