Which statement best describes the effect of increased capillary density on endurance performance?

Which statement best describes the effect of increased capillary density on endurance performance?

• A. It reduces diffusion distance but does not affect oxygen delivery.
• B. It increases heart size dramatically.
• C. It decreases mitochondria count in muscle fibers.
• D. It improves O2 delivery and waste removal, delaying fatigue.

Answer: (D)

Increasing capillary density in muscle enhances the delivery of oxygen to working fibers and speeds the removal of metabolic wastes. More capillaries mean oxygen has a shorter journey from blood to mitochondria and more surface area for exchange, so mitochondria can produce ATP aerobically more efficiently during sustained exercise. Better oxygen supply and quicker waste removal (like lactate and H+) help maintain pH and energy production, which delays fatigue and supports longer endurance performance. The other statements don’t fit because capillary density doesn’t cause dramatic heart enlargement, nor does it reduce the number of mitochondria; rather, it supports oxidative metabolism. It also does affect oxygen delivery, so claiming it wouldn’t is inaccurate.

Increasing capillary density in muscle enhances the delivery of oxygen to working fibers and speeds the removal of metabolic wastes. More capillaries mean oxygen has a shorter journey from blood to mitochondria and more surface area for exchange, so mitochondria can produce ATP aerobically more efficiently during sustained exercise. Better oxygen supply and quicker waste removal (like lactate and H+) help maintain pH and energy production, which delays fatigue and supports longer endurance performance.

The other statements don’t fit because capillary density doesn’t cause dramatic heart enlargement, nor does it reduce the number of mitochondria; rather, it supports oxidative metabolism. It also does affect oxygen delivery, so claiming it wouldn’t is inaccurate.