What effect does prolonged exercise have on muscle glycogen stores?

Prolonged exercise leads to a depletion of muscle glycogen stores because glycogen is the primary carbohydrate source used by muscles during sustained activity. As the duration of exercise increases, the body relies heavily on stored glycogen for energy, which is especially true in activities lasting longer than about 60 to 90 minutes. During this time, glycogen breakdown occurs to provide glucose, which is then used to fuel muscular contractions.

Once glycogen stores are significantly depleted, the body's ability to sustain high-intensity exercise diminishes, potentially leading to fatigue and decreased performance. This depletion is a natural response to extended physical activity, and it highlights the importance of glycogen replenishment through diet and recovery after prolonged bouts of exercise.

Other options that suggest enhancement, unchanged levels, or solely dietary influences do not accurately reflect the physiological changes that occur during extended physical activity.