What Is the Psoas, and How Does It Affect the Lower Back?
The psoas (pronounced so-as) is one of the most important—and often misunderstood—muscles in the body. It plays a critical role in how we sit, stand, walk, breathe, and move through our spine and pelvis. In Pilates, understanding the psoas is key to improving both core control and spinal articulation, especially in the lower back.
Anatomy: What (and Where) Is the Psoas?
The psoas major is a deep, thick muscle that connects the lumbar spine (T12–L5 vertebrae) to the femur (thigh bone). It runs diagonally through the body, passing behind the abdominal contents and in front of the pelvis, and joins with the iliacus muscle to form the iliopsoas—your primary hip flexor.
Unlike many muscles that cross one or two joints, the psoas links your spine directly to your legs. Because of this, it influences everything from posture to pelvic position to the fluidity of your gait.
The Psoas and Lower Back Articulation
Articulation refers to the ability to move the spine one vertebra at a time, with control. This is essential in Pilates for exercises like Pelvic Curl, Roll Up, or Bridging, where you intentionally flex or extend the spine segment by segment.
Here’s how the psoas fits in:
The psoas attaches directly to the lumbar vertebrae, which means any shortening, tightening, or weakness in the muscle can limit movement in the lower back.
A tight psoas pulls the lumbar spine into an exaggerated arch (lumbar lordosis), making it harder to flex or articulate the spine.
A weak or underactive psoas can lead to instability or disconnection between the spine and pelvis, causing the low back to "clunk" or hinge instead of rolling smoothly.
When the psoas is coordinated and lengthened, it supports balanced lumbar movement and helps maintain neutral pelvic alignment, both of which are crucial for healthy articulation.
In short: a responsive, well-functioning psoas helps your lumbar spine move segmentally, while a stuck or disconnected psoas makes the low back feel rigid, grippy, or overly compressed.
In Pilates, We Train the Psoas to Support—Not Hijack—Movement
Because the psoas is so deeply tied to stability, breath, and emotion, we often approach it indirectly in Pilates. Instead of stretching it aggressively, we train deep core coordination, hip mobility, and spinal organization so the psoas can function fluidly.
Exercises like:
Supine Leg Slides
Pelvic Curl / Articulated Bridge
Leg Circles with core engagement
Constructive Rest with breath awareness
...gently teach the psoas to engage and release in harmony with the rest of the system.
Bonus: The Psoas and the Nervous System
The psoas is closely connected to the diaphragm through fascia and location. That means it responds to stress, fear, and shallow breathing. A constantly "on" psoas can contribute to feelings of anxiety and chronic tension in the low back and hips.
In Pilates, when we coordinate breath with movement, we help down-regulate the nervous system and soften this hypervigilant muscle. As a result, the lumbar spine becomes freer, safer, and more expressive.
At SOMA, we don’t treat the psoas like a problem to be fixed—but as a powerful messenger. When the spine isn’t articulating well, the psoas is often trying to tell us something about balance, breath, or support.
By moving with awareness, breathing deeply, and strengthening the deep core system, we give the psoas a chance to return to its natural role: stabilizer, connector, and bridge between spine and stride.