Journal of Applied Physiology AJP: Lung Cellular and Molecular Physiology
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J Appl Physiol 85: 1210-1217, 1998;
8750-7587/98 $5.00
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Vol. 85, Issue 4, 1210-1217, October 1998

Exertional fatigue, sleep loss, and negative energy balance increase susceptibility to hypothermia

Andrew J. Young1, John W. Castellani1, Catherine O'Brien1, Ronald L. Shippee1, Peter Tikuisis3, Lloyd G. Meyer2, Laurie A. Blanchard1, James E. Kain1, Bruce S. Cadarette1, and Michael N. Sawka1

1 United States Army Research Institute of Environmental Medicine, Natick, Massachusetts 01760; 2 Naval Aerospace Medical Research Laboratory, Pensacola, Florida 32508; and 3 Defence and Civil Institute of Environmental Medicine, North York, Ontario, Canada M3M 3B9

The purpose of this study was to determine how chronic exertional fatigue and sleep deprivation coupled with negative energy balance affect thermoregulation during cold exposure. Eight men wearing only shorts and socks sat quietly during 4-h cold air exposure (10°C) immediately after (<2 h, A) they completed 61 days of strenuous military training (energy expenditure ~4,150 kcal/day, energy intake ~3,300 kcal/day, sleep ~4 h/day) and again after short (48 h, SR) and long (109 days, LR) recovery. Body weight decreased 7.4 kg from before training to A, then increased 6.4 kg by SR, with an additional 6.4 kg increase by LR. Body fat averaged 12% during A and SR and increased to 21% during LR. Rectal temperature (Tre) was lower before and during cold air exposure for A than for SR and LR. Tre declined during cold exposure in A and SR but not LR. Mean weighted skin temperature (<OVL>T</OVL>sk) during cold exposure was higher in A and SR than in LR. Metabolic rate increased during all cold exposures, but it was lower during A and LR than SR. The mean body temperature (0.67 Tre + 0.33 <OVL>T</OVL>sk) threshold for increasing metabolism was lower during A than SR and LR. Thus chronic exertional fatigue and sleep loss, combined with underfeeding, reduced tissue insulation and blunted metabolic heat production, which compromised maintenance of body temperature. A short period of rest, sleep, and refeeding restored the thermogenic response to cold, but thermal balance in the cold remained compromised until after several weeks of recovery when tissue insulation had been restored.

exhaustion; underfeeding; sleep deprivation; body temperature regulation


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