Ultimate Guide to the Iliopsoas: What it does, why it hurts, and what to do about it
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Ultimate Guide to the Iliopsoas: What it does, why it hurts, and what to do about it

The iliopsoas is composed of two muscles that together connect your upper half to your lower half, provide stability for your entire lower body, and are chronically underappreciated.

You may not have spent much time thinking about your deeper core muscles - you can’t see or easily touch them, so they stay out of sight and out of mind. 

We take a different angle: we know, from decades of experience, that tension in these deeper muscles is the root cause for many unresolved pains in the hip, back, knee, and even feet. 

If these deeper muscles of your body are tight or imbalanced, it affects your entire body. Just because you can’t see them in the mirror doesn’t mean they aren’t playing a major role in your mobility, your strength, and your aches and pains.

Anatomy of the Iliopsoas

Let’s start by looking at all the parts, like an IKEA furniture diagram. 

The bones and joints around the iliopsoas muscles

  • Hip Joint: The hip joint is a ball and socket joint, formed between the pelvis and the head of the femur.
  • Femur: The femur is the thigh bone, also the longest and strongest bone in the body. 
  • SI Joints: The SI joints are located between the iliac bones and the sacrum, connecting the spine to the hips.
  • Lumbar Vertebrae: The lumbar vertebrae are the bones that make up the spine below the cervical and thoracic vertebrae, but above the sacrum/pelvis. 
  • Ilium: Ilium is made up of two large bones forming each half of the pelvis, after you take out the sacrum.

There are 2 main iliopsoas muscles 

You have two iliopsoas muscles that originate on either side of your pelvis and low back. And each of the iliopsoas muscles are actually made up of two muscles: the psoas and the iliacus. They have different starting places, but both end at the top of the thigh bone (femur), like the letter "Y".

One part of this muscle – the psoas– travels from your lower back, across the front of your pelvis, and attaches to the femur (thigh bone). Too often, we think of ourselves like paper dolls with a front side and a back side. But you’re 3-dimensional! This muscle crosses diagonally through your body in a direction we rarely think about. 

The other part of this muscle (the iliacus) travels from the Iliac fossa (the pelvic bone) and crosses over the hip joint (directly affecting the SI joint) to attach to the femur. Take a Deep Dive into the Anatomy of the Hip Flexors here.

What does the iliopsoas do? 

Short Answer: Stability and hip flexion. 


Both muscles are responsible for general stability and for hip flexion (lifting the knee, as in marching or going up stairs). Due to its insertion to the spine (low back), the psoas is also responsible for arching your lower back. Picture the inside prong of the 'Y' as the psoas, and the outer prong the iliacus. Because of these insertion points, they pull on the thigh bone differently. A tight psoas will pull your low back towards your knee. A tight iliacus will externally rotate your thigh bone, resulting in your foot turning outward. 

The psoas and the iliacus both contribute to hip flexion motion, but their primary job is to hold together the hip, pelvis, and lower back area.  

What does the iliacus do? 

Short answer: it's the glue that holds your hip joint, SI joint, and femur together. 

Primarily, the iliacus stabilizes the hip joint and the SI (sacroiliac) joint. Because it is relatively short and strong and crosses the two joints of the hip as well as the sacroiliac joint, it acts as more of a stabilizer. The iliacus keeps those two joints aligned and strong regardless of whether the body is stationary or moving. Long muscles have good lever arms for moving bones well. A good example of a long muscle is the quadricep, it goes from the hip to below the knee. Short muscles are built to hold parts in place. The iliacus, being more of a short muscle, was born to stabilize the hip and SI joint. Any situation that challenges these two joints will lead to a challenge to the iliacus muscle and possibly the development of chronic tightness.

Ever have a loose thread? What happens when you give it a tug? Usually, everything that attaches to that thread starts to get pulled along with it. You can think of the iliacus this way: if it's tight, it's going to pull the body into misalignment. 

What does the psoas do? 

Short answer: it connects the upper body to the lower body.  

The psoas stabilizes the hip and SI joints just like the iliacus, but it is also responsible for the stability of the lumbar spine and flexion of the hip joint. 

Similar to the iliacus, the psoas stabilizes the hip and SI joint, due to its connection to the lumbar spine. In addition, its close connection to the lumbar vertebrae and its attachment to the front and back of each vertebrae allow it to hold the lumbar spine in place. When there is any issue in the low back, the psoas grabs on for dear life to hold it all together, easily developing into chronic tightness. Its complex attachments at the lumbar spine also contribute to motion of the spine such as rotation, sidebending, flexion and extension, but primarily its job at the lumbar spine is to stabilize.

Why do I have tight hip flexors? Why do my hip flexors hurt?

Happy muscles don’t hurt and short and knotted muscles are not happy.  

The cause of tight hip flexors may vary: Perhaps you sit a lot, or you habitually cross the same leg over the other. Maybe you have to drive often and hover your foot over the pedal more than most. Maybe you played rotary sports like baseball, golf, or hockey that have you twisting primarily in one direction. Maybe your work from home (or work-from-couch) set-up is less than ideal, or your body is protecting past injuries. Any one of these can cause a contracted iliopsoas muscle. Most of us have more than one of these causes, making a perfect storm.

What can I do about my tight hip flexors? 

Stopping the muscle contraction is the first step.

When we say contraction, we mean shortening (and not the buttery kind). Muscles can contract as a whole or only part of the muscle can contract creating what we refer to as a muscle knot. Bring your palm to your forehead; you just shortened your bicep. Now hold that position for at least 8 hours, 7-days a week, and you will have recreated the problem with the iliopsoas. When you sit for eight hours a day, you are contracting (shortening) the iliopsoas. Do this long enough, and the muscle gets stuck trying to hold this position, so that when you stand up or lay down, this muscle is trying to yank you back into that seated position. It’s not worth getting frustrated with the iliopsoas; it's just trying to help you, and it needs some TLC and attention to relax. 

The first steps to relaxing your hip flexors

Relax, then lengthen. 

 If you notice, we keep saying contracted and using (shortened) in parentheses. This is deliberate. Most practitioners (physios, chiropractors, personal trainers) will tell you to stretch a tight muscle. Which would make sense if it was short, but stretching isn’t enough if it's short AND stuck in a contracted state

You’ll need to stop the contraction before you can lengthen the muscle

When any part of your iliopsoas is contracted, stretching it is like walking up to a terrified person in the fetal position and trying to pry them out of it. A better tactic is to calm them down, rub their shoulders, and remind them to take deep breaths. That's exactly the first step in releasing the iliopsoas.

How to release the iliopsoas

The best way to release the iliopsoas is by prolonged pressure: muscles relax first through pressure, then stretching. 

Muscle tissue is smart, and the fascia - the connective tissue that surrounds and holds every organ, blood vessel, bone, nerve fiber and muscle in place - is even smarter. Muscles and fascia both have sensors called mechanoreceptors which means our tissue can sense even the slightest change in temperature, pressure, vibration, even noise. Think of these sensors as two fire alarms: the stretch and pressure alarms. If two alarms are going off and you only silence one, are you going to be able to relax? Probably not. 

Why is pressure on the iliopsoas important? 

Pressure helps to relax the muscle and surrounding connective tissue, and provide immediate relief, calming the area down. The tissue's mechanoreceptors will send signals to the brain that it can relax and stop holding tension in the area. Only then can you begin to correct the issue with stretching and realignment exercises. If you jump right into stretching, you trigger only one of the receptors; by tomorrow you may be back where you started. This is why so many people are stuck on the stretching hamster wheel: the tightness builds back up, so they have to go stretch it out again. The missing ingredient for most tight psoas and tight iliacus muscles is prolonged pressure, best delivered through a massage or using a massage tool.

How to apply pressure to the iliopsoas

You can't just dig into this area all willy-nilly. Not to mention how uncomfortable that would be, this area is crowded with organs, arteries, and nerves. This is a case of “location, location, location”. If you spend the time finding the tight spots in your psoas and iliacus, you will know how to release your own iliopsoas. And it’s so worth it. 

There are many ways to access the psoas for psoas release. Some people prefer their physical therapists get in there manually, the DIYers may prefer a lacrosse ball (although that ball is too small), or a Hip Flexor Release Ball if you have a very tight psoas. Because the psoas is hard to reach and there is no ball or tool that can effectively reach the iliacus, I designed the Hip Hook for all of my suffering clients: the only muscle release tool targeting both the psoas AND the iliacus muscle. The iliacus can only be addressed through specific angular pressure, so finally having a tool that is able to hit those spots is magical.

The Hip Hook is unique because of its angular pressure 

Once you have located the sweet spot, you simply lay on the Hip Hook, allowing it to sink into the psoas for 30-90 seconds. Once you have relaxed, it is time to push down on the lever and feel the tip pressing up and into the iliacus muscle, pinning it against the ilium. Apply this prolonged pressure again for 30-90 seconds while breathing and relaxing. While the pressure can feel intense at first, you’ll likely feel a shift and release after 30-60 seconds. Prolonged pressure is important here. You may feel the desire to move around and rub the spot but in the case of muscles holding tension, they don’t like to be rubbed and any benefit you may feel temporarily will be short term.


When releasing the hip flexors, don’t forget your back side

A tight iliopsoas creates misalignment, causing other muscles to work overtime to compensate. You’ll want to apply pressure to these muscles as well (plus, it feels SO good). This is where the Hip Flexor Release ball comes in handy. Because the glutes, piriformis, and QL (quadratus lumborum) muscles are easier to reach and respond to perpendicular pressure, you don't need an advanced tool to release them. A simple ball or even foam roller will do the trick if you know what you're doing. (If you don't, please check out this video on how to release the back of the hip after you have released the iliopsoas). 

How to stretch the iliopsoas 


After applying prolonged pressure to the iliopsoas and the posterior (back side) hip muscles, now it's time to stretch! The lunge stretch is highly recommended because it stretches the iliopsoas, bringing circulation and length to that muscle. 

Step one foot forward with your spine straight. You can do this stretch with your knee on or off the ground. With this stretch it's important to engage your abdominal muscles or contract your glutes to eliminate the forward tilt of the pelvis while tucking your butt under you. This allows for the iliopsoas muscle to stretch fully over the joint while protecting your lower back from the psoas tugging on it while it's being stretched. 

You should feel the stretch in the front of your hip joint or the front of your thigh. If you're not feeling it there or if you’re feeling it in a different spot, then stop. You can experiment with bending your spine to the opposite side of the leg you're stretching to increase the psoas stretch

To get lasting results from your hip flexor stretch, focus on using proper form and take generously deep breaths.

Developing a plan to take care of your tight hip flexors

Prolonged pressure and light stretching is hopefully all you need to find relief. However, if you have experienced this issue for a very long time you may have more work to do. In my book Tight Hip Twisted Core, I lay out the Three Simple Steps to understanding and relieving unresolved pain. If you want to know what caused your hip flexors to tighten in the first place (and take preventative measures) this is a good place to start.

In over 20 years of clinical physical therapy practice, I have seen that nearly every client on my table had some degree of iliacus tightness causing a twisted pelvis and resulting in misalignment throughout the body. Tight iliopsoas muscles are merely a side effect of modern living, and we all need to be masters of this area of our body to be well and strong. I hope this information has set you on your path to being one of a growing number of iliacus and psoas masters.

FAQs about the iliopsoas

What is the function of the iliopsoas?

The function of the iliopsoas is to connect the lower body to the upper body, maintaining stability, facilitating lumbar rotation, lateral flexion and hip flexion. If the iliopsoas is too tight, it can affect the functioning of the entire body.

How do I release the iliopsoas muscle?

The iliopsoas responds to direct and angular pressure, anywhere from 30-90 seconds. It's a tricky muscle to access, and using a muscle release tool like the Hip Hook is the best way.

How do I stretch the iliopsoas?

A kneeling hip flexor stretch is the simplest way to stretch the iliopsoas and hip flexor complex. But it is most effective when followed by releasing the iliopsoas

By Christine Koth . Wed Dec 30

Author Bio

Uncovering the cause of your pain is my mission. As a bestselling author and holistic physical therapist with decades of experience, I have helped countless people, just like you, recover from long-standing issues. I've discovered a major cause of pain hidden in the hip and this has lead to my "Iliacus Queen" and hip expert status. I'm here to help you discover causes like this. It doesn't have to be complicated to live a pain-free life. We can do this. I look forward to supporting you on your healing journey.