Acclimation to three different hot climates with equivalent wet bulb globe temperatures

The present study examined 2 hypotheses: Irrespective of the actual composition of thermal factors, the course of acclimation is similar in hot climates which are equivalent in terms of the WBGT. Acclimation to a defined hot thermal environment confers equal acclimation to any other equivalent climate. These hypotheses were supported with 3 substantially different but equivalent climates with WBGTs between 33.4 and 33.6 degrees C. Eight subjects (6 male, 2 female, 19-32 yrs) executed a treadmill walk (4 x 25 min, 4 km/h, 0 degree) while exposed to either a warm-humid, a hot-dry or a radiant heat condition on 15 consecutive days. On the following 2 days, those adapted to the warm-humid or to the radiant heat condition were exposed to the hot-dry climate and those adapted to the latter were exposed to the warm-humid climate. During the experiments, rectal temperatures, skin temperatures at three sites (forehead, chest, leg) and heart rates were measured continuously. Sweat loss was determined by weighing the subjects before and after the daily trials and during the breaks. At the same time, the subjects rated their actual well-being. Disregarding minor differences during the courses of acclimation, both hypotheses were verified.