Confirming the attainment of maximal oxygen uptake within special and clinical groups: A systematic review and meta-analysis of cardiopulmonary exercise test and verification phase protocols
Authors: Costa Victor A. B. , Midgley Adrian W. , Baumgart Julia K. , Carroll Sean , Astorino Todd A. , Schaun Gustavo Z. , Fonseca Guilherme F. , Cunha Felipe A. 
Published: March 2024

Background and aim
A plateau in oxygen uptake (V˙O2) during an incremental cardiopulmonary exercise test (CPET) to volitional exhaustion appears less likely to occur in special and clinical populations. Secondary maximal oxygen uptake (V˙O2max) criteria have been shown to commonly underestimate the actual V˙O2max. The verification phase protocol might determine the occurrence of ‘true’ V˙O2max in these populations. The primary aim of the current study was to systematically review and provide a meta-analysis on the suitability of the verification phase for confirming ‘true’ V˙O2max in special and clinical groups. Secondary aims were to explore the applicability of the verification phase according to specific participant characteristics and investigate which test protocols and procedures minimise the differences between the highest V˙O2 values attained in the CPET and verification phase.

Methods
Electronic databases (PubMed, Web of Science, SPORTDiscus, Scopus, and EMBASE) were searched using specific search strategies and relevant data were extracted from primary studies. Studies meeting inclusion criteria were systematically reviewed. Meta-analysis techniques were applied to quantify weighted mean differences (standard deviations) in peak V˙O2 from a CPET and a verification phase within study groups using random-effects models. Subgroup analyses investigated the differences in V˙O2max according to individual characteristics and test protocols. The methodological quality of the included primary studies was assessed using a modified Downs and Black checklist to obtain a level of evidence. Participant-level V˙O2 data were analysed according to the threshold criteria reported by the studies or the inherent measurement error of the metabolic analysers and displayed as Bland-Altman plots.

Results
Forty-three studies were included in the systematic review, whilst 30 presented quantitative information for meta-analysis. Within the 30 studies, the highest mean V˙O2 values attained in the CPET and verification phase protocols were similar (mean difference = -0.00 [95% confidence intervals, CI = -0.03 to 0.03] L·min-1, p = 0.87; level of evidence, LoE: strong). The specific clinical groups with sufficient primary studies to be meta-analysed showed a similar V˙O2max between the CPET and verification phase (p > 0.05, LoE: limited to strong). Across all 30 studies, V˙O2max was not affected by differences in test protocols (p > 0.05; LoE: moderate to strong). Only 23 (53.5%) of the 43 reviewed studies reported how many participants achieved a lower, equal, or higher V˙O2 value in the verification phase versus the CPET or reported or supplied participant-level V˙O2 data for this information to be obtained. The percentage of participants that achieved a lower, equal, or higher V˙O2 value in the verification phase was highly variable across studies (e.g. the percentage that achieved a higher V˙O2 in the verification phase ranged from 0% to 88.9%).

Conclusion
Group-level verification phase data appear useful for confirming a specific CPET protocol likely elicited V˙O2max, or a reproducible V˙O2peak, for a given special or clinical group. Participant-level data might be useful for confirming whether specific participants have likely elicited V˙O2max, or a reproducible V˙O2peak, however, more research reporting participant-level data is required before evidence-based guidelines can be given.

Trial registration
PROSPERO (CRD42021247658) https://www.crd.york.ac.uk/prospero.