Carbohydrates in food are digested. They are degraded into glucose. As blood glucose rises after a meal. The pancreas secretes the hormone insulin. This causes the liver cells to stimulate glycogen synthase, as well as other hormones. Glycogen is formed. Glycogen is made of about 30,000 glucose units.
After a meal has been digested and glucose levels begin to fall, insulin secretion is reduced. Glycogen synthesis stops. About four hours after a meal, the enzyme glycogen phosphorylase begins cause glycogen to be broken down to be converted to glucose for fuel.
The pancreatic hormone glucagon counteracts insulin. When blood glucose levels fall, it is secreted in increasing amounts. It stimulates glycogen breakdown to glucose when insulin levels are high.
Muscle cell glycogen seems to be an immediate reserve source of available glucose for muscle cells. Muscle cells cannot pass glucose into the blood, so the glycogen they store internally is destined for internal use and is not shared with other cells.
The body usually cannot hold more than about 2,000 kilocalories of glycogen. Marathon runners commonly experience a phenomenon referred to as "hitting the wall" around the 20th mile (32nd kilometer) of a marathon. This calculation is based on an average of 100 kilocalories used per mile, varying by the size of the runner and the race course. When experiencing glycogen debt, runners many times experience fatigue.
Disclaimer: None of the information in this blog is intended to take the place of medical advice. Please consult a physician before taking part in an exercise plan, sport, physical therapy, or massage.
Some of the information from this blog was obtained from: http://www.wikipedia.org
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