They're usually referenced a strong shot as pulling strong or hard into the back wall and keeping your front arm moving towards the target so your body is expanding. It can vary, but the key thing is that you're maintaining pressure A weak shot is one that comes of the back wall slightly, or the front arm is not going towards the target. So instead of expanding your losing tension off the back end or front end or maybe both. I'm sure there's other ways to describe it, but this should help.
