Pelvis & HipsSource-checked

Iliopsoas

Iliopsoas (psoas major + iliacus)

Pronunciation: il-ee-oh-SOH-as

Simplified front view of the pelvis showing the wing-shaped hip bones meeting at the pubic symphysis, the ball-and-socket hip joint where each femur meets the acetabulum, and the iliopsoas running from the lower spine across the front of the hip to the femur. — Pelvis & hips — hip bone, hip joint, and iliopsoas (simplified). A beginner-level schematic of the pelvis's bony ring, the hip joint, and the iliopsoas hip-flexor muscle.
Illustration: Anatomy Learning Platform (original) · CC0-1.0 (public domain dedication)

For beginners

This deep muscle group is your main 'hip flexor' — it lifts your knee toward your chest, like the first part of a high step or a kick.

Show the advanced explanation

Because the psoas major attaches directly to the lumbar spine, tightness here can pull the low back into extra arch (anterior pelvic tilt); balancing hip-flexor mobility with core and glute strength is common coaching practice.

Structure & function

Location: A deep muscle group running from the lower spine and the inside of the pelvis, down and forward across the front of the hip to the upper thigh bone.
Origin: Psoas major: bodies and transverse processes of the lumbar vertebrae. Iliacus: inner surface of the ilium.
Insertion: Lesser trochanter of the femur.
Main action(s): Flexes the thigh at the hip (the primary hip flexor); when the thigh is fixed, helps flex the trunk toward the thigh; assists in maintaining lumbar posture.
Joint(s) crossed: Hip joint (and, for the psoas major, the lumbar intervertebral joints)
Movement plane: sagittal
Innervation: Femoral nerve (iliacus) and lumbar plexus branches (psoas major, L1–L3)
In daily movement: Lifting the knee to walk, climb stairs, or kick, and the last part of sitting up from lying down.
In exercise: Prime mover in hip-flexion exercises (leg raises, marching, high-knee drills) and active in the top phase of a squat or lunge as the hip flexes.
Commonly confused with: Often lumped simply as 'hip flexors' along with the rectus femoris (a quad muscle); the iliopsoas is the deeper, primary flexor while the rectus femoris assists.
Common misconceptions: 'Tight hip flexors' is not a diagnosis of injury by itself — mobility work and balanced strength training, not medical treatment, is the usual first approach for simple tightness.

Exercises that use this muscle

As a primary mover

Standing Hip Flexor March

⚠ Safety note

A deep, sharp groin pain with hip flexion (rather than simple tightness) should be assessed by a professional before continuing loaded hip-flexor work.

Sources

“The iliopsoas (psoas major and iliacus) is the primary flexor of the thigh at the hip joint.”

Anatomy and Physiology 2e — OpenStax, Rice University · Ch. 11.6 Appendicular Muscles of the Pelvic Girdle and Lower Limbs

Peer-reviewed textbook · License: CC BY-NC-SA 4.0 · Last checked 2026-07-19

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