What effect does endurance training have on capillary density and VO2 max?

• A. No change
• B. Increases capillary density and capillary-to-fiber ratio, improving O2 delivery and VO2 max
• C. Only increases VO2 max without capillary changes
• D. Decreases capillary density

Answer: (B)

Endurance training drives the growth of the capillary network in skeletal muscle, increasing capillary density and the capillary-to-fiber ratio. More capillaries around each muscle fiber shorten the distance oxygen has to diffuse and expand the surface area for exchange, so oxygen delivery to mitochondria improves. At the same time, endurance training boosts the muscle’s oxidative capacity (more mitochondria and oxidative enzymes) and often enhances cardiac output—together these peripheral and central changes raise the maximum rate of oxygen consumption, VO2 max. So you get better oxygen delivery and better use of that oxygen, leading to a higher VO2 max.