Validation, Recalibration, and Predictive Accuracy of Published VO_2maxPrediction Equations for Adults Ages 50-96 Yr

Purpose Maximal oxygen uptake (V O 2max) is the criterion measure of cardiorespiratory fitness. Lower cardiorespiratory fitness is a strong predictor of poor health outcomes, including all-cause mortality. Because V O 2max testing is resource intensive, several non-exercise-based V˙O2max prediction equations have been published. We assess these equations' ability to predict measured V˙O2max, recalibrate these equations, and quantify the association of measured and predicted V˙O2max with all-cause mortality. Methods Baltimore Longitudinal Study of Aging participants with valid V˙O2max tests were included (n = 1080). Using published V˙O2max prediction equations, we calculated predicted V˙O2max and present performance metrics before and after recalibration (deriving new regression estimates by regressing measured V˙O2max on Baltimore Longitudinal Study of Aging covariates). Cox proportional hazards models were fit to quantify associations of measured, predicted, and recalibration-predicted values of V˙O2max with mortality. Results Mean age and V˙O2max were 69.0 ± 10.4 yr and 21.6 ± 5.9 mL·kg-1·min-1, respectively. The prediction equations yielded root mean square error values ranging from 4.2 to 20.4 mL·kg-1·min-1. After recalibration, these values decreased to 3.9-4.2 mL·kg-1·min-1. Adjusting for all covariates, all-cause mortality risk was 66% lower for the highest quartile of measured V˙O2max relative to the lowest. Predicted V˙O2max variables yielded similar estimates in unadjusted models but were not robust to adjustment. Conclusions Measured V˙O2max is an extremely strong predictor of all-cause mortality. Several published V˙O2max prediction equations yielded the following: 1) reasonable performance metrics relative to measured V˙O2max especially when recalibrated, and 2) all-cause mortality hazard ratios similar to those of measured V˙O2max, especially when recalibrated, yet 3) were not robust to adjustment for basic demographic covariates likely because these were used in the equation for predicted V˙O2max.