Pso What? One Vital Muscle You’ve Probably Never Heard of

by Rachael Ling

What is the psoas and how it can affect you?

The psoas is a large muscle that acts to maintain the muscular connection between your torso and lower body. Specifically, the psoas major connects the thoracic spine to the lumbar spine and travels through the pelvis, SI joint, and femur. Although we tend to think of the psoas as a singular entity, we are usually referring to a combination of muscles known as the “Iliopsoas muscle” when discussing function. The complex includes the iliacus and psoas major (and in some, psoas minor muscles). These muscles originate in different places but unite to cross the hip joint and attach at the femur, and they act as our primary hip flexors.

Fun Fact: Did you know that only a portion of the population has a psoas minor muscle? In fact, some people may only have one! The psoas minor muscle belongs to the category of vestigial muscles. As we became bipeds through the process of evolution, the psoas minor has become less necessary and considered a remnant from our evolutionary past.

Key Iliopsoas Facts1

  1. The iliopsoas is a crucial postural and structural muscle.
  2. It is the primary muscle complex that connects our torso to our legs.
  3. The iliopsoas is the strongest hip flexor.
  4. It is the primary muscle complex responsible for important movements such as walking, running, etc.
  5. It is intimately related to the convergence of tissues and structures often referred to as “the core.”
  6. It spans more joints in the body than any other muscle.

What are some symptoms of dysfunction?

It would be negligent to discuss the psoas without emphasizing its connection to the overarching muscle system, the iliopsoas. Due to the sheer surface area that the iliopsoas complex spans, it’s not hard to imagine why any suboptimal level of function can lead to more global issues. That being said, when we talk about dysfunction in this region, we are mainly referring to issues with the psoas major muscle in particular.

Whether you are sedentary or a professional athlete, a dysfunction of the psoas is not uncommon. In addition to overuse (like athletic training) and limited movement (seated desk job), physical and emotional trauma have been linked to psoas tension (2). You may be familiar with common symptoms such as back, hip, and knee pain. However, did you know a tight psoas can cause seemingly unrelated symptoms including bladder pain, pelvic pain, and digestive, mood, and breathing issues? Most of the large nerves that come out of our lower spine must run through the psoas before connecting to our internal organs, pelvis, and legs. Therefore, our psoas has the potential to influence us biomechanically, physiologically, and psychologically.

What causes Psoas dysfunction?

We use the term “dysfunctional” as an umbrella term. The psoas can be overactive, weak, shortened, or overstretched. A large percentage of the population suffers from a tight, shortened psoas. Two physical therapists, Chris Vodzak and Kristen Henry at Elite PT, state, “Due to our societal demands of sitting excessively throughout the day, this muscle can often become short and tightened. Because of its anatomical location, attachments on the lumbar spine, and insertion onto the anterior pelvis, it can pull the low back into an anterior pelvic tilt. This, in turn, shortens the lumbar erector group, causing lower back stiffness and tightness, and places the antagonistic muscle group, the glutes, at an elongated length, making them difficult to activate.” This scenario sets the stage for an imbalance in the kinetic chain even when no longer in a seated position. Often this imbalance is further exacerbated through activities that require repetitive hip flexion, such as running, biking, skiing, etc.

Another portion of the population encounters an overstretched psoas. In this scenario, these individuals exhibit a posterior pelvic tilt. This creates a flattening of the natural curve of your lumbar spine, making it vulnerable to injury and causing potential pain and instability at the front of the hip.

Left: Good Posture, Middle: Posterior pelvic tilt- Pelvis tilts backward, creating a loss of the natural curve of the lumbar spine, Right: Anterior pelvic tilt- Pelvis tilts forward, creating the appearance of excessive curvature in lower back

Tight or overstretched?

A great place to start assessing the state of your hip flexors is examining your posture from a standing position. Your spine has two natural curves: slight flexion in your thoracic spine and slight extension in your lumbar spine. If either of these curves is exaggerated, it compromises your spine’s ability to move and stabilize your trunk, placing you at risk of pain and injury.3

The Thomas Test

The traditional way in which a physical therapist or sports medicine physician would test the flexibility of your hip flexors is by utilizing a diagnostic tool called the Thomas Test. To perform this test, you would lay face-up on a table with your knees hanging off the edge. Keeping your lower back flat against the table, you would slowly bring one knee towards your chest. If your opposite thigh comes up off the table, you test positive for tight hip flexors. This method offers a basic, quick way in which to assess hip tightness – however, is limited in its ability to identify the root cause. Additional assessments may be required.

Disclaimer: The Thomas Test, when performed without the supervision of a medical professional, is meant to be an evaluative tool, not a diagnostic tool.

What are some common ways to restore balance?

Once it has been determined whether your psoas is shortened or overstretched, you must then determine if it is underactive (weak) or overactive. Your psoas can become overactive due to compensatory efforts from underactive muscle elsewhere. Therefore, if we were to only focus on relaxing a tight psoas, say through stretching or foam rolling, we would be fighting an uphill battle. To tackle this scenario, we would also need to address strengthening the areas the psoas is attempting to compensate for. In the same vein, in the case of a weak, overstretched psoas, the intervention may be to foam roll tight muscles while strengthening the psoas. To further complicate matters, a tight psoas can be weak and need strengthening vs. stretching. Determining the chicken and the egg is essential to ascertain the best course of action to restore balance. Often, we neglect to truly identify the cause, which leads to interventions that may not help or possibly make the situation worse. There is no one-size-fits-all prescription for taking care of your hip flexors.

Depending on the root cause, we may need a combination of approaches:

  • Massage Therapy
  • Rolfing
  • Acupuncture
  • Dry needling
  • Self-myofascial release
  • MAT
  • Stretching and strengthening
  • Pandiculation
  • Breathwork and stress reduction.

A vicious cycle: The Fight or Flight Response

The psoas is attached to the diaphragm through fascia and the medial arcuate ligament. With each breath, the psoas and diaphragm work together to provide anterior spinal stability. A tight psoas muscle can create a thrusting forward of the ribcage. This causes shallow chest breathing, limiting the amount of oxygen taken in, and encourages over usage of your neck muscles along with tight, tense shoulders. The psoas – and, hence, the diaphragm – react to fear and to stress with constriction. Therefore, in addition to poor athletic performance, if we can’t breathe deeply, our nervous system senses a threat or danger and activates the fight-or-flight response. In turn, we literally unconsciously tense the big muscles like the psoas and quadriceps used to fight or run! How’s that for a metaphor in action?!

Another phenomenon worth mentioning is how the vagus nerve innervates with the psoas. The bundle of nerves, also termed vagal nerves, passes through the psoas. This piece of the nervous system controls specific body functions such as your mood, digestion, heart rate, and immune system. These functions are involuntary, meaning you can’t consciously control them. Emotional stress triggers the vagus nerve, causing us to tighten the psoas unconsciously. The reverse is also true – a chronically tightened psoas continually signals your body that you are in danger by activating the vagus nerve, thus indirectly signaling all the bodily functions associated with this piece of the nervous system.

Why stretching isn’t always the fix: We can stretch all day and never make any noticeable change because that may not address the actual cause. Our nervous system sets the resting level of tension in our muscles. Over time, due to repetitive movements and stress, our nervous system learns to keep specific muscles tight. While static stretching temporarily lengthens muscles by reducing the activity of our stretch reflex, the effect is often short-lived. Our muscles typically start tightening up within a few hours as our stretch reflex regains normal function. Therefore, stretching may need to be combined with other modalities to correct the issue. 2



The Psoas: The Muscle of the Soul

by Maria DiCamillo

The psoas plays an instrumental role in all of our yoga postures, and yogis often refer to the psoas as “The Muscle of the Soul.” A deeper understanding of this can add new insight, openness, fluidity, and stability to your yoga practice. This core-stabilizing muscle affects mobility, structural balance, alignment, joint function, flexibility, range of motion, and so much more. For example, in backbends, a released psoas allows the front of the thighs to lengthen and the legs to move independently from the pelvis. The psoas stabilizes the body’s upper and lower half in standing poses and forward bends. Increasing your awareness of this muscle can significantly enhance your physical practice, emotional health, and spiritual mindfulness. It opens the doors to a more conscious attunement to your body’s inner signals relating to safety and danger and developing a greater sense of presence, joy, and inner peace.

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