What is the term for the difference between the oxygen content of arterial blood arriving at the muscles and the venous blood leaving the muscles?

• A. Haemoglobin
• B. Myoglobin
• C. Mitochondria
• D. A-VO2 Difference

Answer: (D)

The key idea is how much oxygen the muscle extracts from the blood as it passes through. The difference in oxygen content between arterial blood (delivered to the muscles) and venous blood (leaving the muscles) shows how much O2 the muscle has used. This is called the arterial-venous oxygen difference, or A-VO2 difference, and it is calculated as CaO2 minus CvO2. It rises during exercise as muscles require more oxygen. The other terms relate to oxygen’s handling or use (haemoglobin carries O2 in blood, myoglobin stores O2 in muscle, mitochondria use O2 to generate energy) but don’t describe this extraction difference.