The primary purpose of carbohydrate loading practiced by endurance athletes is:

The formation of branch points in glycogen is slower than the addition of glucose units to a linear chain. This is the biochemical basis of carbohydrate loading practiced by some endurance athletes. Carbohydrate loading involves exercise to exhaustion (when muscle glycogen is largely depleted) followed by a high-carbohydrate meal, which results in rapid glycogen synthesis, with fewer branch points than normal. This type pf glycogen ensures a uniform sustained release of glucose from muscle which is required for endurance activities like marathon. Carbohydrate loading is not required for sho activities like weight lifting or 100-meter sprints.