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Posterior Compartment of the Leg Muscles Anatomy
Posterior Compartment of the Leg Muscles Anatomy
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The posterior compartment of the leg contains seven muscles, divided into superficial and deep groups.
These muscles primarily plantarflex (point the toes downward) and invert the foot.
They are all innervated by the tibial nerve (a branch of the sciatic nerve) and mainly receive blood from the posterior tibial artery.
The seven muscles are:
Gastrocnemius
Soleus
Plantaris
Popliteus
Flexor hallucis longus
Flexor digitorum longus
Tibialis posterior.
Superficial Compartment
Superficial Compartment
The superficial posterior compartment includes three muscles: the gastrocnemius, soleus, and plantaris. Together, these muscles form the prominent contour of the calf and merge into the calcaneal (Achilles) tendon, which attaches to the calcaneus (heel bone).
Two bursae, or fluid-filled sacs, cushion the tendon to reduce friction during movement:
The subcutaneous calcaneal bursa lies between the skin and the tendon.
The deep calcaneal bursa lies between the tendon and the heel bone itself.
Gastrocnemius
The gastrocnemius is the most superficial and visually dominant calf muscle, forming the bulk of its shape. It contributes significantly to powerful plantarflexion at the ankle and also assists in flexion of the knee, owing to its origins above the knee joint. As the most superficial posterior leg muscle, it forms the prominent contour of the calf and plays a major role in propulsive movements such as running and jumping.
It has two heads:
The lateral head, which originates from the lateral femoral condyle
The medial head, which originates from the medial femoral condyle.
These unite to form a single muscle belly that joins the soleus to create the calcaneal tendon.
Insertion: Calcaneus via the calcaneal (Achilles) tendon.
Innervation: Tibial nerve (S1–S2).
Soleus
The soleus serves as a primary and highly efficient plantarflexor of the foot. Unlike the gastrocnemius, it does not cross the knee, which allows it to act even when the knee is bent. It is essential for maintaining an upright posture during standing, as it counteracts the forward sway of the body caused by gravity.
Origin: Soleal line of the tibia, proximal posterior fibula.
Insertion: Calcaneus via the calcaneal (Achilles) tendon.
Innervation: Tibial nerve (S1–S2).
Plantaris
The plantaris contributes weakly to plantarflexion of the foot and flexion of the knee; it is considered biomechanically minor and is absent in about 10% of the population. Its long tendon is frequently used in surgical grafting due to its expandability.
Origin: Lateral supracondylar line of the femur.
Insertion: Calcaneus (usually through or alongside the calcaneal tendon).
Innervation: Tibial nerve (S1–S2).
Deep Compartment
Deep Compartment
The deep posterior compartment lies beneath the superficial muscles, separated by a strong layer of deep fascia. This group includes four muscles: the popliteus, flexor hallucis longus, flexor digitorum longus, and tibialis posterior.
These muscles act mainly to plantarflex, invert the foot, and flex the toes. They also help stabilize the ankle and support the medial longitudinal arch of the foot, preventing collapse during standing and movement.
Popliteus
The popliteus is essential for initiating knee flexion by “unlocking” the knee joint. It does so by laterally rotating the femur on the tibia during weight-bearing or medially rotating the tibia when the leg is not fixed.
As the most superior muscle of the deep group, it forms the floor of the popliteal fossa and plays a stabilizing role in both standing and movement.
Origin: Lateral femoral condyle, posterior horn of the lateral meniscus.
Insertion: Posterior surface of the proximal tibia (above the soleal line).
Innervation: Tibial nerve (L5–S2).
Quick Reference Table: Muscle Name, Origin, Insertion & Innervation
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Flexor Hallucis Longus
The flexor hallucis longus generates powerful flexion of the great toe and assists in plantarflexion and inversion of the foot.
Because the hallux is the final point of ground contact during the gait cycle, it plays a critical role in push-off during walking, running, and jumping.
Origin: Distal two-thirds of the posterior fibula, interosseous membrane.
Insertion: Base of the distal phalanx of the great toe (hallux).
Innervation: Tibial nerve (S2–S3).
Flexor Digitorum Longus
The flexor digitorum longus flexes the lateral four toes at both the metatarsophalangeal and interphalangeal joints. It also assists in plantarflexion and inversion of the foot. Functionally, it contributes to balance by helping the toes grip the ground during walking and stance.
Origin: Posterior surface of the tibia (inferior to the soleal line).
Insertion: Distal phalanges of toes 2–5 (plantar surfaces).
Innervation: Tibial nerve (S1–S2).
Tibialis Posterior
The tibialis posterior is the primary inverter of the foot and also contributes to plantarflexion. Importantly, it provides critical support to the medial longitudinal arch. Weakness or dysfunction of this muscle is a major cause of adult-acquired flatfoot deformity.
Origin: Posterior surface of the tibia, posterior surface of the fibula, and interosseous membrane.
Insertion: Navicular tuberosity, all three cuneiform bones, bases of metatarsals 2–4, and (sometimes) cuboid bone.
Innervation: Tibial nerve (L4–L5).
Need a recap? Take a look at the Posterior Compartment of the Leg anatomy notes here.
Need a recap? Take a look at the Posterior Compartment of the Leg anatomy notes here.
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References
References
Gray, H. (2009). Anatomy of the human body, part 2 (LibriVox Volunteers, Narr.) [Audiobook]. LibriVox. https://librivox.org/anatomy-of-the-human-body-part-2-by-henry-gray/ (Original work published 1858)
J Gordon Betts, Desaix, P., Johnson, E., Johnson, J. E., Korol, O., Kruse, D., Poe, B., Wise, J., Womble, M. D., & Young, K. A. (2013). Anatomy & physiology. Openstax College, Rice University. https://openstax.org/details/books/anatomy-and-physiology
Based on OpenStax, Anatomy and Physiology (2013), licensed under CC BY 4.0.
Access for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction.
Content paraphrased; adaptations were made.
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