If he injected himself with a viral vector to silence myostatin, he is a complete idiot. There is so many problems with this, i don't even want to get into it.
Gene therapy has been almost universally unsuccessful, requires repeated dosing and continued modification of one's genomic DNA, and has resulted in many deaths. For instance, from the induction of cancer.
I am amazed he got ahold of this. Basically, this is really only available for use in laboratory animals.
EVERYONE: DO NOT DO THIS. ITS THE MOST STUPID IDEA IMAGINABLE AT THIS POINT.