If you're a guy who lifts weights, your front thigh muscle works way harder during leg extensions than during leg presses — probably because the movement challenges how that muscle crosses two joints at once.

If you want to make the front part of your thigh (rectus femoris) bigger, leg extensions work better than leg presses — after 12 weeks, leg extensions made it grow 12% more than leg presses did.

For guys who lift weights, the inner thigh muscle works just as hard during leg presses and knee extensions — these two exercises use that muscle in a similar way.

When healthy guys push with their legs at a 90-degree bend, their quad muscles don’t fire in a straight line with how hard they push — the muscle activity changes unevenly as they push harder from 20% to 100% effort.

Doing leg presses and leg extensions for 12 weeks both make your main thigh muscles bigger in about the same way, but only leg extensions make the front part of your thigh (rectus femoris) grow significantly.

When bodybuilders push hard with their legs, the stiffness in a key thigh muscle changes depending on leg position—but the usual muscle activity sensors (EMG) don’t pick up these differences, suggesting they might miss some real muscle behavior.