Amino acids are the building blocks of protein. Branched chain amino acids - made up of Leucine, Isoleucine and Valine - comprise approximately 35% of the amino acid composition of muscle tissue.
Branched chain amino acids (BCAAs) have attracted a lot of interest in body building and strength based sports because they are the only amino acids that are actually metabolised in the muscle.
BCAA's are converted into two other amino acids - glutamine and alanine - which are released in large quantities during intense aerobic exercise. They can also be used directly by the muscles, particularly when muscle glycogen is depleted.