The purpose of this study is to determine the progress of whole body sweating rate (SR) in the initial stage of moderate work in two hot environments, and to relate the SR to the body temperature attained.
Four healthy males, 28 to 31 years of age, performed leg exercise of 40% VO₂max with a Monark bicycle ergometer set up on a platform scale (Potter bed balance) . All the experiments were carried out in a climatic chamber at ambient temperature (Ta) of 30°C or 40°C (relative humidity, 45%) in winter season following body heating for 30 min at a room temperature of 30°C. Skin sweating was monitored by the bed balance with automatic weight change indicator throughout the experimental period. Rectal (Tre) and 7 skin temperatures were measured every minute by a thermistor and thermocouples, respectively. Oxygen consumption was determined before and during the work by the Douglas bag method. Heart rate was recorded by electrocardiography throughout the experiment.
At Ta 40°C, the SR increased as soon as the work started, whereas at Ta 30°C it took a few minutes. The mean SR during the work at Ta 40°C was significantly higher than that at Ta 30°C. The level of mean skin temperature (Tsk) was higher at Ta 40°C (35°C) than Ta 30°C (33°C), and Tre was approximately 37.3°C at Ta 30°C and 40°C. The changes in the Tre and Tsk were similar in two different conditions. The negative correlations were found between the SR and the Tsk during the work. The regression line was significantly different at Ta 30°C and 40°C. The Tsk decreased in proportion to increase of the SR. Moreover, there was a good correlation between the SR and heart rate during the work in both environments. Heat production stood at the same level in two different thermal conditions.
The present study suggests that the body core temperature in working men is maintained at least constant level, since the evaporation in the initial stage of the work is largely stimulated, and the reduction of skin temperature may be caused by other factors than the evaporation.