Which of the following is a determinant of VO2 Max related to capillarization?

• A. The heart's pumping capacity
• B. The oxygen-carrying capacity of the blood
• C. The capillarization within a muscle
• D. The number of mitochondria and aerobic enzymes

Answer: (C)

Capillarization within a muscle refers to how well the muscle is served by its capillary network, including capillary density and the capillary-to-fiber ratio. This network increases the surface area available for oxygen to diffuse from the blood into the muscle fibers and shortens the distance O2 must travel to reach mitochondria. With more capillaries supplying a muscle, the muscle can extract more oxygen during maximal effort, raising the arteriovenous oxygen difference and, therefore, VO2 max when cardiac output is at its peak. Endurance training boosts capillarization, which helps explain why VO2 max can improve with training even if other factors remain constant. The other options describe determinants not tied to capillary networks: pumping capacity drives cardiac output, oxygen-carrying capacity affects blood oxygen content, and mitochondria/enzyme content governs oxidative capacity inside the muscle.