There are at least 650 skeletal muscles in the human body, and some sources put that number at more than 700. It’s hard to pin down the exact number down since there are so many variations in muscle anatomy. For example, we divide some muscles into sections, like anterior, lateral, and posterior deltoids and these might be included as separate muscles by some counts.
Some of the muscles in your body are small, like those in the eye and others are relatively obscure. The ones we think most about in the fitness world are muscles that move body parts and stabilize the spine. We have particular respect for large muscles, like the glutes, as they play such an important role in movement. Maintaining these muscles is vital to health, fitness, and avoiding injury. One group of muscles you don’t hear enough about are the hip flexors. In this muscle group is the psoas muscle, a muscle that plays a key role in hip flexion and spine stabilization.
Why the Psoas Muscle is So Important
What makes the psoas major muscle so unique is it’s a multi-joint muscle and one of only two muscles that connect the spine to the femur. Its main function is to flex the hip or shorten the distance between the thigh and the pelvis, but it also rotates the thigh in an outward direction. At the lower tip of the psoas, muscle is a smaller muscle called the iliacus and the two form a network called the iliopsoas, a hip flexor muscle, although not necessarily the strongest one. You use your iliopsoas muscle all the time. For example, you activate your iliopsoas when you bend over to pick something up and when you do exercises like crunches.
Hip flexion is only one of the functions of the iliopsoas. It’s also an important stabilizing muscle. In this role, it helps keep your spine stable when you sit and stand. In fact, some experts claim that the iliopsoas is the most important postural muscle in the body. You use your psoas muscle when you run, walk uphill, and go up a flight of stairs as you flex your hips when you do these movements.
Being such a critical muscle for stabilizing the spine, both weakness of the iliopsoas and excessive tightness can trigger back pain. People who suffer from chronic, lower back pain often have an overly weak iliopsoas muscle and this forces other muscles, like the glues and quads, to work harder to compensate. When the psoas muscle is weak it can also trigger anterior hip and groin pain.
Are Your Iliopsoas Muscles Too Tight?
How do you know if you have iliopsoas muscles? One sign would be an anterior pelvic tilt. When the hip flexor muscles, including the iliopsoas, are tight, they shorten in length and when they shorten, they pull the lower back forward. This leads to a classic postural problem called anterior pelvic tilt. It’s easier to see an anterior pelvic tilt if you look at yourself in a mirror from the side. If you stand up straight and see your lower back curves inward and your buttocks and tummy stick out, it’s likely that you have anterior pelvic tilt, brought on by tight iliopsoas muscles.
How does this happen? Sitting for long periods of time is a factor. Sitting causes your hip flexors to shorten and the shortening pulls on your lower back and even crowds the discs closer together. No wonder it’s linked with back problems! Another way you can develop iliopsoas tightness is from overuse. Some athletes, such as cyclists and runners, are prone toward this problem as they maintain a certain body position for long periods of time.
Here’s a simple test to see if you have tight hip flexors. Lie down on a mat face up with your legs straight. Notice how your back feels when your legs are stretched out on the mat. Does your lower back feel tight or do you feel a pulling sensation in your back? Slide your hand underneath your lower back. Is it easy to insert your hand because there’s lots of space? That’s a sign of tight hip flexors. This position pulls on your hip flexors. If they’re tight, you may notice discomfort or pulling and a space between your lower back and the mat. However, this test isn’t diagnostic. A physical therapist can do a more thorough assessment, including a test called the Thomas test, to diagnose tight hip flexors.
If you have tight iliopsoas muscles, work on lengthening the muscles with hip flexors stretches. A particularly effective one is a kneeling hip flexor stretch, which you’re probably already familiar with. Try foam rolling your hips to ease some of the tightness. Then, work on strengthening the opposing muscles, the glutes, and hamstrings. These muscles lengthen and weaken when your hip flexors are tight, and you need to help them become stronger to reduce the dominance of the hip flexors, including the iliopsoas.
What about Weak Iliopsoas Muscles?
As mentioned, the iliopsoas muscles also cause problems when they’re too weak. To test for iliopsoas weakness, sit in a chair. Raise one leg off the chair and have someone push it down toward the chair as you resist. If they can easily push your leg down to the chair, you have a weak iliopsoas on that side. Test both legs to check for discrepancies. If you have weak iliopsoas muscles, do strengthening exercises that target these muscles. Two effective exercises are leg raises on hanging leg raises on a Captain’s chair.
The Bottom Line
Yes, a strong, but not tight, iliopsoas muscle is vital for stabilizing your spine and pelvis and many people suffer from problems with their hip flexors due to lifestyle habits like too much sitting. Don’t neglect this muscle when you train! Also, make sure you’re walking around every hour throughout the day.
Orthop J Sports Med. 2013 Aug; 1(3): 2325967113500638.
David Campbell MDPA. “Tight Hip Flexor Muscles May Be Causing Your Low Back Pain”