The |rectus femoris| is one of the four bellies of the quadriceps muscle group. The quadriceps muscle group consists of four muscles: the |rectus femoris|, the |vastus lateralis|, the |vastus intermedius|, and the |vastus medialis|. It is a large fleshy mass that covers the front and sides of the |femur| bone (upper leg bone). The muscles work together as the primary extensor of the knee. The |rectus femoris| is the only two-joint muscle in the group, crossing both the knee and the hip joint. It originates at the back of the inferior iliac |spine| and inserts in the top of the |patella| (knee cap). This long, flat muscle extends the leg at the |knee joint| and flexes the thigh at the hip joint. When the |rectus femoris| is contracted, the |knee joint| is straightened and the lower leg is extended. When it is relaxed, the lower leg is flexed (bent at the knee).
