What happens to muscle glycogen levels during continuous exercise at 60-80% of maximum for 2-3 hours?

During continuous exercise at an intensity of 60-80% of maximum for a duration of 2-3 hours, muscle glycogen levels are significantly depleted. This is because glycogen serves as the primary fuel source for muscle contractions during high-intensity exercise. When engaging in prolonged activities at this intensity, the body relies heavily on glycogen stores to meet the energy demands.

As the exercise continues, the stored glycogen is broken down into glucose to provide the necessary energy for sustaining muscle activity. After about an hour of continuous exercise, glycogen stores begin to decrease, and by the 2-3 hour mark, they can become critically low, often leading to fatigue and diminished performance—commonly referred to as "hitting the wall."

This process is influenced by several factors, including the initial levels of glycogen stored in the muscles, the availability of carbohydrates in the diet, and the overall fitness level of the individual. The depletion of glycogen emphasizes the importance of proper nutrition and carbohydrate intake for athletes engaged in prolonged exercise.