The vastus lateralis is the largest of the quadriceps muscles. The quadriceps muscle group consists of four muscles: the rectus femoris, the vastus lateralis, the vastus intermedius, and the vastus medialis. They form a large fleshy mass that covers the front and sides of the femur (upper leg bone) and work as the primary extensor of the knee. The vastus lateralis occupies the outside of the thigh and extends partially around to the front and back of the thigh. It extends the lower leg at the knee joint and is used when rising from a squatting position.
