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J Appl Physiol 87: 243-246, 1999;
8750-7587/99 $5.00
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Vol. 87, Issue 1, 243-246, July 1999

Thermoregulatory responses to cold water at different times of day

John W. Castellani, Andrew J. Young, James E. Kain, and Michael N. Sawka

Thermal and Mountain Medicine Division, US Army Research Institute of Environmental Medicine, Natick, Massachusetts 01760-5007

This study examined how time of day affects thermoregulation during cold-water immersion (CWI). It was hypothesized that the shivering and vasoconstrictor responses to CWI would differ at 0700 vs. 1500 because of lower initial core temperatures (Tcore) at 0700. Nine men were immersed (20°C, 2 h) at 0700 and 1500 on 2 days. No differences (P > 0.05) between times were observed for metabolic heat production (M, 150 W · m-2), heat flow (250 W · m-2), mean skin temperature (<OVL>T</OVL>sk, 21°C), and the mean body temperature-change in M (Delta M) relationship. Rectal temperature (Tre) was higher (P < 0.05) before (Delta  = 0.4°C) and throughout CWI during 1500. The change in Tre was greater (P < 0.05) at 1500 (-1.4°C) vs. 0700 (-1.2°C), likely because of the higher Tre-<OVL>T</OVL>sk gradient (0.3°C) at 1500. These data indicate that shivering and vasoconstriction are not affected by time of day. These observations raise the possibility that CWI may increase the risk of hypothermia in the early morning because of a lower initial Tcore.

circadian rhythm; immersion; norepinephrine; shivering; vasoconstriction


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K. Aoki, D. P. Stephens, A. R. Saad, and J. M. Johnson
Cutaneous vasoconstrictor response to whole body skin cooling is altered by time of day
J Appl Physiol, March 1, 2003; 94(3): 930 - 934.
[Abstract] [Full Text] [PDF]


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