Thermoregulation during cold exposure after several days of exhaustive exercise

This study examined the hypothesis that several days of exhaustive exercise would impair thermoregulatory effector responses to cold exposure, leading to an accentuated core temperature reduction compared with exposure of the same individual to cold in a rested condition. Thirteen men (10 experiment al and 3 control) performed a cold-wet walk (CW) for up to 6 h (6 rest-work cycles, each Ih in duration) in 5 degreesC air on three occasions. One cyc le of CW consisted of 10 min of standing in the rain (5.4 cm/h) followed by 45 min of walking (1.34 m/s, 5.4 m/s wind). Clothing was water saturated a t the start of each walking period (0.75 do vs. 1.1 do when dry). The initi al CW trial (day 0) was performed (afternoon) with subjects rested before i nitiation of exercise-cold exposure. During the next 7 days, exhaustive exe rcise (aerobic, anaerobic, resistive) was performed for 4 h each morning. T wo subsequent CW trials were performed on the afternoon of days 3 and 7, si milar to2.5 h after cessation of fatiguing exercise. For controls, no exhau stive exercise was performed on any day. Thermoregulatory responses and bod y temperature during CW were not different on days 0, 3, and 7 in the contr ols. In the experimental group, mean skin temperature was higher (P < 0.05) during CW on days 3 and 7 than on day 0. Rectal temperature was lower (P < 0.05) and the change in rectal temperature was greater (P < 0.05) during t he 6th h of CW on day 3. Metabolic heat production during CW was similar am ong trials. Warmer skin temperatures during CW after days 3 and 7 indicate that vasoconstrictor responses to cold, but not shivering responses, are im paired after multiple days of severe physical exertion. These findings sugg est that susceptibility to hypothermia is increased by exertional fatigue.