Human Adaptation to Work in Two Different Climates

The processes of acclimation to hot-dry and to warm-humid climates were studied using two approaches: a quantitative analysis of literature data and an experimental study in the laboratory concerning the physiological parameters of heart rate, rectal temperature, sweat loss, and subjective assessment. Analysis o f literature data: Data from 62 experiments with a total of 813 participants were pooled and recalculated. The experiments ranged from 6 to 24 days, air temperatures from 30.4 to 50.0°C, water vapor pressures from 1.5 to 6.5 kPa, and wet bulb globe temperatures (WBGT) from 27.4 to 38.6°C. Laboratory studies: In the laboratory, 8 participants were acclimated during 15 consecutive days to a hot-dry climate and to a warm-humid climate, which were equivalent in terms of the WBGT (33.5 and 33.6°C, respectively). The participants walked four times for 25 min on a treadmill at a speed of 4 km/h. The hot-dry climate caused somewhat greater strain than the warm-humid condition. In the course of acclimation to the hot-dry climate, heart rate and rectal temperature started at higher levels, decreased slightly steeper but remained on a higher level throughout. Nevertheless, the differences between both thermal conditions were small, and both physiologic functions reached the point of acclimation almost at the same time under warm-humid and under hot-dry exposure. Sweat loss, which is not regarded as a valid predictor for acclimation, was considerably higher but increased less in the hot-dry than in the warm-humid climate.