The Effect of Ten Days of Heat Acclimation on Exercise Capacity during Acute Altitude Exposure (4350 m)

Acclimation to one environmental stressor may enhance adaptations to various other stressors in humans; this phenomenon has been described as cross-tolerance. Approaches to induce altitude acclimation in a relatively short time frame are needed, thus the purpose of our study was to examine the effect of heat acclimation on exercise capacity during acute altitude exposure (4350 m). Eight trained men residing at approximately 1600 m performed tests of maximal aerobic capacity (VO2max) at 1600 m and 4350 m, a 16 km time-trial (TT) (4350 m), and a heat tolerance test (1600 m) before and after a 10 d heat acclimation (HA) protocol (40°C, 20% RH). Blood samples were taken at rest preand post-HA to estimate changes in plasma volume with HA. Heat acclimation was achieved, as indicated by a significantly lower post-exercise heart rate (p < 0.01) and rectal temperatures (p = 0.42) on the last versus the first day of HA. Heat acclimation did not alter plasma volume (p = 0.61, 1.8 ± 9.9%) or VO2max at 1600 m (4.02 ± 0.58 L/min vs. 4.03 ± 0.43 L/min, p = 0.88) or at 4350 m (3.40 ± 0.33 L/min vs. 3.46 ± 0.38 L/min, p