I've had injuries to my back and knees for years and it always hurt. They always told me don't squat, lunge, deadlift or anything else remotely challenging. Since I began doing all of those things on the don't do list, my knees and back have never felt better. I am stronger now than I have ever been. Use good form and build up gradually but don't fear the weights. Free your mind and your glutes will follow. Today's workout consisted of Leg presses and V-squats. The video's are of a 540 lb leg press, 250 lb & 270 lb deep V-Squat. Guess what? It was heavy as hell but my knees and back didn't hurt a bit and felt great afterward. I rehab myself. Skip the physical therapy and do your therapy with heavy iron.