Rectus Femoris

The rectus femoris, a component of the quadriceps muscle group, is a long and straight muscle located in the front of the thigh. The muscle got its name from the Latin word, Rectus, which means ‘Straight’. 

It is the only two-joint muscle of the quadriceps group, having action on both the hip and knee joints. 

It is often referred to as the ‘kicking muscle’ because it simultaneously produces hip flexion and knee extension, the two essential movements required to deliver a powerful kick. 

It contributes to the explosive power and speed required to lift the thigh and extend the leg rapidly.

Anatomy:

Proximal attachment: 

Proximally, it has two heads attaching to the pelvis: 

  • A Straight head from the Anterior inferior iliac spine(AIIS), and 
  • A reflected head from the superior rim of the acetabulum. 
 

Distal attachment: 

It combines with other quadriceps muscles to form the quadriceps tendon and attaches to the patella. Then, it continues as the patellar tendon to the tibial tuberosity. 

 

Nerve innervation: 

The rectus femoris gets innervated by the Femoral nerve(L2, L3, L4). 

 

Blood supply: 

Arterial supply: Femoral artery 

Venous drainage: Femoral vein 

Function:

Rectus femoris, being a two-joint muscle, will act on both the hip and knee. 

 

Concentric action(shortening): 

Standard mover action (distal attachment moving towards proximal): 

 

Knee extension: 

The Rectus femoris extends the leg at the knee joint, as when straightening our knee while sitting on a chair. 

 

Hip flexion: 

The Rectus femoris flexes the thigh at the hip joint. However, it is not a main hip flexor; it assists the other hip flexors, like Iliopsoas, especially when the hip is flexed from the extended position. 

Reverse mover action:

(proximal segment moving towards distal)

When the tibia is fixed, rectus femoris contracts to extend the thigh at the knee joint, as in standing up from a chair. 

At the hip joint, it causes an anterior pelvic tilt when the pelvis moves over the fixed femur. 

 

Eccentric contraction(lengthening): 

The rectus femoris eccentrically contracts, allowing a smooth and controlled knee flexion. 

It helps in controlling and slowing down the hip extension.

Isometric contraction: 

The rectus femoris contracts isometrically to stabilize the knee joint and hip joint during the lower limb movements.

 

Pennation of rectus femoris and force production: 

 Pennation is the angular arrangement of muscle fibers while attaching to the tendon. This arrangement allows a greater number of muscle fibers within a given cross-sectional area, resulting in increased force production. 

 

Rectus femoris is a bipennate muscle, where the muscle fibers are arranged obliquely on both sides of the central tendon(feather-like). This pennation enhances the force production ability, making it well-suited for performing explosive movements like sprinting, running, jumping, etc. 

 

Insufficiencies of the Rectus Femoris: 

 Insufficiency is a biomechanical phenomenon that occurs with two-joint muscles. It refers to the inability of the muscle to function efficiently at both joints it crosses simultaneously.  

 

Active insufficiency: 

  • Active insufficiency is the inability of the muscle to produce force efficiently when it is shortened at both the joints it crosses. 
  • In case of the Rectus femoris, when the hip is flexed and the knee is extended, the muscle is already shortened at both ends. It becomes inefficient to produce additional force. 
 

Passive insufficiency: 

  • Passive insufficiency is the inability of the muscle to lengthen completely at both joints simultaneously. 
  • For the Rectus Femoris, this occurs when the hip is extended and the knee is flexed. In this position, the muscle is stretched over both joints and reaches its maximum attainable length. 
  • It will not be able to lengthen any further. This is why we feel a strong stretch in the prone quadriceps stretch, where the knee is flexed and the hip is extended, stretching/lengthening the muscle at both joints. 
Insufficiencies of the rectus femoris

What is the purpose of your Rectus Femoris?

  • The rectus femoris is a very important muscle that coordinates the movements of both the hip and knee joints, allowing smoother movements during functional activities and athletic performance as well.  It is essential for walking, sprinting, squatting, etc. 

 

  • It is a powerful knee extensor as it pulls the tibia forward (anterior translation) and helps straighten the knee. It is more powerful at mid-range knee flexion because, at that range, it will have the optimal length for force production. 

 

  • Even though it is not a primary hip flexor, it assists the other hip flexor. It effectively flexes the hip when the knee is bent.

 

  • Rectus femoris muscle strength is crucial for activities that require rapid hip flexion, such as sprinting.