Limited Sex Differences in Energy Balance and Body Composition during 61+ d of U.S. Army Ranger Training

Area of Science:

• Military science
• Human physiology
• Sports medicine

Background:

• Soldiers often face negative energy balance (Ebal) and body composition changes during intense combat training due to high energy expenditure and restricted food intake.
• Previous research has not clarified potential sex differences in these physiological responses.

Purpose of the Study:

• To investigate sex-based differences in energy balance and body composition changes in Soldiers undergoing the US Army Ranger Training Course (RTC).

Main Methods:

• Compared body composition (BM, FM, FFM) and energy balance (Ebal) in 10 females and 27 males during RTC using dual-energy X-ray absorptiometry and doubly labeled water.
• Assessed total daily energy expenditure (TDEE) and dietary energy intake via food wrapper analysis.

Main Results:

• Females had lower baseline body mass (BM) and fat-free mass (FFM) but higher fat mass (FM) than males; these differences persisted throughout training.
• Males showed greater BM loss, while females maintained FFM more effectively across all training phases.
• Total daily energy expenditure (TDEE) was higher in males during early phases, and females increased dietary intake more significantly between phases 1 and 2.

Conclusions:

• The magnitude of change in energy balance (Ebal) did not differ between sexes during Ranger training.
• Males experienced greater body mass (BM) loss, whereas females demonstrated superior fat-free mass (FFM) preservation.
• Findings highlight sex-specific adaptations in body composition during demanding military training.