During exercise, what percentage of blood is directed to active muscles?

• A. 20%
• B. 50%
• C. 90%
• D. 100%

Answer: (C)

Blood flow during exercise is massively redirected to active muscles to satisfy their higher energy needs. This happens because the body reduces blood flow to nonessential areas via sympathetic vasoconstriction while active muscles dilate their vessels in response to metabolites from increased activity. The result is a large portion of the heart’s output goes to the working muscles. At high-intensity exercise, skeletal muscles can receive around 85–90% of cardiac output, far more than at rest, though not 100% since organs like the brain and heart still require perfusion. This substantial shift explains why the percentage directing blood to active muscles is so high during vigorous activity.