A Human Web
Join

Muscle guide · Hips and glutes

Iliopsoas

Also called psoas, hip flexor muscle

The iliopsoas is two muscles that share a tendon: the psoas major, a long rope of muscle running from the sides of the lower spine through the pelvis, and the iliacus, which fills the inside of the bowl of the hip bone. They join to cross the front of the hip and attach to the inner thigh bone.

It is the main muscle that lifts the knee toward the chest, and with the legs fixed it helps curl the trunk up, as in the second half of a sit-up.

5 exercises3 stretches8 with 3D demos13 sourcesUpdated 17 October 2026

Where the iliopsoas is and what it does

Shaded: the hip flexors area. It marks the region, not the exact outline of the iliopsoas.
What it does
  • Lifts the knee toward the chest: climbing stairs, the knee drive of a sprint.Hip flexion (the primary hip flexor)
  • With the feet fixed, curls the trunk up toward the thighs.Trunk flexion with the limb fixed
  • Helps hold the low back upright, especially sitting tall.Lumbar stabilisation in sitting
Nerve supply
Psoas: lumbar plexus branches (L1 to L3, or L1 to L4). Iliacus: femoral nerve (L2 to L4, with sources differing).

Sources 1, 2, 3

The parts of the iliopsoas

PartStarts atAttaches toWhat it does
Psoas majorSides of the first four lumbar vertebrae (one source says T12 to L5)A bony bump on the inner upper thigh bone (lesser trochanter)Bends the hip; steadies the lumbar spine, especially sitting upright
IliacusThe inner bowl of the hip bone and the side of the sacrumJoins the psoas tendon to the same bumpBends the hip; can steady the pelvis on its own

Sources 1, 2, 3

Exercises for the iliopsoas

A review of 9 EMG studies found iliopsoas activity highest between about 30 and 60 degrees of hip flexion, above 60% of maximum in straight-leg raises and lying leg lifts; sit-ups worked the psoas far more than curl-ups.

Straight-leg raise demonstrated on the 3D figure3D demoStraight-leg raiseBeginner · No equipmentLying leg raise on a bench demonstrated on the 3D figure3D demoLying leg raise on a benchBeginner · A bench or boxSit-up (3/4 sit-up) demonstrated on the 3D figure3D demoSit-up (3/4 sit-up)Intermediate · No equipmentStanding march demonstrated on the 3D figure3D demoStanding marchBeginner · No equipmentStanding band hip flexion demonstrated on the 3D figure3D demoStanding band hip flexionBeginner · A band + An anchor point

Stretches for the iliopsoas

In a crossover trial, tucking the pelvis under (a posterior tilt) during the half-kneeling stretch reduced hip-flexor resistance more than the usual version; two 30-second holds were used. Active and passive home stretching both improved hip extension over 6 weeks in another trial.

Half-kneeling hip flexor stretch demonstrated on the 3D figure3D demoHalf-kneeling hip flexor stretchBeginner · No equipmentCouch stretch demonstrated on the 3D figure3D demoCouch stretchIntermediate · A wallLow lunge (Anjaneyasana) demonstrated on the 3D figure3D demoLow lunge (Anjaneyasana)Beginner · No equipment

Problems linked to the iliopsoas

Hip flexor pain, tendinitis and snapping

Overload can inflame the iliopsoas tendon or its bursa and cause groin pain. The tendon can also snap over the front of the hip (internal snapping hip), common in dancers and athletes and often painless.

Sources 1, 5

Psoas abscess

Rarely, an infection collects in the psoas, causing back, groin or hip pain with a fever. It needs prompt medical care.

Sources 1, 2

Myths worth dropping

Each grade rates the evidence for the correction.

A tight psoas pulls your back into an arch and causes back painMixed evidence

In 600 adults, iliopsoas length was not associated with low back pain, and in healthy adults hip extension range did not predict pelvic tilt or the curve of the low back. Biomechanical studies found the psoas has very little leverage to change the lumbar curve.

StatPearls articles still say the psoas can contribute to non-specific back pain. A causal link between tight hip flexors and back pain is not established, and no study shows that stretching the psoas relieves back pain.

Sources 6, 7, 8, 1

Routines that train it

Hip mobility routine

A 15-minute hip opener: 90/90 switches, windshield wipers, CARs, Cossack squats, frog and pigeon.

15 minIntermediate8 movesA wall

5-minute desk stretches

A quick stretch break you can do beside your desk: neck, back, chest, wrists, hips and quads.

5 minBeginner7 movesA wall

Questions people ask

What does the psoas do?

With the iliacus it lifts the knee toward the chest, helps curl the trunk up when the feet are fixed, and helps hold the low back upright when you sit tall.

Does a tight psoas cause lower back pain?

The evidence does not support it: hip-flexor length was not associated with back pain in 600 adults, and the psoas has little leverage to change the curve of the low back.

How do you stretch the psoas?

A half-kneeling hip-flexor stretch with the pelvis tucked under worked better than the usual version in a crossover trial. Hold for about 30 seconds, twice.

What is the difference between the psoas and the iliacus?

The psoas starts on the lumbar spine and the iliacus inside the hip bone; they share a tendon to the thigh bone and are usually called the iliopsoas together.

Muscles it works with

Sources

  1. StatPearls · Anatomy, Bony Pelvis and Lower Limb: Iliopsoas Muscle (2026)
  2. StatPearls · Anatomy, Bony Pelvis and Lower Limb: Psoas Major (2023)
  3. StatPearls · Anatomy, Abdomen and Pelvis: Posterior Abdominal Wall Nerves (2022)
  4. Cleveland Clinic · Psoas muscle
  5. Cleveland Clinic · Snapping hip syndrome
  6. Nourbakhsh & Arab 2002 · Which physical factors relate to low back pain? (600 adults, JOSPT, abstract)
  7. Heino 1990 · Hip extension range, pelvic tilt and lumbar lordosis (JOSPT, abstract)
  8. Bogduk 1992 · What the psoas does and does not do to the lumbar spine (Clin Biomech, abstract)
  9. Juan 2024 · Iliopsoas activation across exercises (systematic review, J Clin Med)
  10. Juker 1998 · Psoas and abdominal wall activity in a range of tasks (fine-wire EMG, Med Sci Sports Exerc, abstract)
  11. Escamilla 2006 · Abdominal and hip-flexor activity in ab devices and exercises (Phys Ther, abstract)
  12. González-de-la-Flor 2024 · Half-kneeling hip-flexor stretch with and without a posterior pelvic tilt (crossover trial, BMC Musculoskelet Disord, abstract)
  13. Winters 2004 · Active vs passive hip-flexor stretching (RCT, Phys Ther, abstract)

Anatomy and movement education, not a diagnosis or treatment plan. If you have pain that follows an injury, is severe or getting worse, or comes with numbness, weakness or swelling, get it assessed. Health disclaimer.