Final answer:
The rectus femoris muscle of the quadriceps femoris group performs both extension of the knee and flexion of the hip.
Step-by-step explanation:
The quadriceps femoris muscles are responsible for extension of the knee. The muscle group consists of four individual muscles: the rectus femoris, the vastus lateralis, the vastus medialis, and the vastus intermedius. Of these, the rectus femoris is unique as it also performs flexion of the hip. This is due to its attachment to the ilium, which allows it to act on the hip joint. The other three muscles are primarily responsible for knee extension.