What are good exercises for strengthening quad muscles?

Quad exercises: The muscles of the quadriceps femoris include the rectus femoris and the three vastus muscles (medius, intermedius, and lateralis). They primary function to help extend the knee, but the rectus also helps flex the hip. Exercises that strengthen the quads include leg extensors, squats, lunges and leg presses. Cardio exercises that condition the quads include running, cycling, and stair climbing.