Which of the following is a result of prolonged submaximal exercise?

• A. An increase in fat metabolism
• B. A decrease in fat metabolism
• C. Increased carbohydrate oxidation
• D. Decreased blood flow

Answer: (A)

During prolonged submaximal exercise, the body shifts toward using fat as the main fuel to sustain energy and spare glycogen stores. As duration extends, lipolysis increases, delivering more free fatty acids to muscles, and the oxidative capacity of muscle mitochondria improves, allowing greater fat oxidation. This is reflected in the energy mix shifting toward fat, rather than relying heavily on carbohydrates throughout the activity. Blood flow to working muscles remains high to meet oxygen and substrate needs, so a decrease in blood flow isn’t expected. The idea that fat metabolism would decrease or that carbohydrate oxidation would dominate throughout is inconsistent with how energy substrates are managed during long, steady efforts.