Could this be a way to tell if you are hitting harder?

[Douglas]

Man this has to be the biggest load of crap ive ever heard. I always tell by punching the heavy bag.

I figured it was, but I was just making sure. But you can't always tell by hitting the punching bag, either. I've noticed when I hit the bag, the dents on impact have gotten a bit bigger. Also, when I hit it really hard, the bag shakes from up to down.