When you release the shot, you do have to relax the muscles in your hand, whether consciously or unconsciously. Relaxing the muscles in the hand sometimes triggers relaxing muscles in the back. This wouldn't be a problem if it could be done simultaneously, but what usually happens is that the back muscles start to relax in anticipation of the hand muscles being relaxed, which results in creeping or collapse. So we have to train the back muscles to remain contracted until after the shot is released; that is, as a part of followthrough. The same thing happens with the bow arm, which is usually what we think of when we think of followthrough, but there are other things that need to continue after release. This is my list of things I want to continue after release as a part of followthrough:
Keep bow arm in place
Maintain back tension
Maintain focus on target
Keep head still
Keep holding your breath
I try to do all these things until the arrow hits the target.