Is a verification phase useful for confirming maximal oxygen uptake in apparently healthy adults? A systematic review and meta-analysis

Abstract

Background: The 'verification phase' has emerged as a supplementary procedure to traditional maximal oxygen uptake (VO2max) criteria to confirm that the highest possible VO2 has been attained during a cardiopulmonary exercise test (CPET).

Objective: To compare the highest VO2 responses observed in different verification phase procedures with their preceding CPET for confirmation that VO2max was likely attained.

Methods: MEDLINE (accessed through PubMed), Web of Science, SPORTDiscus, and Cochrane (accessed through Wiley) were searched for relevant studies that involved apparently healthy adults, VO2max determination by indirect calorimetry, and a CPET on a cycle ergometer or treadmill that incorporated an appended verification phase. RevMan 5.3 software was used to analyze the pooled effect of the CPET and verification phase on the highest mean VO2. Meta-analysis effect size calculations incorporated random-effects assumptions due to the diversity of experimental protocols employed. I2 was calculated to determine the heterogeneity of VO2 responses, and a funnel plot was used to check the risk of bias, within the mean VO2 responses from the primary studies. Subgroup analyses were used to test the moderator effects of sex, cardiorespiratory fitness, exercise modality, CPET protocol, and verification phase protocol.

Results: Eighty studies were included in the systematic review (total sample of 1,680 participants; 473 women; age 19-68 yr.; VO2max 3.3 ± 1.4 L/min or 46.9 ± 12.1 mL·kg-1·min-1). The highest mean VO2 values attained in the CPET and verification phase were similar in the 54 studies that were meta-analyzed (mean difference = 0.03 [95% CI = -0.01 to 0.06] L/min, P = 0.15). Furthermore, the difference between the CPET and verification phase was not affected by any of the potential moderators such as verification phase intensity (P = 0.11), type of recovery utilized (P = 0.36), VO2max verification criterion adoption (P = 0.29), same or alternate day verification procedure (P = 0.21), verification-phase duration (P = 0.35), or even according to sex, cardiorespiratory fitness level, exercise modality, and CPET protocol (P = 0.18 to P = 0.71). The funnel plot indicated that there was no significant publication bias.

Conclusions: The verification phase seems a robust procedure to confirm that the highest possible VO2 has been attained during a ramp or continuous step-incremented CPET. However, given the high concordance between the highest mean VO2 achieved in the CPET and verification phase, findings from the current study would question its necessity in all testing circumstances.

Prospero registration id: CRD42019123540.

Fig 1. Flowchart of the systematic review and meta-analysis according to the PRISMA guidelines.

VO_2max: maximal oxygen uptake.

Fig 2. Forest plot of all studies included in the meta-analysis (k = 54) for the highest VO₂ responses attained in the cardiopulmonary exercise test and verification phase using random effects analyses.

Data are reported as mean differences (MD) adjusted for control data (95% CIs).

Fig 3. Funnel plot assessment of publication bias for the studies investigating the highest VO₂ responses attained in the cardiopulmonary exercise test and verification phase.

Fig 4. Mean differences (95% CIs) between the highest VO₂ responses in the cardiopulmonary exercise test (CPET) and verification phase according to the verification-phase characteristics for intensity (i.e. sub WR_peak vs. supra WR_peak), recovery (i.e. active vs. passive), adoption of criterion threshold (i.e. yes vs. no), timing (performed on the same day vs. a different day to the CPET), and duration (i.e. no longer than 80 s, from 81 to 120 s and longer than 120 s).