Even though squats work your legs hard, muscles like the hamstrings and front thigh muscle don't grow much because they get pulled in two directions at once during the movement.

Bi-articular muscles, such as the rectus femoris, exhibit reduced force production during compound movements that demand simultaneous hip and knee extension due to active insufficiency.

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).

Isolation exercises targeting a single joint (e.g., leg extensions) produce greater hypertrophy in bi-articular muscles (e.g., rectus femoris) compared to multi-joint compound movements (e.g., squats) due to avoidance of active insufficiency.

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.

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.