Glutamine

Glutamine and L-Glutamine are extremely popular supplements these days, and for good reason.  Glutamine is a hydrophilic amino acid that is in most proteins--and of course, you need protein to increase muscle mass.  It is one of the 20 amino acids that are in the standard genetic code, and while it's not considered an 'essential' amino acid, it is necessary for intense athletic training, such as high intensity cardio workouts or strength training.

Glutamine works in protein synthesis, meaning it helps to produce protein.  Take glutamine or l-glutamine supplements in powder form.  You should add it to liquid and drink before bed, and on non-training days. Just two grams has been shown to increase your growth hormone by over 400%.