Yeah - you could be right.

It might be fluency - perhaps I have lost fluency with back pain and stiffness.

I know it's not the weight of the bag since the hard bag we have is only a half length bag and the full length bags which are a bit softer are not a problem.

I do feel if I contacted the bag when my shoulder was already further into the punch the jarring might not be as bad.

Hopefully I'll grow out of it