Now, lactic acid can basically break down into its conjugate base, lactate and this releases H plus ions into the cell and that means it decreases the PH of the cell by increasing the concentration of H plus ions. So the build up of lactic acid in the cell decreases its PH and it's the decrease in PH that basically causes the feeling of fatigue following our vigorous exercise. Now, the lactic acid must eventually be transformed back into Pyruvate and this takes place in the liver. So once we form our lactic acid, the lactic acid travels back into the liver. And inside the liver, the lactic acid undergoes a process known as the core cycle. In the core cycle, we basically use oxygen to transform our lactic acid back into Pyruvate.