Endurance training increases fat metabolism primarily through which change in the muscle?

• A. Increasing the volume of mitochondria in the muscle fiber
• B. Increasing glycolytic enzyme activity
• C. Decreasing capillary density
• D. Decreasing mitochondrial content

Answer: (A)

Endurance training increases fat metabolism primarily by increasing the volume of mitochondria in the muscle fiber. With more mitochondria, the muscle has a greater oxidative capacity to oxidize fatty acids, supporting sustained, submaximal exercise where fat becomes a larger energy source. This mitochondrial expansion goes hand in hand with boosts in oxidative enzymes and pathways that drive beta-oxidation, effectively allowing more fat to be burned for ATP during prolonged activity.

If glycolytic enzyme activity were increased, the muscle would be better at burning carbohydrates via glycolysis, not fats. Decreasing capillary density would hinder delivery of oxygen and fatty acids to muscle fibers, reducing fat oxidation, while decreasing mitochondrial content would lower oxidative capacity and fat metabolism.