High aerobic capacity is necessary to maintain high intensity, wholebody physical exercise for several minutes. Any steps in the chain of the oxygen delivery and mitochondrial consumption can be a rate-limiting factor of the aerobic functional system. Many examples in the field of the pathology and of the performance physiology demonstrate limiting functions in the elements of this function. Central factors (cardiac output, gas exchange in the lungs, oxygen transport capacity of the blood) and the oxidative capability of the muscle play a probably well integrated role in functioning of the system. A couple of interventions--increase by training, adaptation to the circumstances, medicaments etc are available to restore the failing functions which serve as the physiologic basis of the rehabilitation.