Guh? I don't recall seeing many people blaming knee pain on back pressure. It's still a compressive force on the knee, same as pedaling, same as walking down stairs and crouching down to tie one's shoes. That's what the knee was designed for. It's the tensile stress of pulling that can cause knee damage. Pulling up on one pedal while pushing on the other when skidding. I'm no doctor, but the way I understand it that by doing this, one can start creating gaps between the cartilage of the joint and the meniscus, forming bubbles of fluid which end up causing pain and hindering the knee's normal operation. At least that's what the internet told me.