The squat and its variations are at the foundation of many of the programs I design for a variety of clientele. One of the common form faults that I find in trainees during the barbell back squat is the end of the bar traveling in front the front of the foot during the eccentric phase (descent) due usually to mobility restrictions in the hip. Clients who squat this way often complain of back pain as this faulty movement pattern places much of the stress on the lower back and takes it away from the glutes and hamstrings. The back is overloaded with such form because the load has shifted too far forward. With proper squat mechanics the back, glutes, and hamstrings work synergistically to stabilize the trunk and extend the hip (stand up).
Here are two pictures respectively showing proper bar path over the base of support (foot) during the squat and another picture showing that the bar has shifted in front of the foot and is no longer over the base of support. If a plum line were dropped from the end of the bar, the line should always fall within the framework or the foot no matter the phase of the squat.
Now that you have the awareness of the bar path during the squat, you can have your training partner identify whether the end of the bar tracks over your foot throughout the eccentric and concentric portions of your back squat. If it does not, work with a professional to identify and improve the form and reduce your mobility restrictions and then start to attack the exercise once again after form has been corrected. If you continue to squat with poor form, you will continually program the wrong motor pattern into the nervous system and continue to overload the back and take the stress of the exercise off of the glutes and hamstrings where it should be.
