National Academy of Sports Medicine (NASM) Performance Enhancement Specialist (PES) certification Practice Exam

The last energy supply to be utilized during prolonged exercise or when other energy sources are depleted is proteins. While muscle glycogen and fatty acids are primary energy sources for activities such as endurance training, and creatine phosphate is used for immediate, short bursts of energy, proteins are typically utilized only after the body has exhausted its carbohydrate and fat stores.

This is because proteins primarily serve as building blocks for muscle tissue and other functions in the body, and their breakdown for energy is not the most efficient method for fueling exercise. The body prefers to preserve protein for its vital roles, using it only when carbohydrate and fat sources are insufficient to meet energy demands, particularly during prolonged periods of fasting or extensive exercise where other fuel sources become depleted.

Understanding the hierarchy of energy sources is crucial for designing effective training and nutrition strategies for athletes, ensuring they have adequate glycogen and fat stores conserved for performance, while protein intake is still critical for recovery and muscle maintenance.