The Branched-Chain Amino Acids are essential both in a strict sense - our bodies can't manufacture them - and because during stress like training or lack of optimal nutrition they are used up first by the muscles. Leucine is one of the essential aminos that belongs to the BCAA group. Cutting-edge scientific results prove that leucine is one of the most important aminos, because it directly stimulates skeletal muscle protein synthesis - high leucine levels in the body is a signal for the anabolic state. Leucine promotes recovery and protects muscle tissues from breakdown (anti-catabolic effect). Leucine has been found useful even when the overall dietary protein intake is high, and even when you combine it with fast digesting protein shakes. BCAA's can also be used by muscles for energy when engaging in high intensity activity