Individual response to physical work in the heat in relation to sweating and skin blood flow.

The aim of the present study was to examine heart rate and rectal temperature responses to dynamic exercise in a hot environment and their relationship to sweating and skin blood flow. Eight physically trained men were the study subjects. The experiments consisted of 60-min bicycle ergometer tests at intensities of 50 and 100 W in the heat (36 degrees C/30% relative humidity). During the tests, oxygen consumption, heart rate, rectal temperature, and skin temperatures on eight sites were measured. The whole-body sweat rate and evaporation rate and the rate of dripping sweat were measured by a continuous weighing technique. Skin blood flow was estimated from the changes in forearm blood flow. In all, 13 tests were done at 50 W and 10 tests were conducted at 100 W. At 50 W, a physiological steady state was attained in all tests, i.e. the rise in heart rate was less than 10 beats min-1. At 100 W, in all experiments the heart rate and rectal temperature increased continuously throughout the tests. At the end of exercise, the heart rate varied from 98 to 150 beats min-1. At 50 W work load, the heart rate and rectal temperature did not significantly correlate with any of the thermoregulatory parameters. At 100 W, the heart rate and rectal temperature correlated with the total sweat rate (r = -0.66 and -0.71, respectively; P less than 0.05), with the onset of dripping (r = 0.74 and 0.66, respectively, P less than 0.05), and with the ratio of forearm blood flow to dripping sweat rate (r = 0.83 and 0.85, respectively; P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)