Glutamine is highly in demand throughout the body. It is used in the immune system extensively to maintain optimal performance. 60% of free-form amino acids floating in skeletal muscles is L-glutamine.
L-glutamine plays a very important role in protein metabolism, and it appears to be a very important nutrient for athletes. When taken as a supplement, it helps reduce the amount of muscle deterioration that occurs because other tissues that need glutamine will not deplete the glutamine stored in the muscle cells.
Catabolism is the breaking down of your muscles, which is something that you don't want to happen. Doing cardio or aerobic activity could have a catabolic effect on your muscles. Your body needs something to burn for energy when you run, cycle, take an aerobics class or do any other form of cardio. This is where L-Glutamine comes into play. Since it is an "Anti-catabolic" it will allow you to maintain as much muscle as possible and prevents muscle cell breakdown.