Why the Hip Flexor Gets Blamed

The logic seems straightforward — you have pain at the front of the hip, the hip flexors live at the front of the hip, therefore the hip flexors are the problem. But this reasoning ignores a fundamental aspect of running biomechanics.

During the stance phase of running — when your foot is in contact with the ground and you're loading through the leg — the hip flexors are not the primary active muscles. They are most active during the early swing phase, when the leg is moving forward and off the ground.

This means that if your anterior hip pain is triggered during foot strike, during the loading phase, or during activities that compress or load the hip joint — rather than during the swing phase of running — the hip flexors are unlikely to be the primary driver.

For sprinters, the picture is different. The hip flexors work at much higher intensity and velocity during sprinting, and hip flexor strain is a genuine and common presentation in that population. But for the recreational 5km runner, the half-marathoner or the Hyrox athlete — who makes up the vast majority of the runners we see — the hip flexor explanation often doesn't fit the clinical picture.

What Else Could Be Causing It?

When a runner presents with anterior hip pain and the story doesn't fit a hip flexor strain, several other diagnoses need to be considered carefully.

• Femoral neck stress reaction or stress fracture

This is the one that matters most to get right — and the one most likely to be missed if the assessment stops at "hip flexor strain."

The femoral neck is one of the most common sites for bone stress injury in endurance runners. A stress reaction or stress fracture in this area can irritate the surrounding soft tissues — including the hip flexor tendon — producing anterior hip pain that feels exactly like a muscle or tendon problem. The key distinction is that the pain is bone-related, not muscle-related.

This matters enormously for management. A hip flexor strain can continue to be loaded with appropriate modification. A femoral neck stress fracture requires a very different — and much more conservative — approach. Missing this diagnosis and continuing to run on a femoral neck stress fracture can result in complete fracture, which is a serious injury requiring surgery.

Red flags that increase suspicion for bone stress injury include:

• Pain that worsens progressively with running rather than warming up and settling
• Pain that persists at rest or disturbs sleep
• A recent significant increase in training volume or intensity
• Young female athletes — the female athlete triad increases stress fracture risk significantly
• Pain on single leg hop testing

If any of these features are present, imaging is warranted before a return to running is advised.

• Femoroacetabular Impingement (FAI)

FAI occurs when the ball and socket of the hip joint make abnormal contact due to bony morphology — either extra bone on the femoral head (cam impingement), the acetabulum (pincer impingement) or both. This impingement can cause anterior hip or groin pain, particularly with hip flexion activities, and is often aggravated by the repeated hip flexion of running.

FAI is increasingly recognised as a contributor to anterior hip pain in active people and is worth considering when pain is deep, difficult to localise and associated with hip flexion loading.

• Labral pathology

The acetabular labrum — the cartilage ring that deepens the hip socket — can be torn or degenerated, often in association with FAI. Labral tears can produce anterior hip pain, clicking or a catching sensation, and groin pain that is difficult to pinpoint. They are often found in runners and athletes doing high volumes of hip flexion activity.

• Iliopsoas bursitis

The iliopsoas bursa sits between the hip flexor tendon and the hip joint. Inflammation of this bursa can produce anterior hip pain that mimics hip flexor tendinopathy but has a different treatment approach. It is often associated with repetitive hip flexion loading and can occur alongside FAI or labral pathology.

• Referred pain from the lumbar spine or pelvis

The hip flexors and anterior hip receive nerve supply from the lumbar plexus — nerve roots that originate in the lower back. Disc pathology, nerve root irritation or sacroiliac joint dysfunction can all refer pain into the anterior hip and groin in patterns that closely mimic local hip pathology. A runner who has anterior hip pain but also has lower back stiffness or tightness worth assessing for a lumbar contribution.

Why This Matters for Treatment

The reason getting the diagnosis right matters so much is that these conditions have very different management pathways.

• Hip flexor strain — relative rest, progressive loading, return to running.
• Femoral neck stress fracture — immediate cessation of running, possible non-weight bearing, lengthy rehabilitation before return to impact.
• FAI — movement modification, hip strengthening, possible surgical referral for significant impingement.
• Labral tear — rehabilitation focused on hip stability and joint centration, possible surgical referral for significant tears.
• Lumbar referred pain — treatment directed at the lumbar spine rather than the hip.

Treating a femoral neck stress fracture as a hip flexor strain — which unfortunately does happen — can have serious consequences. Getting a proper assessment before committing to a treatment approach is not overcautious. It's essential.

What Assessment Should Include

A thorough assessment of anterior hip pain in a runner should include:

• A detailed history — when did it start, what makes it worse, how does it respond to running, has training load changed recently, any history of previous stress injuries.
• Provocation testing — specific clinical tests to reproduce the pain and identify the likely structure involved. The FADIR test for FAI and labral pathology, the hop test for bone stress injury, resisted hip flexion testing for the hip flexors and psoas.
• Strength assessment — hip flexor, abductor, external rotator and posterior chain strength. Weakness patterns can point toward the underlying diagnosis and are essential for rehabilitation planning.
• Movement assessment — how the hip moves during squatting, single leg stance and running-specific tasks.
• Imaging consideration — where bone stress injury is suspected, MRI is the most sensitive imaging modality and should be pursued promptly. X-ray misses early stress reactions. For FAI and labral pathology, X-ray and MRI are both relevant.

The Takeaway

Anterior hip pain in runners is not always — or even usually — a hip flexor problem. The differential diagnosis is broad, includes some conditions that require urgent management, and benefits enormously from a careful clinical assessment rather than a default explanation.

If you're a runner with persistent anterior hip pain that isn't responding to rest and basic management, don't keep assuming it's your hip flexor. Get it properly assessed.



Book online or call us on (08) 7123 4148 to get a thorough assessment and a clear diagnosis — not just a label that fits the location of your pain.