VO2Max (maximal aerobic capacity) is the maximum amount of oxygen an individual can utilize during intense, or “maximal” exercise. This is measured as milliliters of oxygen used in one minute per kilogram of body weight (ml/kg/min). It is the best and highest predictor of fitness age and risk for mortality, according to the literature.
Studies have indicated that for every 1 MET (1 MET = 3.5 mL/kg/min) increase in performance, there is a 12% improvement in survival and/or decrease in morbidity and mortality across the board independent of age, gender or cardiovascular status. In other words, there is an inverse relationship between exercise capacity and mortality from any cause.