Soleus muscle

At a glance

English

Soleus muscle

Latin (TA2)

Musculus soleus

System

Muscle

Region

Lower limb

Side

Paired, left and right

Arises from

The tibia

About the soleus muscle

The soleus is a broad, flat muscle of the calf lying directly under the gastrocnemius. With the two heads of gastrocnemius it forms the triceps surae, and the three share a single tendon of insertion. Its name comes from the Latin for sandal, a reference to its flat shape. Between it and gastrocnemius runs the slender plantaris and its tendon.

It arises below the knee from both bones of the leg: the back of the fibular head and the upper part of the fibular shaft, the soleal line and the middle stretch of the tibia's medial border, and a fibrous arch bridging the two. Many of its fibres spring from an internal sheet of tendon and are arranged in a complex multipennate pattern. Lower down, its own aponeurosis merges with that of gastrocnemius to form the calcaneal (Achilles) tendon, which fixes to the back of the calcaneus.

Deep to the soleus a fascial septum divides off the deep posterior compartment, holding tibialis posterior, flexor digitorum longus, flexor hallucis longus and the posterior tibial vessels with the tibial nerve. The tibial nerve and the popliteal vessels pass under the tendinous arch to enter that space.

Soleus plantarflexes the ankle. Because it does not cross the knee, it keeps full strength when the knee is bent, whereas gastrocnemius loses force in that position. It is rich in slow, fatigue-resistant fibres and works almost continuously in standing, stopping the body from falling forward over the ankles. Its contractions also squeeze the large veins within it and drive blood back towards the heart, so it is often called the calf muscle pump; stagnant flow in these veins during immobility is a classic setting for deep vein thrombosis. Swelling inside the tight fascial compartments of the leg can cause compartment syndrome.

Attachments, action and supply

Origin

Back of the fibular head and upper fibular shaft, the soleal line and medial border of the tibia, and the tendinous arch between them.

Insertion

Posterior surface of the calcaneus through the calcaneal (Achilles) tendon.

Action

Plantarflexes the ankle, most effectively with the knee bent; steadies the leg over the foot in standing and pumps venous blood upward.

Nerve supply

Tibial nerve (S1, S2).

Blood supply

Posterior tibial, fibular (peroneal) and sural arteries.