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Leg Muscles
The muscles of the leg are organized into anterior, lateral, and posterior compartments. They act primarily on the ankle and foot, producing dorsiflexion, plantarflexion, inversion, eversion, and toe movements while contributing to balance, gait, and stabilization of the lower limb.
Region-
SystemMusculoskeletal System
The muscles of the leg are the muscles located between the knee and ankle. Anatomically, the term leg refers specifically to this region rather than the entire lower limb. The muscles are enclosed by the crural fascia and organized into anterior, lateral, and posterior compartments.
These compartments differ in their muscular contents, innervation, vascular supply, and principal actions. The anterior compartment primarily produces dorsiflexion of the ankle and extension of the toes. The lateral compartment primarily everts the foot. The posterior compartment primarily produces plantarflexion, toe flexion, and inversion.
Most leg muscles originate from the tibia, fibula, interosseous membrane, or adjacent structures and send long tendons across the ankle to insert into the bones of the foot. Their actions are therefore essential for standing, walking, running, balance, propulsion, and adaptation of the foot to the supporting surface.
Compartments of the Leg
| Compartment | Major Muscles | Innervation | Major Actions |
|---|---|---|---|
| Anterior | Tibialis anterior, extensor hallucis longus, extensor digitorum longus, fibularis tertius | Deep fibular nerve | Dorsiflexion and toe extension |
| Lateral | Fibularis longus, fibularis brevis | Superficial fibular nerve | Eversion |
| Posterior, superficial | Gastrocnemius, soleus, plantaris | Tibial nerve | Plantarflexion |
| Posterior, deep | Popliteus, tibialis posterior, flexor digitorum longus, flexor hallucis longus | Tibial nerve | Plantarflexion, inversion and toe flexion |
Crural Fascia
The crural fascia is the deep fascia surrounding the leg. It is continuous proximally with the fascia lata of the thigh and attaches to prominent bony margins of the tibia and fibula.
Intermuscular septa and the interosseous membrane divide the leg into muscular compartments. Because these fascial boundaries are relatively resistant to expansion, they are clinically important in compartment syndrome.
Interosseous Membrane
The interosseous membrane of the leg is a strong fibrous sheet extending between the interosseous borders of the tibia and fibula. It contributes to compartmental organization, provides attachment for muscles, and helps transmit forces between the two bones.
Anterior Compartment
The anterior compartment lies between the lateral surface of the tibia, medial surface of the fibula, interosseous membrane, and surrounding deep fascia. Its muscles are primarily dorsiflexors of the ankle and extensors of the toes.
The compartment contains tibialis anterior, extensor hallucis longus, extensor digitorum longus, and fibularis tertius.
Tibialis Anterior
The tibialis anterior is the most medial and superficial muscle of the anterior compartment. Its tendon crosses the anterior ankle and passes toward the medial side of the foot.
| Feature | Tibialis Anterior |
|---|---|
| Origin | Lateral condyle and superior lateral surface of tibia, adjacent interosseous membrane |
| Insertion | Medial cuneiform and base of first metatarsal |
| Action | Dorsiflexes ankle and inverts foot |
| Innervation | Deep fibular nerve |
Function of Tibialis Anterior
Tibialis anterior is an important dorsiflexor. During walking it helps lift the forefoot during swing so that the toes clear the ground.
After heel contact it contracts eccentrically to control lowering of the forefoot toward the ground. Its medial insertion also allows it to produce inversion and contribute to support of the medial longitudinal arch.
Extensor Hallucis Longus
The extensor hallucis longus lies deep between tibialis anterior and extensor digitorum longus through much of the leg. Its tendon passes across the ankle to the great toe.
| Feature | Extensor Hallucis Longus |
|---|---|
| Origin | Middle portion of anterior fibula and adjacent interosseous membrane |
| Insertion | Dorsal base of distal phalanx of great toe |
| Action | Extends great toe and dorsiflexes ankle |
| Innervation | Deep fibular nerve |
Extensor Digitorum Longus
The extensor digitorum longus occupies the lateral portion of the anterior compartment and divides distally into four tendons for toes 2 to 5.
| Feature | Extensor Digitorum Longus |
|---|---|
| Origin | Lateral condyle of tibia, anterior fibula, and interosseous membrane |
| Insertion | Extensor expansions of toes 2 to 5, ultimately reaching middle and distal phalanges |
| Action | Extends lateral four toes and dorsiflexes ankle; assists eversion |
| Innervation | Deep fibular nerve |
Fibularis Tertius
The fibularis tertius is often considered the distal portion of extensor digitorum longus. It is variable and may be absent in some individuals.
| Feature | Fibularis Tertius |
|---|---|
| Origin | Inferior anterior fibula and adjacent interosseous membrane |
| Insertion | Dorsal surface near base of fifth metatarsal |
| Action | Dorsiflexes ankle and assists eversion |
| Innervation | Deep fibular nerve |
Anterior Compartment Innervation
All muscles of the anterior compartment are supplied by the deep fibular nerve, a terminal branch of the common fibular nerve.
The deep fibular nerve travels through the anterior compartment with the anterior tibial artery and continues onto the dorsum of the foot.
Anterior Compartment Blood Supply
The principal artery of the anterior compartment is the anterior tibial artery. It enters the compartment through an opening in the proximal interosseous membrane and descends toward the ankle.
At the ankle it continues onto the dorsum of the foot as the dorsalis pedis artery.
Lateral Compartment
The lateral compartment contains fibularis longus and fibularis brevis. These muscles are primarily responsible for eversion of the foot and also assist plantarflexion.
Both are supplied by the superficial fibular nerve.
Fibularis Longus
The fibularis longus is the more superficial and longer of the two major lateral compartment muscles. Its tendon passes posterior to the lateral malleolus and then crosses the plantar aspect of the foot.
| Feature | Fibularis Longus |
|---|---|
| Origin | Head and superior lateral surface of fibula |
| Insertion | Plantar aspect of medial cuneiform and base of first metatarsal |
| Action | Everts foot and assists plantarflexion |
| Innervation | Superficial fibular nerve |
Fibularis Longus and the Foot Arches
The tendon of fibularis longus crosses the sole from lateral to medial. Its course allows it to contribute to stabilization of the transverse arch and the first ray of the foot.
Its action is functionally balanced by muscles such as tibialis anterior and tibialis posterior.
Fibularis Brevis
The fibularis brevis lies deep to fibularis longus. Its tendon passes behind the lateral malleolus before inserting onto the fifth metatarsal.
| Feature | Fibularis Brevis |
|---|---|
| Origin | Inferior portion of lateral fibula |
| Insertion | Tuberosity at base of fifth metatarsal |
| Action | Everts foot and assists plantarflexion |
| Innervation | Superficial fibular nerve |
Superficial Fibular Nerve
The superficial fibular nerve supplies fibularis longus and fibularis brevis. It descends within the lateral compartment before becoming superficial in the distal leg and providing cutaneous innervation to much of the dorsum of the foot.
Blood Supply of the Lateral Compartment
The lateral compartment receives blood through branches of nearby arterial systems, particularly perforating branches associated with the fibular artery and contributions from the anterior tibial circulation.
Posterior Compartment
The posterior compartment contains the major plantarflexors of the ankle and flexors of the toes. A strong transverse intermuscular septum divides it into superficial and deep groups.
All muscles of the posterior compartment are supplied by the tibial nerve.
Superficial Posterior Compartment
The superficial posterior group consists of gastrocnemius, soleus, and plantaris. Gastrocnemius and soleus form the powerful triceps surae complex and share a common insertion through the calcaneal tendon.
Triceps Surae
The term triceps surae refers primarily to the two heads of gastrocnemius together with soleus. These muscles form the prominent muscular mass of the calf.
They converge into the calcaneal tendon, commonly called the Achilles tendon, which inserts onto the posterior calcaneus.
Gastrocnemius
The gastrocnemius is a large superficial muscle with medial and lateral heads. Because it crosses both the knee and ankle, it acts at both joints.
| Feature | Gastrocnemius |
|---|---|
| Origin | Posterior aspects of medial and lateral femoral condylar regions |
| Insertion | Posterior calcaneus through calcaneal tendon |
| Action | Plantarflexes ankle and flexes knee |
| Innervation | Tibial nerve |
Function of Gastrocnemius
Gastrocnemius is particularly important during forceful plantarflexion when the knee is extended. It contributes substantially to activities such as running, jumping, and raising the heel from the ground.
Because it crosses the knee, its effectiveness as a plantarflexor is influenced by knee position.
Soleus
The soleus lies deep to gastrocnemius and is a broad, powerful plantarflexor. Unlike gastrocnemius, it does not cross the knee.
| Feature | Soleus |
|---|---|
| Origin | Posterior fibular head and proximal fibula, soleal line and adjacent medial tibia, and tendinous arch |
| Insertion | Posterior calcaneus through calcaneal tendon |
| Action | Powerful plantarflexion and postural stabilization |
| Innervation | Tibial nerve |
Soleus and Posture
Soleus is an important postural muscle. During standing, it helps control forward movement of the tibia over the planted foot and contributes to maintaining the body's center of mass over the base of support.
Musculovenous Pump
Contraction of the calf muscles compresses deep veins and assists venous return toward the heart. The calf musculature is therefore an important component of the lower limb musculovenous pump.
Venous valves help direct blood proximally and reduce retrograde flow between contractions.
Plantaris
The plantaris is a small muscle with a long, slender tendon. It is variable and may be absent.
| Feature | Plantaris |
|---|---|
| Origin | Lateral supracondylar region of femur and adjacent knee capsule |
| Insertion | Posterior calcaneus, often near or with calcaneal tendon |
| Action | Weak plantarflexion and weak knee flexion |
| Innervation | Tibial nerve |
Calcaneal Tendon
The calcaneal tendon is the strong common tendon formed primarily by gastrocnemius and soleus. It inserts onto the posterior surface of the calcaneus.
It transmits powerful plantarflexion forces and is subjected to substantial mechanical loading during walking, running, and jumping.
Deep Posterior Compartment
The deep posterior compartment contains popliteus, tibialis posterior, flexor digitorum longus, and flexor hallucis longus. The tibial nerve and posterior tibial vessels descend through this compartment.
Popliteus
The popliteus is a small triangular muscle located posterior to the knee. It forms part of the floor of the popliteal fossa and acts primarily at the knee rather than the ankle.
| Feature | Popliteus |
|---|---|
| Origin | Lateral femoral condyle and associated knee structures |
| Insertion | Posterior tibia superior to soleal line |
| Action | Initiates flexion of locked knee by rotating femur laterally on fixed tibia or tibia medially on femur |
| Innervation | Tibial nerve |
Unlocking the Knee
At the beginning of knee flexion from a fully extended position, popliteus helps unlock the knee. In a weight-bearing limb it produces a small lateral rotation of the femur relative to the tibia.
Tibialis Posterior
The tibialis posterior is the deepest centrally located muscle of the posterior leg. Its tendon passes behind the medial malleolus before expanding to multiple attachments in the foot.
| Feature | Tibialis Posterior |
|---|---|
| Origin | Posterior tibia and fibula and intervening interosseous membrane |
| Insertion | Primarily navicular tuberosity with expansions to cuneiforms, cuboid and bases of several metatarsals |
| Action | Inverts foot and assists plantarflexion; supports medial longitudinal arch |
| Innervation | Tibial nerve |
Tibialis Posterior and Arch Support
Tibialis posterior is an important dynamic supporter of the medial longitudinal arch. Its broad insertion allows muscular force to influence multiple bones of the midfoot.
Dysfunction of the tendon can therefore alter alignment and mechanics of the foot.
Flexor Digitorum Longus
The flexor digitorum longus arises from the posterior tibia and sends four tendons to the lateral four toes.
| Feature | Flexor Digitorum Longus |
|---|---|
| Origin | Posterior surface of tibia inferior to soleal line |
| Insertion | Bases of distal phalanges of toes 2 to 5 |
| Action | Flexes toes 2 to 5, assists plantarflexion and supports longitudinal arches |
| Innervation | Tibial nerve |
Flexor Hallucis Longus
The flexor hallucis longus is a powerful flexor of the great toe. Its large muscle belly occupies much of the deep posterior fibular region.
| Feature | Flexor Hallucis Longus |
|---|---|
| Origin | Inferior posterior surface of fibula and adjacent interosseous membrane |
| Insertion | Base of distal phalanx of great toe |
| Action | Flexes great toe, assists plantarflexion and supports medial longitudinal arch |
| Innervation | Tibial nerve |
Flexor Hallucis Longus During Gait
Flexor hallucis longus becomes particularly important during the late stance and push-off phases of gait. It stabilizes and flexes the great toe as body weight progresses across the forefoot.
Deep Posterior Tendons at the Ankle
The tendons of tibialis posterior, flexor digitorum longus, and flexor hallucis longus pass posterior to the medial malleolus beneath the flexor retinaculum.
The tibial nerve and posterior tibial vessels also pass through this region.
Tarsal Tunnel
The tarsal tunnel is the fibro-osseous passage located posterior and inferior to the medial malleolus beneath the flexor retinaculum.
Structures passing through this region include the tendons of tibialis posterior, flexor digitorum longus, and flexor hallucis longus together with the posterior tibial vessels and tibial nerve.
Posterior Compartment Innervation
The tibial nerve supplies both the superficial and deep posterior compartments. It is one of the two major terminal components of the sciatic nerve and travels through the popliteal fossa into the posterior leg.
Posterior Compartment Blood Supply
The posterior compartment is supplied principally by the posterior tibial and fibular arteries. These vessels arise from the arterial system distal to the popliteal artery.
Posterior Tibial Artery
The posterior tibial artery descends through the deep posterior compartment and passes behind the medial malleolus before dividing into the medial and lateral plantar arteries.
Fibular Artery
The fibular artery descends along the medial aspect of the fibula within the deep posterior region and supplies surrounding muscles and adjacent structures through multiple branches.
Summary of Leg Muscle Innervation
| Compartment | Nerve |
|---|---|
| Anterior | Deep fibular nerve |
| Lateral | Superficial fibular nerve |
| Posterior superficial | Tibial nerve |
| Posterior deep | Tibial nerve |
Summary of Major Leg Muscles
| Muscle | Compartment | Major Action | Innervation |
|---|---|---|---|
| Tibialis anterior | Anterior | Dorsiflexion and inversion | Deep fibular nerve |
| Extensor hallucis longus | Anterior | Great toe extension and dorsiflexion | Deep fibular nerve |
| Extensor digitorum longus | Anterior | Toe extension and dorsiflexion | Deep fibular nerve |
| Fibularis tertius | Anterior | Dorsiflexion and eversion | Deep fibular nerve |
| Fibularis longus | Lateral | Eversion and plantarflexion | Superficial fibular nerve |
| Fibularis brevis | Lateral | Eversion and plantarflexion | Superficial fibular nerve |
| Gastrocnemius | Posterior superficial | Plantarflexion and knee flexion | Tibial nerve |
| Soleus | Posterior superficial | Plantarflexion | Tibial nerve |
| Plantaris | Posterior superficial | Weak plantarflexion and knee flexion | Tibial nerve |
| Popliteus | Posterior deep | Unlocks knee | Tibial nerve |
| Tibialis posterior | Posterior deep | Inversion and plantarflexion | Tibial nerve |
| Flexor digitorum longus | Posterior deep | Flexes toes 2 to 5 | Tibial nerve |
| Flexor hallucis longus | Posterior deep | Flexes great toe | Tibial nerve |
Dorsiflexion
Dorsiflexion decreases the angle between the dorsum of the foot and the anterior leg. Tibialis anterior is a major dorsiflexor, assisted by extensor hallucis longus, extensor digitorum longus, and fibularis tertius.
Plantarflexion
Plantarflexion moves the foot downward at the ankle. Gastrocnemius and soleus are the major plantarflexors, assisted by muscles of the deep posterior and lateral compartments.
Inversion
Inversion turns the plantar surface of the foot toward the medial side. Tibialis anterior and tibialis posterior are the principal muscular contributors.
Eversion
Eversion turns the plantar surface laterally. Fibularis longus and fibularis brevis are the major evertors, assisted by fibularis tertius and extensor digitorum longus.
Functional Balance Around the Ankle
Normal foot positioning depends on coordinated activity between muscles with opposing actions. Tibialis anterior and tibialis posterior favor inversion, while the fibular muscles favor eversion.
Likewise, anterior compartment muscles dorsiflex the ankle while posterior muscles generate plantarflexion.
Leg Muscles and the Arches of the Foot
Several leg muscles provide dynamic support to the foot arches through their long tendons. Tibialis posterior is particularly important for the medial longitudinal arch, while fibularis longus contributes to transverse arch stability.
Medial Longitudinal Arch
Tibialis posterior, tibialis anterior, flexor hallucis longus, and flexor digitorum longus contribute to dynamic support of the medial longitudinal arch.
Transverse Arch
The tendon of fibularis longus crosses the plantar foot and acts with tibialis posterior and intrinsic structures to support the transverse configuration of the foot.
Leg Muscles During Gait
The muscles of the leg are active throughout the gait cycle. They control foot placement, absorb impact, stabilize the ankle, maintain toe clearance, and generate propulsion.
Initial Contact
At initial contact, the ankle is positioned to allow the heel to meet the ground. The dorsiflexors prepare the foot for controlled loading.
Loading Response
After heel contact, tibialis anterior and other dorsiflexors contract eccentrically to control plantarflexion as the forefoot lowers toward the ground.
Midstance
During midstance, soleus and gastrocnemius increasingly control forward progression of the tibia over the planted foot.
Terminal Stance
As the heel rises, the plantarflexors contribute to stabilization and progression of the body over the forefoot.
Push-Off
During push-off, plantarflexor activity and elastic recoil within the muscle-tendon system contribute to propulsion. Flexor hallucis longus and flexor digitorum longus stabilize the toes as forces pass through the forefoot.
Swing Phase
During swing, the anterior compartment muscles maintain ankle dorsiflexion so that the toes clear the ground.
Leg Muscles During Running
Running increases the forces and rates of loading experienced by the leg muscles. The plantarflexor complex stores and returns substantial elastic energy through the calcaneal tendon while also generating active force.
Leg Muscles During Jumping
Powerful plantarflexion by gastrocnemius and soleus contributes to takeoff during jumping. During landing, coordinated eccentric muscular activity helps absorb energy and control ankle movement.
Common Fibular Nerve and Leg Function
The common fibular nerve winds around the neck of the fibula before dividing into superficial and deep fibular branches. Its superficial position near the fibular neck makes it vulnerable to injury.
Foot Drop
Foot drop results from significant weakness or paralysis of ankle dorsiflexion. It may occur with injury to the common fibular nerve, deep fibular nerve, or more proximal neural structures.
During walking, inadequate dorsiflexion can cause the toes to drag during swing.
Steppage Gait
A person with foot drop may compensate by excessively flexing the hip and knee during swing to increase toe clearance. This pattern is commonly called a steppage gait.
Tibial Nerve Injury
Injury to the tibial nerve can weaken plantarflexion, inversion, and toe flexion depending on the level and severity of the lesion. More distal lesions may selectively affect particular branches or intrinsic foot muscles.
Superficial Fibular Nerve Injury
Damage to the superficial fibular nerve can weaken eversion through loss of fibularis longus and fibularis brevis function.
Deep Fibular Nerve Injury
Damage to the deep fibular nerve can weaken dorsiflexion and toe extension. The extent of weakness depends on the location of the lesion.
Compartment Syndrome
Compartment syndrome occurs when pressure rises within a closed fascial compartment sufficiently to compromise tissue perfusion and neural function.
The relatively noncompliant fascia surrounding the leg compartments limits expansion when bleeding or edema develops.
Anterior Compartment Syndrome
The anterior compartment is a clinically important site of acute and exertional compartment syndromes. Structures at risk include the anterior compartment muscles, deep fibular nerve, and anterior tibial vessels.
Muscle Ischemia
Persistent elevation of compartment pressure can impair capillary perfusion and produce ischemic injury to muscles and nerves. Acute compartment syndrome is therefore an anatomical and surgical emergency.
Calcaneal Tendon Injury
The calcaneal tendon can develop tendinopathy or undergo partial or complete rupture. Rupture substantially impairs the ability of gastrocnemius and soleus to transmit plantarflexion force to the calcaneus.
Calcaneal Tendon Rupture
Complete rupture can produce weakness of plantarflexion and difficulty performing a single-leg heel raise. Clinical examination assesses continuity and functional transmission of force through the tendon.
Calf Muscle Strain
Sudden acceleration, jumping, or forceful eccentric loading can injure the gastrocnemius or other calf muscles. The medial head of gastrocnemius is a common site of muscular injury.
Posterior Tibial Tendon Dysfunction
Dysfunction of the tibialis posterior tendon can reduce dynamic support of the medial longitudinal arch and contribute to progressive alteration of foot alignment.
Fibular Tendon Injury
The tendons of fibularis longus and brevis can be affected by overuse, instability, trauma, or abnormal mechanical loading around the lateral ankle.
Muscle Testing
Individual compartments can be assessed by testing their characteristic movements against resistance.
| Test Movement | Major Muscles Assessed |
|---|---|
| Dorsiflexion | Tibialis anterior and other anterior compartment muscles |
| Great toe extension | Extensor hallucis longus |
| Toe extension | Extensor digitorum longus |
| Eversion | Fibularis longus and brevis |
| Plantarflexion | Gastrocnemius and soleus |
| Inversion | Tibialis anterior and posterior |
| Great toe flexion | Flexor hallucis longus |
| Lesser toe flexion | Flexor digitorum longus |
Testing Plantarflexion
A single-leg heel raise provides a functional assessment of the plantarflexor mechanism. Repeated heel raises can provide additional information about calf muscle endurance.
Testing Dorsiflexion
Dorsiflexion can be tested against resistance, with tibialis anterior emphasized by combining dorsiflexion with inversion.
Testing Eversion
Resisted eversion assesses the lateral compartment, particularly fibularis longus and fibularis brevis.
Testing Tibialis Posterior
Tibialis posterior can be assessed by resisted inversion with plantarflexion and by observing its contribution during a heel-rise maneuver.
Key Anatomical Features
| Feature | Key Point |
|---|---|
| Anatomical extent | Knee to ankle |
| Main compartments | Anterior, lateral and posterior |
| Anterior compartment nerve | Deep fibular nerve |
| Lateral compartment nerve | Superficial fibular nerve |
| Posterior compartment nerve | Tibial nerve |
| Major dorsiflexor | Tibialis anterior |
| Major plantarflexors | Gastrocnemius and soleus |
| Major evertors | Fibularis longus and brevis |
| Major invertors | Tibialis anterior and tibialis posterior |
| Great toe extensor | Extensor hallucis longus |
| Great toe flexor | Flexor hallucis longus |
| Common plantarflexor tendon | Calcaneal tendon |
| Primary functions | Ankle movement, toe movement, balance, arch support and locomotion |
Anatomical and Functional Importance
The muscles of the leg form the principal muscular system controlling the ankle and many movements of the toes. Their compartmental arrangement closely reflects their function and innervation. The anterior compartment dorsiflexes the ankle and extends the toes, the lateral compartment everts the foot, and the posterior compartment produces powerful plantarflexion, inversion, and toe flexion.
The superficial posterior muscles form the major propulsive apparatus of the ankle. Gastrocnemius and soleus transmit their forces through the calcaneal tendon and are essential for heel elevation, walking, running, and jumping. The deeper posterior muscles provide additional control of the toes and foot while supporting the longitudinal arches.
The anterior and lateral muscles provide equally important control during locomotion. The dorsiflexors maintain toe clearance during swing and control the foot after heel contact, while the fibular muscles stabilize the lateral side of the ankle and oppose excessive inversion.
Understanding the leg muscles is therefore fundamental to the anatomy of ankle movement, foot movement, gait, lower limb compartments, peripheral nerve lesions, foot drop, compartment syndrome, arch support, calf function, and the biomechanics of walking and running.
Published on October 17, 2026
Last updated on October 17, 2026
Last updated on October 17, 2026