Glutamine is the most abundant amino acid in muscle and plasma. It is produced in your muscles, combining ammonia and the amino acid glutamate, and makes up more than 60% of the free amino acid pool in muscle cells. A high glutamine level in the muscle cells stimulates the entry of other amino acids, along with water.  Overtraining depletes your body of glutamine to the point that you can't efficiently recover. It also supports your immune system, gastrointestinal integrity, digestion, insulin secretion, neurological activity, muscle protein synthesis, and inhibition of myostatin.
        Your body produces glutamine from other amino acids, but may not make enough for the demands of heavy training.        
    Glutamine, along with the BCAA's (leucine, isoleucine, valine) should be taken before, during and after lifting weights - best on an empty stomach.
       read this great article on glutamine