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Flexor hallucis longusMusculus flexor hallucis longus

Deep muscle on the outer back of the leg that bends the big toe and gives the push-off in walking, running and rising onto the toes.

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LatinMusculus flexor hallucis longus
Origin
  • Lower two-thirds of the posterior surface of the fibula (except the lowest 2.5 cm)
  • Lower part of the interosseous membrane
  • Septum between it and the fibular muscles, and fascia covering tibialis posterior
Insertion
  • Base of the distal phalanx of the big toe (plantar surface)
Action
  • Flexes the big toe (bends it down), giving push-off in walking
  • Assists plantarflexion of the ankle (pointing the foot)
  • Assists inversion of the foot (turning the sole inwards)
NerveTibial nerve (L5–S2)
NameLatin: the 'long bender of the big toe (hallux)'.

Palpation

  1. Client prone with a bolster under the ankle.
  2. Place your fingers on the lower third of the back of the leg, on the outer (fibular) side, just beside the Achilles tendon.
  3. Press gently forward through the soleus towards the back of the fibula.
  4. Hold the big toe and ask the client to bend it down against light resistance; feel a faint firming under your fingers.

Landmarks: Medial malleolus · Calcaneus

Flexor hallucis longus is one of the three deep muscles at the back of the leg. Oddly for a big-toe muscle, it lies on the outer (fibular) side of the leg, under Soleus. Its lowest fibres sit just in front of and beside the Achilles (calcaneal) tendon, which is where it is easiest to reach. Its tendon then runs behind the inner ankle, under a shelf of the Calcaneus (the sustentaculum tali) and along the sole to the big toe.

It gives the final push-off from the big toe in walking and running, so dancers, runners and gymnasts commonly report tenderness behind the inner ankle or under the big toe. Work directly on the tendon and at the inner ankle belongs to remedial training.

It works against Extensor hallucis longus, which lifts the big toe. In the sole, its tendon crosses above the tendon of Flexor digitorum longus and is linked to it by a fibrous slip, so the two muscles usually work together.

Source notes. Nerve roots differ: Gray’s Anatomy (1918) gives L5, S1 and S2, while Wikipedia’s infobox gives S2 and S3. This note uses L5–S2. For the origin, Wikipedia’s infobox says the middle third of the back of the fibula, but its text agrees with Gray (the lower two-thirds). Wikipedia includes inversion among the actions; Gray does not.

Techniques

  • Compression — Pressing straight down into a muscle with the palm, fist or forearm, holding briefly, then releasing and moving on.
  • Stripping — A slow, deep, narrow glide along the length of a single muscle with the thumb, knuckle or elbow, pausing over tight bands on the way.
  • Trigger point pressure release — Sustained thumb or finger pressure on a tender spot within a taut band of muscle, held until the client reports the discomfort easing, then slowly released.

Works with

  • Flexor digitorum longus — Deep muscle on the inner back of the leg that curls the four small toes and helps point the foot.
  • Tibialis posterior — The deepest muscle at the back of the leg; it turns the sole inwards, helps point the foot and is a major support for the inner arch.
  • Soleus — Broad, flat calf muscle lying under the gastrocnemius that points the foot and keeps the body from tipping forward when standing.

Opposes

  • Extensor hallucis longus — Thin muscle on the front of the lower leg, partly hidden by its neighbours, that lifts the big toe and helps lift the foot.

Sources

  1. Wikipedia: Flexor hallucis longus muscle
  2. Wikipedia: Tibial nerve
  3. Gray's Anatomy of the Human Body (1918), Myology 8c: The Muscles and Fasciae of the Leg (archived Bartleby page) (Public domain. Used for attachments and nerve roots (L5–S2). Wikipedia's infobox gives S2–S3.)