Validation, Recalibration, and Predictive Accuracy of Published Vֻ™O2max Prediction Equations for Adults Ages 50 - 96
Journal: Med Sci Sports Exerc
Benjamin T Schumacher et al
PURPOSE: Maximal oxygen uptake (Vֻ™O2max) is the criterion measure of cardiorespiratory fitness (CRF). Lower CRF is a strong predictor of poor health outcomes, including all-cause mortality. Since Vֻ™O2max testing is resource intensive, several non-exercise based Vֻ™O2max prediction equations have been published. We assess these equations' ability to predict measured Vֻ™O2max, recalibrate these equations, and quantify the association of measured and predicted Vֻ™O2max with all-cause mortality.
METHODS: Baltimore Longitudinal Study of Aging participants with valid Vֻ™O2max tests were included (n = 1,080). Using published Vֻ™O2max prediction equations, we calculated predicted Vֻ™O2max and present performance metrics before and after recalibration (deriving new regression estimates by regressing measured Vֻ™O2max on BLSA covariates). Cox proportional hazards models were fit to quantify associations of measured, predicted, and recalibration-predicted values of Vֻ™O2max with mortality.
RESULTS: Mean age and Vֻ™O2max were 69.0 ֲ± 10.4 years and 21.6 ֲ± 5.9 mLֲ·kg-1ֲ·min-1, respectively. The prediction equations yielded root mean squared error values ranging from 4.2-20.4 mLֲ·kg-1ֲ·min-1. After recalibration, these values decreased to 3.9-4.2 mLֲ·kg-1ֲ·min-1. Adjusting for all covariates, all-cause mortality risk was 66% lower for the highest quartile of measured Vֻ™O2max relative to the lowest. Predicted Vֻ™O2max variables yielded similar estimates in unadjusted models but were not robust to adjustment.
CONCLUSIONS: Measured Vֻ™O2max is an extremely strong predictor of all-cause mortality. Several published Vֻ™O2max prediction equations yielded: (1) reasonable performance metrics relative to measured Vֻ™O2max,especially when recalibrated, (2) all-cause mortality hazard ratios similar to those of measured Vֻ™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 Vֻ™O2max.