How does the body primarily utilize energy during prolonged exercise?

During prolonged exercise, the body primarily utilizes fats as a source of energy. This occurs after the initial phase of exercise, where carbohydrates are more readily used. As the duration of the exercise increases, the body's glycogen stores become depleted, leading to a greater reliance on fat stores.

Fats provide a substantial energy reserve, and their metabolism yields a high number of calories when oxidized, making them suitable for sustained, lower-intensity activities and endurance exercises. This shift from carbohydrates to fats as a primary energy source is crucial for maintaining energy levels over long periods, which is especially vital in endurance sports and activities.

Additionally, while proteins can be used for energy, they are not a primary source during exercise; their role is more significant in muscle repair and development rather than immediate energy production. Creatine is also not a primary energy source for prolonged exercise, as it mainly supports short bursts of high-intensity activity. Thus, fat metabolism becomes pivotal in sustaining energy during extended physical activities.