Rectus femoris
The only one of the four quadriceps that crosses the hip, which changes everything about how it behaves.
- Type
- Muscle
- Region
- Thigh
- Standard name
- m. rectus femoris
- Origin
- Two heads — the anterior inferior iliac spine (straight head) and the groove above the acetabulum (reflected head)
- Insertion
- Base of the patella, then the tibial tuberosity via the patellar ligament
- Actions
- knee extensionhip flexion
- Verify
- TA2 2614 TA98 A04.7.02.018
What it is
The central, superficial head of the quadriceps, running straight down the front of the thigh — rectus means straight. It has two origins on the pelvis: a straight head from the bony point below the front of the iliac crest, and a reflected head from just above the hip socket. The two merge and descend to join the other three quadriceps at the patella.
It is the only quadriceps head that does not arise from the femur, and therefore the only one that crosses the hip joint.
What it does
Extends the knee and flexes the hip — both, at the same time, because it crosses both joints.
This makes it a two-joint muscle, and two-joint muscles behave in a way one-joint muscles do not: their available length depends on both joints at once. Straighten your hip and it is already partly lengthened, so it has less range left for extending the knee. Bend your hip and it slackens, and its ability to extend the knee changes accordingly.
That is why kicking a ball is a combination this muscle is well suited to — the hip flexes and the knee extends together, both its actions in one motion — and why a stretch for the front of the thigh has to extend the hip to reach it at all.
What loads it
Squatting and lunging load it as part of the group. Its distinctive contribution shows up where hip flexion and knee extension happen together, or where it has to lengthen across the hip while working at the knee — the trailing leg of a lunge, or a split squat.
The goblet squat loads it, though as a hip-and-knee movement it does not isolate the two-joint behaviour.
What is commonly got wrong about it
That the quadriceps behave as one muscle. Three of them cross one joint and this one crosses two, so its length, leverage and contribution change with hip position while theirs do not. Any statement about "the quads" that ignores this is wrong about a quarter of the group.
That a standing quad stretch is a quad stretch. Pulling the heel to the buttock bends the knee but leaves the hip roughly neutral, which reaches this muscle only partially. The hip has to extend as well.
Rectus femoris and rectus abdominis. Different muscles in different places. Rectus simply means straight, and several unrelated muscles carry it.