Most people have never heard of the psoas muscles, much less know where they are or how to pronounce the name (“SO-as”). Yet problems with these muscles often play a role in hip, groin, and low back pain. There are two of them, one on each side of the body. Each of these long, thick muscles originates deep in the abdominal cavity, from the sides of vertebrae in the lower half of the spine, and runs downward into the pelvis where it joins with another muscle (the iliacus) before attaching to the femur (thigh bone). Basically, the two psoas muscles connect the low back to the thighs, as shown in the illustration below.

As part of a group of muscles categorized as hip flexors, the psoas muscles’ primary action is to flex the hips in order to lift the thighs toward the torso, which allows you to run, walk uphill, and climb stairs, for example. They are vital for flexibility and movement of the back, pelvis, legs, and hips. And along with the core muscles, they help stabilize the spine.

If the psoas muscles become shortened or tight—from overuse or injury, for instance—they pull the small of the back forward, leading to excess curving (lordosis) of the lower back, which increases stress and pressure on the lumbar vertebrae. Sit­ting for hours on end, such as at work or in a car, is probably the most common contributor to shortening of the psoas muscles.

On the other hand, many athletes, including runners, soccer players, and cyclists, as well as dancers, end up with tight psoas muscles because they are prone to overuse them. Having tight psoas muscles reduces the length of your stride when you walk or run, since your hip can’t extend as much as it needs to, and the tightness can affect your performance in other ways as well.

Getting to the core of the problem
If you have low back, hip, or groin pain, there are many possible causes. A physical therapist, physiatrist, or other health care practitioner with expertise in musculoskeletal conditions can evaluate and treat you. One quick test often used by these practitioners to deter­mine if a tight psoas, in particular, is contributing to the problem is called the Thomas test (see illustration below). This involves lying on your back on the exami­nation table with your knees hugging your chest; you then extend one leg at a time to see how far you can hang it off the end of the table (see illustration below).

If the muscle is tight, it won’t drop very far, and you will wind up arching your lower back in the attempt. It’s common to have imbalances such that the muscle on one side is fine, but its counterpart on the other side is tight. If you are not having acute pain or just want to check your psoas muscles yourself, you can try this test at home, lying on the floor or another firm surface and bringing one leg up to your chest while trying to keep the extended leg and the small of your back in contact with the floor.

Treating a tight psoas muscle is not a matter of simply stretching it, as discussed in a paper in the Orthopaedic Journal of Sports Medicine that focused on dancers. A physical therapy regimen should also include strengthening and stretching the surrounding muscles—includ­ing the abdominal, gluteal, hamstring, and piriformis muscles—along with range of motion, pelvic mobiliza­tion, and postural exercises that help counter any excess lumbar lordosis. It’s important to learn proper technique, since even slight alterations in the exercises can reduce their effectiveness.

The doctor or physical therapist should also review any lifestyle factors that may be contributing to the problem, such as prolonged sitting, poor posture, sleep­ing in a fetal position, and doing sit-ups incorrectly. Some physical therapists, physiatrists, and osteopathic physicians work on trigger points, which may be causing referred pain (see Dealing with Painful Trigger Points), and can show you techniques for doing self-release or massage of trigger points at home.

Help for your hip flexors
Many people, especially those who sit for prolonged periods, can ben­efit from stretching their psoas and other hip flexor muscles as part of a balanced exercise routine. Don’t wait until you start having pain to take action. Here are some tips:

• Lying on the floor face up, flatten the small of your back (your thighs should not lift off the floor) and contract your abdominal muscles. Then bring one knee to your chest, keeping your lower back and extended leg on the floor (or as close to it as possible); hold for 30 seconds, repeat five times, then alternate with the other leg.
• Other good exercises include the fencer’s stretch, modified lunges, and the half-kneeling psoas stretch. To do the half-kneeling stretch, as shown below, begin by kneeling on one leg. Squeezing the buttock muscle of the leg that’s in back, and keeping your tailbone tucked under, shift your hips forward a bit. You should feel the stretch deep in the front of the hip that’s positioned back. Hold for 20 to 30 seconds, then switch legs. Repeat 2 or 3 times a day.

• Several yoga poses stretch and strengthen the psoas muscles, including the warrior pose. For examples, go to How to Stretch and Strengthen the Psoas.
• If you engage in a lot of hip-flexor-heavy exercise (like cycling or running), replace some with exercises that have a hip-extension effect (such as skating or cross-country skiing).
• If you do sit-ups, don’t hook your ankles under something, since that adds strain to the psoas. Instead, keep your knees and hips flexed at 90 degrees (a neutral pelvic position) when doing the sit-ups. This concentrates the contraction on the abs (which is what you want anyway).
• Limit sitting time, especially in a leaning-forward position. You might consider a workstation that allows you to alternate between sit­ting and standing. Or at least take frequent standing breaks.