ABSTRACT
During physical activity, several organs share the demand for increased perfusion. The heart must supply adequate blood to its own contracting muscle as well as to the contractile apparatus of skeletal muscle. Blood flow to the central nervous system must be maintained and skin perfusion augmented to allow for the dissipation of metabolic heat. During exercise, cardiac output, heart rate, oxygen consumption and systolic blood pressure are linearly related to the intensity of the activity performed. Indeed, during isotonic exercise in a thermally controlled environment, blood flow to skeletal muscle may be increased twentyfive-fold. Such an increase is mediated by means of an increase in cardiac output, a redistribution of the cardiac output and a reduction in muscle vascular resistance. According to the Pick principle ( O2=cardiac output (Q)× arteriovenous difference for oxygen (a-vO2 diff)), oxygen consumption is also elevated by increasing oxygen extraction in the muscle (during exercise).
