The Psoas Major: More Than a Hip Flexor

Sep 4

11 min read

Why this deep muscle may influence the lower back, pelvis, nerves, and the ability to rest in a deep squat

The psoas major is often described as a tight hip flexor that simply needs to be stretched. That explanation is easy to understand, but it is incomplete.

The psoas is a deep muscle that connects the lumbar spine directly to the femur. It helps coordinate the lumbar spine, pelvis, and hip, while much of the lumbar plexus lies within the substance of the muscle. Because of this unique position, the psoas may influence much more than hip flexion.

It may affect:

Lumbar and pelvic control
Hip movement
Load transfer between the trunk and lower limbs
Neural sensitivity
Groin and anterior hip symptoms
Movement symmetry
Recovery from recurrent low-back and lower-limb pain

At YOON CLINIC, we do not view the psoas as an isolated muscle. We view it as part of a larger clinical system.

Where Is the Psoas Major?

The psoas major begins along the lower thoracic and lumbar spine. Its more superficial fibers attach to the sides of the vertebral bodies and adjacent intervertebral discs. Its deeper fibers attach to the lumbar transverse processes.

The muscle then travels downward through the pelvis, joins the iliacus to form the iliopsoas, and inserts

onto the lesser trochanter of the femur. This creates a direct anatomical connection:

Lumbar spine-> Pelvis and hip -> Femur

Because of this position, the psoas can participate in hip flexion, lumbar stabilization, pelvic control, and the transfer of force between the trunk and lower limbs. It is not simply a muscle that lifts the leg; it is one of the structures through which the spine and lower body interact.

The Psoas and the Lumbar Plexus

One of the most clinically important features of the psoas is its relationship with the lumbar plexus. The lumbar plexus is not simply located behind the muscle. Anatomical studies show that much of it lies within the substance of the psoas, with its position varying by spinal level and between individuals.

The lumbar plexus contributes to nerves including the:

Femoral nerve
Obturator nerve
Lateral femoral cutaneous nerve
Genitofemoral nerve
Ilioinguinal nerve
Iliohypogastric nerve

This does not mean that every tense psoas compresses these nerves. It does mean that the psoas forms an unusually close mechanical interface between muscle and nerve. Changes in muscle tension, tissue pressure, movement, or local sensitivity may therefore alter the environment surrounding these neural structures in some patients.

This relationship may help explain why the clinical significance of the psoas can extend beyond the lower back or the front of the hip.

Why Can the Psoas Matter in Low-Back and Pelvic Pain?

The psoas should not be blamed for every form of low-back pain. However, it may become an important contributor through several different patterns:

1. Persistent tension

Following injury, prolonged sitting, repetitive hip flexion, or altered movement, the psoas may remain in a protective state of increased tension. This may be associated with:

Deep anterior hip or groin pressure
Discomfort during active hip flexion
Reduced tolerance to hip extension
Compensatory lumbar movement
Recurrent low-back or pelvic discomfort
Increased sensitivity around the lumbar plexus

Persistent tension does not necessarily mean that the muscle has become physically shortened. It may represent an ongoing protective motor response.

2. Reduced length or adaptability

If the iliopsoas cannot lengthen adequately as the hip moves into extension, the body may compensate through the lumbar spine, pelvis, or lower limb. This may become visible during walking, running, squatting, split-stance movement, standing after prolonged sitting, or prone hip extension.

The compensation may include excessive lumbar extension, pelvic rotation, side shifting, or asymmetric loading.

3. Weakness or poor coordination

Not every painful psoas is too tight. In some patients, the muscle may be weak, poorly coordinated, or unable to work effectively with the trunk, pelvis, and hip. This is one reason that simply stretching or releasing the psoas is not always the correct solution.

MRI research examining psoas size and quality in people with low-back pain has produced mixed findings. One observational study found an association between greater psoas muscle area and lower pain intensity, while a broader systematic review did not find consistent differences in psoas morphology or composition between people with and without low-back pain. These findings suggest that the psoas may matter, but no single imaging measurement can determine whether it is the primary pain generator.

4. Altered hip–spine coordination

Patients with low-back pain commonly demonstrate differences in hip range of motion, strength, muscle activation, and movement performance compared with people without low-back pain. A recent systematic review therefore concluded that clinicians should pay greater attention to the hip when assessing and managing low-back pain.

The psoas may be one of the central structures within this altered hip–pelvic–lumbar system, particularly when the patient demonstrates:

Reduced hip extension
Pelvic rotation
Side shifting
Poor squat mechanics
Asymmetric loading
Recurrent pain with bending, lifting, or prolonged sitting

What Symptoms May Be Associated With the Psoas Region?

A psoas-related clinical pattern may include:

Low-back pain
Deep groin pain
Anterior hip discomfort
Reduced hip extension
Anterior thigh pain or altered sensation
Medial thigh symptoms
Lateral thigh sensory symptoms
Difficulty standing upright after prolonged sitting
Asymmetric squat mechanics
Recurrent pelvic or lower-limb discomfort

In clinical practice, psoas-related dysfunction may also contribute to more complex symptom patterns involving the lower back, groin, pelvic region, or nearby neural structures. However, none of these symptoms is specific to the psoas. Similar symptoms may arise from lumbar radiculopathy, hip-joint pathology, femoral neuropathy, meralgia paresthetica, iliopsoas tendinopathy or bursitis, adductor pathology, sacroiliac or posterior pelvic pain, inguinal hernia, or abdominal, urinary, or retroperitoneal conditions.

For this reason, the psoas should never be selected as a treatment target based only on where the patient feels pain. The entire clinical pattern must be considered.

Clinical Note: Groin or testicular pain in particular can have non-musculoskeletal causes. Sudden, severe, unexplained, or progressively worsening symptoms require appropriate medical assessment before they are attributed to the psoas or surrounding tissues.

The Deep Squat as a Human Resting Position

The deep squat is often viewed as an exercise. But it is also a position that the human body is capable of using for rest, work close to the ground, and daily activities.

Research involving Hadza adults in Tanzania found that squatting and kneeling were regularly used during non-walking rest. These active-rest positions also maintained more lower-limb muscle activity than sitting in a chair. The deep squat is therefore not merely an athletic skill; it is a whole-body position requiring the ankles, knees, hips, pelvis, lumbar spine, and nervous system to cooperate. Remove chairs and raised toilets from daily life, and the ability to settle close to the ground becomes practically important.

At YOON CLINIC, we use the ability to remain reasonably comfortable in a deep-squat resting position for approximately one to two minutes as a practical functional benchmark. This is not a universal medical cutoff. Age, previous injury, joint disease, pain, body proportions, and individual anatomy all influence how a person squats.

The more useful question is: Can the body access and maintain this basic position without marked pain, imbalance, or excessive compensation?

When the deep squat is no longer available, the body must find another way to move. That compensation may appear as:

Side shifting
Pelvic rotation
Knee collapse
Excessive forward trunk lean
Heel elevation
Uneven hip loading
Lumbar compensation
Pain or loss of balance

The inability to deep squat does not prove that one particular muscle is responsible. The restriction may arise from the ankle, knee, hip joint, nervous system, pain-related guarding, balance, or impaired movement control. However, in our repeated clinical experience, the psoas major is one of the most frequent—and often one of the most influential modifiable barriers within this pattern.

Why the Psoas Is So Important

The psoas occupies a unique position between the lumbar spine and the femur. It crosses the hip, interacts mechanically with the lumbar spine and pelvis, and maintains a close anatomical relationship with the lumbar plexus. Because of this position, dysfunction of the psoas may affect several parts of the system at the same time:

Hip mobility
Pelvic position
Lumbar movement
Side-to-side loading
Neural sensitivity
Coordination between the trunk and lower limbs

When the psoas remains tense, shortened, irritable, or poorly coordinated, the patient may lose the ability to descend evenly into a deep squat. The body then moves around the restriction rather than through it. A shift at the pelvis may alter loading through the hip. The knee may collapse inward to create additional space. The trunk may lean or rotate. The lumbar spine may compensate for movement that is not occurring adequately through the hip.

The visible problem may appear at the knee, back, groin, or lower limb even when the dominant barrier lies deeper within the lumbopelvic system. This is why the psoas is evaluated early at YOON CLINIC, not because it is responsible for every symptom, but because repeated clinical experience has shown that it often has a disproportionately large influence on the system below the lumbar spine.

How Do We Evaluate It?

At YOON CLINIC, the question is not simply: "Is the psoas tight?"

The more useful question is: "Is the psoas acting as a meaningful barrier to this patient’s recovery?"

Assessment may include:

The deep squat
Hip-extension range
Active and resisted hip flexion
Modified Thomas testing
Prone hip extension
Lumbar movement
Pelvic rotation
Gait and terminal hip extension
Split-squat mechanics
Neural tension
Reflexes, strength, and sensation
Hip-joint provocation tests

The goal is to identify a coherent clinical pattern rather than rely on one isolated test. Limited hip extension alone does not prove that the psoas is shortened. An abnormal squat alone does not prove that the psoas is responsible. Each finding must be interpreted within the context of the patient’s symptoms, activity, examination, and response to treatment.

Treatment Becomes Part of the Assessment

When the psoas appears to be a meaningful barrier, treatment is followed by immediate reassessment. The same deep squat is repeated. We look for changes in:

Pain
Squat depth
Side shifting
Pelvic rotation
Knee alignment
Weight distribution
Trunk control
Movement confidence
Overall symmetry

A frequent YOON CLINIC observation is that psoas-focused treatment is followed by an immediate and visible improvement in both symptoms and deep-squat mechanics. When pain decreases while squat depth, symmetry, and control improve at the same time, it strongly supports the interpretation that the psoas was contributing meaningfully to the patient’s problem.

This does not prove that the psoas was the only source of pain, but it does provide valuable clinical feedback. If local tenderness improves but the patient’s primary symptom and movement pattern remain unchanged, the psoas may not have been the dominant barrier. If repeated treatment produces no meaningful change, the hypothesis should be reconsidered.

From Restoring the Squat to Maintaining Recovery

Improving the deep squat is not the end of treatment; it is the beginning of movement retraining. Treatment may reduce the barrier and allow the patient to reach a position that was previously painful, restricted, or asymmetrical, but the body must still learn how to use that movement repeatedly.

Deep-squat practice can reinforce:

More balanced loading
Better hip–pelvic coordination
Improved squat depth
Reduced side shifting
Better knee alignment
Increased movement confidence
Greater tolerance to daily activity

This is why treatment and rehabilitation are not separated at YOON CLINIC. Treatment helps restore access to the movement; practice helps make the movement familiar, repeatable, and durable. The deep squat is the bridge between psoas treatment and long-term recovery.

Why Symptoms Sometimes Return

A repeated clinical pattern is that a patient improves, stops practising the deep squat, and returns months or years later with a similar complaint. When this happens, we often find that:

The previous side shift has returned
Pelvic control has deteriorated
Knee alignment is less stable
The squat has become shallower or less symmetrical
The same pain pattern has reappeared

When asked whether they continued the exercise, many patients explain that they stopped as soon as they felt better. This highlights an important distinction: pain relief can occur before movement recovery has become durable.

Treatment may remove enough of the barrier for symptoms to settle. But if the improved movement is not used, the previous strategy may gradually return. Patients who continue practising the deep-squat resting position tend to maintain better movement quality and experience fewer recurrences. Patients who stop may slowly lose access to the position again, particularly when their work, sport, or daily routine continues to place repetitive stress on the hip flexors and lumbopelvic system.

What Has YOON CLINIC Observed?

Over many years of clinical practice, psoas-focused treatment has repeatedly been useful in patients presenting with patterns such as:

Low-back pain
Sciatic-type symptoms
Groin pain
Testicular or genital-region pain
Pelvic discomfort
Hip restriction
Asymmetric lower-limb loading

A repeated observation is that treatment of a clinically relevant psoas barrier can produce meaningful improvement in both symptoms and deep-squat mechanics. Another repeated observation is that patients who continue practising the squat tend to maintain their improvement more successfully.

When patients return after a long interval with the same complaint, their squat mechanics have often deteriorated again, and they frequently report that the exercise was discontinued once the original pain improved.

Note: These are repeated clinical observations, not the results of a completed prospective trial. YOON CLINIC has begun more structured outcome tracking so that these patterns can be documented and evaluated more formally over time.

What Does Current Research Tell Us?

Current research supports several parts of this clinical model:

The lumbar plexus has a close anatomical relationship with the psoas.
The psoas contributes to the mechanical relationship between the lumbar spine, pelvis, hip, and femur.
People with low-back pain frequently demonstrate altered hip mobility, strength, muscle activation, and movement performance.
Psoas morphology and muscle quality may be related to low-back pain in some populations, although findings are not consistent across all studies.
Iliopsoas-directed interventions may improve symptoms in selected patients with iliopsoas-related anterior hip and groin conditions.
Myofascial interventions may improve pain or disability in some people with chronic low-back pain, although the magnitude and clinical importance of the benefit remain uncertain.

Published research has not yet adequately examined the complete clinical pathway used at YOON CLINIC:

Psoas-focused assessment -> Treatment -> Immediate deep-squat reassessment -> Continued movement practice -> Long-term recurrence monitoring

That integrated pathway should therefore be understood as a YOON CLINIC clinical model supported by anatomy, related research, and repeated clinical observation, not as a universally established treatment protocol. Structured outcome tracking may help clarify which patients benefit most, which movement changes are most meaningful, and how long those improvements are maintained.

Treatment Should Match the Barrier

The psoas should not always be stretched, released, strengthened, or treated in the same way. Different patients may present with different underlying barriers.

When tension or irritability is dominant: The goal may be to reduce sensitivity, improve tissue mobility, and restore tolerance to hip extension.
When weakness or poor coordination is dominant: The goal may be to improve controlled hip flexion, trunk stability, and coordination between the hip and pelvis.
When compensation is dominant: The psoas may not be the only or even the primary problem. Treatment may also need to address hip-joint mobility, gluteal function, ankle mobility, pelvic control, lumbar load tolerance, balance, and movement retraining.

The intervention should follow the patient’s clinical pattern, not simply the name of the muscle.

The YOON CLINIC Perspective

The psoas major is neither a universal villain nor an unimportant hip flexor. It is a deep muscular and neurological interface connecting the lumbar spine, lumbar plexus, pelvis, hip, and femur. At YOON CLINIC, it is evaluated early because repeated clinical experience has shown that it frequently acts as a dominant and modifiable barrier in pain arising below the lumbar region.

The deep squat allows us to observe the entire system working together. It shows whether the body can still access one of its most fundamental resting positions, reveals the compensations used when that position is no longer available, and allows us to compare movement immediately before and after treatment. When continued as part of rehabilitation, it helps maintain the movement that treatment restored.

The goal is not to assume that the psoas is responsible for every symptom. The goal is to determine whether it is making a meaningful contribution to this patient’s pain, movement, and recovery.

That question is answered through: