Influence of heat stress and acclimation on maximal aerobic power

Thirteen male volunteers performed cycle ergometer maximal oxygen uptake ( \(\dot V_{{\text{O}}_{{\text{2max}}} }\) tests) in moderate (21‡ C, 30% rh) and hot (49‡ C, 20% rh) environments, before and after a 9-day heat acclimation program. This program resulted in significantly decreased (P<0.01) final heart rate (24 bt·min⁻¹) and rectal temperature (0.4‡ C) from the first to last day of acclimation. The \(\dot V_{{\text{O}}_{{\text{2max}}} }\) was lower (P0.05) shown for maximal power output (PO max, watts) between environments either before or after acclimation. The \(\dot V_{{\text{O}}_{{\text{2max}}} }\) was higher (P<0.01) by 4% after acclimation in both environments. Also, PO max was higher (P<0.05) after acclimation in both the moderate (4%) and hot (2%) environments. The reduction in \(\dot V_{{\text{O}}_{{\text{2max}}} }\) in the hot compared to moderate environment was not related to the difference in core temperature at \(\dot V_{{\text{O}}_{{\text{2max}}} }\) between moderate and hot trials, nor was it strongly related with aerobic fitness level. These findings indicate that heat stress, per se, reduced the \(\dot V_{{\text{O}}_{{\text{2max}}} }\) . Further, the reduction in \(\dot V_{{\text{O}}_{{\text{2max}}} }\) due to heat was not affect be state of heat acclimation, the degree of elevation in core temperature, or level of aerobic fitness.