I've never hurt myself lifting weights...until today. I was squatting 225 using the Starting Strength program, and was concentrating on keeping my knees out and achieving proper depth. Too bad I forgot to keep my chest up and lower back tight. The end result was a muscle pull in my back that makes it hard to even walk or sit up that well. I'm learning the hard way to respect the weight I'm lifting and to keep everything tight at all times. I hope I'm good to go again in a week's time, but it could be two. This really sucks, as I was really starting to make some good progress. Another thing...in Starting Strength increases of five pounds per workout seem to the standard. That worked for a month or so but I think fractional plates and one to two pound increases are the way to go from here on out. I just think it's safer to progress slowly.