Rushall notes (1990).
Glucose is absorbed in the form of glucose, fructose, and galactose and transported to the liver. There it is converted to glycogen and stored or transported to the muscles as glucose and used for energy or stored as muscle glycogen. Other amounts are circulated as blood glucose. Some blood glucose is metabolized by the brain, kidney, and blood cells as part of normal functioning. Once liver and muscle glycogen stores are filled excess glucose is stored as fat, in the form of triglycerides, in adipose tissue.
Blood glucose levels represent a balance between the rate of glucose and glycogen production by the liver and use by muscle and other tissues. Muscle lacks the enzyme glucose 6-phosphatase and is unable to produce glucose from glycogen. Thus, correct liver functioning is an important aspect of performance potential because it is a primary reservoir of glucose.
The lactacid energy system supports glycolysis (anaerobic), an action where glucose is converted in the absence of oxygen to produce lactate. In aerobic glycolysis, pyruvate crosses the mitochondrial membrane and ultimately produces electrons which are used to produce mitochondrial ATP, the fuel for muscle contraction in aerobic activities.
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