Temperature Regulation during Exercise Dehydration in Man

The effects of mild exercise dehydration (1 % of the body weight) on temperature regulation were investigated in 3 men during continuous and intermittent exercise of 1 hr duration on a Krogh bicycle ergometer with the same average heat production at a relative O 2 uptake of 62 % in the environment‐independent zone (22° C T a and 38 % rh). In both hydration and dehydration, during intermittent work, equilibrium levels of rectal temperature (T re ) were 0.3° C higher than during continuous work. Progressive dehydration elevated equilibrium levels of Tre and mean body temperatures 0.3 to 0.4° C above hydration control values while mean skin temperatures (Ts) were essentially constant at 30±0.2° C. The elevation of Tre with dehydration was due, predominantly, to reduced sweating. It is suggested the sweat depression was due to reduced stimuli from the central nervous system to the glands. These results emphasize the sensitivity of the thermoregulatory system to dehydration and point up the need to control water intake during such experiments.