Muscles, ligaments and tendons provide for movement at the knee joint. There are two sets of muscles, one set the anterior or front of the knee, and another working the posterior or back of the knee.
A group of four muscles, often called the quadriceps, act as a strap over the front of the knee. The quadricep muscles include the vastus medialis, vastus intermedius, vastus lateralis and rectus femoris. These muscles connect from the thigh to a point on the patela, or knee cap. The quadriceps help extend or straighten the knee, such as when kicking a football.
Three main muscles over the back of the knee are responsible for bending the knee. These muscles are often called the hamstrings, and include the biceps femoris, semitendinosus and semimembranosus.