And so the glycogen storages are essentially depleted. We break down glycogen into glucose six phosphate and that is then used to produce pyruvate molecules and ATP molecules and then to reform the NAD pluses. Because initially, as we begin sprinting, we have plenty of oxygen, the Pyruvate will go into the mitochondria where we produce many more ATP molecules and regenerate those NAD plus coenzymes that are then reused by glycolysis. In addition, we also produce carbon dioxide and water molecules. Now, at the same exact time our glycogen storages are being depleted, what that means is the skeleton muscle cell will have to look elsewhere for the glucose supplied. So because we have plenty of glucose in our bloodstream, that glucose is essentially uptaken by the skeleton muscle cells.