Eric Roberts explains why pointing your feet straight ahead during squats limits depth. A slight outward toe angle and a stance just wider than hip-width increases hip mobility for a deeper squat. Keep the angle modest so the movement stays natural.
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When you're doing squats, stop keeping your feet pointed straight forward. And here's why. When your feet are pointed straight forward, you are giving your hips less range of motion to work in, which means as you get to the bottom or try to get to the bottom, you're going to kind of feel like you can't get any lower because your hips don't have the proper range of motion. But if you just slightly point your toes out and take a little bit of a wider stance, about a little outside hip width, you will now give your hips more range of motion and you'll be able to get down lower into your squat. You don't need to point your toes out like a penguin or like you're salsa dancing. That's how you salsa dance. But just slightly point your toes out and then drop down into your squat. Try it out. Hope it helped.