Author(s): DEBEVEC, T., NARANG, B.J., REMEC, K., KAVČIČ, K., KOVAČIČ, A., LEPLA, M., RABERIN, A., MILLET, G.P., Institution: UNIVERSITY OF LJUBLJANA, Country: SLOVENIA, Abstract-ID: 1597

INTRODUCTION:
Continuous hypoxic exposure induces systemic cardiovascular and cellular adaptations that may influence tolerance to other environmental stressors [1]. Whether such adaptations confer cross-adaptation to exercise-induced heat stress – particularly in women who remain under-represented in thermoregulatory research [2] – remains poorly understood [3].
METHODS:
Healthy, active women were studied before and after a ten-day intervention. The experimental group participants (n=14) continuously resided in normobaric hypoxia (PiO2=98 mmHg; ~3500 m), while control participants (n=13) were free-living in normoxia. At baseline and post-intervention, participants cycled for 45 min at 40% maximal aerobic power (Mean±SD; 102±14 W) under heat-stress conditions induced via insulated clothing in a thermoneutral ambient environment (24±2°C ambient temperature, 51±6% relative humidity). Core body temperature (rectal; pill backup) was measured continuously, alongside gas exchange (metabolic cart) and heart rate (chest strap). Capillary blood samples were obtained at rest and during the final three minutes of exercise for blood lactate analysis. Subjective ratings of perceived exertion (RPE; 6 to 20) and thermal sensation (TS; -4 to 4) were recorded in the final minute. Circulating heat shock proteins (HSP) were measured in resting venous blood samples. Data were analysed using two-way ANOVA (group [hypoxia, control] x time [baseline, post]); interaction effects guided interpretation with significance accepted at p<0.05.
RESULTS:
During the 45-min exercise, core temperature rise did not differ between groups or time (hypoxia: 1.2±0.4 to 0.9±0.4°C; control: 1.0±0.5 to 0.9±0.4°C; interaction p=0.083). From pre- to post-, relative oxygen uptake exhibited a significant group x time interaction (p=0.002), decreasing more markedly following hypoxic residence (35±4 vs. 32±2 ml/kg/min) than in control (31±4 vs. 29±3 ml/kg/min). Similar interaction effects indicated greater hypoxia-group decreases for heart rate (173±16 to 159±15 bpm vs. 163±13 to 160±11 bpm, interaction p<0.001), blood lactate concentration (4.5±2.5 to 1.8±1.6 mmol/L vs. 2.5±0.9 to 2.0±1.1 mmol/L, interaction p<0.001), RPE (14.3±1.9 to 12.1±1.5 vs. 13.3±2.2 to 13.0±2.2, interaction p=0.001) and TS (3.2±1.0 to 2.2±1.2 vs. 3.0±0.8 to 2.8±0.9, interaction p=0.014). Circulating HSP72 and HSP90a concentrations were unaffected by hypoxic residence (interaction p=0.459 and 0.405, respectively).
CONCLUSION:
Overall, ten days of continuous normobaric hypoxic residence attenuated the metabolic, cardiovascular, and perceptual responses to exercise heat stress in women, without a corresponding reduction in core temperature rise. This pattern suggests enhanced tolerance to sustained exercise under thermal stress following hypoxic residence, potentially mediated by peripheral thermoregulatory adaptations.
1. Sotiridis et al. (2022) Am J Physiol Regu
2. Hutchins et al. (2021) Sports Med Open
3. Sotiridis et al. (2018) J Appl Physiol