Runners rely on muscles to propel them as they run. Muscles require a continuous supply of oxygen and glucose for contraction. Metabolism of these reactants generates carbon dioxide and lactate. Consider as the system the thigh muscle of a person during a 1000-m race. You wish to model glucose during the race.

The Cori cycle is the cyclic circulation of glucose and lactate between muscle and liver.

Muscle cells feed primarily on glucose from their glycogenic stores and especially from what comes through the bloodstream from the liver. During muscular work, in the presence of great anaerobic glycogenolytic activity, large amounts of lactate are produced, which diffuses into the blood to be taken to the liver. This is because muscle cells lack the enzyme glucose-6-phosphatase, so phosphorylated glucose cannot go into circulation. Lactate in the liver is converted back to glucose by gluconeogenesis, returning to the circulation to be taken back to the muscle. It represents the integration between glycolysis and gluconeogenesis of different body tissues.