Glutamine is the most abundant single amino acid in the blood and in the intracellular free amino acid pool (most abundant amino acid in muscle tissue). It represents 61% of the amino acid pool in skeletal muscle. Glutamine's unique structure, containing two nitrogen side chains, consists of 19% nitrogen - making it the primary transporter of nitrogen into the muscle cell. Glutamine alone is responsible for 35% of the nitrogen that gets into the muscle cell.

Glutamine concentrations fall markedly after training and remain low until complete recovery. This fall in glutamine is catabolic to muscle tissue. Supplementing with glutamine spares free glutamine in muscle tissue, counteracts the fall in muscle protein synthesis and improves nitrogen balance.