The primary source of energy for high-intensity workouts is carbohydrates. During intense physical activities, the body relies on stored glycogen in muscles and liver to fuel performance. Carbohydrates provide quick energy, allowing athletes to sustain their effort levels for optimal performance. While fats are used during lower-intensity exercise, carbohydrates are essential for high-intensity workouts due to their efficiency in generating energy rapidly, making them vital for athletes and individuals engaging in demanding training sessions.