After you\\\'ve been training, your muscles are damaged. The body then rebuilds them and makes them a bit stronger than they were before. To do this, the body uses the nutrients from your food. One such nutrient is the amino acid L-leucine, which plays a special role in this recovery process. It plays - as scientists say - an active role. Simply put, leucine tells the body that it can do the repair work somewhat faster. This makes it an interesting supplement.