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°C, 30% relative humidity). Males of moderate fitness [<50 ml · kg⁻¹ · min⁻¹ maximal O₂ consumption (V˙O_{2 max} )] were tested while euhydrated or hypohydrated by ≈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% V˙O_{2 max} for 12 days; n = 8) or a control period (n = 7), which had no effect on any measured variable. The training increased V˙O_{2 max} 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. Accepted: 12 November 1997