CHANGES IN THERMAL HOMEOSTASIS IN HUMANS DUE TO REPEATED COLD-WATER IMMERSIONS

The purpose of this study was to monitor changes in body and skin temp eratures, heat production, subjective shivering, cold sensation and bo dy fat content in humans after intermittent cold water immersion. Repe aled exposures of young sportsmen to cold water (head out, 14 degrees C, 1 h, 3 times per week for 4-6 weeks) induced changes in regulation of thermal homeostasis. ''Cold acclimated'' subjects exhibited an hypo thermic type of adaptation. Central and peripheral body temperatures a t rest and during cold immersion were lowered. The metabolic response to cold was delayed and subjective shivering was attenuated. The obser ved hypothermia aas due to the shift of the threshold for induction of cold thermogenesis to lower body temperatures, ''Cold acclimated'' su bjects also showed a lowered cold sensation. Because of the observed p hysiological changes, about 20% of the total heat production was saved during one cold water immersion of ''cold acclimated'' subjects. Maxi mal aerobic and anaerobic performances were not altered. No change in the thermosensitivity of the body temperature controller, as assessed from the unchanged slope of the relation between the deep body tempera ture and total heat production, was observed. Changes in cold sensatio n and regulation of cold thermogenesis were noticed first after four c old water immersions and persisted for at least 2 weeks after terminat ion of the adaptation procedure. A trend towards a small increase in t he body fat content was also observed. This finding, as well as the in creased vasoconstriction, evidenced by the lowered skin temperature, i ndicate that slight changes in body insulation may also occur after '' cold acclimation'' in humans.