THE PERSISTENCE OF HEAT ACCLIMATIZATION IN MAN

Abstract

The performance of muscular work in dry heat was studied in 24 normal young [male][male] under controlled conditions of diet, environment and work routine. The environmental temps, were 110[degree] F. during the mornings, 120[degree] F. during the afternoons, and 85[degree] to 90[degree] F. at night. The relative humidity was 20-25%. The work consisted of walking on a motor-driven treadmill at 3.25 miles/hr. and a 7.5% angle of climb. Work of this intensity demands an O2 consumption about 7 times the basal rate. Comparisons were made between the performance in heat on two occasions of two days each separated by from 1-4 wks. of cold weather. Work pulse rates, rectal temps. and, to a lesser degree, vasomotor stability tests showed that heat acclimatization persists during at least 3 wks. of cold weather. The benefits conferred by the acclimatization developed during a 2 days exposure to heat are important in withstanding a subsequent exposure to heat, but the advantage decreases from wk. to wk.