I have back problems, too, and for me, the pain is from bending forward and holding that position. So I try to keep the area I am working on close to the belly bar if I am working at the front of the machine, so I can remain very upright. If doing a pantograph, I try to remember not to lean forward. And when my back starts to hurt, I lay down until it's better. Working in spurts like that is what works for me.