Impact of the administration type for normobaric hypoxia on the maximal aerobic capacity: A systematic review and meta-analysis

Normobaric hypoxia (NH) is a frequent strategy for training under hypoxic conditions that can be administered through different equipment, including face masks or hypoxic chambers/tents. Nonetheless, the versatility of administration methods may influence the outcomes.

Web of Science, Scopus, SPORTDiscus and PubMed/MEDLINE were searched to identify studies assessing the effect of NH administered by face mask or chamber/tent equipment on maximal oxygen uptake ( $\dot{\mathrm{V}}$O2max) after a training period. An overall meta-analysis and sub-analysis of total program session volume (low, moderate, high), participants’ training level (trained, active, sedentary), and the severity of hypoxia (moderate, severe) were conducted to explore the effects of the NH-administration system.

Eighteen studies were included. Compared with normoxia, NH showed a moderate global improvement in $\dot{\mathrm{V}}$O2max (standardized mean difference [SMD] ​= ​0.74; p ​= ​0.06), favoring the chamber/tent (SMD ​= ​1.30; p ​< ​0.01) over the face mask. Sub-analysis showed a very large effect in support of the hypoxic chamber/tent among sedentary individuals and training programs with a high volume of sessions. Severe hypoxia did not yield conclusive findings in $\dot{\mathrm{V}}$O2max improvements, although the chamber/tent proved more effective (SMD ​= ​1.42; p ​< ​0.01) than the face mask under moderate hypoxia.

Chambers/tents may slightly accentuate the benefit of NH on aerobic performance, particularly in participants with limited training experience following a high volume of sessions under moderate hypoxia. However, the variability of sub-analysis factors (session volume, participants' training level, and methodological approaches) between studies using each type of hypoxia-generating equipment may influence this result.