A muscle in the quadriceps, the rectus femoris muscle is attached to the hip and helps to extend or raise the knee. This muscle is also used to flex the thigh. The rectus femoris is the only muscle that can flex the hip.

Injury to the rectus femoris muscle may result from overuse, as seen with kicking- or sprinting-related injuries. Inflammation of the muscle causes pain in the groin during physical exercises that use this muscle. The patient may experience pain during knee raises if the muscle is ruptured (torn) or inflamed. An operation may be necessary if the muscle is torn.

Some patients with cerebral palsy — a movement disorder — may have an irregular stride or gait due to problems related with the rectus femoris. In this case, surgery may be performed to transfer the rectus femoris onto a knee flexor. Although research has shown that this surgery can improve the knee flexion, other studies have shown that rectus femoris muscle transfer surgery is best performed in conjunction with other surgeries.