It may be the most popular muscle in the world. 

For some reason, it gets a lot of credit for things and stirs up more debate than any other muscle (at least from what I’ve seen). 

Yes, we’re talking about the muscle of the soul! The wonderful Psoas. 

It’s been given credit for many a thing, including but not limited to: 

• anterior pelvic tilt
• breathing disruption
• manifesting physical symptoms of fear
• knee pain
• digestive problems
• low back pain
• and even somehow is part of our reptilian brain?

Whoa, this muscle is doing a lot!

When we look at some of these statements, they are often prefaced with “believed to,” and while people are entitled to believe whatever they want, some of these things are also taken as fact within our profession. 

When I was in college, this was often touted as the main reason people have low back pain. 

The muscle’s biomechanics showed us how a tight psoas was creating an increased lumbar lordosis when it was in a “shortened” position in everyone from office workers to cyclists. 

But what does the updated research say? Well…let’s get into that!

Biomechanics

First, it’s probably important to do a quick review (and yes, I had to look this up). 

It starts on the transverse process of T12-L4 as well as the intervertebral discs and inserts on the lesser trochanter of the femur. 

This research article⁽¹⁾ takes that a bit deeper and shows there are attachments on the anterior part of all lumbar TVP’s and the anteromedial aspect of the lumbar discs and bodies except on the L5/S1 disc. Where it attaches to the TVP’s is considered the posterior attachments, whereas the disc and bodies’ connections are considered the anterior attachments. There was an argument that those anterior attachments would pull the lumbar spine into and increased lordosis, but that  was with an assumption the attachments were more on the anterior surface of the vertebral body, not the TVP. 

When I was in school (and granted that was quite a while ago), we were taught that Psoas was primarily a hip flexor that worked along with Iliacus to accomplish the movement. However, some more recent studies⁽¹⁾ have shown it plays some other roles, including: 

• advancing the lower limb while walking
• controlling deviation of the trunk while sitting
• some action with rotation, abduction, and adduction of the hip
• lumbar spine stabilization
• hip stabilizer

Interestingly, the study ⁽¹⁾ looked at how the Psoas influenced hip pain in a hockey player, but not much discussion around low back pain. 

So, is the Psoas a culprit for patients presenting with low back pain?

Size And Role

A couple of studies looked at Psoas under MRI to compare cross-sectional size between those with low back pain and those without, and the results are pretty to interesting. 

They found those patients dealing with low back pain had a larger Psoas Major than those without pain. ⁽²⁾

One possible reason for this is that Psoas is a lumbar spine stabilizer; the muscle’s hypertrophy was due to increased activity in those with some degenerative disorders in the lumbar spine, so it’s working as a support or protection for the area. ⁽²⁾

When they looked at fat infiltration and whether it plays a role, there was a correlation with some atrophy of the lumbar paraspinal muscles, which would cause Psoas to increase its activity as a stabilizer for the lumbar spine. However, there was minimal infiltration of fatty tissue within Psoas. 

One other study looked at how Psoas was affected in older generations and did show there was a difference in size between men and women, which is likely due to hormone deficiencies after menopause. ⁽³⁾

When there were degenerative changes with the lumbar discs or segmental instability in the spine, they noticed that Psoas actually got smaller. However, this is likely because more pain is associated with these degenerative changes, so the size change is because of disuse. This could also directly correlate to fear avoidance, where a person stops certain activities because they’re worried about reinjuring the area or making it worse, especially after getting what sounds like a scary diagnosis. 

To me this is a little bit of a chicken or the egg. Could Psoas be causing pain, or is it’s size adapting because of pain resulting from something else? I’d argue it’s the latter.

So now we understand that Psoas is more of a support to the lumbar spine rather than something that is pulling it into lordosis or causing pain; the question remains…do we treat it?

Well, there’s a lot of controversy around this, and I’d say it depends.

Although I know if I do a treatment in this area in the way I was shown in school, I can definitely feel the psoas “pop up” under my fingers. However, we also know there is A LOT of stuff in the way to be able to palpate something that deep. Because in reality, we can’t palpate something that deep even though we can feel it “pop up”. 

I have a person who comes in once a month for treatment and really enjoys getting their Psoas worked on. They feel it benefits them greatly for the activities they participate in. So, yeah, I’ll treat it for them. However, if this was a new person coming in and saying their back pain is a result of the Psoas, well then I’d be digging a bit deeper into their reasoning and having more of a conversation to educate them on how Psoas is probably helping more than it is causing an issue. It’s one of those things where our clinical experience and decision making have to come in to play. Some say we should never treat the area but we also have to take patient preference into account and what they believe will help them. If you’ve been treating the area and having reasonable success and your patients like it, then keep on keeping on. But change the narrative around it. Take the time to educate a little and see if it’s really necessary. Especially if you’ve been giving this kind of treatment and the person is uncomfortable during the treatment (let’s be honest, it’s a pretty sensitive area), then offer to change things up and try something different. Just make it a joint decision between the two of you and strengthen that therapeutic relationship. 

If you haven’t subscribed yet, check out our new podcast HERE, we’ll be discussing Psoas this week and discussing some of the research around it. 

References

1. Sajko S, Stuber K. Psoas Major: a case report and review of its anatomy, biomechanics, and clinical implications. The Journal of the Canadian Chiropractic Association. 2009 Dec;53(4):311.
2. Arbanas J, Pavlovic I, Marijancic V, Vlahovic H, Starcevic-Klasan G, Peharec S, Bajek S, Miletic D, Malnar D. MRI features of the psoas major muscle in patients with low back pain. European spine journal. 2013 Sep;22(9):1965-71.
3. Sions JM, Elliott JM, Pohlig RT, Hicks GE. Trunk muscle characteristics of the multifidi, erector spinae, Psoas, and quadratus lumborum in older adults with and without chronic low back pain. journal of orthopaedic & sports physical therapy. 2017 Mar;47(3):173-9.