What macronutrient is primarily used for energy during high-intensity exercise?

Carbohydrates are primarily used for energy during high-intensity exercise due to their ability to be rapidly broken down into glucose. This glucose is then utilized by the body through anaerobic glycolysis, which generates ATP quickly to meet the immediate energy demands of intense physical activity. During high-intensity workouts, the demand for energy exceeds what can be supplied through aerobic metabolism. As a result, carbohydrates serve as the preferred fuel source because they can provide quick bursts of energy without requiring oxygen.

Fats, while they are a significant energy source during prolonged, low to moderate-intensity activities, are metabolized more slowly and are not as efficient for quick energy demands. Proteins can contribute to energy supply, especially in prolonged exercise or when carbohydrate stores are low, but they are not the primary source for energy during high-intensity efforts. Vitamins do not provide energy but are essential for various metabolic processes, making them unrelated to direct energy production during exercise.