Hip flexors

The iliacus and nearby muscles

Iliac colon, sigmoid or pelvic colon, and rectum seen from the front, after removal of pubic bones and bladder. (Ilio-psoas labeled at center right.)

In human anatomy, the hip flexors are a group of skeletal muscles that act to flex the femur (thigh bone) onto the lumbo-pelvic complex, i.e., pull the knee upward.

The hip flexors are (in descending order of importance to the action of flexing the hip joint):

• Collectively known as the iliopsoas or inner hip muscles:
  • Psoas major
  • Psoas minor
  • Iliacus muscle

• Anterior compartment of thigh
  • Rectus femoris (part of the quadriceps muscle group)
  • Sartorius

• One of the gluteal muscles:
  • Tensor fasciae latae

• Medial compartment of thigh
  • Pectineus
  • Adductor longus
  • Adductor brevis
  • Gracilis

Without the iliopsoas muscles, flexion in sitting position is not possible across the horizontal plane.

Other actions

Muscles that act as hip flexors frequently perform other actions. Due to this, they can be strengthened with movements besides those involving hip flexion, and stretched with movements that do not involve hip extension (or hyper extension). Awareness of these actions allows trainers to modify flexion/extension movements/stretches to modify the work done and emphasize different hip flexor muscles Examples include:

• Knee extensor: rectus femoris
• Knee flexor: gracilis, sartorius

• Hip abductor: sartorius, tensor fasciae latae
• Hip adductor: adductor brevis/longus, gracilis, pectineus

• Hip lateral rotator: adductor longus, psoas, sartorius
• Hip medial rotator: pectineus

• Spine lateral flexor and anti-rotator: psoas
• Spine flexor: psoas (both sides)

References

• Platzer, Werner (2004). Color Atlas of Human Anatomy, Vol 1: Locomotor system (5th ed.). Thieme. ISBN 3-13-533305-1.  (ISBN for the Americas 1-58890-159-9.)
• "Iliopsoas". http://www.exrx.net/Muscles/Iliopsoas.html. Retrieved 1 September 2010. 

See also

• Hip extensors, the antagonist muscles to the hip flexors