“Textbook form” dictates that you should set up for a squat with your feet shoulder width apart and toes flared out 30°. You should squat deep, so your hip crease goes below your knees. Your knees should stay perfectly aligned with your second toe. When viewed from the side, your torso and shins should be parallel.
Textbook form is great in theory, but it ignores the anatomical fact that no two people’s bodies are exactly the same. For example, differences in limb lengths and femuropelvic structure affect the way we squat. Short of limb lengthening surgery, these factors are non-modifiable. Taller squatters usually have to squat with more forward lean than shorter squatters. This is because taller squatters’ femurs are often longer relative to their torsos and tibias. Similarly, femoral anteversion, femoral angle of inclination, and acetabular orientation all contribute to a squatter’s most natural stance, depth, and alignment.
Perhaps you’ve seen recommendations to squat like a baby. In reality, that’s physically impossible. One of the reasons babies are able to squat so effortlessly is because their heads weigh a ton relative to the rest of their bodies. Moreover, “textbook” squatters also tend to have excellent ankle dorsiflexion mobility. Unrestricted ankle dorsiflexion allows the knees to translate forward over the toes (a good thing!), which then allows for an upright torso. If ankle mobility is restricted, we’ll see a different squat style – be it more forward lean, a wider stance, or a shallower squat depth.
Granted, there are some general features we do look for in a squat. We typically want the heels to remain in contact with the ground. We want to limit an unintended knock-kneed position. And we want to avoid excessive dynamic lumbar flexion under heavy load.
But even those “rules” can sometimes be broken, or at least worked around. If someone’s heels come off the ground, they can squat with their heels elevated. Many elite powerlifters and Olympic lifters purposely allow their knees to visit valgus as their ascend in their squat. This movement strategy enables them to lift more weight. Finally, some degree of lumbar flexion occurs every time we squat. For most people, it’s perfectly safe, especially if loading is submaximal and has been applied progressively over time.
Frankly, textbook form is a myth. Anatomical differences necessitate deviations from textbook form in terms of foot width, toe flare, depth, and torso and shin angles. Just because a squat deviates from textbook doesn’t mean it’s unacceptable, though (let alone injurious, as some pundits claim). On the contrary: the squatter has simply selected the strategy that’s right for them based on their unique structure.