During prolonged exercise, the body uses fat as fuel through a process called lipolysis. As glycogen stores deplete, the body shifts its energy source to fatty acids. This transition occurs primarily when exercise lasts longer than 30 minutes at moderate intensity. Oxidation of fatty acids occurs within mitochondria, producing ATP, the energy currency for muscle activity. This efficient fat utilization helps spare glycogen reserves, allowing individuals to maintain endurance during extended activities. Adaptations from consistent training improve the body’s ability to utilize fat, enhancing overall performance and sustainability during long-distance events.