Why does the percentage of energy derived from carbohydrates increase as exercise intensity increases?

• A. Higher intensities create greater ATP demand and lower local oxygen availability; carbohydrate oxidation produces ATP more rapidly and can proceed anaerobically, so muscles rely more on carbohydrates.
• B. As intensity rises, body temperature drops and enzymes required for fat oxidation stop working, so only carbohydrate pathways remain active.
• C. Carbohydrates are stored in unlimited amounts and therefore always become the preferred fuel regardless of oxygen availability or metabolic rate.
• D. Fats cannot be mobilized during exercise because hormone-sensitive lipase is inactivated by exercise, forcing total dependence on carbohydrates even at low intensities.

Answer: (A)