No ergogenic effects of a 10-day combined heat and hypoxic acclimation on aerobic performance in normoxic thermoneutral or hot conditions

PurposeHypoxic acclimation enhances convective oxygen delivery to the muscles. Heat acclimation-elicited thermoregulatory benefits have been suggested not to be negated by adding daily exposure to hypoxia. Whether concomitant acclimation to both heat and hypoxia offers a synergistic enhancement of aerobic performance in thermoneutral or hot conditions remains unresolved.MethodsEight young males (V</mml:mover>O2max: 51.64.6 mL min(-1) kg(-1)) underwent a 10-day normobaric hypoxic confinement (FiO2=0.14) interspersed with daily 90-min normoxic controlled hyperthermia (target rectal temperature: 38.5 degrees C) exercise sessions. Prior to, and following the confinement, the participants conducted a 30-min steady-state exercise followed by incremental exercise to exhaustion on a cycle ergometer in thermoneutral normoxic (NOR), thermoneutral hypoxic (FiO2=0.14; HYP) and hot (35 degrees C, 50% relative humidity; HE) conditions in a randomized and counterbalanced order. The steady-state exercise was performed at 40% NOR peak power output (W-peak) to evaluate thermoregulatory function. Blood samples were obtained from an antecubital vein before, on days 1 and 10, and the first day post-acclimation.ResultsV<mml:mo></mml:mover>O2<mml:mo movablelimits="true">max and ventilatory thresholds were not modified in any environment following acclimation. W-peak increased by 6.3 +/- 3.4% in NOR and 4.0 +/- 4.9% in HE, respectively. The magnitude and gain of the forehead sweating response were augmented in HE post-acclimation. EPO increased from baseline (17.8 +/- 7.0 mIU mL(-1)) by 10.7 +/- 8.8 mIU mL(-1) on day 1 but returned to baseline levels by day 10 (15.7 +/- 5.9 mIU mL(-1)).DiscussionA 10-day combined heat and hypoxic acclimation conferred only minor benefits in aerobic performance and thermoregulation in thermoneutral or hot conditions. Thus, adoption of such a protocol does not seem warranted.