I discovered about 5 weeks ago that I can't do back squats with a bar anymore, this sucks!!!!! I was doing my normal squat workout and at about 315# (still working up) I started getting low back pain, the only trainer in the gym that has the knowledge of proper form (I believe; he competes in powerlifting) checked my form and said it was spot on, attepmted to finish the set with less than optimal results, and then the next morning I felt like I was 100 y/o took me about 10 min and a very hot shower to straighten up and walk normally.
Wasn't able to do any DL's or pretty much any thing that required the low back to be involved. I had been getting discomfort from back squats in the past but this took me out for 3 weeks!!!! I just got back to deads at 315 for 2 set of 8-10 a far cry from what I usually work with ( deads don't bother my back, weird). But I did discover that I can back squat in the smith machine with almost no pain, I know the smith sucks, and makes a better coat rack but it allows me to squat. I guess years of abuse and a couple of back injuries (work related)have finally caught up with me.