Final answer:
During exercise, muscle glycogen is broken down into glucose, which is used to produce energy through glycolysis and the Krebs cycle. As glycogen stores are depleted, the liver releases glucose and the body starts oxidizing fats. Muscle glycogen is crucial for energy production, especially during vigorous activity.
Step-by-step explanation:
The usual fate of muscle glycogen during exercise is its breakdown to produce glucose, which is then utilized to generate ATP, the energy currency of the cell. Initially, muscle glycogen undergoes glycogenolysis, where it is broken down into glucose-1-phosphate (G-1-P). This glucose-1-phosphate is then converted into glucose-6-phosphate (G-6-P) and enters the glycolytic pathway.
During glycolysis, pyruvate is produced, which in the presence of oxygen enters the Krebs cycle and chemiosmosis to produce carbon dioxide, water, and ATP. When muscle glycogen levels start to deplete, the liver releases glucose into the bloodstream, and the body increases fat metabolism to fuel aerobic pathways, which includes using stored glycogen and body fat as energy sources.
Approximately 70% of the body's glycogen is stored in the muscle cells, and it serves as a readily available source of glucose during vigorous exercise. This stored glycogen is vital as it can be quickly mobilized to sustain energy production for muscle activity.