I had a client come up to me the other day and ask, “Is that person squatting correctly? Her squat doesn’t look anything like the guy you were coaching earlier.”
I simply replied, “Yes, both squats are correct. Those two people have very different body levers that make their positioning much different.” From the look on this person’s face I could tell that wasn’t a very good explanation:) 
So today I am going to explain how squat form can change depending on a person’s body levers and what muscles of the body we are trying to load.
This difference in body levers is referred to as anthropometry, which is “concerned with the comparative measurements of the human body and its parts.” The most important measurements for the squat are the relative length of the femurs and the trunk.
Before we move onto examples, it is important to know that the ideal pattern will always keep the bar or weight centered over the middle of the foot. How much we bend our hips, knees, and ankles are all important in determining where the weight is in relation to our foot.
So let’s take someone who has a relatively long torso compared to his or her femurs. This individual will have a very upright squat compared to someone with a relatively short torso compared to his or her femurs.
Let’s look at the picture below which demonstrates how bar placement can effect the angle of the torso.
In all three bar placements the bar is kept in line with the middle of the foot. The image on the far left is a front squat, which will allow the torso to remain much more upright. The middle image is a high bar back squat and the image on the far right is a low bar back squat. As you can see, the low bar back squat forces the torso to be inclined forward the most.
Now, let’s look at the guy in the middle. Can you imagine what he would look like if his thighs were the same length, but his torso was longer. If he kept that same torso angle the bar would be out in front of his feet, right? This means he would need to be more upright to keep the bar over the middle of the foot. Make sense?
Now the opposite scenario is also true. If the guy had the same thigh length, but his torso was shorter he would need to lean over more. So this is why a relatively long torso means a more upright squat.
Lastly, we can also target different muscles by how much we bend our hips and knees. If we want to target the hip muscles we simply sit back more, which means a more inclined torso and less knee bend. On the other hand, if we want to target the thigh muscles we bend at the hips less and the knees more, which will allow the torso to stay more upright.
The image on the far left will target the hips the most while the image on the far right will target the thighs the most.
I hope this helps you realize why not all squats look the same. The ideal position will vary depending on anthropometry and the goals of the exercise.
Have a great week!
Great explanation Zach, thanks!