Answer :
Toward the end of heavy exercise lasting 3 hr or more, glycogen provides almost all the carbohydrates used by the muscles.
Glycogen stored in active muscles supplies almost all of the energy in the transition from rest to moderate submaximal exercise. During the initial hour of submaximal prolonged exercise, muscle glycogen is the main carbohydrate source. However, muscle glycogen levels decrease over time and more blood glucose is used. It takes 3,500 calories to burn a pound of fat.
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