The BCAAs, l-leucine, l-isoleucine, and l-valine, are probably the most essential amino acids for athletes in training. They account for 33% of muscle protein. Some experts believe that even moderate exercise can increase your body's need for leucine by up to 240%. 

The amino acid, Glutamine, has become more prominent as new studies reveal its unique contribution to protein synthesis (muscle growth), anti-proteolytic (prevents muscle tissue breakdown) functions and growth hormone elevating effects.