The body utilizes glycogen during exercise as a primary energy source, particularly for activities involving high intensity. Stored in the muscles and liver, glycogen can be rapidly converted into glucose, which is utilized for energy during physical exertion. In the initial stages of exercise, glycogen provides quick energy bursts, especially during anaerobic activities like sprinting or weightlifting. As exercise continues, the body may start to tap into fat reserves for longer-lasting energy, but glycogen stores remain critical for optimal performance, especially in endurance sports.