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Flexor digitorum longusMusculus flexor digitorum longus

Deep muscle on the inner back of the leg that curls the four small toes and helps point the foot.

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LatinMusculus flexor digitorum longus
Origin
  • Posterior surface of the tibia, from just below the soleal line to about 7–8 cm above its lower end
  • Fascia covering tibialis posterior
Insertion
  • Bases of the distal phalanges of the 2nd–5th toes (plantar surface), each tendon passing through a split in the flexor digitorum brevis tendon
Action
  • Flexes the 2nd–5th toes (curls them), helping them grip the ground
  • Assists plantarflexion of the ankle (pointing the foot)
  • Assists inversion of the foot (turning the sole inwards)
NerveTibial nerve (L5–S1)
NameLatin: the 'long bender of the digits (toes)'.

Palpation

  1. Client prone with a bolster under the ankle, or side-lying on the side being worked.
  2. Find the inner (medial) edge of the tibia in the lower half of the leg.
  3. Slide your fingers just behind this edge, pressing gently forward against the back of the tibia, under the edge of soleus.
  4. Ask the client to curl the four small toes against light resistance; feel a faint firming along the back of the tibia.

Landmarks: Medial malleolus

Flexor digitorum longus is one of the three deep muscles at the back of the leg, with Tibialis posterior and Flexor hallucis longus. It lies under Soleus on the inner (tibial) side, so it is reached by working along the inner edge of the tibia in the lower leg. These deep muscles do not join the Achilles (calcaneal) tendon; their tendons pass behind the Medial malleolus into the sole instead.

Its tendon crosses under the foot and splits into four, one for each small toe. On the way it crosses the tendon of flexor hallucis longus in the sole and is joined by a small sole muscle, quadratus plantae, which straightens its pull (see Plantar intrinsic muscles). Clients who walk barefoot on sand or uneven ground, or who grip with their toes, sometimes report aching along the inner shin or in the arch.

Source notes. Wikipedia includes inversion among its actions; Gray’s Anatomy (1918) lists only toe flexion and pointing the foot. Wikipedia gives no nerve root levels, so L5–S1 comes from Gray only.

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 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.
  • 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 digitorum longus — Feather-shaped muscle on the outer front of the lower leg that lifts the four small toes and helps lift the foot.

Sources

  1. Wikipedia: Flexor digitorum 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. Attachments agree with Wikipedia. Used for nerve roots (L5–S1); the Wikipedia article gives no root levels.)