What is the role of capillarisation in HIIT adaptations?

• A. Reduces blood flow to muscles
• B. Improves oxygen delivery to working muscles during repeated high-intensity bouts
• C. Increases resting heart rate permanently
• D. Decreases capillary density

Answer: (B)

Capillarisation means more capillaries around muscle fibers, which increases the surface area for oxygen and nutrient exchange. In HIIT, the repeated high-intensity efforts create strong metabolic and shear stress that promotes new capillary formation. This makes oxygen easier to deliver to working muscles and helps remove waste products between and after bouts, improving performance during repeated high-intensity work and speeding recovery. So the role of capillarisation in HIIT adaptations is to improve oxygen delivery to working muscles during repeated high-intensity bouts. The other ideas don’t fit: capillarisation enhances, not reduces, blood flow efficiency; resting heart rate changes are not driven by capillary density; and capillary density does not decrease with training.