The psoas is the most important muscle group you’ve never heard of

The psoas muscles play an important role in stabilizing your spine and maintaining posture

Quick notes

  • Without the psoas muscles, you wouldn’t be able to stand, walk, jump, climb stairs, or even get out of bed

  • Iliopsoas imbalance can result in “sway back” or “flat back” posture

  • A few simple daily exercises can help keep your psoas muscles limber and strong

The psoas muscle just might be the most important muscle in your body. Any time you do anything that involves moving your legs (like walking, biking, dancing, or just getting up out of a chair), your psoas is involved. It’s the muscle that stabilizes your spine and allows you to stand upright. Unfortunately, unless you’re an athlete or a bodybuilder, you’ve likely never heard of it.

When people complain of lower back pain or poor hip mobility, the psoas are often the culprit. Because they are a major part of the hip flexor group, weak psoas muscles can absolutely wreak havoc on your entire core area — and often, it’s NOT being active enough that can cause problems. Here’s what you need to know about the rock star of your hip flexors and how to keep yours in check.

What is your psoas muscle, and why does it matter?

When you think of your “core” you probably think of abdominal muscles: Transverse abdominis, internal obliques, external obliques, rectus abdominis. But your psoas muscle (pronounced “so-as”) is a VERY important part of your core. The psoas major attaches the lumbar vertebrae to the lesser trochanter — or, in layman’s terms, it attaches your spine to your femur. It’s often grouped together with the iliacus muscle, and together they’re referred to as the iliopsoas.

Fun fact: There is a third muscle, only possessed by roughly 40% of the population, called the psoas minor. It’s in important muscle for many animals, but in humans it’s fairly inconsequential.

Located deep within your core, the psoas is difficult to feel with your hands or even sense internally but trust us: It’s there. Along with the iliacus, the psoas is the strongest muscle in your hip flexor group (the muscles responsible for controlling the thighs and torso and how they move together). Unfortunately, it’s also very difficult to stretch . . . which is why it tends to hold so much pain for so many people.

What causes painful psoas contractions?

It’s super easy to throw your psoas completely out of whack — even if you haven’t done any exercise at all. What can do it? Sitting for long periods of time. Sleeping in the fetal position. Walking or running long distances. Doing a lot of sit-ups. Highly stressful situations. Pretty much just being alive. Why? Because anything that compresses your hip shortens your psoas muscle.

A compressed psoas muscle can be super painful, as can be attested to by anyone who has experienced it. However, hip or back pain doesn’t automatically mean you have a psoas problem — like any medical issue, there could be dozens of different causes. Before you start any treatment plan, check with your doctor or another healthcare professional to determine the true root of your discomfort.

How to tell if you have a psoas imbalance

Two of the telltale signs of psoas weakness are “swayback” posture of “flat back” posture, though they are not always present. Often, there will be no physical signs at all — only pain — and that can make the issue difficult to diagnose. Other symptoms, like lower back soreness, tightness in the hips, and unexplained knee pain are common but can be caused by many different issues.

[AndiP]/[AndiP] via pixabay
Luckily, there are a few symptoms that are dead giveaways. For instance, a tight psoas muscle can drive your femur up into the hip socket, making one leg appear shorter than the other, while a too-short psoas can pull your pelvis into an anterior tilt, causing “duck butt”. On the more embarrassing end of the spectrum, a tight psoas can directly contribute to constipation — so if you can’t poo, it might not from lack of fiber.

How to relieve pain in your psoas

When you find out you have a tight psoas, you may be tempted to hop on the floor and just stretch the heck out of it. Though a few down dogs or child poses may open up your hip area in general, they’re not going to give you the deep release needed to really fix those flexors.  And, unfortunately, those static stretches can actually make your psoas problem worse.

What can you do? Experts suggest pandiculation, or active stretching. This is a somatic movement (like yawning when you wake up in the morning) that activates your body’s nervous system. There are three steps to a pandiculation: Flex, extend, and relax. Start with contracting and releasing one muscle at a time and then progress to larger groups of muscles, and then your entire body. You’ll release all that tension in no time!

A deeper dive – Related reading on the 101:

Here are five simple stretches everyone can do to relieve low back discomfort