Background Maximal oxygen uptake (VO₂max) is a powerful predictor of health outcomes. Valid and portable reference values are integral to interpreting measured VO₂max; however, available reference standards lack validation and are specific to exercise mode. This study was undertaken to develop and validate a single equation for normal standards for VO₂max for the treadmill or cycle ergometer in men and women. Methods Healthy individuals ( N = 10,881; 67.8% men, 20-85 years) who performed a maximal cardiopulmonary exercise test on either a treadmill or a cycle ergometer were studied. Of these, 7617 and 3264 individuals were randomly selected for development and validation of the equation, respectively. A Brazilian sample (1619 individuals) constituted a second validation cohort. The prediction equation was determined using multiple regression analysis, and comparisons were made with the widely-used Wasserman and European equations. Results Age, sex, weight, height and exercise mode were significant predictors of VO₂max. The regression equation was: VO₂max (ml kg^-1 min^-1) = 45.2 - 0.35*Age - 10.9*Sex (male = 1; female = 2) - 0.15*Weight (pounds) + 0.68*Height (inches) - 0.46*Exercise Mode (treadmill = 1; bike = 2) ( R = 0.79, R²= 0.62, standard error of the estimate = 6.6 ml kg^-1 min^-1). Percentage predicted VO₂max for the US and Brazilian validation cohorts were 102.8% and 95.8%, respectively. The new equation performed better than traditional equations, particularly among women and individuals ≥60 years old. Conclusion A combined equation was developed for normal standards for VO₂max for different exercise modes derived from a US national registry. The equation provided a lower average error between measured and predicted VO₂max than traditional equations even when applied to an independent cohort. Additional studies are needed to determine its portability.

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