RECTUS FEMORIS Why does rectus femoris, one of your quads, matter so much when it comes to back pain?Your quadriceps are comprised of four muscles, three of them, vastus medialis, intermedius and lateralis act exclusively to extend the knee - his is because the vastus group only cross the knee, a muscle that only crosses one joint is known as monoarticulate.The fourth quad, rectus femoris, is biarticulate, or it crosses both the hip and the knee and acts to extend the leg as well as being one of