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Eighty-Four Hours of Sustained Operations Alter Thermoregulation during Cold Exposure

CASTELLANI, JOHN W.; STULZ, DEAN A.; DEGROOT, DAVID W.; BLANCHARD, LAURIE A.; CADARETTE, BRUCE S.; NINDL, BRADLEY C.; MONTAIN, SCOTT J.

Medicine & Science in Sports & Exercise: January 2003 - Volume 35 - Issue 1 - p 175-181
Applied Sciences: Physical Fitness and Performance

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.

Purpose This study examined the effects of short-term (3.5 d) sustained military operations (SUSOPS) on thermoregulatory responses to cold stress.

Methods 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.

Results 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.

Conclusion 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.

U.S. Army Research Institute of Environmental Medicine, Natick, MA

Address for correspondence: John W. Castellani, Ph.D., Thermal and Mountain Medicine Division, U.S. Army Research Institute of Environmental Medicine, 42 Kansas Street, Natick, MA 01760-5007; E-mail: john.castellani@na.amedd.army.mil.

Submitted for publication May 2002.

Accepted for publication September 2002.

©2003The American College of Sports Medicine