What is the muscle group that extends the knee?

The quadriceps muscles of the anterior compartment of the thigh are responsible for the action of extending the knee. The quadriceps are actually four muscles all working together. They consist of the rectus femoris, the vastus lateralis, the vastus medialis, and the vastus intermedius.They are all monoarticulate, except the rectus femoris which is diarticulate, which means that it acts on two joints.