L-Glutamine is the most abundant amino acid in your muscles (over 61% of skeletal muscle is Glutamine!), and is used in large amounts by your body. During intense training, or times of stress, Glutamine stores are depleted, and supplementation may be required to aid in immune fortification, muscle development and maintenance. 

L-Glutamine is effective for those who are training and wanting to preserve muscle and strengthen their immune system.