The maximal oxygen consumption VO2max is the maximum capacity of an individual's body to transport and utilize oxygen during incremental exercise.The higher the value the higher the aerobic capacity of the athlete.This value is expressed in ml/kg/min (milliliters per kilogram of body weight per minute). The VO2max can be measured directly through the use of sophisticated and expensive equipment, requiring highly skilled staff, or through indirect methods, accessible to all on the cardio machines (usually used bike or run). These latter methods exploit the correlation between VO2max and HRMax, which is the maximum heart rate achieved during maximum physical exertion. The correlation is now accepted as follows :

%VO2max	%HRmax Karvonen
35	50
48	60
60	70
73	80
86	90
100	100

The maximum heart rate can be derived in a theoretical formula by Anstrad (220 - age). By detecting the heartbeat during exercise is possible to know what kind of work we are running: Aerobic 50-60% of VO2max, Aerobic - Anaerobic 65-70%, 75-80% Anaerobic. In this way we will know if we're always using the fatty deposits (aerobic workout), muscle/liver glycogen (Anaerobic work) or both (work Aerobic-Anaerobic). To determine the percentage of training Heart Rate using 2 formulas, the formula of Cooper and the formula of Karvonen.Cooper's formula determines the % of HR max obtained with Anstrad % (220-age), not taking into account differences between individuals. Karvonen instead uses the resting heart rate , derived from an average of 3 measurements of heart rate in the morning just wake up.The formula is (% ((220-age)-HR rest)) + HR rest. Karvonen's formula is certainly more accurate than Cooper and is the that most approaches to the percentages of VO2max as shown in the table above. Here it is possible to derive the maximum percentage of the HR workout consider:

%HRmax Karvonen	"Fuel" type
less than 65%	Aerobic
65-75%	Aerobic-Anaerobic
80-90%	Anaerobic