Which peripheral adaptation most directly improves oxygen extraction in working muscle?

• A. Increased capillarisation
• B. Increased stroke volume
• C. Increased blood volume
• D. Increased heart rate

Answer: (A)

Increased capillarisation directly enhances how much oxygen a working muscle can extract. More capillaries around muscle fibers increase the surface area for gas exchange and shorten the distance O2 must diffuse from the blood to the mitochondria. This boosts the arteriovenous oxygen difference during exercise, so muscles can take more O2 from each unit of blood.

The other changes mainly increase oxygen delivery rather than extraction. Higher stroke volume, greater blood volume, or a faster heart rate improve how much oxygen-rich blood gets to the muscles, but they don’t directly raise the muscle’s ability to pull oxygen out of the blood. Increased capillarisation is the key peripheral adaptation that directly improves oxygen extraction.