Thanks for your input JohnnyCoho,
I didn't realise you could so much on a Swiss ball
I'm also using it to stretch my lower back and my shoulders
I've a trully screwed back
I've been able to avoid back surgery so far but I know I have to be careful when doing GM, DL, squats ...
so I'm looking for anything that could counterbalance the stress put by those exercises on my lower back
As for the shoulders I'd like to emphasize the underdeveloped rear delt/rhomboids compared to the chest