The psoas is a deep, ribbon-shaped muscle that runs from your lower spine to your upper thigh bone. It’s one of the few muscles in your body that connects your spine directly to your legs, making it essential for walking, standing, and maintaining upright posture. Most people never think about it until it starts causing problems, but it plays a role in nearly every movement that involves your trunk or hips.
Where the Psoas Sits in Your Body
The psoas major originates from the vertebrae in your lower back. Research using MRI imaging found that it most commonly begins at the disc between the T12 and L1 vertebrae (roughly where your ribcage meets your lower back) and doesn’t start any lower than the L2 vertebra. From there, it travels downward through the pelvis and attaches to a small bony bump called the lesser trochanter on the inner side of your upper thigh bone.
This path makes the psoas unique. It’s one of the only muscles that bridges the gap between your upper and lower body, crossing both the hip joint and multiple spinal segments along the way. Because it sits so deep in the body, tucked behind the organs of your abdominal cavity, you can’t see or easily feel it from the surface.
The psoas major also has an important relationship with several major nerves. The lumbar plexus, a network of nerves that supplies sensation and movement to your legs, runs partly within the muscle itself. The femoral nerve (which controls the front of your thigh) and the obturator nerve (which supplies your inner thigh) both pass through the psoas muscle fibers before continuing down into your pelvis and legs. This is one reason psoas problems can sometimes produce symptoms that radiate into the leg or groin.
The Psoas and the Iliacus: A Working Pair
You’ll often hear the term “iliopsoas” used interchangeably with psoas. That’s because the psoas major teams up with a separate muscle called the iliacus, which lines the inside of your pelvis, to form the iliopsoas muscle group. The two muscles merge into a shared tendon before attaching to the thigh bone. While they originate from different places, they work together to produce the same core movement: pulling your thigh upward toward your torso.
There’s also a much smaller muscle called the psoas minor. It sits in front of the psoas major but is far less important functionally. Only about 30% of people even have one, based on anatomical studies. When it is present, it plays a minimal role compared to the psoas major.
What the Psoas Actually Does
The psoas is often called a hip flexor, and that’s accurate, but it doesn’t tell the whole story. Cadaver research has shown that the muscle works differently depending on the position of your hip. At small angles of hip flexion (0 to 15 degrees, essentially when you’re standing upright), the psoas acts primarily as a stabilizer. It holds the head of your thigh bone snugly in the hip socket and helps keep your lumbar spine erect. Between 15 and 45 degrees, it continues to support spinal posture but contributes less to hip stabilization. Only at deeper flexion angles (45 to 60 degrees) does it become a powerful hip flexor.
In practical terms, the psoas is at work during activities like:
- Walking and climbing stairs, where it lifts each leg forward with every step
- Sitting up from a lying position, where it pulls your trunk upward
- Standing upright, where it stabilizes your lower spine and hip joints
- Holding posture while seated, where it helps keep your lower back from collapsing
Because the psoas crosses so many joints and serves both stabilizing and movement functions, it’s involved in a surprisingly wide range of daily activities. Any motion that shifts weight between your legs and trunk relies on it to some degree.
How Sitting Affects the Psoas
When you sit, your hips stay in a flexed position for hours at a time. The psoas, which shortens during hip flexion, can gradually adapt to that shortened state. Over time, a chronically shortened psoas pulls on the lower spine and tilts the pelvis forward (a posture sometimes called anterior pelvic tilt). This shift increases the curve in your lower back and can create a cascade of discomfort.
People with a tight or overworked psoas commonly experience lower back pain concentrated at the very base of the spine, stiffness that’s worse after long periods of sitting, and discomfort when trying to stand fully upright. The pain can spread into the groin, buttocks, hips, or even down the legs. In more pronounced cases, it can alter your walking pattern, causing a limp or a shortened, shuffling stride.
Psoas Syndrome: When the Muscle Causes Pain
Psoas syndrome is the clinical term for pain and dysfunction stemming from this muscle. It isn’t a single injury but rather a pattern of symptoms that can result from overuse, prolonged sitting, repetitive hip flexion (common in runners and cyclists), or direct trauma. The hallmark symptoms include lower back pain in the lumbosacral region, hip pain, groin pain, and stiffness that worsens when you try to straighten up.
Diagnosing psoas problems can be tricky because the muscle is so deep. A provider will typically examine your hips, legs, and spine, asking you to move into various positions that stretch or engage the psoas to see if they reproduce your pain. Imaging may be used to rule out other causes, but the diagnosis often comes down to how your body responds during the physical exam.
Because the lumbar plexus nerves run through the psoas, inflammation or significant tightness in the muscle can irritate those nerves, producing symptoms that mimic disc problems or nerve root compression. This overlap is one reason psoas issues are frequently misdiagnosed or overlooked in favor of more familiar back pain diagnoses.
Stretching and Releasing the Psoas
The psoas responds well to targeted stretching and manual release, but its depth makes it harder to reach than superficial muscles. A common stretch is the half-kneeling hip flexor stretch: kneel on one knee with the other foot forward, then gently shift your hips forward while keeping your torso upright. This lengthens the psoas on the kneeling side. Holding for 30 seconds and repeating several times on each side is a reasonable starting point.
For more direct intervention, myofascial release of the psoas involves applying sustained pressure through the abdomen. A therapist typically works with you lying on your back with knees and hips bent (to relax the abdominal wall), then uses fingertip pressure along a line between the navel and the front of the hip bone to access the muscle. A randomized clinical trial found that adding psoas myofascial release to standard physical therapy improved pain and disability scores in people with chronic low back pain. This isn’t something to attempt aggressively on your own, since the area also contains organs and blood vessels, but gentle self-massage with a small, firm ball is a common at-home adaptation.
Regular movement breaks throughout the day matter as much as dedicated stretching. Simply standing and walking for a few minutes each hour prevents the psoas from locking into a shortened position. Exercises that take your hip through its full range of motion, like lunges, leg raises, and bridge poses, help maintain both strength and flexibility in the muscle over time.