Which factor increases the ability to transport free fatty acids in individuals who undergo endurance training?

• A. Increase in capillary density
• B. Increase in intramuscular triglyceride stores
• C. Decrease in mitochondrial density
• D. Decrease in fatty-acid oxidation enzymes

Answer: (A)

In endurance-trained muscle, the key change that boosts the delivery of free fatty acids from the blood to the muscle fibers is an increase in capillary density. More capillaries per muscle fiber creates a larger surface area and shorter distances for fatty acids to diffuse from the bloodstream into the muscle tissue, making it easier for fats to be delivered and taken up for oxidation during prolonged activity. This improved vascular network enhances the rate at which FFAs can reach the muscle cells where they are needed for energy.

Increasing intramuscular triglyceride stores does not directly raise the bloodstream-to-muscle transport capacity; it simply provides more stored substrate once fatty acids are inside. Conversely, decreasing mitochondrial density or lowering fatty-acid oxidation enzymes would impair fat utilization, not promote transport.