During intense exercise, the body primarily utilizes carbohydrates as a key energy source. This macronutrient is converted into glucose, which is utilized for quick energy through the glycolysis process. As exercise intensity increases, the demand for glucose rises, leading the body to rely heavily on stored carbohydrates, mainly in the form of glycogen in muscles and the liver. Once glycogen stores are depleted, the body begins to utilize fats and proteins, but performance may decline. Thus, adequate carbohydrate intake is crucial for sustained energy during high-intensity activities.