Semper Fit Basic Fitness Course Exam 2025 – Complete Practice Resource

In prolonged aerobic activity, the primary energy source utilized by the body is fat. When engaging in activities such as long-distance running, cycling, or swimming, the body relies on aerobic metabolism, which primarily uses fats as fuel after the initial glycogen stores (from carbohydrates) are depleted.

Fats provide a more abundant energy source for sustained activity since they yield more energy per gram compared to carbohydrates and proteins. During prolonged exercise, the efficiency of fat oxidation increases, leading to a greater reliance on fat as exercise duration extends. The body can access and oxidize fat stores more effectively in an aerobic environment where oxygen is available, supporting endurance performance.

Carbohydrates do play a significant role, especially in the early stages of exercise, but when the activity extends into longer durations, fats become the dominant energy source. Proteins are generally not utilized directly for energy unless under extreme circumstances, while water is essential for hydration and temperature regulation rather than a direct energy source.