Rectus Femoris Muscle Anatomy

Location & Overview

The rectus femoris is a large, superficial muscle located in the anterior compartment of the thigh, forming a significant part of the quadriceps muscle group. The other quadricep muscles include: the vastus medialis, vastus intermedius, and the vastus lateralis. These four muscles collectively contribute to knee extension and, to some extent, hip flexion. The rectus femoris is unique among the quadriceps muscles because it crosses both the hip and knee joints, making it the only quadriceps muscle involved in both actions. The fibers of all four quadriceps muscles converge into a single quadriceps tendon, which attaches to the patella ^{[1] [2]}.

The rectus femoris is a bi-articular muscle, which means it has the ability to act on two joints simultaneously. This characteristic allows for a more efficient transfer of forces between the hip and knee joints, contributing to coordinated lower limb movements during various activities, such as walking, running, and jumping ^[3].

Exercises that specifically target the rectus femoris should emphasize both hip flexion and knee extension, either concurrently or separately, as the rectus femoris spans both the knee and hip joints. One such exercise that combines both hip flexion and knee extension simultaneously is the Bulgarian split squat. This exercise engages the rectus femoris by incorporating hip flexion and knee extension while promoting greater muscle elongation in the posterior leg ^[4]. Walking lunges have a similar effect on stretching the rectus femoris in the posterior leg, albeit to a lesser extent, as the hip is less extended compared to the Bulgarian split squat ^[5].

Conventional compound exercises like squats and leg presses also activate the rectus femoris, but at a more shortened muscle length than Bulgarian split squats and lunges ^[6]. Neglecting to include any rectus femoris training at extended muscle lengths in one’s program may lead to suboptimal muscle development.

Here we can see the rectus femoris from a superficial view.

Here we can see the rectus femoris muscle in isolation.

Origin & Insertion

The rectus femoris muscle is unique among the quadriceps muscles, as it has two heads of origin: the direct (straight) head and the indirect (reflected) head. The direct head originates from the anterior inferior iliac spine (AIIS), while the indirect head arises from the superior part of the acetabulum, on the acetabular ridge or the ilium just above the acetabulum (the acetabulum is the the ‘ball-and-socket’ joint the hip sits in) ^{[7] [8] [9]}. These two heads merge to form the main muscle belly ^[10].

As the rectus femoris descends down the leg, it converges with the other three quadriceps muscles (vastus medialis, vastus intermedius, and vastus lateralis) to form the quadriceps tendon. This tendon’s fibers travel superficial to the patella and continue distally, as the patellar ligament. The patellar ligament inserts onto the tibial tuberosity ^{[11] [12]}.

Anatomical variations in the origins of the rectus femoris have been reported, though they are relatively rare. In some cases, the muscle may have additional heads or slips originating from the ilium or the capsule of the hip joint ^{[13] [14] [15]}

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Here we can see the two heads of origin of the rectus femoris. The direct head (originating at the anterior aspect of the inferior iliac spine) and the indirect head (originating at the acetabular ridge).

Here we can see the origins of the rectus femoris muscle. The direct head originates at the anterior aspect of the inferior iliac spine and the indirect head originates at the acetabular ridge.

Here we can see the insertion of the patellar ligament on the tibial tuberosity. The rectus femoris inserts into the patellar ligament.

Actions

The rectus femoris is a biarticular muscle, meaning it crosses two joints: the hip and the knee. Due to this, the rectus femoris plays a dual role in the movement of these joints ^{[16] [17] [18]}.

The primary action of the rectus femoris at the knee joint is knee extension. As a part of the quadriceps muscle group, it works synergistically with the vastus medialis, vastus intermedius, and vastus lateralis to extend the knee, especially during activities like walking, running, jumping, and squatting ^{[19] [20] [21]}.

At the hip joint, the rectus femoris acts as a hip flexor, working in conjunction with other muscles such as the iliopsoas and sartorius to flex the hip. This action is particularly important during the swing phase of gait, as well as during activities that require hip flexion, such as sprinting and walking up stairs ^{[22] [23] [24]}.

Due to its dual role in both hip flexion and knee extension, the rectus femoris functions as an antagonist to the hamstring muscles at both the hip and knee joints. The hamstrings are primarily responsible for hip extension and knee flexion, so their actions oppose those of the rectus femoris ^{[25] [26]}.

In this image, you can see an example of knee extension, which is the action of straightening out your leg at the knee. The opposite movement of knee flexion is knee extension. The primary role of the rectus femoris is knee flexion.

In this image, you can see an example of hip flexion, which is the action of raising your leg up in front of you and causing your hip to bend. If both legs are fixed, the torso will lean forward towards the legs. The opposite movement of hip flexion is hip extension. A secondary role of the rectus femoris is hip flexion.

Innervation

The innervation of the rectus femoris muscle is provided by the femoral nerve, a nerve that originates from the lumbar plexus and is composed of fibers from the L2, L3, and L4 spinal nerve roots. Apart from the rectus femoris, the femoral nerve also innervates the remaining quadriceps muscles: vastus medialis, vastus intermedius, and vastus lateralis ^{[27] [28]}.

The femoral nerve plays a vital role in transmitting motor commands from the spinal cord to the rectus femoris, allowing for the execution of movements such as knee extension and hip flexion. Furthermore, the nerve is responsible for transmitting sensory information from the skin and deeper structures of the anterior thigh and medial leg back to the central nervous system ^{[29] [30]}.

Blood Supply

Blood is supplied to the rectus femoris from the femoral artery. The other three quadricep muscles (vastus medialis, vastus intermedius and the vastus lateralis) also get their blood supply from the femoral artery ^[31].