Final answer:
Athletes have larger glycogen stores in their muscles compared to inactive people, due to their muscles adapting to the energy demands of regular exercise. Glycogen is critical for energy storage and is used during periods of exertion or fasting. 'Carbo-loading' before events like marathons increases glycogen stores to improve endurance.
Step-by-step explanation:
Athletes have larger glycogen stores than inactive individuals, primarily because their muscles adapt to the demands of regular and vigorous exercise. Glycogen plays a crucial role as an energy reserve carbohydrate for animals, with about 70% of the body's glycogen stored in muscle cells. Skeletal muscles store a greater total amount of glycogen due to their mass. Meanwhile, the liver contains a higher percentage of glycogen by weight and is essential for maintaining blood glucose levels.
Glycogen synthesis occurs when there is excess ATP and glucose in the body, allowing glycogen to be used in the future to produce energy in scenarios like food scarcity. During periods of fasting, glycogen reserves are tapped into to maintain metabolic balance. Hence, athletes often practice 'carbo-loading' to boost their glycogen levels, enhancing their muscular endurance and performance during extended periods of exertion like marathons.
The body utilizes stored glycogen during exertion, breaking it down into glucose for glycolysis and further into ATP via aerobic pathways. When muscle glycogen depletes, the liver releases glucose into the bloodstream, and fat metabolism increases to compensate. This adaptive response underscores the importance of glycogen in both liver and muscle cells for the homeostasis of blood glucose levels and endurance in physical activities.