Exercise cardiorespiratory and thermoregulatory responses in normoxic, hypoxic, and hot environment following 10-day continuous hypoxic exposure

We examined the effects of acclimatization to normodotic hypoxia on aerobic performance and exercise thermoregulatory responses under normoxic, hypoxic, and hot conditions. Twelve men performed tests of maximal oxygen uptake (<(V)over dot>O-2max) in normoxic (NOR), hypoxic [HYP; 13.5% fraction of inspired oxygen (FIO2)], and hot (HE; 35 degrees C, 50% relative humidity) conditions in a randomized manner before and after a 10-day continuous normodotic hypoxic exposure [FIO2 = 13.65 (0.35)%, inspired partial pressure of oxygen = 87 (3) mmHg]. The acclimatization protocol included daily exercise [60 min at 50% hypoxia-specific peak power output (Wpeak)]. All maximal tests were preceded by a steadystate exercise (30 min at 40% Wpeak) to assess the sweating response. Hematological data were assessed from venous blood samples obtained before and after acclimatization. <(V)over dot>O-2max increased by 10.7% (P = 0.002) and 7.9% (P = 0.03) from pre-acclimatization to post acclimatization in NOR and HE, respectively, whereas no differences were found in HYP [pre: 39.9 (3.8) vs. post: 39.4 (5.1) ml.kg(-1).min(-1), P = 1.0]. However, the increase in V. O2max did not translate into increased Wpeak in either NOR or HE. Maximal heart rate and ventilation remained unchanged following acclimatization. = o differences were noted in the sweating gain and thresholds independent of the acclimatization or environmental conditions. Hypoxic acclimatization markedly increased hemoglobin (P < 0.001), hematocrit (P = 0.001), and extracellular HSP72 (P = 0.01). These data suggest that 10 days of normodotic hypoxic acclimatization combined with moderate-intensity exercise training improves <(V)over dot>O-2max in NOR and HE, but does not seem to affect exercise performance or thermoregulatory responses in any of the tested environmental conditions. NEW & NOTEWORTHY The potential crossover effect of hypoxic acclimatization on performance in the heat remains unexplored. Here we show that 10-day continuous hypoxic acclimatization combined with moderate-intensity exercise training can increase maximal oxygen uptake in hot conditions.