What is the primary fuel source utilized during high-intensity exercise?

During high-intensity exercise, the primary fuel source utilized by the body is carbohydrates. This is due to the energy demands that high-intensity activities place on the body's muscle systems, which require quick access to energy. Carbohydrates are stored in the muscles and liver as glycogen, which can be rapidly broken down into glucose and used for energy. This quick conversion is vital for sustaining energy levels during bouts of intense physical activity.

Unlike fats and proteins, carbohydrates provide a more readily available energy source when the body is under stress from high-intensity exercise. Fats, while a significant energy source during lower-intensity and longer-duration activities, take longer to metabolize and are not utilized as effectively when the body requires immediate energy. Proteins primarily serve as building blocks for tissues and are not typically used as a primary energy source during exercise. Vitamins do not provide energy, though they play critical roles in various metabolic processes that can affect overall energy levels and performance.