What does the arterio-venous oxygen difference (VO2difference) measure?

The arterio-venous oxygen difference (VO2difference) specifically measures how much oxygen is extracted from the blood by the tissues, particularly muscles, during physical activity. It reflects the difference between the oxygen content in arterial blood (which carries oxygen from the lungs to the body) and the oxygen content in venous blood (which returns to the heart after delivering oxygen to the tissues) after it has been used by the muscles.

A higher VO2difference indicates that the muscles are utilizing more oxygen for aerobic metabolism, which is crucial during exercise. This metric is essential for evaluating the efficiency of oxygen usage in the body and assessing an individual's aerobic fitness level. In contrast, the other options relate to different physiological functions unrelated to the direct measurement of oxygen extraction in the muscles.