Influence of heat stress and acclimation on maximal aerobic power

Summary

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 (P<0.01) in the hot environment relative to the moderate environment both before (8%) and after (7%) acclimation with no significant difference (P>0.05) 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.