Cardiac output x(a-v)O2 difference represents _______, which determines caloric cost of the exercise.

The relationship between cardiac output and the (a-v)O2 difference indeed yields oxygen consumption, commonly denoted as VO2.

Cardiac output is defined as the volume of blood the heart pumps per minute, while the (a-v)O2 difference refers to the difference in oxygen content between the arterial and venous blood. When these two variables are multiplied together, they provide a measure of how much oxygen is being delivered to the tissues and utilized during physical activity. As exercise intensity increases, so does the demand for oxygen by the muscles; consequently, both cardiac output and the (a-v)O2 difference increase to meet this demand.

This measure is crucial because it provides insight into the efficiency of the cardiovascular and muscular systems during exercise, ultimately determining the caloric cost of that activity. A higher VO2 indicates a greater ability to consume oxygen, which is correlated with higher energy expenditure.

Other options such as blood pressure, rate-pressure production, and myocardial demand do not directly represent the efficiency of oxygen utilization in relation to caloric expenditure during physical activity. While they are related to cardiovascular function and overall heart health, they do not specifically quantify how oxygen consumption correlates with energy expenditure during exercise.