Alex and Max squat differently because of their anatomy. Short femurs and good ankle mobility let Alex stay upright and hit depth easily. Long femurs and tight ankles force Max to lean forward, which is fine—both work, just emphasize different muscles.
Why do some people squat like this and others like this? Which form is correct? Let me explain. This is Alex. He has short femurs and excellent ankle mobility, the perfect body structure for squatting. This means he can squat almost perfectly upright and get super deep without losing balance. This is Max. He has long femurs and his ankle mobility isn't quite as good as Alex. So to keep his body balanced, he has to push his hips back by bending over more. This also means he can't get quite as deep without rounding his lower back. Now, both squat forms are correct, but will work slightly different muscles. Alex's form will work his quads more, whereas Max's form will work his glutes more. If Max wanted to work his quads more, his best option is to elevate his heels to improve his ankle mobility. Whereas if Alex wanted to work his glutes instead, he'd bend his torso over and limit how far his knees bend forward. Your body will determine what your squat looks like, but there are ways to modify it based on your goal.
