Leg training requires the glutes, hamstrings and quads to work in unison, often antagonistically to one another. With careful exercise manipulation, you can actually tweak which one (or two) of those muscle groups get more attention, which allows you to better focus on particular area(s).
Multi-joint exercises are the name of the game here. Aside from free-weight squatting – which always requires your feet to be directly beneath you – there are plenty of opportunities to manipulate foot position with machines, including the back squat, leg press and even the Smith machine.
A higher placement on the footplate means more hams and glutes recruitment and less quads, while a lower position does just the opposite. Wider stances hit the inner quads better, while closer stances hit the outer. What’s more, if you squat more deeply, you’ll get better hamstring and glute engagement. Just remember that individual flexibility can affect how deep you squat, so don’t overdo it.