Influence of short-term aerobic training and hydration status on tolerance during uncompensable heat stress.

The purpose of the present study was to determine the separate and combined effects of a short-term aerobic training program and hypohydration on tolerance during light exercise while wearing nuclear, biological, and chemical protective clothing in the heat (40 degrees C, 30% relative humidity). Males of moderate fitness [< 50 ml x kg(-1) x min(-1) maximal O2 consumption (VO2max)] were tested while euhydrated or hypohydrated by approximately 2% of body weight through exercise and fluid restriction the day preceding the trials. Tests were conducted before and after either a 2-week program of daily aerobic training (1 h treadmill exercise at 65% VO2max for 12 days; n = 8) or a control period (n = 7), which had no effect on any measured variable. The training increased VO2max by 6.5%, while heart rate (f(c)) and the rectal temperature (T(re)) rise decreased during exercise in a thermoneutral environment. In the heat, training resulted in a decreased skin temperature and increased sweat rate, but did not affect f(c), T(re) or tolerance time (TT). In both training and control groups, hypohydration significantly increased T(re) and f(c) and decreased the TT. It was concluded that the short-term aerobic training program had no benefit on exercise-heat tolerance in this uncompensable heat stress environment.