Which substrate pattern best describes fuel use in resting vs trained skeletal muscle during aerobic respiration?

• A. Resting uses fats; trained uses only glucose.
• B. Resting uses glucose only; trained uses protein.
• C. Resting uses mostly fatty acids and glucose; trained muscles have increased mitochondrial density and oxidative capacity, allowing greater fat oxidation and glucose utilization efficiency.
• D. Resting uses mostly proteins; trained uses fats.

Answer: (C)