We already know that amino acids come from protein that we eat, however most of the good protein that we get in the average protein shake is a milk based protein, which if you are lactose intolerant can be a bad thing when you are a bodybuilder.
Basically the body needs the 9 essential amino acids to do life supporting repair and the constant maintenance that is done in our bodies. The proteins that we eat get digested into over 50 000 different forms of proteins creating over 15 000 different enzymes used for digestion and many other processors in the body.

The fact remains that without the regular influx of amino acids into our bloodstreams we would die. But the kind of people that can also benefit from taking amino acids besides bodybuilders are vegetarians and people with any allergies or stress-related fatigue like ME or hypoglycemia.
It was recently demonstrated in a study done at the Ball State University that was done specifically on amino acid supplementation taking in a total of 0.88 grams per pound of the body weight. This dose was given to 20 men who trained with weights on a regular basis and all showed an increase in the prevention of overtraining.

The study also measured increased testosterone levels that was seen in the men that were not taking the placebo when training with a heavy weight with less reps. There have been many other studies done and one of them worth mentioning was a study done at the University of Texas Medical Branch which showed an increase in the L-phenylalanine uptake.

The increased L-phenylalanine uptake was found in those bodybuilders who were taking both protein and carb shakes within 90 minutes after an intense training session. The amount of L-phenylalanine uptake was three times larger than the other groups measured in the same study

The bottom line is that if you want to increase the protein synthesis as well as the muscle sparing effect and the improvement of your recovery, plus your endurance, then taking around 0.88 grams of amino acids per pound of bodyweight will improve the results that you get from your hard training.