Precision Nutrition L- Glutamine 100% L-Glutamine. L-Glutamine makes up to 63% of the amino acid content in muscle tissue. Intense training and exercise has a greater demand on the bodies need for L-Glutamine, making it an essential amino acid for the repair of muscle tissue and immune function.L-Glutamine is used by athletes for greater recovery and muscle growth. Whilst training, L-Glutamine levels are greatly depleted in the body, which can decrease strength, stamina and recovery. It could take up to 6 days for L-Glutamine levels to return to normal.Train like a Possessed Animal Then Recover for Your Next Heavy WorkoutStudies have shown supplementing with L-Glutamine can minimise breakdown of muscle tissue and improve protein metabolism which makes L-Glutamine an essential amino acid for all athletes.