Quantifying assumptions underlying peak oxygen consumption equations across the body mass spectrum

The goal of this study is to quantify the assumptions associated with the Wasserman-Hansen (WH) and Fitness Registry and the Importance of Exercise: A National Database (FRIEND) predictive peak oxygen consumption (pVO₂) equations across body mass index (BMI). Assumptions in pVO₂ for both equations were first determined using a simulation and then evaluated using exercise data from the Stanford Exercise Testing registry. We calculated percent-predicted VO₂ (ppVO₂) values for both equations and compared them using the Bland–Altman method. Assumptions associated with pVO₂ across BMI categories were quantified by comparing the slopes of age-adjusted VO₂ ratios (pVO₂/pre-exercise VO₂) and ppVO₂ values for different BMI categories. The simulation revealed lower predicted fitness among adults with obesity using the FRIEND equation compared to the WH equations. In the clinical cohort, we evaluated 2471 patients (56.9% male, 22% with BMI >30 kg/m², pVO₂ 26.8 mlO₂/kg/min). The Bland–Altman plot revealed an average relative difference of −1.7% (95% CI: −2.1 to −1.2%) between WH and FRIEND ppVO₂ values with greater differences among those with obesity. Analysis of the VO₂ ratio to ppVO₂ slopes across the BMI spectrum confirmed the assumption of lower fitness in those with obesity, and this trend was more pronounced using the FRIEND equation. Peak VO₂ estimations between the WH and FRIEND equations differed significantly among individuals with obesity. The FRIEND equation resulted in a greater attributable reduction in pVO₂ associated with obesity relative to the WH equations. The outlined relationships between BMI and predicted VO₂ may better inform the clinical interpretation of ppVO₂ values during cardiopulmonary exercise test evaluations.