I've been squatting for a while, although I see posts of guys pushing a huge weight and complaining about their knees or whatever. Does no-one find it hard on the back as me?? I try to ensure correct form with my butt out and my back straight, but after a set of 20 or a work set of 12 I'm really feeling it in my lower back rather than my quads. Do you think a few sets of leg extensions / leg curls that exaust my legs would be benficial??