Most amino acids can be metabolized in the liver only. However, BCAAs can be directly metabolized in the muscle cells to increase energy. Using BCAA to load up the muscles before a workout was proven, in several scientific studies, to boost endurance and overall performance. This is seeming because they intensify the quantity of fuel instantly available to cells. This can be transformed into ATP, which provides energy for the contractions of the muscle. During a workout, BCAAs are severely depleted and this occurs because they are used to fuel the workout.