Reference equations for peak oxygen uptake for treadmill cardiopulmonary exercise tests based on the NHANES lean body mass equations, a FRIEND registry study

ABSTRACT BACKGROUND Cardiorespiratory fitness (CRF), measured by peak oxygen uptake (VO 2 peak), is a strong predictor of mortality. Despite its widespread clinical use, current reference equations for VO 2 peak show distorted calibration in obese individuals. Using data from the Fitness Registry and the Importance of Exercise National Database (FRIEND), we sought to develop novel reference equations for VO 2 peak better calibrated for overweight/obese individuals - in both males and females, by considering body composition metrics. METHODS AND RESULTS Graded treadmill tests from 6,836 apparently healthy individuals were considered in data analysis. We used the National Health and Nutrition Examination Survey equations to estimate lean body mass (eLBM) and body fat percentage (eBF). Multivariable regression was used to determine sex-specific equations for predicting VO 2 peak considering age terms, eLBM and eBF. The resultant equations were expressed as VO 2 peak (male) = 2633.4 + 48.7✕eLBM (kg) - 63.6✕eBF (%) - 0.23✕Age 2 (R 2 =0.44) and VO 2 peak (female) = 1174.9 + 49.4✕eLBM (kg) - 21.7✕eBF (%) - 0.158✕Age 2 (R 2 =0.53). These equations were well-calibrated in subgroups based on sex, age and body mass index (BMI), in contrast to the Wasserman equation. In addition, residuals for the percent-predicted VO 2 peak (ppVO 2 ) were stable over the predicted VO 2 peak range, with low CRF defined as < 70% ppVO 2 and average CRF defined between 85-115%. CONCLUSIONS The derived VO 2 peak reference equations provided physiologically explainable and were well-calibrated across the spectrum of age, sex and BMI. These equations will yield more accurate VO 2 peak evaluation, particularly in obese individuals.