If you're new to working out, doing leg presses twice a week might build more leg muscle in less time than just doing knee extensions, because leg presses work more muscles at once — like your quads, butt, and inner thighs.

If you're new to working out, doing leg presses twice a week for 12 weeks can noticeably grow your butt and inner thigh muscles, but doing just knee extensions won’t help those muscles much.

Pushing a heavy leg press machine makes the outer part of your thigh muscle grow more than doing leg extensions, because it puts more overall stress on that part of the muscle.

Leg presses make your butt and inner thigh muscles bigger, but leg extensions don’t — if you want to grow those muscles, leg presses are the better choice.

If you're new to working out, doing leg presses or knee extensions twice a week for 12 weeks will grow your thigh muscles about the same amount—so pick the one you like!

If you want to grow the outer part of your thigh (vastus lateralis), leg presses might be more effective than leg extensions.