Response of unacclimatized males to repeated weekly bouts of exercise in the heat

The purpose of the present study was to determine if there is an acclimation effect when unacclimatized males exercise in the heat at weekly intervals. Five subjects performed four exercise bouts, each lasting 1 h at 55% VO2max. The first trial was in moderate conditions (mean(s.d.) temperature (Ta) = 22.0(0.8)degrees C; mean(s.d.) relative humidity (rh) = 67(6)%) and the subsequent three trials were carried out at weekly intervals in the heat (mean(s.d.) Ta = 34.6(0.6)degrees C; mean(s.d.) rh = 60(7)%). There were no significant differences between trials in the heat for heart rate, rectal temperature, skin temperature or VO2 (repeated measures analysis of variance), and total sweat loss (one-way analysis of variance). As changes in these variables are seen with heat acclimation it was concluded that there was no heat acclimation effect and separating exercise bouts by 1 week was a valid method for comparing the effects of different treatments on unacclimatized males during exercise in the heat.