A framework for estimating cardiorespiratory fitness from diverse exercise tests

Comparisons of cardiorespiratory fitness across population studies are hindered by a lack of standardisation in exercise testing and reliance on estimation methods that assume steady-state exercise. We developed a generalised framework that standardises maximal oxygen consumption estimation by harmonising dynamic heart rate modelling with individualised calibration of exercise energetics. We constructed and evaluated the framework using submaximal and maximal tests (treadmill walking and running, cycle ergometer, stepping, overground walking) from 911 adults. Agreement between framework estimates and directly measured was strong (non-significant bias, Pearson’s r=0.80). We then applied both framework and canonical methods to estimate in 11,307 UK Fenland Study adults and examined associations with cardiometabolic risk. Framework-estimated was more strongly associated with blood glucose, fasting insulin, and high-density lipoprotein cholesterol (combined risk factor model AIC=125,743) compared to canonical estimates (AIC=129,227). The framework standardises fitness estimation across diverse tests, yielding a more reliable and comparable biomarker of cardiometabolic health.