A correct squat can always be identified, no matter what skeletal anatomy the squatting person has.
At the top of the movement, all the skeletal components that support the bar – especially the knees, hips, and spine – will be locked in extension so that the muscles have to exert only need to provide enough force to maintain this position. In the upright position, compression is the primary force on the skeletal components. The job of the muscles here is to keep the bones lined up correctly so they can hold up the load. The bar is over the middle of the foot. The heavier the weight, the more critical this position will be.
During the ride to the bottom, the bar must maintain its position over the mid-foot. The correct bottom position is identified by definite anatomical position markers:
- The spine will be held rigid in lumbar and thoracic extension
- The bar will be directly over the middle of the foot
- The feet will be flat on the ground at the correct angle for the stance
- The thighs will be parallel to the feet
- The hip joint will be in a position lower than the top of the patella
And this is how it looks like, with a bucket weight instead of a bar on the shoulders:
And that is me, in the lower squatting position, with 182.5kg weight on my shoulder, at the Singapore Powerlifting Invitationals 2018. Five guardian angels watching over my life during the exercise.
If you keep the bar in the correct vertical position over the mid-foot on the way down and back up – as if the bar were riding in a narrow slot directly plumbed to the mid-foot – you will have done it right. Your skeleton will have solved the problem of how to most efficiently use your muscles to get the job of squatting done.
Check out this book for more information Mark Rippetoe & Stef Bradford, “Starting Strength – Basic Barbell Training”.