I'm currently reading through the NASM Personal Training Manual. While I'm an avid tmuscle reader and enthusiast for all sorts of athletic training, my university background is in history, rather than kin or anything like that.
In the section on flexibility, external rotation of the feet while performing squats is mentioned as something bad:
"For example, externally rotating the feet when squatting forces the tibia and femur to also externally rotate.This alters length-tension relationships of the muscles at the knee and hips, putting the gluteus maximus (agonist) in a shortened position and decreasing its ability to generate force.This causes the bicep femoris and piriformis (synergists) to become synergistically dominant, altering force-couple relationships (recruitment patterns), altering arthrokinematics (joint motion) and increasing stress to the knees and low back. Over time, this stress can lead to pain which can further alter muscle recruitment and joint mechanics."
I'd always been under the impression that the feet should be somewhat externally rotated, so as to track in the same line as the knees. Is NASM the same type of people that don't want you to squat below parallel? I'm hoping someone more well-versed in all this could throw me a bone.