Your maximal oxygen consumption score (e.g., VO₂Max or MaxVO₂) is often described as the single best indicator of your cardiovascular fitness.  VO₂Max represents the efficiency of the respiratory (lungs), cardiovascular (heart), circulatory (blood) and muscular systems’ abilities to perform under increased work demands.  It is usually determined either by direct gas consumption measures or predicted from heart rate responses to particular work loads while either walking or jogging on a treadmill or pedaling on the bike. 

See chart on Training Effect (click here)

See for VO2Max norms (click here)

VO₂Max or maximal oxygen consumption measures ones ability to generate work over a prolonged period of time. It is generally considered an oxygen delivery measure (marker). A high maximal capacity to deliver blood (w/oxygen) means there is the potential for more muscles to be active simultaneously during exercise. VO₂ max levels are affected greatly by genetics, decline with age, and are generally much higher in endurance trained individuals. Values range between 40-80 ml/kg/min (in terms relative to body weight) and between 2.5 l/min (smaller people) to 6 l/min. (larger people) in absolute terms.  

More precisely, VO₂ Max best describes the capacity for oxygen delivery and is generally most limited by the maximum pumping capacity of the heart, and the specific arterial development to the active muscles.  In relative terms (relative to an individuals body weight) VO₂ max represents the maximum amount of oxygen per kilogram of weight that a person can use in converting fuel to energy.