What is the effect of prolonged exercise on muscle glycogen stores?

Prolonged exercise leads to a gradual depletion of muscle glycogen stores. During sustained physical activity, the body relies heavily on glycogen as a primary energy source, especially during high-intensity and endurance activities. As the exercise continues, the glycogen stored in muscle cells becomes increasingly utilized for ATP production, leading to a decline in available glycogen.

This phenomenon occurs because the muscle cells must continuously generate energy to maintain performance, and glycogen is a readily accessible form of energy. When exercise persists for long durations, such as in endurance sports, muscle glycogen can become significantly depleted, which may subsequently affect performance, leading to fatigue or hitting the "wall" in athletes.

After the exercise session, replenishment of glycogen stores can occur with proper nutrition, particularly through carbohydrate intake, but during the prolonged exercise itself, these stores are actively consumed and not replenished until post-exercise recovery. Thus, the understanding of glycogen utilization is crucial for athletes and trainers to help manage energy levels and optimize training and recovery protocols.