I have to agree with mgf, and some of the others such as TG. The answer is in form and using your back instead of other muscles to hold the shot.
Note. . although we talk of holding still till the arrow hits, in reality, that arrow is gone in a flash and everything you do after that matters not. It is that split second where we release, the arrow is in motion, and so is our body because the tension that WAS holding it together just left.
Use your back and lock in.
ChuckC