For people who don't usually work out, using a knee extension machine grows the front thigh muscle much more than using a leg press machine.

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.

Doing leg extensions might grow your front thigh muscle more than leg presses, even though both workouts work the other big thigh muscles just as hard.

Doing leg extensions (kicking your leg out while sitting) makes the front thigh muscle right above your knee grow more than doing leg presses (pushing a heavy platform with both legs).

Doing leg extensions makes the front thigh muscle bigger along its whole length more than doing squats, especially near the knee.

The rectus femoris muscle exhibits greater hypertrophic adaptation to isolated knee extension exercises than to compound movements involving hip and knee flexion due to biomechanical limitations in force production during multi-joint movements.