Heat acclimatization while wearing vapor barrier clothing

Acclimatization to a hot, humid environment was studied in 9 men who performed moderate work at an air temperature of 37°C while wearing vapor barrier suits, for 6 successive days. Heart rate, rectal and skin temperatures, sweat rate and oxygen consumption were recorded. The results showed only partial acclimatization, which was indicated by decreases in heart rate and in rectal and skin temperatures of 16 beats/min, 0.5°C and 0.6°C respectively from the first to the sixth exposure. Sweat rate increased 25%, oxygen consumption decreased 13%, and resting rectal temperature decreased by 0.3°C. These changes enabled an increase of 13 min in tolerance time. Since the evaporation of sweat was minimal, due to the vapor barrier suits, acclimatization was attributed to the lowering of resting body temperature and to the decrease in heat production.