"If there is not enough oxygen to remove the (H+), the (NADH) build up in the cell. To once again prevent over-acidity, the pyruvic acid accepts the (H+) and forms Lactic Acid. The Pyruvic Acid is like a backup to the (NADH). It then reduces to Lactate and (H+), and some of the Lactate molecules take (H+) with them to help lower the level of acidity in the muscle, whose normal pH is between 7.25 to 7.4*. If the lactate molecules don't round up enough (H+) to take with them into the blood stream, the pH scale drops to about 7.3, where the pain starts "