Altitude training is frequently used by elites athletes. Several hypoxic methods have been developed to improve sea-level performances and the Live High-Train Low approach, where athletes live and sleep at altitudes between 2200 and 2500 m and train under 1200 m is recognized as effective. Recent research focused on the potential differences between normobaric (NH) and hypobaric hypoxia (HH), i.e. simulated and real altitudes. Slight physiological differences have been found between either acute or chronic hypoxic exposure in NH and HH. Taken together, these differences intimate larger physiological responses to hypoxic exposure in "terrestrial" (i.e. HH) versus "simulated" altitudes (i.e. NH). However, there is not a sufficient body of knowledge to confirm if one hypoxic condition could induce larger performance enhancement than the other, either during or after acute hypoxic exposure or altitude camps (i.e. chronic hypoxic exposure). Many confounding factors and the large inter- individual variability to hypoxic exposure make the comparison very challenging.
Consequently, we first designed a crossover study to assess these potential differences and confirmed for the first time with direct comparison on the same subjects that HH induces different physiological adaptations compared to NH during a 3 weeks LHTL camp. However, physiological differences were not clinically sufficient to induce sea-level performance disparities. Secondly, we showed that acute high altitude hypobaric hypoxia (24h, 3450 m) is more demanding than normobaric hypoxia and induces larger performance impairments on a 250-kJ cycle time trial. Finally, our work demonstrated that sleep is further disturbed in HH compared to NH in both acute and chronic hypoxia.
As previously suggested, HH seems to be a more stressful stimulus than NH at iso-PiO2. Consequently, NH and HH should not be used interchangeably and the main factor seems to be the lower peripheral oxygen saturation in HH at rest, as well as during exercise.