The psoas (pronounced SO-az) is a deep muscle that runs from your lower spine through your pelvis to the top of your thighbone. It’s the body’s primary hip flexor, responsible for lifting your knees, bending at the waist, and stabilizing your lower back when you stand or sit. You actually have two psoas muscles, one on each side of the spine, and they play a surprisingly large role in how you move, how you stand, and whether your lower back feels comfortable or painful.
Where the Psoas Sits in Your Body
The psoas major is a long, thick muscle that originates along the sides of your lowest thoracic vertebra (T12) and the first four lumbar vertebrae, attaching to both the vertebral bodies and the discs between them. It has two layers: a deeper segment anchored to the lumbar vertebrae and a more superficial segment that grabs onto the lower thoracic spine and nearby discs. From there, the muscle fibers travel downward through the pelvis, changing direction as they cross the pelvic brim, and attach via a thick tendon to a small bony bump on the inner side of your upper thighbone called the lesser trochanter.
This path makes the psoas unusual. Most muscles cross one joint. The psoas crosses multiple, connecting your spine directly to your leg. That’s why it influences both your hip and your lower back at the same time.
There’s also a smaller companion called the psoas minor, but not everyone has one. Cadaver studies find it present in roughly 60% of people, with some variation by population (about 37% in Indian populations, closer to 66% in American ones). The psoas minor runs a shorter course and attaches to the front of the pelvis rather than the thighbone. Its job is limited to a small amount of spinal flexion, and its absence causes no functional problems.
What the Psoas Actually Does
The psoas major teams up with another muscle called the iliacus to form what’s often referred to as the iliopsoas complex. Together, they are the strongest hip flexors in the body. Every time you lift your knee, climb a stair, get out of a car, or shift from sitting to standing, you’re using this muscle pair. The iliopsoas can also rotate your thigh slightly outward and pull it toward your midline.
The two muscles can work independently, though. The iliacus primarily stabilizes the pelvis and helps with smooth hip flexion during running. The psoas major stabilizes the lumbar spine when you’re sitting and helps flex your thigh when you’re lying down or standing. If your legs are fixed in place, contracting the psoas flexes your trunk forward, which is why it fires during sit-ups.
One of the psoas’s less obvious roles is maintaining the natural curve of your lower back. Research suggests it acts as a passive stabilizer of lumbar lordosis (the inward curve of your lower spine) during upright standing. Its individual muscle fibers appear to adjust their tension in response to changes in spinal curvature, helping keep your spine balanced without requiring much active effort. This stabilizing function may explain why problems with the psoas so often show up as lower back pain rather than hip pain.
The Psoas-Diaphragm Connection
The psoas shares a fascial connection with your breathing diaphragm. The fascia covering the top of the psoas continues upward to become the medial arcuate ligament, a fibrous arch that the diaphragm attaches to. The diaphragm’s spinal anchors, called the crura, attach to the upper lumbar vertebrae and overlap with the psoas, their tissues appearing nearly continuous before they separate and blend into the spinal ligaments. This anatomical link is one reason chronic psoas tension can influence breathing patterns, and why deep breathing exercises sometimes help release tightness in the hip flexors.
What Psoas Problems Feel Like
When the psoas becomes tight, irritated, or inflamed, it creates a pattern of symptoms that can be confusing because the pain often shows up far from the muscle itself. The most common complaint is deep pain in the front of the hip or groin, but it frequently radiates to the lower back (particularly the border between the bottom of the spine and the buttocks), the thigh, or even the opposite buttock. Pain typically worsens with activity and improves with rest. It rarely extends below the knee.
Specific movements tend to trigger it: standing up from a chair, trying to walk with a full upright posture, extending your hip backward, or resisting while someone pushes your knee down. Some people feel a catching or snapping sensation in the groin when the knee bends to 90 degrees. Adolescent athletes going through growth spurts are particularly prone to this snapping hip presentation, especially in sports that involve kicking.
In chronic cases, a tight psoas can pull the pelvis into an exaggerated forward tilt, which deepens the lumbar curve and puts extra compression on the spinal discs. You might notice that your lower back arches more than normal, that your belly pushes forward even if you’re not carrying extra weight, or that hip extension feels noticeably restricted on one side.
Diagnosis is primarily clinical. A provider will test your hip range of motion and may use the Thomas test (lying on your back and pulling one knee to your chest to see if the other thigh rises off the table) or a resisted straight-leg raise. Imaging like X-rays or MRI is generally unremarkable for psoas syndrome and is mainly used to rule out other causes of hip or back pain.
Psoas Abscess: A Rarer, Serious Problem
Psoas syndrome is a musculoskeletal issue, but the psoas can also develop an abscess, which is an infection that collects within or around the muscle. This is uncommon but serious. The classic presentation is fever, back pain, and a limping gait with limited hip motion, though this full triad only appears about 30% of the time. More often, symptoms are vague: dull abdominal pain, fatigue, pain radiating to the hip or thigh, nausea, or unexplained weight loss.
Primary psoas abscesses tend to develop in people with diabetes, kidney failure, or compromised immune systems. Secondary abscesses arise from nearby infections or diseases, including Crohn’s disease, kidney infections, or bone infections. A missed diagnosis can lead to sepsis, so persistent fever combined with deep hip or back pain warrants prompt evaluation.
Exercises That Help
Because the psoas spends most of the day in a shortened position whenever you’re sitting, the most effective approach combines stretching it back to its full length with strengthening it through its range of motion. Since the psoas lifts your knee, exercises that work this movement pattern target it directly.
Strengthening
- Standing knee raises: Stand with feet shoulder-width apart. Lift one leg by bending at the knee, toes pointing down, while keeping the other foot planted with the knee straight but not locked. Hold for a few seconds, lower, and repeat on each side for several reps.
- Marching: March in place, bringing your knees up toward your chest. You can hold the back of a chair for balance. Try marching across your house instead of walking, or march while seated to work the psoas with less demand on your balance.
- Quadruped leg lifts: On hands and knees, lift one leg toward the ceiling with the knee bent (like a donkey kick). Lower it slowly and repeat. This exercise strengthens the glutes, which allows the psoas to relax and work through a healthier range of motion.
Stretching
The classic psoas stretch is a half-kneeling lunge: drop one knee to the floor, plant the other foot in front of you, and gently shift your hips forward until you feel a stretch deep in the front of the hip on the kneeling side. Keep your torso upright rather than leaning forward. Holding for 20 to 30 seconds and repeating two to three times per side is a standard approach. People who sit for long stretches during the day benefit from doing this daily.
The key with psoas work is consistency over intensity. This is a deep, postural muscle that responds better to gentle, sustained effort than to aggressive stretching. If a stretch or exercise reproduces sharp groin pain or snapping, back off the range of motion and build up gradually.