Author(s): NARANG, B., REMEC, K., KAVCIC, K., KOVACIC, A., LEPLA, M., RABERIN, A., MILLET, G.P., DEBEVEC, T., Institution: JOŽEF STEFAN INSTITUTE, Country: SLOVENIA, Abstract-ID: 910

INTRODUCTION:
Continuous hypoxic exposure can improve exercise capacity, yet the relative contribution of central versus peripheral adaptations remains unresolved [1,2]. This uncertainty is especially relevant in women, who are under-represented in hypoxia research despite physiological differences which may be pertinent to adaptation [3]. We investigated whether ten days of continuous hypoxic residence results in higher exercise capacity via central or peripheral mechanisms in women, and whether such effects depend on oxygen availability.
METHODS:
Healthy, physically active women were randomized to intervention (n=14) or control (n=13). The intervention group lived continuously in normobaric hypoxia (PiO2=98 mmHg; ~3500 m) for ten days, whereas the control group continued normoxic free-living. At baseline and post-intervention, participants completed incremental exercise tests to exhaustion in normoxia and normobaric hypoxia (PiO2=89 mmHg; ~3800 m). Gas exchange, cardiac output, and vastus lateralis tissue oxygenation were recorded via metabolic cart, bioelectrical impedance, and near-infrared spectroscopy, respectively. Outcomes were averaged across the final 20 s pre-exhaustion. Earlobe capillary samples were obtained immediately post-exercise during early active recovery, and analysed for blood gases. Outcomes were analyzed using linear mixed-effects ANCOVA models to test intervention effects (group) and their dependence on exercise condition (group*condition), with baseline values included as covariates. All values represent post-intervention baseline-adjusted estimated marginal means (±95%CI).
RESULTS:
Baseline-adjusted post-intervention peak oxygen uptake was higher in the intervention group compared with control (43±1 vs 40±1 ml/kg/min; group p=0.014) across both exercise conditions (interaction p=0.41). Maximal aerobic power showed a similar group-specific effect (218±7 vs 199±7 W; group p=0.001; interaction p=0.17). The intervention did not affect cardiac output (21±2 vs 20±2 L/min; group p=0.22, interaction p=0.55) or ventilation (116±5 vs 110±5 L/min; group p=0.14, interaction p=0.80). Capillary oxygen tension in early recovery was higher in the intervention group compared with control (100±5 vs 82±6 mmHg; group p<0.001), with no group*condition interaction (p=0.26). Vastus lateralis oxygenation showed a significant interaction (p<0.001), with higher values in the intervention group during normoxic (72±2 vs 69±2%) but not hypoxic (69±2 vs 71±2%) exercise.
CONCLUSION:
Ten days of continuous normobaric hypoxic residence at ~3500 m resulted in higher exercise capacity in women, similarly during normoxic and hypoxic exercise. The absence of clear systemic cardiorespiratory effects, alongside condition-specific changes in muscle oxygenation, indicates that peripheral mechanisms may contribute to these differences.

1. Wagner (1993) Respir Physiol, 93, 221-37.
2. Calbet et al. (2003) Am J Physiol Regul Integr Comp Physiol, 284, 291-303.
3. Raberin et al. (2024) Sports Med, 54, 271-87.