Leg muscles: Overview

Tibialis anterior muscle

The tibialis anterior is a fusiform muscle that originates from the lateral surface of the tibial condyle and the superior two-thirds of the proximal shaft of tibia. It courses inferiorly down the leg until it reaches the distal third of the tibia, where it extends into a cord-like tendon. The tendon continues across the ankle and dorsum of the foot to insert into the medial cuneiform bone and the base of the first metatarsal bone of the foot.

The tibialis anterior is innervated by the deep fibular (peroneal) branch of the common fibular nerve. Its blood supply is derived from branches of the anterior tibial artery, and to a smaller extent, the posterior tibial artery.
The functions of the tibialis anterior are dorsiflexion of the foot at the talocrural joint and inversion of the foot at the subtalar joint. It also assists in the dynamic support of the medial arch of the foot.

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Extensor digitorum longus

The extensor digitorum longus is a feather-like muscle originating from the proximal half of the medial surface of fibula, the anterior surface of the lateral tibial condyle and the anterior surface of the interosseous membrane. It descends inferiorly to just above the ankle, where it extends into a tendon that passes under the superior extensor retinaculum and through the inferior extensor retinaculum. Within the extensor retinaculum, the tendon splits into four smaller tendons that insert onto the dorsal surface of the middle and distal phalanges of the lateral four toes.

The extensor digitorum longus is innervated by the deep fibular (peroneal) nerve (L5, S1), and vascularized by the anterior tibial and fibular (peroneal) arteries.
The functions of the extensor digitorum longus are extension of the 2nd-5th toes and dorsiflexion of the foot. It also assists the tibialis anterior with inversion of the foot at the subtalar joint.

Fibularis tertius

The fibularis tertius, also called the peroneus tertius is a slender muscle that is often described as a part of the extensor digitorum longus. It originates from the medial aspect of the distal third of fibula, the adjacent anterior surface of interosseous membrane and the anterior intermuscular septum and runs downwards along the lateral aspect of the leg. It then extends into a tendon that passes deep to the superior extensor retinaculum, accompanied by the extensor digitorum longus. The tendon of the fibularis tertius then inserts onto the dorsal surface of the base of the fifth metatarsal.

The fibularis tertius is innervated by the deep fibular nerve (L5, S1). Its blood supply is derived from branches of the anterior tibial, posterior tibial and dorsalis pedis arteries.
The main function of the fibularis tertius is a weak dorsiflexion of the foot at the ankle, that complements the actions of the tibialis anterior and extensor digitorum longus. The fibularis tertius can also act on the subtalar joint assisting the fibularis longus and fibularis brevis in the eversion of the foot.

Learn everything about the fibularis tertius here:

Extensor hallucis longus

The extensor hallucis longus is a unipennate muscle found between the tibialis anterior and extensor digitorum longus muscles. It originates from the anteromedial aspect of the middle third of the fibula and the adjoining interosseous membrane. The muscle courses downwards and medially and extends into a slender tendon that runs along the dorsal surface of the foot, passing beneath the superior extensor retinaculum. The tendon inserts at the base and dorsal surface of the distal phalanx of the great toe (hallux).

The extensor hallucis longus is innervated by the deep fibular nerve (L5). It receives its blood supply mainly from the anterior tibial artery, with contributions from the fibular (peroneal) artery, anterior medial malleolar artery, dorsalis pedis artery, and the plantar metatarsal artery of the first digit.
The main function of the extensor hallucis longus is extension of the big toe (hallux) at metatarsophalangeal joints. In addition, the muscle can act on the ankle joint and assist the other muscles of the anterior group to produce dorsiflexion of the foot.

Getting a bit overwhelmed? Get a quick overview of the attachments, innervation and function of the leg muscles with our muscle fact charts!

Superficial layer

The superficial layer of the posterior group consists of the gastrocnemius, plantaris and soleus. The two heads of gastrocnemius together with the soleus comprise a three headed compound muscle collectively known as the triceps surae.

Gastrocnemius

The gastrocnemius is a two-headed muscle that forms the bulk of soft tissue on the posterior leg, referred to as the calf.

• The medial head of the gastrocnemius arises from the posterior surface of the medial condyle and the popliteal surface of the femoral shaft.
• The lateral head originates from the lateral surface of the lateral condyle and the lower part of the supracondylar line.

The two muscle bellies come together in the midline at the inferior margin of the popliteal fossa into a single muscle belly. Its fleshy fibers continue to the midpoint of the calf, where they gradually develop a broad aponeurosis. Upon receiving the soleus tendon, the aponeurosis narrows into the calcaneal (Achilles) tendon and inserts at the posterior surface of the calcaneus.

The gastrocnemius is innervated by the tibial nerve (S1, S2). Its blood supply is mainly derived from the lateral and medial sural branches of the popliteal artery, with contributions from the superior genicular arteries.
The function of the gastrocnemius is usually discussed in conjunction with the soleus as the triceps surae muscle. This muscle acts as a chief plantar flexor of the foot at the ankle joint. In addition, the gastrocnemius portion can act on the knee joint and produce a flexion of the knee.

Soleus

The soleus is a broad, triangular muscle situated deep to the gastrocnemius. It originates from the soleal line on the posterior surface of the tibia, medial border of the tibia and the posterior surface of the upper third of the fibula. The muscle extends downwards until the midpoint of the calf, where it transforms into an aponeurosis that joins the tendon of the gastrocnemius to form the calcaneal tendon.

The soleus is innervated by the tibial nerve (S1-S2). It receives blood supply mainly from the branches of the popliteal artery, with contributions from the posterior tibial or fibular (peroneal) arteries.
As discussed, the main function of the soleus as a part of the triceps surae is plantar flexion of the foot. In addition, the soleus has a role in postural control by balancing the leg during standing or walking.

Plantaris

The plantaris is a muscle comprised of short fusiform muscle belly and a long, very slender tendon. It arises from the lower part of the lateral supracondylar line of femur. It quickly extends into a tendon that courses inferomedially along the medial border of the gastrocnemius. The plantaris tendon inserts onto the posterior surface of the calcaneus, medial to the calcaneal tendon.

The plantaris is innervated by the tibial nerve (S1, S2). Its fleshy part receives blood supply from the lateral sural and superior lateral genicular branches of the popliteal artery, while its tendinous part is vascularized by the calcaneal branches of the posterior tibial artery.
The plantaris muscle is a weak muscle by itself. It rather acts as an assisting muscle to the triceps surae to produce plantar flexion of the foot. The plantaris can also act on the knee joint with the gastrocnemius and produce flexion of the knee.

Deep layer

The deep layer of the posterior group of the leg consists of the popliteus, flexor digitorum longus, flexor hallucis longus and the tibialis posterior.

Popliteus

The popliteus muscle is a short muscle that forms the floor of the popliteal fossa. It arises by the popliteus tendon from the posterolateral surface of the lateral femoral condyle, and the lateral meniscus of the knee joint. The tendon then expands into a triangular muscle belly that passes inferomedially and inserts onto the posterior shaft of the proximal tibia above the soleal line.

The popliteus receives innervation from the tibial nerve (L4-S1), and blood supply popliteal artery, posterior tibial recurrent artery and the nutrient artery of the tibia.
The popliteus plays an important function in initiating the flexion of the fully extended (“locked”) knee. Namely, the popliteus laterally rotates the femur on the tibia, thereby “unlocking the knee” and allowing flexion to occur.

Flexor digitorum longus

The flexor digitorum longus muscle is a thin muscle found on the tibial side of the posterior leg. It arises from the medial side of the posterior surface of the tibia inferior to the soleal line and descends along the medial aspect of the posterior leg. Above the ankle joint, the muscle extends into a tendon that runs behind to the medial malleolus and deep to the flexor retinaculum. The tendon goes on to divide into four smaller tendons that insert onto the plantar bases of the distal phalanges of the lateral four toes.

The flexor digitorum longus is innervated by the tibial nerve (L5-S2). Its blood supply is derived from the posterior tibial artery.
The main function of the flexor digitorum longus is flexion of the lateral four toes, in addition to plantarflexion and inversion of the foot.

Flexor hallucis longus

The flexor hallucis longus is an unipennate muscle found on the fibular side of the posterior aspect of the leg. It arises from the distal two thirds of the posterior surface of the fibula and courses inferiorly towards the foot, where it inserts onto the plantar surface of the base of the distal phalanx of the hallux.

The flexor hallucis longus is innervated by the tibial nerve (L4-S3), and vascularized by branches of the fibular (peroneal) artery.
The main function of the flexor hallucis longus is flexion of the hallux. It also assists in plantar flexion and inversion of the foot.

Tibialis posterior

The tibialis posterior is the deepest muscle of the posterior flexor group. It arises from the posterior surface of the interosseous membrane, the upper two-thirds of the posterior surface of tibia and the posterior surface of the fibula. It then courses downwards to the lower third of the tibia, where it extends into a tendon that passes behind the medial malleolus and passes deep to the flexor retinaculum to enter the plantar aspect of the foot. Here, the tibialis posterior tendon divides into two divisions; a superficial division, which inserts on the medial side of the navicular and the plantar surface of the medial cuneiform bone, and a deep division, which inserts on the intermediate cuneiform and the bases of the second, third and fourth metatarsal bones.

The tibialis posterior is innervated by the tibial nerve (L4, L5). Its muscular portion receives blood supply from the branches of the posterior tibial and fibular (peroneal) arteries, while its tendinous portion is supplied by the medial malleolar network and the medial plantar artery.
The main function of the tibialis posterior is plantar flexion of the foot at the ankle joint and inversion of the foot at the subtalar joint. This muscle also plays an important role in reinforcing the medial longitudinal arch of the foot.

Fibularis longus

The fibularis longus muscle arises from the fibular head, the proximal two-thirds of the lateral fibular shaft, and the intermuscular septa of the leg. The muscle courses inferiorly and extends into a tendon that passes behind the lateral malleolus. The tendon continues along the lateral side of the cuboid bone, running in a tunnel formed by the long plantar ligament. It ends by inserting onto the lateral surface of the medial cuneiform and the first metatarsal bones.

The fibularis longus receives innervation from the superficial fibular nerve (L5, S1), and blood supply from the fibular (peroneal) artery.
The main function of the fibularis longus is eversion of the foot at the subtalar joint, and plantar flexion of the foot at the ankle joint. Eversion of the foot is particularly important when walking or running on rough surfaces. In addition, it supports the lateral longitudinal and transverse arches of the foot.

If you want to get more into depth about the fibularis longus, click on the link below and read the dedicated article about this muscle.

Fibularis brevis

The fibularis brevis is a short muscle that arises from the distal two-thirds of the lateral surface of the fibula, and the adjoining anterior intermuscular septum. It courses inferomedially along the lateral border of fibula and extends into a tendon that passes behind the lateral malleolus to enter the foot. The fibularis brevis inserts to the base of the 5th metatarsal bone, posterior to the insertion of fibularis tertius muscle.

The fibularis brevis is innervated by the superficial fibular (peroneal) nerve (L5-S1). Its blood supply is mainly derived from the anterior tibial artery, while its distal tendinous part is supplied by the anastomotic network around the ankle.
Similarly to the fibularis longus, the main function of the fibularis brevis is eversion and plantar flexion of the foot.

To find out more about the fibularis brevis, check out our article below.

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