The Maximal Oxygen Uptake Verification Phase: a Light at the End of the Tunnel?

Commonly performed during an incremental test to exhaustion, maximal oxygen uptake (V̇O_2max) assessment has become a recurring practice in clinical and experimental settings. To validate the test, several criteria were proposed. In this context, the plateau in oxygen uptake (V̇O₂) is inconsistent in its frequency, reducing its usefulness as a robust method to determine "true" V̇O_2max. Moreover, secondary criteria previously suggested, such as expiratory exchange ratios or percentages of maximal heart rate, are highly dependent on protocol design and often are achieved at V̇O₂ percentages well below V̇O_2max. Thus, an alternative method termed verification phase was proposed. Currently, it is clear that the verification phase can be a practical and sensitive method to confirm V̇O_2max; however, procedures to conduct it are not standardized across the literature and no previous research tried to summarize how it has been employed. Therefore, in this review the knowledge on the verification phase was updated, while suggestions on how it can be performed (e.g. intensity, duration, recovery) were provided according to population and protocol design. Future studies should focus to identify a verification protocol feasible for different populations and to compare square-wave and multistage verification phases. Additionally, studies assessing verification phases in different patient populations are still warranted.