After two weeks of slipping about the inevitable happened yesterday and I did the both-feet-in-the-air-flat-on-the-back thing. I landed on the right side of my upper back. Now it's painful when I push anything, and I can feel the muscle that's giving the problem. I've always been a bit crap at benching - I can't lift what I should be able to. I reckon that when I try to push I contract the non-working back muscles, which should be relaxed. Firing these muscles prevents injury if you throw a punch, but I don't think they should be working on a slow push. I don't seem to do the same thing when pulling. I suppose one of the things you do if you train regularly on an exercise is teach yourself to stop unhelpful involuntary movements.