Muscle obtains ATP from glycolysis. When exercise conditions are anaerobic, glucose is degraded to lactate. Lactate is exported into the circulation and is taken up by the liver. The liver synthesizes glucose again from lactate via the gluconeogenic pathway. These two metabolic pathways that allow the coupling of the function of two tissues is what is known as the Cori cycle. The energy cost is 4 P bonds / each glucose that travels both glycolytic-gluconeogenic pathways.
