So in our body, lactate is transformed into Pyruvate by using lactate dehydrogenase. In the process, we reduce nicotine amide adenine dinucleotide. Now, Pyruvate NADH are basically used to basically form ATP molecules, the energy molecules used by our cells. Now the question is, how do we measure the activity of this enzyme? So we can measure the activity of this enzyme indirectly by measuring how much of the product is actually formed. So our choice is we can either measure Pyruvate or we can measure NADH.