It's funny how some things just get repeated so often that no one questions it. Such is the case with many exercise "traditions" as I call them, for they are not scientifically tested. It's just always been that way, so it must be true.
The one that I have heard most often lately involves the squat. Almost every person that has had a personal trainer or fitness instructor show them squats has heard the following : "Don't let you knees go over your feet".
I wish I knew how this one started because I believe that the only research study to indicate high knee stress in this position, also indicates high low back stress in the other position. Somehow someone decided to only follow half of what this study concluded.
Basically what happens that is if you restrict your knee movement to the point where they don't go past the feet, then the torque in the hips increases. This means that the butt sticks out more, and they resulting position is more of a bow than a squat. Here is the direct quote from the study published in the Journal of Strength and Conditioning Research :
http://journals.lww.com/nsca-jscr/abstract/2003/11000/effect_of_knee_position_on_hip_and_knee_torques.1.aspx
"Although restricting forward movement of the knees may minimize stress on the knees, it is likely that forces are inappropriately transferred to the hips and low-back region. Thus, appropriate joint loading during this exercise may require the knees to move slightly past the toes."
As a former personal trainer, I am familiar with good form during a squat. I am also familiar with numerous patients with low back pain from this misinformation. What's the take-home message here? Consider your source. Even "professionals" are often misinformed.
