The primary source of energy for the human body during high-intensity exercise is carbohydrates. The body relies heavily on glycogen, which is stored in muscles and the liver, to provide the necessary fuel for quick bursts of activity. Carbohydrates break down into glucose, which can be rapidly converted into energy. When exercising intensely, muscle cells preferentially utilize glucose via aerobic and anaerobic pathways to sustain performance levels. Maintaining adequate carbohydrate intake is crucial for athletes and individuals engaging in high-intensity workouts.