Even if you work out the same amount and intensity, what exercise you pick can change which part of your muscle gets bigger.

Different leg exercises make different parts of your thigh muscles grow bigger—leg extensions grow all parts of one muscle, while squats mainly grow the middle part of another.

Leg extensions make the whole front of your thigh muscle grow evenly, while squats mainly make the middle part of a different thigh muscle grow.

Squats make the outer thigh muscle bigger near the knee more than leg extensions do, but both exercises build it similarly higher up on the thigh.

Which leg exercise you choose matters: leg extensions grow the front thigh muscle more, squats grow the lower outer thigh more and make you stronger at squats—but both help you get stronger at leg extensions.

If you want to get stronger at squats, doing squats is way better than doing leg extensions — but if you want to get stronger at leg extensions, both exercises work about the same.