When I was doing Hack squats the other day, instead of feeling it in my quads, i felt it mostly in my upper back, and behind the shoulder area. and then the next day, the back of my shoulders were sore. Am I doing it wrong, or is this normal? I checked my form, and it seems i'm doing it the way I'm supposed to be, but I'm not feeling it at all in my quads like i usually do with normal squats.