EXERCISE IN THE HEAT - INDIVIDUAL IMPACTS OF HEAT ACCLIMATION AND EXERCISE TRAINING ON CARDIOVASCULAR PERFORMANCE

1. The individual contributions of heat acclimation and exercise train ing to improving cardiovascular reserves during exercise under differe nt environmental conditions [normothermia: 24 degrees C, 40% relative humidity (RH); hot/wet: 35 degrees C, 70% RH; hot/dry: 40 degrees C, 2 0% RH; and work loads mild: 15 m min(-1); moderate: 25 m min(-1)) were studied in chronically cannulated conscious rats. 2. Heat acclimation elicited a decrease in blood pressure before and during the exercise (20 min). Both heat acclimation and training induced bradycardia, alth ough the training effect was more pronounced. During the exercise accl imated rats showed a delayed increase in heart rate compared with that of non-acclimated rats. 3. The results suggest that both heat acclima tion and exercise training increase cardiac efficiency, as demonstrate d by the double product index. This was achieved, however, in differen t ways by the trained and the acclimated rats.