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The human foot is a complex structure, with 20-plus muscles enabling movement and giving the foot its shape. These muscles can be divided into two groups: extrinsic and intrinsic. The extrinsic muscles are located in the anterior, posterior, and lateral compartments of the leg, while the intrinsic muscles are found within the foot itself. The intrinsic muscles can be further divided into dorsal and plantar groups, with the dorsal muscles responsible for extending the toes and the plantar muscles flexing them. The plantar muscles are arranged in four layers, with the first layer being the most superficial and located immediately underneath the plantar fascia. The foot also contains two intrinsic muscles: the extensor digitorum brevis and extensor hallucis brevis, which are responsible for extending the lateral four toes and the big toe, respectively.
| Characteristics | Values |
|---|---|
| Number of muscles in the foot | 20+ |
| Number of extrinsic muscles | 10 |
| Number of intrinsic muscles | 19 |
| Number of intrinsic muscles on the dorsal aspect of the foot | 2 |
| Number of plantar layers | 4 |
| Muscles that extend the toes | Extensor digitorum brevis, Extensor hallucis brevis, Extensor digitorum longus, Peroneus quartus |
| Muscles that extend the big toe | Extensor hallucis brevis, Extensor hallucis longus, Peroneus tertius |
| Muscles that dorsiflex the foot | Anterior tibialis, Extensor hallucis longus, Peroneus tertius |
| Muscles that plantarflex the foot | Gastrocnemius, Soleus, Plantaris, Posterior tibialis |
| Muscles that invert the foot | Anterior tibialis, Posterior tibialis |
| Muscles that evert the foot | Peroneus tertius, Peroneus longus, Peroneus brevis |
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What You'll Learn
Extensor hallucis longus
The Extensor Hallucis Longus (EHL) is a thin skeletal muscle that is situated in the anterior compartment of the lower leg. It is one of 29 muscles associated with the human foot. The EHL is responsible for extending the big toe (also known as the hallux) at the metatarsophalangeal and interphalangeal joints. This extension is a crucial movement in walking and running.
The EHL is located between the tibialis anterior and the extensor digitorum longus muscles. It acts in three foot joints: the talocrural, metatarsophalangeal, and interphalangeal joints. The muscle originates from the anteromedial aspect of the fibula, lateral to the origin of the tibialis anterior muscle, and medial to the extensor digitorum longus muscle. It runs inferomedially towards the foot, ending in a tendon. The tendon passes through a distinct compartment in the inferior extensor retinaculum of the foot.
The EHL is innervated by the deep fibular nerve (root value L5 and S1). The blood supply for the EHL mainly comes from the anterior tibial artery and its branches. In addition, the muscle can be supplied by the branches of the fibular artery. The venous blood from this compartment is drained by the anterior tibial vein, which empties into the popliteal vein.
Weakness of the EHL can cause the toe to fold under the foot when putting on socks or shoes, and it can also cause tripping. Hyperextension of the great toe can cause pain and calluses, or corns, on the dorsal surface of the interphalangeal joint.
The EHL can be strengthened through exercises such as big toe lifts, big toe extension with heel raises, and short foot exercises. These exercises help to improve isolation, range of motion, and strength in the big toe extensor muscles.
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Extensor digitorum brevis
The extensor digitorum brevis (EDB) is an intrinsic muscle on the dorsum, or upper surface, of the foot. It is a small, thin muscle that lies underneath the long extensor tendons of the foot. The EDB arises from the upper and lateral surface of the calcaneus, the floor of the tarsal sinus, the talocalcaneal ligament, and the stem of the inferior extensor retinaculum.
The EDB is divided into four slips, or tendons, that pass anteromedially, from the lateral side towards the medial side of the foot. The most medial slip and tendon of the EDB constitute a distinct muscle named the extensor hallucis brevis. The lateral three tendons course anteriorly over the tarsal and metatarsal bones, inserting at the lateral aspect of the tendons of the extensor digitorum longus.
The EDB is richly vascularized and has a well-developed vascular network. Proximally, it is supplied by the branches of the fibular artery and branches of the anterior tibial artery. Distally, it is supplied by the dorsalis pedis artery and its branches, including the lateral tarsal arteries, arcuate artery, and dorsal metatarsal arteries. The muscle also receives innervation from the lateral terminal branch of the deep fibular (peroneal) nerve, arising from the L5 and S1 spinal nerves.
The EDB works in unison with other muscles to raise the toes off the ground when walking or running. Specifically, it extends the first four digits at the metatarsophalangeal joint and assists in extending the second, third, and fourth digits at the interphalangeal joint. The fifth digit, lacking any insertion from the EDB, can only be raised by the long extensor.
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Extensor hallucis brevis
The Extensor Hallucis Brevis is a short and slender muscle located in the dorsum of the foot. It is considered an intrinsic muscle, which means it originates within the foot. It is one of two intrinsic muscles located within the dorsal aspect or top of the foot, the other being the extensor digitorum brevis.
The Extensor Hallucis Brevis originates from the superior aspect of the calcaneus, just posteriorly to the calcaneocuboid joint. It courses medially over the dorsum of the foot, giving off a tendon that inserts onto the base of the proximal phalanx of the hallux (big toe). It is innervated by the deep fibular nerve (root value L5-S1) and receives its blood supply from the dorsal artery of the foot, a continuation of the anterior tibial artery.
The Extensor Hallucis Brevis works in synergy with the Extensor Hallucis Longus to assist in the extension of the big toe at the metatarsophalangeal joint. This action returns the hallux from a flexed position to a neutral position, or into hyperextension if the contraction continues. This movement is important for gait, as raising the big toe clear of the ground facilitates walking and running.
The Extensor Hallucis Brevis is sometimes considered to be the medial part of the Extensor Digitorum Brevis muscle, rather than a separate structure. In some cases, the fibres of these two muscles fuse together, creating a single muscle that extends the toes.
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Peroneus longus
The peroneus longus is a muscle in the lateral compartment of the lower limb. It is one of three muscles that span the lateral leg, the others being the peroneus tertius and peroneus brevis muscles. The peroneus longus arises from the head and upper half of the fibular shaft, crosses the ankle joint, and passes into a groove of the cuboid bone. The muscle then inserts onto the posterolateral aspect of the medial cuneiform bone and the lateral portion of the base of the first metatarsal. The peroneus longus is the longest and most superficial of the three peroneus muscles.
The primary function of the peroneus longus muscle is to tilt the sole of the foot away from the midline of the body (eversion) and to extend the foot downward away from the body (plantar flexion) at the ankle. This movement is critical to the eversion of the foot and can be injured by forced inversion and dorsiflexion of the ankle. The peroneus longus is supplied by the superficial fibular nerve and the anterior tibial and peroneal arteries.
The peroneus longus is susceptible to several pathologies, including tendonitis, tendon dislocation, subluxation, rupture, and acute and chronic compartment syndrome. Peroneal tendon injuries are common in young, active individuals and those who participate in sports such as football, soccer, and running. Injury to the peroneus longus tendon can cause lateral ankle pain and may lead to ankle instability.
The peroneus longus muscle is involved in several pathologies, including traumatic injury, tendinitis, dislocation, acute rupture, and chronic tear. The peroneus longus tendon passes inferior to the cuboid bone in a bone tunnel called the cuboid tunnel. Several variants of the peroneus longus tendon exist, which may possess one or more accessory tendinous slips that insert into other neighbouring bones or tendons.
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Soleus
The soleus is a powerful lower limb muscle found in the back part of the lower leg (the calf). It is a wide, flat muscle that runs from just below the knee to the heel and is involved in standing and walking. The soleus is located in the superficial posterior compartment of the leg, situated deep to the gastrocnemius muscle. Together with the gastrocnemius and plantaris, it forms the calf muscle or triceps surae.
The soleus muscle arises from the soleal line on the dorsal surface of the tibia, the medial border of the tibia, the head of the fibula, and the posterior border of the fibula. Part of the fibres arises from the tendinous arch of the soleus, which spans between the tibia and fibula and arches over the popliteal vessels and tibial nerve. The soleus muscle runs along the gastrocnemius muscle and together they insert onto the posterior surface of the calcaneus via the calcaneal tendon, also known as the Achilles tendon.
The soleus is the most effective muscle for plantar flexion in a bent-knee position. Its contraction results in strong plantar flexion, which increases the angle between the foot and the leg. This enables movements such as walking, running, and leaping. The soleus is a major postural muscle, playing an important role in maintaining standing posture by preventing the body from falling forward.
The soleus muscle is composed predominantly of slow-twitch muscle fibres, which resist fatigue. This composition makes the soleus preferentially activated in the concentric phase of muscle movement.
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Frequently asked questions
The foot has extrinsic and intrinsic muscles. The extrinsic muscles are located in the anterior, posterior, and lateral compartments of the leg, while the intrinsic muscles are located within the foot. The extensor digitorum brevis and extensor hallucis brevis are intrinsic muscles that extend the toes.
The extrinsic muscles are located in the lower leg and are responsible for actions such as dorsiflexion, plantarflexion, inversion, and eversion of the foot. Examples of extrinsic muscles include the extensor digitorum longus, extensor hallucis longus, and peroneus tertius.
The intrinsic muscles are located within the foot and are responsible for fine motor actions such as the movement of individual digits. There are two types of intrinsic muscles: dorsal and plantar. The dorsal muscles extend the toes, while the plantar muscles flex the toes.
The extensor hallucis brevis is an intrinsic muscle that aids in extending the big toe. It originates from the calcaneus and inferior extensor retinaculum and attaches to the base of the proximal phalanx of the great toe.
