Exploring the iliopsoas muscle

Iliopsoas: Iliacus and Psoas Major Muscle

Some key iliopsoas facts

  • The iliopsoas is a key postural and structural muscle.
  • It is the primary muscle that connects our torso to our legs.
  • The iliopsoas is the strongest hip flexor.
  • It is the primary muscle responsible for an important movement: walking.
  • It is intimately related to the convergence of tissues and structures often referred to as “the core”.
  • It spans more joints in the body than any other muscle.

What is the iliopsoas muscle?

Iliopsoas could be associated with three different muscles:

  • Iliacus
  • Psoas major
  • Psoas minor

However, the psoas minor is a fairly insignificant muscle that is absent in approximately half of the population. Because the relevance of psoas minor is generally insignificant, when we say “iliopsoas” we are referring to just iliacus and psoas major.

Iliacus and psoas major are frequently grouped together as the “iliopsoas” because they share a common attachment and they work together to the same primary movement.

Where is iliopsoas located?

The proximal end of iliacus originates on the fossa of the anterior ilium. This is the broad area on the inside of the pelvic bowl.

The proximal end of psoas major originates on the body of the vertebrae from T12 to L5.

Psoas major has a long path from its proximal end to its distal end where it meets up with iliacus. It runs down the sides of the spine, anteriorly over the front of the pubic bone, and then  heads posteriorly to meet up with the iliacus. Along its path, psoas major crosses nine joints: T12–L1, L1–L2, L2–L3, L3–L4, L4–L5, L5–sacrum, sacrum–ilium (SI joint), pubic symphysis, and the hip joint.

When the iliacus and psoas major join fibers at their distal ends, they form a common tendon and insert on the lesser trochanter of the femur.

What actions does the iliopsoas do?

Iliacus flexes and externally rotates the femur.

Both iliacus and psoas major flex the hip joint. This is their primary action.

Psoas major can also contribute to external rotation of the hip joint and adduction of the hip joint.

Remember, actions can go origin to insertion OR insertion to origin. Iliopsoas is the strongest hip flexor, whether this means we are standing and bringing the leg to the torso or we are sitting on the floor and bringing the torso towards the legs.

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