Fibularis longus (peroneus longus)

Pronunciation: fib-yoo-LAIR-iss LONG-gus

Structure & function

Location

A long muscle running down the outer side of the lower leg, along the fibula.

Origin

Upper lateral surface of the fibula.

Insertion

First metatarsal and medial cuneiform (crossing under the sole of the foot).

Main action(s)

Everts the foot (turns the sole outward) and assists plantarflexion; helps support the foot's arches.

Joint(s) crossed

Ankle joint

Movement plane

frontal

Innervation

Superficial fibular (peroneal) nerve (L5–S1)

In daily movement

Stabilizing the outer ankle on uneven ground, resisting an ankle rolling inward too far.

In exercise

A stabilizer rather than a prime mover in most standard exercises; specifically targeted in ankle-eversion rehabilitation and balance work.

Commonly confused with

Its role is often reduced to 'foot stabilizer' generally, without recognizing its specific eversion action, which is functionally opposite to the tibialis anterior's inversion assistance.

Common misconceptions

Ankle sprains are not purely a ligament issue — the surrounding dynamic stabilizers like the fibularis longus play a real role in prevention and rehabilitation.