Rectus Femoris

legsMusculus rectus femoris

The rectus femoris is the middle quadriceps muscle and the only one that crosses the hip as well as the knee. That makes it both a knee extender and a hip flexor.

Rectus Femoris highlighted on an anatomical figure, from the front.
Where it sits, from the front.

Rectus femoris runs straight down the front of the thigh — which is what its name says — from the pelvis to the kneecap, lying on top of the vastus intermedius and between the lateralis and medialis. It is the most superficial of the four and the one you see running down the middle of the thigh.

It arises by two heads from the hip bone, one from the bony point at the front and one from a groove above the hip socket. Crossing the hip is the whole of what distinguishes it: it is the only quadriceps muscle that can flex the hip, and the only one whose length depends on hip position.

That has a direct practical consequence. When the hip is already flexed — sitting on a leg extension machine, or at the bottom of a squat — rectus femoris is short at the hip and can contribute less at the knee. When the hip is extended, it is long and can contribute fully. A muscle that crosses two joints cannot be shortened at both at once and still produce much force.

It also means it works during running in a way the other three do not: swinging the leg forward is hip flexion, and rectus femoris is one of the muscles doing it.

Training notes

Movements that keep the hip extended while the knee works train it best. Leg extensions with the torso reclined, and split squats or lunges where the rear leg's hip is open, both put it in a better position than an upright seated extension does.

In a squat its contribution is limited by hip flexion at the bottom, so a squat trains the vasti more thoroughly than it trains this. That is an argument for including something else, not against squatting.

It works as a hip flexor in leg raises and knee raises alongside the iliopsoas, which is a real second job and a reason it is rarely completely untrained.

Its superficial position down the middle of the thigh means its development is visible in a way vastus intermedius underneath it never is.

Anatomy

Origin
  • Straight head: anterior inferior iliac spine
  • Reflected head: groove above the rim of the acetabulum
Insertion
  • Base of the patella, through the quadriceps tendon
Actions
  • Extends the knee
  • Flexes the hip, bringing the thigh forward
Innervation
Femoral nerve (L2–L4)

Exercises

Antagonists

Synergists