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

• We examined the effects of acclimatization to normobaric hypoxia on aerobic performance and exercise thermoregulatory responses under normoxic, hypoxic and hot conditions. Twelve males performed tests of maximal oxygen uptake (V̇O2max) in normoxic (NOR), hypoxic (13.5% FiO2; HYP) and hot (35℃, 50% RH; HE) conditions in a randomized manner before and after a 10-day continuous normobaric hypoxic exposure (FiO2 = 13.65(0.35)%, PiO2 = 87(3) mmHg). The acclimatization protocol included daily exercise (60min @ 50% hypoxia-specific peak power output, Wpeak). All maximal tests were preceded by a steady-state exercise (30 min at 40% Wpeak) to assess the sweating response. Hematological data were assessed from venous blood samples obtained before and after acclimatization. V̇O2max increased by 10.7% (P = 0.002) and 7.9% (P = 0.03) from pre- 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 V̇O2max did not translate into increased Wpeak in either NOR or HE. Maximal heart rate and ventilation remained unchanged following acclimatization. Νo 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 normobaric hypoxic acclimatization combined with moderate-intensity exercise training improves V̇O2max in NOR and HE, but does not seem to affect exercise performance or thermoregulatory responses in any of the tested environmental conditions.

Nyckelord

acclimatization

cross-adaptation

exercise performance

hypoxia

thermoregulation

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