Atlas · Lower Leg

Flexor Hallucis Longus

Flexor hallucis longus has its muscle belly in the deep posterior lower leg and a long tendon that reaches the underside of the big toe. Pain behind the inner ankle, in the arch or under the big toe can involve that tendon or neighboring foot structures. There is no FHL muscle belly in the arch.

Body region

Lower Leg · Foot

Trigger points

documented in this muscle

Common symptoms

patterns cataloged

Contributors

Factors to assess

Muscle overview

Symptoms and first steps

Practical first steps

Reduce repeated painful push-off or toe-pointing while maintaining comfortable movement.
Use footwear with adequate toe space and avoid forcing the big toe through a painful catch.
Do not dig into the arch as if it contains the FHL belly.

When to seek assessment

New severe escalating leg pain, a tense swollen compartment, pain with passive toe movement or a cold/pale foot requires emergency assessment.
New foot drop, repeated foot slapping, progressive weakness or persistent numbness needs prompt neurological assessment.
New unilateral swelling/warmth, a suspected fracture or inability to bear weight warrants medical assessment before massage or loading. Breathlessness or chest pain with leg swelling is an emergency.

Distinguish the leg belly from the tendon as it curves behind the ankle and through the foot. Comparing big-toe motion with the ankle in different positions helps assess tendon excursion, not a foot muscle trigger point.

Examination, palpation and treatment evidence

Illustrated overview

Flexor Hallucis Longus · Anatomy 1. Anatomical view of the illustrated muscle. — **Flexor Hallucis Longus · Anatomy 1**
Anatomical view of the illustrated muscle.
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Trigger points

Select a trigger point

1. Foot tendon region

Location. Foot/tendon symptom region beneath the hallux; the FHL muscle belly is in the deep posterior lower leg, not the arch

Flexor Hallucis Longus — Flexor Hallucis Longus · Trigger-point examples 1 — Trigger point map

Pain referral. Plantar hallux/forefoot or tendon-course discomfort requiring local assessment

Pain Pattern

Plantar big-toe symptom region
Medial arch along the tendon course
Posteromedial ankle tendon region

What This Pain Feels Like

Pain beneath the big toe or during push-off may involve FHL tendon loading, the first toe joint, sesamoids or other foot structures. FHL originates in the lower leg; pressing the arch does not palpate its muscle belly. The legacy foot marker is not a validated belly location.

What Patients Report

Pain under big toe
Ball of foot discomfort
Toe cramping

What Makes It Worse

Pushing off
Running
Toe flexion
Dancing

Browse related exercises (1)

Symptoms patients report

Pain during big-toe push-off Walking, running or dance may reproduce pain under the hallux or along the tendon course.

Posteromedial ankle or arch discomfort The tendon can be symptomatic at several levels, including its passage behind the ankle.

Painful or restricted toe excursion Catching, triggering or motion that changes with ankle position warrants assessment of the tendon and toe joint.

Contributors to assess

Increased push-off or dance load Repeated heel rise, pointe/demi-pointe work or a rapid running increase can change tendon demand.

Tendon-sheath restriction or posterior ankle disease These can limit excursion; a painful hallux is not automatically a calf muscle referral.

Neurological toe-flexor overactivity Involuntary hallux flexion after neurological injury is assessed separately from ordinary cramp or tendon pain.

For clinicians and supervised training

Clinical reference

The foot marker shows a foot/tendon symptom region. The FHL muscle belly lies in the lower leg; examine the painful foot structures locally and use separate anatomical localization for procedures.

Anatomy and palpation

Anatomical relationships

The belly arises mainly from the posterior fibula in the deep posterior lower leg. Its tendon passes behind the talus, under the sustentaculum tali and into the plantar foot, crossing the FDL tendon before reaching the distal phalanx of the hallux. It flexes the big-toe interphalangeal joint and contributes to push-off.[1][2][3]

Posterior fibular region locates the deep leg belly indirectly.
Posteromedial ankle marks the tendon course near its fibro-osseous tunnel.
The tendon continues beneath the first toe toward its distal phalanx; this is tendon, not a foot belly.

Nearby structures. Tibialis posterior, FDL, tibial nerve and posterior tibial vessels share the deep-leg/retromalleolar region. The talus, os trigonum region, sesamoids and first MTP joint are potential alternative pain sources.

Palpation

Patient position. Seated or supine with the leg supported and foot accessible; clinician assessment is preferable for deep or retromalleolar symptoms.

Find the landmarks

Posteromedial ankle
Plantar tendon course toward the hallux
Deep lower-leg belly behind the fibula

Examination sequence

Observe swelling and big-toe movement before applying pressure.
Use gentle hallux flexion to identify accessible tendon movement, then compare tenderness along the symptomatic tendon region.
Record local foot/tendon pain separately from deep calf sensitivity. Do not claim to isolate the deep belly through the calf or palpate it in the arch.

Document the findings

Familiar tendon pain, restricted glide or catching may support a tendon/synovial assessment.
A sensitive plantar site does not validate the legacy muscle-belly point.

Limits and precautions

Avoid sustained pressure on the tarsal-tunnel neurovascular bundle or a painful sesamoid.
Do not force a locked/triggering toe or press deeply behind the ankle.

[1][2][3]

Examination and tests

Resisted hallux interphalangeal flexion[1][3]

Assess long-toe-flexor loading and localize symptoms.

Position: Seated with the foot supported and hallux accessible.
Technique: Stabilize the proximal phalanx and ask the patient to bend the tip of the big toe against light resistance. Compare force and symptom location; avoid substituting only MTP flexion.
Positive finding: Familiar tendon-course pain, loss of flexion or a painful catch.
Interpretation: IP flexion emphasizes FHL more than an undifferentiated toe-grip task and directs assessment along its tendon.
Limitations: It does not prove a muscle trigger point; pain, tendon restriction and neurological weakness can all alter performance.

FHL excursion test across ankle positions[3]

Compare big-toe extension as tension changes along the long flexor tendon.

Position: Seated or supine with the ankle and hallux moved gently by a clinician.
Technique: Compare comfortable hallux MTP extension with the ankle plantar flexed, then dorsiflexed, keeping the first ray supported consistently. Record motion, familiar tendon pain or triggering rather than forcing a target angle.
Positive finding: Reduced hallux extension or familiar tendon symptoms particularly when ankle dorsiflexion tensions the FHL.
Interpretation: May support restricted FHL excursion when combined with its tendon tenderness and history.
Limitations: Hallux rigidus, sesamoid pain and other structures also limit extension. The clinical series does not establish a definitive accuracy cutoff.

Distinguishing other causes

FHL tendinopathy or stenosing tenosynovitis[3][4]

Findings that matter. Tenderness along the tendon, painful hallux flexion, restricted excursion or triggering near the posterior ankle.

Next step. Foot/ankle examination; use ultrasound or MRI selectively if the diagnosis or mechanical restriction is unclear.

First MTP disease, sesamoid disorder or bone stress injury[3][5]

Findings that matter. Focal plantar-first-ray tenderness, joint swelling/stiffness or progressively painful impact.

Next step. Examine local joints and bone and reduce impact when stress injury is suspected; do not attribute focal forefoot pain to the leg map.

Posterior ankle impingement or tibial nerve involvement[2][3]

Findings that matter. Posterior pain with forced plantar flexion, or burning/numbness rather than only tendon-load pain.

Next step. Assess ankle and neural findings separately; persistent neurological symptoms require medical evaluation.

Treatment selection and progression

Exercise and rehabilitation

Reduce provocative push-off and rebuild hallux loading[1][4]

Consider when. An assessed tendon or load-related presentation without rupture, fracture or acute neural compromise.

Start with comfortable seated hallux-tip flexion against light resistance, then supported heel rises. Temporarily reduce repeated toe-pointing, sprinting or high-demand dance positions.

Dose and review: Illustrative entry point: a small set of slow comfortable repetitions, followed by a check of walking and next-day pain; adjust with the clinician.
Progression: Progress resistance and heel-rise demand before returning to repeated rapid push-off or dance extremes.
Stop or reassess: Stop for sharp pain, a new catch, swelling or loss of toe flexion.
Evidence and limits: Loading is an anatomy-informed rehabilitation choice. FHL clinical studies concern tendon disease and do not establish this dose as a muscle-MPS treatment.

Exercise and rehabilitation

Gentle excursion work for assessed FHL tendon restriction[3][4]

Consider when. A clinician identifies limited FHL glide and excludes a painful fixed joint block or acute injury.

Use gentle coordinated ankle and big-toe movement within an agreed range. The clinician may teach a specific tendon-stretch approach, keeping it below a painful catch and adapting for first-MTP symptoms.

Dose and review: Short, comfortable practice individualized to the examination; do not force the toe or copy a maximum stretch from an atlas.
Progression: Monitor excursion and the chosen push-off task rather than pursuing range for its own sake.
Stop or reassess: Stop for triggering, increasing forefoot pain, numbness or sustained symptom worsening.
Evidence and limits: Clinical cohorts report improvement with an FHL-focused nonoperative program, sometimes including immobilization; uncontrolled design and selection mean the contribution of stretching is uncertain.

Clinician-delivered care

Foot-and-ankle care for persistent mechanical tendon symptoms[3][4]

Consider when. Persistent catching, restricted excursion or disabling tendon-course pain despite an appropriate conservative program.

Reassess tendon sheath, posterior ankle and first-ray disease. A specialist can consider temporary immobilization for a markedly irritable tendon and discuss operative decompression only when a defined mechanical problem and ongoing disability justify it.

Dose and review: The duration of protection and any procedure plan follow the diagnosis and response; no routine injection or surgical timetable applies.
Progression: Review walking, toe motion and recurrence after gradual return to loading.
Stop or reassess: Promptly reassess progressive weakness, marked swelling, skin problems from immobilization or new neurological symptoms.
Evidence and limits: The 2005 series and 2021 retrospective cohort support a staged clinical pathway but do not prove comparative superiority or a universal success rate.

Clinician-delivered care

Botulinum toxin for diagnosed flexor hallucis longus spasticity[7]

Consider when. Neurological spasticity, such as after stroke, in which involuntary flexor hallucis longus activity interferes with comfortable hallux position, footwear or gait. Ordinary cramping, tendon pain and a tender point do not establish this indication.

A rehabilitation/spasticity specialist evaluates the whole limb, passive range, weakness and the role of each involved muscle. If appropriate, use guided muscle localization and pair treatment with rehabilitation or orthotic care to address comfortable hallux position, footwear or gait.

Dose and review: Drug selection and dose are prescribed individually. Agree on a review around 4–6 weeks and reassess before any repeat treatment.
Progression: Compare the agreed functional goal and adverse effects, not tone alone; a fixed contracture or weakness may need a different strategy.
Stop or reassess: Report new troublesome weakness or falls. Difficulty swallowing or breathing after toxin treatment requires urgent medical help.
Evidence and limits: The US label supports adult lower-limb spasticity. Its 468-person post-stroke trial used several muscles and followed participants for 12 weeks; benefits in ankle tone/global response at weeks 4/6 do not establish isolated-muscle pain relief or efficacy for MPS.

Reassessment and follow-up

Compare hallux IP flexion, gentle excursion and the same push-off task.
Record where symptoms arise: lower-leg belly, retromalleolar tendon, arch or first-ray joint/bone.
Mechanical catching or unresolved focal forefoot pain should trigger diagnostic review before repeated muscle treatment.

Evidence and sources

University of Washington Muscle Atlas: Flexor hallucis longus
2026 · Institutional anatomy reference
Undated anatomy page, verified September 2026; the year records this review. Supports attachments and actions, not diagnostic accuracy of palpation or a trigger-point map. No atlas illustration reproduced.
Anatomy, Bony Pelvis and Lower Limb: Leg Posterior Compartment
2026 · Anatomy reference
Deep posterior compartment and neurovascular relationships; reviewed September 2026. Does not validate selective deep-muscle palpation or the legacy foot point coordinates.
Tenosynovitis of the flexor hallucis longus: a clinical study of the spectrum of presentation and treatment
2005 · Prospective clinical series
81 patients, mean follow-up 21.3 months; describes FHL excursion testing and staged tendon care. No randomized comparator and no muscle trigger-point validation.
What Is the Efficacy of a Nonoperative Program Including a Specific Stretching Protocol for Flexor Hallucis Longus Tendonitis?
2021 · Retrospective therapeutic cohort
656 records reviewed; 180/409 patients in the reported stretching-program analysis chose to forgo surgery. Selection and follow-up limitations prevent a universal recovery rate or causal treatment claim.
AAOS OrthoInfo: Stress Fractures of the Foot and Ankle
2026 · Professional society clinical information
Undated page verified September 2026; focal bone-load pain and the limits of early plain radiography.
AAOS OrthoInfo: Compartment Syndrome
2026 · Professional society clinical information
Undated page verified September 2026; differentiates acute emergencies from exertional presentations. Muscle palpation cannot exclude either.
BOTOX (onabotulinumtoxinA): US prescribing information
2026 · Official prescribing information
Adult lower-limb spasticity indication includes tibialis posterior, FHL and FDL. The 468-person post-stroke trial followed a multi-muscle protocol for 12 weeks; ankle tone/global response at weeks 4/6 cannot establish isolated toe-muscle analgesia or an MPS indication.

Associated Trigger Points

Flexor hallucis brevis
Plantar fascia medial