Exercise in the Heat Blunts Improvements in Aerobic Capacity

The exercise-induced rise in PGC-1α is blunted when acute exercise takes place in the heat. However, it is unknown if this alteration has functional implications after heat acclimation and exercise training. Purpose : To determine the impact of three weeks of aerobic exercise training in the heat compared to training in room temperature on thermoregulation, PGC-1α mRNA response, and aerobic capacity. Methods Twenty-three untrained college aged males (age, 24±4 yrs; height, 178±6 cm) were randomly assigned to three weeks of aerobic exercise training in either 33°C (n=12) or 20°C (n=11) environmental temperatures. Results The 20°C training group increased VO2peak from 3.21±0.77 L·min-1 to 3.66±0.78 L·min-1 (p<0.001) while the 33°C training group did not improve (pre, 3.16±0.48 L·min-1; post, 3.28±0.63 L·min-1; p=0.283). PGC-1α increased in response to acute aerobic exercise more in 20°C (6.6±0.7 fold) than 33°C (4.6±0.7 fold, p=0.031) before training, but was not different after training in 20°C (2.4±0.3 fold) or 33°C (2.4±0.5 fold, p=0.999). No quantitative alterations in mitochondrial DNA were detected with training or between temperatures (p>0.05). Conclusions This research indicates that exercise in the heat may limit the effectiveness of aerobic exercise at increasing aerobic capacity. Furthermore, this study demonstrates that heat induced blunting of the normal exercise induced PGC-1α response is eliminated after 3 weeks of heat acclimation.