This is another myth Katie discussed. Based on old data showing that there was increased stress on your knees when you go past a certain depth, people have said that your knees should never go over your toes in squats. But, she said, nothing stated that the knees couldn't tolerate that load. Plus, "The other thing is when people try really hard to not make their knees pass their toes, but they want to get to certain depth, they translate more stress to their lower back."
Of course, if you have bad knees, don't do a knee-dominant squat, Katie advised. But, "if you look at some of the best squatters in the world, like Olympic lifters, their knees go quite forward over their toes because they physically have to go that deep." When you're first starting out, your knees probably won't go much past your toes anyway because you're not going super deep into your squat, Katie said. But, when you get to a certain point, going into that depth is necessary for squatting. As long as you feel safe and comfortable when you're squatting heavier weights, knees over toes isn't a bad thing, she said. And, you still need to push your hips back like you're sitting in a chair and keep your core engaged.