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Plantar intrinsic muscles

Group of small muscles in the sole of the foot, arranged in four layers, that move the toes and help hold up the arches.

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Origin
  • First layer: medial and lateral processes of the tuberosity of the calcaneus and the plantar aponeurosis (abductor hallucis, flexor digitorum brevis, abductor digiti minimi)
  • Second layer: medial and lateral undersurface of the calcaneus (quadratus plantae); tendons of flexor digitorum longus (lumbricals)
  • Third layer: cuboid and lateral cuneiform (flexor hallucis brevis); bases of the 2nd–4th metatarsals and the plantar ligaments of the toe joints (adductor hallucis); base of the 5th metatarsal (flexor digiti minimi brevis)
  • Fourth layer: sides and bases of the metatarsals (dorsal and plantar interossei)
Insertion
  • Big-toe muscles (abductor hallucis, flexor hallucis brevis, adductor hallucis): base of the proximal phalanx of the big toe
  • Little-toe muscles (abductor digiti minimi, flexor digiti minimi brevis): lateral side of the base of the proximal phalanx of the fifth toe
  • Flexor digitorum brevis: middle phalanges of the 2nd–5th toes
  • Quadratus plantae: tendon of flexor digitorum longus
  • Lumbricals and interossei: bases of the proximal phalanges and the extensor expansions of the lesser toes
Action
  • Flexor digitorum brevis and flexor hallucis brevis: bend (flex) the toes
  • Abductors and dorsal interossei: spread the toes apart
  • Adductor hallucis and plantar interossei: draw the toes together
  • Quadratus plantae: straightens the pull of flexor digitorum longus so the toes curl in line
  • Lumbricals and interossei: bend the toes at the ball of the foot while straightening the toe joints
  • As a group: help hold up the arches of the foot and stabilise the foot in standing and walking
NerveLateral plantar nerve, except abductor hallucis, flexor digitorum brevis, flexor hallucis brevis and the first lumbrical (medial plantar nerve); both are branches of the tibial nerve
NameLatin planta, 'sole of the foot'; 'intrinsic' because they start and finish within the foot.

Palpation

  1. Client prone with the foot hanging just off the end of the table, or supine with the knee bent and the sole towards you.
  2. Place your thumbs on the sole just in front of the heel and feel the firm band of the plantar aponeurosis with the thick, soft first layer of muscle beneath it.
  3. Slide along the inner edge of the sole to feel abductor hallucis, and along the outer edge for abductor digiti minimi.
  4. Ask the client to curl the toes against light resistance; the middle of the sole firms as flexor digitorum brevis contracts.

Landmarks: Calcaneus

The sole of the foot has its own set of small muscles. Anatomists describe them in four layers, in the order you would meet them from the skin:

  1. First layer: abductor hallucis (inner edge), flexor digitorum brevis (centre) and abductor digiti minimi (outer edge), lying just under the plantar aponeurosis, a tough sheet of fascia under the sole.
  2. Second layer: quadratus plantae and the four lumbricals, both attached to the tendons of Flexor digitorum longus. The tendons of that muscle and of Flexor hallucis longus also run through this layer.
  3. Third layer: flexor hallucis brevis, adductor hallucis and flexor digiti minimi brevis, the short muscles of the big and little toes.
  4. Fourth layer: the dorsal and plantar interossei, between and under the metatarsals.

In massage you work mostly through the first layer, with the plantar aponeurosis and the thick fat pad of the heel and ball of the foot between your hands and the deeper layers. Firm, slow thumb strokes along the sole, from the Calcaneus towards the toes, are common in foot work. People who stand all day or wear unsupportive shoes commonly report tired or aching soles. The foot is also the focus of Reflexology, which uses different ideas from muscle-based massage.

These muscles are not part of the calf. The Achilles (calcaneal) tendon ends at the back of the heel, while the plantar muscles start under the heel and run forwards.

Source notes. Neither Wikipedia nor Gray’s Anatomy (1918) gives spinal root levels for the plantar nerves, so roots is left blank (unverified). Gray adds that the first two dorsal interossei often get extra twigs from the deep fibular nerve. Wikipedia also groups these muscles into compartments (medial, central, lateral) as well as layers.

Techniques

  • Effleurage — Long, gliding strokes with the whole palm that spread the medium, warm the tissue and link the other strokes together.
  • Circular friction — Small circles made with the finger or thumb pads that move the skin over the deeper tissue without sliding, to work a specific spot.
  • 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.

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.
  • 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.

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.
  • 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.

Used in routines

Sources

  1. Wikipedia: Sole (foot)
  2. Wikipedia: Medial plantar nerve
  3. Wikipedia: Lateral plantar nerve
  4. Gray's Anatomy of the Human Body (1918), Myology 8e: The Muscles and Fasciae of the Foot (archived Bartleby page) (Public domain. Used for the four-layer arrangement, attachments, actions and nerve supply. Neither source gives spinal root levels for these muscles.)