Soleus: origin, insertion, action and innervation

The soleus is a broad, flat muscle deep to the gastrocnemius. Its name comes from the sole, the flat fish it's shaped like.

Where it is

It lies at the back of the leg, under the gastrocnemius, and is visible on either side of it in the lower calf. Its fibres converge on the Achilles tendon.

Origin and insertion

• Origin: the back of the head and upper shaft of the fibula, the soleal line and medial border of the tibia, and a tendinous arch between the two bones, under which the tibial nerve and popliteal vessels pass.
• Insertion: the calcaneus, through the calcaneal (Achilles) tendon, shared with the gastrocnemius.

What it does

1. Plantar flexion of the ankle. Since it doesn't cross the knee, it works whatever the knee position, and it's the main plantar flexor when the knee is bent.
2. Postural muscle: when you stand, the body tends to sway forward over the ankles. The soleus contracts continuously to hold it back.
3. Its contractions squeeze the deep veins of the leg and help return blood to the heart, part of what is often called the calf muscle pump.

Innervation and blood supply

The tibial nerve (S1–S2) supplies it. Blood comes from the posterior tibial, fibular and sural arteries.

How to remember it

• Soleus = shaped like a sole fish, flat and broad.
• One joint (ankle) only: the soleus is the bent-knee plantar flexor.

Frequently asked questions

What is the difference between the soleus and the gastrocnemius?

The gastrocnemius crosses the knee and the ankle; the soleus only the ankle. Both form the Achilles tendon.

Where does the soleus insert?

On the calcaneus, through the calcaneal (Achilles) tendon.

Which nerve supplies the soleus?

The tibial nerve, from S1 and S2.

Sources

• OpenStax, Anatomy and Physiology 2e, 11.6 Appendicular muscles of the pelvic girdle and lower limbs
• Z-Anatomy, the libre 3D atlas of anatomy