Fifty U.S. Marine recruits (30 men, 20 women) were studied during a physically intense, energy intake-restricted, winter-time 54-h field training exercise (FEX) at Parris Island Marine Corps Recruit Depot. Men and women completed the same physical tasks.
Purpose: To characterize and compare the total energy expenditure (TEE) and core temperature responses in men and women working almost continuously for 2.25 d in an outdoor environment while developing a substantial energy deficit.
Methods: TEE was measured using doubly labeled water (D218O). Energy intake was estimated using beverage diaries and collecting ration wrappers saved by each volunteer and adding the known caloric value of each food item consumed. Core temperature was measured using an ingested thermometer pill. Physical activity level (PAL) was calculated by dividing TEE by the calculated basal metabolic rate.
Results: TEE was higher (P < 0.001) for the men (25.7 MJ·d−1) than women (19.8 MJ·d−1), but there were no differences between men and women in TEE normalized to body mass (men, 0.35 ± 0.05 MJ·d−1·kg−1; women, 0.34 ± 0.06 MJ·d−1·kg−1), corrected body mass (men, 0.29 ± 0.04 MJ·d−1·kg−1 corrected body mass; women, 0.27 ± 0.04 MJ·d−1·kg−1 corrected body mass), fat-free mass (men, 0.41 ± 0.07 MJ·d−1·kg FFM−1; women, 0.46 ± 0.07 MJ·d−1·kg FFM−1), or corrected fat-free mass (men, 0.30 ± 0.05 MJ·d−1·kg−1 corrected body mass; women, 0.30 ± 0.04 0.30 ± 0.05 MJ·d−1·kg−1 corrected body mass). PAL was the same for men (3.4 ± 0.5) and women (3.3 ± 0.4). Energy intakes were higher (P < 0.05) in men (6.0 ± 2.0 MJ·d−1) than women (4.8 ± 1.8 MJ·d−1). The average minimum core temperature was 36.0 ± 0.4°C, and the mean maximum core temperature was 38.5 ± 0.3°C.
Conclusions: For both men and women, total energy expenditures were among the highest observed for a military FEX. TEE, when normalized or corrected to body mass and fat-free mass, and PAL were the same for men and women.