Carbohydrates contribute to energy levels during prolonged exercise by serving as the primary fuel source for muscles. When engaging in endurance activities, the body breaks down carbohydrates into glucose, which provides quick energy. This is particularly important during high-intensity workouts that last extended periods. Inadequate carbohydrate supply can lead to decreased performance, early fatigue, and a drop in endurance. Therefore, athletes often emphasize proper carbohydrate intake before and during prolonged exercise to sustain energy levels and optimize performance.