The Role of Body Habitus in Predicting Cardiorespiratory Fitness: The FRIEND Registry

This study aimed to validate and cross-validate a non-exercise prediction model from a large and apparently healthy US cohort of individuals who underwent an analysis of body habitus (waist circumference (WC) and body mass index (BMI)) with measured CRF. The large cohort (5 030 individuals) was split into validation (4 030) and cross-validation (1 000) groups, whereby waist circumference and maximal aerobic capacity (VO2max) were assessed by rigorously approved laboratories. VO2max was estimated in 2 multiple regression equations using age, sex and either WC (r=0.77; standard error of the estimate (SEE) 6.70 mLO2∙kg(-1)∙min(-1)) or BMI (r=0.76; SEE 6.89 mLO2∙kg(-1)∙min(-1)).Cross-validation yielded similar results. However, as VO2max increased, there was increased bias, suggesting VO2max may be underestimated at higher values. Both WC and BMI prediction models yielded similar findings, with WC having a slightly smaller SEE. These measures of body habitus appear to be adequate in predicting CRF using non-exercise parameters, even without a measure of physical activity. Caution should be taken when using these equations in more fit individuals.