Flexor Hallucis Longus
Leg · Lower Limb
The flexor hallucis longus is a powerful deep muscle of the posterior compartment of the leg, lying on the lateral side despite serving the great toe. It arises from the distal two-thirds of the posterior surface of the fibula and the interosseous membrane, and its tendon passes behind the medial malleolus and beneath the sustentaculum tali to insert on the base of the distal phalanx of the great toe. It flexes the great toe, assists plantarflexion of the ankle, and supports the medial longitudinal arch, providing the final push-off from the big toe at the end of the stance phase of gait. It is supplied by the tibial nerve (S2, S3). It is especially well developed in dancers and sprinters who rely on strong toe-off.
Origin, Insertion, Action & Nerve
Origin
Distal two-thirds of posterior surface of fibula and interosseous membrane
Insertion
Base of distal phalanx of great toe (1st Toe) (hallux)
Action
Flexion of great toe (1st Toe); plantarflexion of ankle; supports medial arch
Nerve
Tibial nerve (S2, S3)
Attachments explained
The Flexor Hallucis Longus is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.
Origin
Distal two-thirds of posterior surface of fibula and interosseous membrane
Insertion
Base of distal phalanx of great toe (1st Toe) (hallux)
Action & function
When the Flexor Hallucis Longus contracts, it produces the following movements: Flexion of great toe (1st Toe); plantarflexion of ankle; supports medial arch.
As part of the Leg group of the Lower Limb, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.
Nerve supply & clinical relevance
The Flexor Hallucis Longus receives its nerve supply from the Tibial nerve (S2, S3). This nerve carries fibres from spinal segment(s) S2, S3.
Because a muscle can only contract when its nerve is intact, injury to the Tibial nerve or to its spinal roots (S2, S3) can weaken or paralyse the Flexor Hallucis Longus, impairing the movements it normally produces (flexion of great toe (1st Toe)). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Flexor Hallucis Longus (the OIANS method)
Fix the flexor hallucis longus as the long flexor of the big toe and the muscle of push-off, since its contraction drives the final propulsive thrust of the great toe as the foot leaves the ground. Note the anatomical quirk that although it powers the medial great toe, its belly lies on the fibula, the lateral bone; tracing its tendon under the sustentaculum tali of the calcaneus explains how it reaches the medial side.
Pair it with the flexor digitorum longus as the deep plantarflexors of the toes, both supplied by the tibial nerve at S2, S3 and both passing behind the medial malleolus. Distinguish them by target: hallucis longus serves only the great toe, digitorum longus the other four. Linking its arch support and toe-off role to this comparison keeps the deep compartment organised.
Frequently asked questions
Where is the Flexor Hallucis Longus located?
The Flexor Hallucis Longus is a muscle of the Leg group, located in the Lower Limb.
What is the origin of the Flexor Hallucis Longus?
Distal two-thirds of posterior surface of fibula and interosseous membrane
What is the insertion of the Flexor Hallucis Longus?
Base of distal phalanx of great toe (1st Toe) (hallux)
What movements does the Flexor Hallucis Longus produce?
Flexion of great toe (1st Toe); plantarflexion of ankle; supports medial arch
What nerve supplies the Flexor Hallucis Longus?
Tibial nerve (S2, S3)
Is the Flexor Hallucis Longus free to study in OIANS?
The Flexor Hallucis Longus is always free to browse. Its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory. Quiz and Flashcard practice for the Lower Limb is part of the one-time Lifetime upgrade, though; only the Upper Limb decks are free to test yourself on.
Related muscles
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