Sure, first forgive me as I am just a visitor here and likely do not know all your boards proper etiquette and no doubt will say something not common to the board. As I have learned to tell my wife...sorry in advance.
First, since I do not know the generation demographics here I will try to introduce myself without looking like an idiot. My name is Author L. Rea though I have two legal names (the other being Scott Jensen) due to being a bastard at birth and more so since. But since I pay taxes in two countries one under each name I suppose using what was once a pen name to honor my mother is legal based upon our legal teams evaluation and the fun times I have had in court rooms answering to AKA. I wrote a few books some years ago: Building the Perfect Beast, Chemical Muscle Enhancement and have written columns for MD, Planet Muscle, Ironman, Olympain's New, and a book on natural training/diet called Building The Perfect Beast Naturally. (Big deal, Huh? lol) In short I started ALR Industries on $100 in 2002, later, after selling my first hard core DEA favorite company HM Gear we pushed full ahead to get ALR Industries moving and allow me to finish school (still at it)
Now that I have made everyone yawn, the answer to that question is very basic physiology in that adults require all 8 Essential Amino acids (EEAs) to be present or NONE of the 23 common nor the over 46000 others have any value as a protein. Kind of like forgetting to put the front piston in a Harley: It may start, even run badly for a few seconds but it will die. For kids there are 9 EAAs and one likely semi-essential amino acid. Why are they essential? The human body has a specific to human's amino acid profile requirement all of which the body can make from the 8 EAAs but you die if you lack even one of the EAAs. Now, there are ratios that ebb and flow based upon momentary needs such as anabolic phase and catabolic phases, training or recovering etc, thus the EAAs much all be present in the correct human ratios to allow the metabolic miracle of life to go on...bigger faster and better if done right and specific to needs. Reagrdless, the best way to short cut the answer is to simply say that lacking one EAAs and you die, not grow, plus the more perfect the ratio of 8 specific to human athletes with least the waste by-products allows for increase progress rates. Damn I hope that came out clear.