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Eur J Appl Physiol. 2019 Sep 25. doi: 10.1007/s00421-019-04215-5. [Epub ahead of print]

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

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Department of Automation, Biocybernetics and Robotics, Jozef Stefan Institute, Jamova 39, SI-1000, Ljubljana, Slovenia.
Jozef Stefan International Postgraduate School, Ljubljana, Slovenia.
Section of Sport Medicine and Biology of Exercise, School of Physical Education and Sport Science, National and Kapodistrian University of Athens, Athens, Greece.
Department of Automation, Biocybernetics and Robotics, Jozef Stefan Institute, Jamova 39, SI-1000, Ljubljana, Slovenia.



Hypoxic 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.


Eight young males ([Formula: see text]: 51.6 ± 4.6 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 °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 °C, 50% relative humidity; HE) conditions in a randomized and counterbalanced order. The steady-state exercise was performed at 40% NOR peak power output (Wpeak) to evaluate thermoregulatory function. Blood samples were obtained from an antecubital vein before, on days 1 and 10, and the first day post-acclimation.


[Formula: see text] and ventilatory thresholds were not modified in any environment following acclimation. Wpeak 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).


A 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.


Aerobic performance; Heat acclimation; Hypoxic acclimation; Thermoregulation


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