What is glycogen depletion and its implication for endurance performance?

• A. Reduction of muscle glycogen stores during prolonged exercise; leads to fatigue and decreased performance; fueling strategies aim to delay depletion.
• B. Increase in muscle glycogen stores during endurance exercise.
• C. Glycogen stores remain constant.
• D. Glycogen depletion improves endurance performance.

Answer: (A)

Glycogen depletion means the muscle’s glycogen stores are reduced during prolonged exercise. Glycogen is the fast, readily available fuel for contracting muscles, so as these stores fall, the muscle loses its primary high‑intensity energy source. That makes it harder to sustain the same pace, increases fatigue, and leads to a drop in endurance performance.

In endurance events, delaying glycogen depletion is key. By fueling with carbohydrates before and during exercise, and by training to become more efficient at burning fat, athletes can spare muscle glycogen and maintain a steadier pace for longer. Once glycogen is depleted, the body relies more on fat, which is slower to turn into usable energy at high intensities, so performance suffers.

Other options don’t fit because glycogen stores do not increase during prolonged exercise, they typically decline unless carb intake is sufficient; stores do not stay constant; and depletion does not improve endurance.