When a person runs for an extended period of time, the main source of glucose for muscle cells comes from the breakdown of glycogen in the

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When a person runs for an extended period of time, the main source of glucose for muscle cells comes from the breakdown of glycogen in the liver. The liver stores glycogen and can release it into the bloodstream as needed to maintain blood glucose levels during exercise. As muscle glycogen stores become depleted, the liver becomes the primary source of glucose for the muscles. The electron transport chain, lungs, and heart do not play a major role in providing glucose for muscle cells during exercise.

When a Person Runs for an Extended Period of Time