Fysiqal
Anatomy
Anatomy

Fibularis Longus (Peroneus Longus)

1 min read
Sources and review status

Review pending — this text hasn’t been signed off by a reviewer yet.

See this lesson’s sources
lower-leganklefibularisperoneal

0% read · 1 min left

DefinitionA short reference note, not a full lesson.
Definition

The lateral lower-leg muscle that everts the foot and helps support the arch — the antagonist to the tibialis posterior.

Detail

The fibularis longus (older name: peroneus longus) runs down the lateral (outer) side of the lower leg, its tendon passing behind the lateral malleolus and under the foot to anchor near the base of the first metatarsal. Its primary action is eversion — rolling the sole of the foot outward, away from the midline — and it assists plantarflexion. Together with fibularis brevis it is the main dynamic stabilizer against ankle inversion (the "rolled ankle" mechanism), and its long tendon path under the foot also helps support the transverse arch.

Key facts

  • Action: eversion of the foot; assists plantarflexion.
  • Primary dynamic stabilizer against inversion ankle sprains.
  • Antagonist to the tibialis posterior (which inverts the foot).
  • Tendon passes under the foot, contributing to arch support.

Connections

Sources

Cited in text — not yet linked
Not present in the original source corpus for this knowledge base (no source_pages). Added to close a taxonomy gap surfaced during the page-by-page foundations review: ankle eversion/inversion existed as valid motions with zero muscle attribution or exercises. Standard kinesiology fact, consistent with the Thompson structural-kinesiology terminology already used throughout this graph — flagged here as an explicit exception to this corpus's page-cited sourcing convention.

Keep this lesson, or ask how it applies to you.

Save the lessonFree account · keeps it in your LibraryAsk a question about thisAnswers cite the Library’s own articles

Educational content only — not medical advice. Always consult a qualified professional for individualized guidance, especially around injury, pregnancy, or medical conditions.

Explore related topics

Atlas Connections

Eversion
Turning the sole outward, placing weight on the inner edge of the foot.
Foot / Ankle Range of Motion
Plantar flexion of the foot 45°, dorsiflexion of the foot 10–15°.
Gastrocnemius
A 2-joint calf muscle that plantar-flexes the ankle and flexes the knee; origin at the femoral condyles, insertion at the calcaneus.
Tibialis PosteriorClosely related
The deep calf muscle that inverts the foot and is the primary dynamic support of the medial arch — the antagonist to the fibularis (peroneal) muscles.