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CASTELLANI, J. W., D. A. STULZ, D. W. DEGROOT, L. A. BLANCHARD, B. S. CADARETTE, B. C. NINDL, and S. J. MONTAIN. Eighty-Four Hours of Sustained Operations Alter Thermoregulation during Cold Exposure. Med. Sci. Sports Exerc., Vol. 35, No. 1, pp. 175–181, 2003.This study examined the effects of short-term (3.5 d) sustained military operations (SUSOPS) on thermoregulatory responses to cold stress.Ten men (22.8 ± 1.4 yr) were assessed during a cold-air test (CAT) after a control week (control) and again after an 84-h SUSOPS (sleep = 2 h·d−1, energy intake = ∼1650 kcal·d−1, and energy expenditure = ∼4500 kcal·d−1). CAT consisted of a resting subject (seminude) being exposed to an ambient temperature ramp from 25°C to 10°C during the initial 30 min of CAT, with the ambient temperature then remaining at 10°C for an additional 150 min.SUSOPS decreased (P < 0.05) body weight, % body fat, and fat-free mass by 3.9 kg, 1.6%, and 1.8 kg, respectively. During CAT, rectal temperature decreased to a greater extent (P < 0.05) after SUSOPS (0.52 ± 0.09°C) versus control (0.45 ± 0.12°C). Metabolic heat production was lower (P < 0.05) after SUSOPS at min 30 (55.4 ± 3.3 W·m−2) versus control (66.9 ± 4.4 W·m−2). Examination of the mean body temperature-metabolic heat production relationship indicated that the threshold for shivering was lower (P < 0.05) after SUSOPS (34.8 ± 0.2°C) versus control (35.8 ± 0.2°C). Mean weighted skin temperatures (°C) were lower during the initial 1.5 h of CAT in SUSOPS versus control. Heat debt was similar between trials.These results indicate that sustained (84-h) military operations leads to greater declines in core temperature, due to either a lag in the initial shivering response or heat redistribution secondary to an insulative acclimation.