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.

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.

For guys who lift weights, doing leg presses or kickbacks works the butt muscle just about the same — neither one gives you a bigger advantage in muscle activation.

When healthy guys push with their legs, the electrical activity in one specific thigh muscle (vastus lateralis) goes up steadily with how hard they push — unlike two other thigh muscles — so it might be a better way to measure how much force their whole quad is producing.

When guys who’ve never lifted weights before start training, the more their thigh muscles ‘fire up’ during max efforts, the stronger they tend to get—both in holding a heavy position and in lifting one heavy weight.

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.