Optimum Nutrition's BCAA 1000 capsules contain a powerful balance of Branched Chain Amino Acids which are the building blocks of muscle mass and size. Metabolized directly in the muscle, BCAAs may improve nitrogen retention by sparing other amino acid groups for repair and rebuilding. The Branched Chain Amino Acids (BCAA's), so named because of their unique branched chemical structure, are necessary in that the body cannot make them from other compounds. In recent times, these amino acids have been researched for their possible anticatabolic (preventing muscle breakdown) and anabolic (muscle building) effects.