I think what you are are looking for are myostatin blockers or anti-myostatin. Myostatin regulates muscle growth and Follistatin works against myostatin. But you would almost have to infect yourself with a viral dose of anti-myostatin to block the gene or the receptor. Probably injecting a substance that would limit myostatin would not do the trick...unless it was done using stem cells. Stem cells could be harvested from the body and radiated and put back in the body thus blocking the recepitor or blocking the gene.
I guess the gamble becomes does it effect all muscle? Smooth and striated muscle? the difference between your tongue and your biceps. What the muscles around your eyes. Freaky shit...and it does exist. If they are doing it in labs and animals then somewhere someone is using this. You just have to be willing to be infected with a virus that turns off the myostatin gene...how do you regulate muscle growth? When you become the human juggernot is there any going back? And have some serious money to throw at it.
The German kid that was born with out the myostatin gene was born this way so his body knows how to regulate itself...i wonder what happens when we try to perform gene therapy.