Normal hemodynamic, ventilatory, and metabolic response to exercise.

An integrated response to exercise must occur among the cardiovascular, pulmonary, and regional circulations. The increased oxygen inspired by the lungs must be transported through the circulation and taken up by the exercising muscles. The cardiovascular adaptations to maximal exercise include an increase in cardiac output (predominantly by a rise in the heart rate) and a widening of the arteriovenous oxygen difference. In the regional circulations, there are increases in both the rate of skeletal blood flow and the rate of arteriovenous oxygen extraction. Pulmonary ventilation also increases by a rise in both the respiratory rate and tidal volume. The fuel necessary for maximal exercise is derived initially from accelerated breakdown of muscle glycogen and later by an increase in the hepatic glucose production. A combination of aerobic and anaerobic metabolism generates the adenosine triphosphate necessary for muscular contraction.