A Focused Review on the Maximal Exercise Responses in Hypo- and Normobaric Hypoxia: Divergent Oxygen Uptake and Ventilation Responses

Abstract

The literature suggests that acute hypobaric (HH) and normobaric (NH) hypoxia exposure elicits different physiological responses. Only limited information is available on whether maximal cardiorespiratory exercise test outcomes, performed on either the treadmill or the cycle ergometer, are affected differently by NH and HH. A focused literature review was performed to identify relevant studies reporting cardiorespiratory responses in well-trained male athletes (individuals with a maximal oxygen uptake, VO2max > 50 mL/min/kg at sea level) to cycling or treadmill running in simulated acute HH or NH. Twenty-one studies were selected. The exercise tests in these studies were performed in HH (n = 90) or NH (n = 151) conditions, on a bicycle ergometer (n = 178) or on a treadmill (n = 63). Altitudes (simulated and terrestrial) varied between 2182 and 5400 m. Analyses (based on weighted group means) revealed that the decline in VO2max per 1000 m gain in altitude was more pronounced in acute NH vs. HH (−7.0 ± 1.4% vs. −5.6 ± 0.9%). Maximal minute ventilation (VEmax) increased in acute HH but decreased in NH with increasing simulated altitude (+1.9 ± 0.9% vs. −1.4 ± 1.8% per 1000 m gain in altitude). Treadmill running in HH caused larger decreases in arterial oxygen saturation and heart rate than ergometer cycling in acute HH, which was not the case in NH. These results indicate distinct differences between maximal cardiorespiratory responses to cycling and treadmill running in acute NH or HH. Such differences should be considered when interpreting exercise test results and/or monitoring athletic training.

High-Intensity Interval Training (HIIT) in Hypoxia Improves Maximal Aerobic Capacity More Than HIIT in Normoxia: A Systematic Review, Meta-Analysis, and Meta-Regression

“…It may be that as VO 2max acutely decreases with increasing altitude [ 56 ], the additional challenge of hypoxia increases the relative intensity of exercise, providing an added stimulus for adaptation. VO 2max declines to a larger extent in acute normobaric hypoxia compared to hypobaric hypoxia, occurring alongside a higher VEmax in hypobaric hypoxia [ 57 ]. Therefore, this may explain the differences in training adaptations between simulated [ 45 , 46 , 48 , 50 , 51 , 52 ] and natural altitude [ 44 , 49 ] studies.…”

Ski Mountaineering: Perspectives on a Novel Sport to Be Introduced at the 2026 Winter Olympic Games

“…This confirms previous comparisons of the effects of hypoxia on elite and recreational endurance athletes ( MacInnis et al, 2015 ) and underlines the importance of this environmental factor ( Faiss et al, 2014 ). Moreover, the responses to normobaric and hypobaric hypoxia while skiing on a treadmill or exercising on a cycle ergometer differ and such differences must be taken into consideration when interpreting the results of exercise tests and/or monitoring athletic training ( Treml et al, 2020 ).…”

How important is V̇O2max when climbing Mt. Everest (8,849 m)?

“…This well-acclimatized climber was characterized by above-average values of maximal voluntary ventilation (MVV), resting lung diffusion capacity for carbon monoxide (DLCO) and DLCO divided by the alveolar volume, and a baseline V� O2max of 65 mL/min/kg (M. Burtscher et al, 2009). Compared to data from well-trained athletes (Treml et al, 2020), his peripheral oxygen saturation (SpO2) during exercise at altitude was maintained at above-average values. Likely due to previous high-altitude acclimatization, maximal exercise testing at a simulated altitude of about 5,000 m revealed a V� O2max reduction by only 25% from baseline, which is comparable to that determined in the OEII study, but is much less compared to data from the AMREE (West et al, 1983) (Fig.…”

“…Sufficient increase in minute ventilation is the most important factor to maintain SpO2 when exercising in hypoxia. As the decrease in SpO2 is strongly associated with the decrease in V� O2max, explaining more than 80% of the V� O2max loss at altitude (Ferretti et al, 1997;Treml et al, 2020;Wehrlin and Hallén, 2006), factors that help to maintain SpO2 are of utmost importance. Beside inappropriate ventilatory acclimatization, low SpO2 values may also result from particular anthropometric characteristics (small lung size), relative hypoventilation and diffusion limitation (Dempsey and Wagner, 1999).…”