Development and validation of cardiorespiratory fitness prediction equations from 6-minute walk test: the Coronary Artery Risk Development in Adults (CARDIA) study

BACKGROUND: Assessing maximal oxygen consumption (VO2max), the gold standard for assessing cardiorespiratory fitness, is often impractical in large-scale studies. We derived sex-specific VO2 max and graded exercise test duration (GXTd) prediction equations from 6-minute walk test (6MWT) performance. METHODS: Data were from 564 Coronary Artery Risk Development in Young Adults (CARDIA) participants (mean age: 61.5 years; 58% women; 40% Black) who completed the 6MWT and symptom-limited modified Balke treadmill graded exercise test at the Year 35 (2021-2022) follow-up exam. Sex-stratified samples were randomly split (2/3 for training, 1/3 for testing) to derive and evaluate prediction equations. Stepwise linear regression identified predictors of VO2max and GXTd from 6MWT distance. Sex-specific VO2max CARDIA equations were compared with Burr and FRIEND equations. Models' accuracies were evaluated by comparing the predicted values to measured values using Student's t-test and Pearson correlation coefficients (r). Bland-Altman plots used to evaluate agreement between measured and predicted values. RESULTS: Sex-specific VO2max CARDIA equations explained 53% and 57% of the variance in men and women, respectively, with strong correlations between measured and predicted values (r = 0.73 and 0.78). The Burr and FRIEND equations showed larger biases and weaker correlations compared with the CARDIA equations. The GXTd equations explained 59% and 62% of the variance in men and women, with strong correlations (r = 0.71 and 0.72) and no significant mean differences between observed and predicted. CONCLUSIONS: The CARDIA prediction equations for VO2max and GXTd from 6MWT enhance accuracy and accessibility, providing a practical tool for large-scale studies and clinical assessments, particularly in aging populations.