Ok, I need some advice on some leg exercises I can do without loading my spine or mess up my knees. I herniated my disk a year and a half ago and have to be mindful of this. I'm doing legs twice a week and that works fine being my legs are the lacking body part. At the moment I'm doing leg extensions and read how that can screw up my knees. Also I do dumbbell lunges, hamstring curls, leg press, inner and outer leg machine not sure what its actually called, one legged squats with no weight and ball squats any advice would be greatly appreciated.