Cardiorespiratory training increases which of the following?

• A. Greater capillary density
• B. Lower capillary density
• C. Unchanged capillary density
• D. Reduced blood flow to muscles

Answer: (A)

Cardiorespiratory training prompts the body to grow more capillaries in skeletal muscle, a process called angiogenesis. This increases capillary density around each muscle fiber, which reduces the diffusion distance for oxygen and nutrients and expands the surface area for exchange. With more capillaries, delivering oxygen to active muscles becomes more efficient, and waste products are removed more rapidly, supporting higher aerobic performance and VO2 max. The other ideas—lower or unchanged capillary density, or reduced blood flow to muscles—don’t reflect how endurance training adapts the circulatory system; during exercise, blood flow to working muscles actually increases to meet the greater demand.