Vastus lateralis. The vastus lateralis muscle is located on the side of the thigh. This muscle is the largest of the quadriceps group (often called quads) which also includes the rectus femoris, the vastus intermedius, and the vastus medialis.Collectively, the quadriceps muscle is the largest in the human body and its purpose is to extend the knee.The specific task of the vastus lateralis muscle is to extend the lower leg and allow the body to rise up from a squatting position.On the upper end, the muscle attaches to the femur; on the lower end it attaches to the patella, or kneecap.ollectively, the quadriceps muscle is the largest in the human body and its purpose is to extend the knee. The specific task of the vastus lateralis muscle is to extend the lower leg and allow the body to rise up from a squatting position.