Hi, I’m sure there is a solution to make bending the spine without chest’s ugly deformation. Can you help?
Before you get into a real rigging solution for that deformation, do you realize that a real spine can’t bend in that fashion anyway? Try to bend only the upper portion of your chest over at that pivot point. Bet you can’t.
What that means is that you can either make sure not to do poses like that when you animate, rig up a solution to keep the chest volume even in that very unnatural situation, or use some limits on the rotations of that spine bone to prevent it from bending that far.
Ok, thx 
I’ve added IK for the the spine and wanted to bend it with only one bone, will try othe solution.