When most people come in for a first session with me, they have some knowledge of their body. Most people know about quads, hamstrings, calves, biceps, and a handful of other muscles, but most people have less overall knowledge of the rest of the muscles – of which there are a lot! Today, we’re going to take a look at the psoas.
Where is it and what does it do?
The psoas is one of the muscles that most people don’t know much about. The psoas is the largest and strongest of the muscles that flex the hip (quite accurately referred to as the hip flexors, as a group). Psoas major and its friend, Iliacus may often be referred to together as “Iliopsoas”, because at their lower attachment, they are usually indistinguishable. Just to throw a little more fun into the mix, we’ll also consider the psoas minor, since it shares a half a name with psoas major.
The psoas major is the longest, strongest muscle of this group, and is found deep to the abdominal contents. It originates from the lumbar vertebrae and travels down to attach on the lesser trochanter, on the back (top) of the femur.
The iliacus is shorter and wider, located deep in the abdomen, originates in the iliac fossa (better understood as the area just inside your hip bone), and attaches at the same spot as the psoas major.
The psoas minor is less relevant, largely because it is only found in around 40% of the population. It originates from the lumbar vertebrae (along with the psoas major) and attaches on the superior ramus of the pubis (so, on the pelvis as opposed to on the femur bone in the leg). Interestingly, it does the opposite of the psoas major – when present, it assists in bringing a posterior tilt to the pelvis (upward rotation).
Because of its location connecting the torso and the legs, your psoas is involved in a lot of different movements – walking, running, sitting, twisting. Hip flexion is the psoas’ major job (bringing your thigh towards your torso or vice versa depending on what position you’re in). In addition to hip flexion, it stabilizes your lumbar spine, and it assists in laterally rotating the hip and adducting it (rotating out and bringing the leg towards the midline).
Why is it relevant?
If you sit a lot (for example, you sit at a desk for work ~8 hours a day), your psoas is shortened while you sit. If you do this often and/or for extended periods of time, they can become short and tight. Short, tight psoas muscles may lead to low back pain (since the muscle originates on your lumbar vertebrae- remember?)
The photo above gives you a pretty good idea of one way the psoas can contribute to low back pain. When the psoas shortens, it gives a downward pull (blue arrow). Since you don’t want to go through life bent over, your body’s response is to right itself (white arrow), and this causes an increase in the lumbar curve (lordosis).
Short and tight isn’t the only problem the psoas can have. It can also become overstretched, which makes it weak. In this scenario, there is a flattening of the lower back, a posterior tilt to the pelvis, and resultant tightening in the hamstrings. The flattened lumbar curve makes one particularly susceptible to disc damage in that area.
Balancing tension in the psoas
Given modern human’s proclivity towards sitting (working at a desk, driving, watching tv, etc), the psoas is often tight, short, and needs to be stretched. But stretching the psoas shouldn’t be your go-to move: there are other considerations.
1. In the first scenario described above – where the psoas is shortened, tight, and yanking the lumbar spine into an increased curvature – the body is in a position where there is a strong pull downward on the psoas. Stretching a muscle that is already being pulled on isn’t the best idea. In this case, you’d be better off contracting the muscle and then relaxing it a few times instead of giving it a traditional stretch. (This contract-relax method is PNF stretching – there’s a good description here)
2. In the second scenario that we described above – where the psoas is overstretched, weak, and there is a flattening of the lumbar curve – the body is in a position where there is a strong upward pull on the psoas. This comes partly from overly tight glutes and hamstrings which are basically taking advantage of the weak psoas and pulling the tension posteriorly. If you stretch the psoas further, it will allow the glutes and hamstrings to pull even more, which puts an even greater load on the psoas – effectively making the problem worse. A better solution here would be to release the tension on the glutes and hamstrings, which will lighten the load on the psoas.