So we can get the glucose from the glycogen or we can get it from that circulating blood plasma. Now, really quickly, if we're sprinting very rapidly, then what that means is the two will be depleted very quickly and we're going to enter anaerobic conditions in which we're going to use lactic acid fermentation to basically produce lactate molecules from Pyruvate, in the process regenerating those NAD plus coenzymes. Now, what happens to the lactate? Well, once we produce the lactate, these cells have special type of membrane transporters that stimulate these lactate molecules to actually move into the bloodstream. Why? Well, because generally speaking, skeleton muscle cells don't actually do anything useful with the lactate molecules and so they deposited into the bloodstream with the hopes that other cells, specialized cells, will pick them up and essentially recycle them and use them for something useful.