This is the best way to build quads!!!! It’s called a stiletto squat, and sometimes I call them a cyclist squat. But it’s the same thing. It positions your body in a way that you load the quads maximally and it’s the perfect supplementary exercise for powerlifters to pair with their low bar squats because low bar squats neglect quads, which is why combining them with a specific quad builder like a stiletto squat is hugely beneficial. No this doesn’t hurt my knees. In fact it strengthens my knees