What is the primary nutrient source that the body relies on for immediate energy during intense exercise?

During intense exercise, the body primarily relies on carbohydrates as its immediate source of energy. When muscles are engaged in high-intensity activities, they require a rapid supply of energy that can be quickly mobilized. Carbohydrates, specifically in the form of glucose, are stored in the muscles and liver as glycogen. During exercise, glycogen is broken down into glucose, which is then utilized to produce ATP (adenosine triphosphate), the energy currency of the cell.

This process is efficient for high-intensity efforts because carbohydrates can be metabolized more quickly than fats or proteins, which is crucial when the body needs immediate energy. While fats can provide energy during lower intensity or longer-duration exercises, they require more time to break down. Proteins are generally not used as a primary energy source for immediate needs unless carbohydrate stores are severely depleted, making carbohydrates the key nutrient for those moments of vigorous physical activity.