Acclimation processes by daily exercise stints at temperate conditions followed by short heat exposures

In order to improve the conventional procedures for heat acclimation by making the process shorter and more efficient, four daily regimens of 30 min of exercise under temperate ambient conditions (22 degrees C) followed by a 30-min walk (5.6 km/hr under hot dry ambient conditions (50 degrees/25 degrees C, Tdb/Twb) were administered to three groups of subjects. The respective exercise part for each group was as follows: 1) 30 min of descent on a laddermill (negative work); 2) 30 min of ascent on a laddermill (positive work), and 3) 15 min of descent followed by 15 min of ascent on the laddermill. The four daily regimens of exercise and heat exposure were followed by four consecutive daily walks of up to 120 min in dry heat. A fourth control group was not subjected to the special acclimation regimen, but underwent the eight daily conventional acclimation procedures. Acclimation was judged by the increase in tolerance time (T) for the walk in the heat and decrease in heart rate (HR) rectal temperature (Tre) and mean skin temperature (Tsk). Partial acclimation was observed after the 4 d of the regimen for the three experimental groups and the 4 d of the conventional procedure on the fourth control group. The final state of acclimation was apparent on the eighth day for all four groups. When the partial acclimation after the 4-d regimen was compared to the final state of acclimation, the following improvements were observed: 90% increase in T; 72% decrease in HR; 56% decrease in Tre, and 45% fall in Tsk. These improvements were similar to those observed after the 4 d of the conventional treatment on the control group as well as to those reported by others.