The VO2 max can be estimated using direct or indirect methods. VO2 max is expressed as liters/min as an absolute value or in milliliters /kg/min as relative VO2 max.
VO2 max is the maximum amount of oxygen a person can intake and the value does not change despite an increase in workload over time period. The maximal oxygen consumption attained during a graded maximal exercise to voluntary exhaustion has long since been considered by the World Health Organization as the single best indicator of cardio respiratory fitness.