The soleus muscle is a major muscle of the calf. It plays a key role in walking and running by plantarflexing the foot. The tendons of the soleus, gastrocnemius, and plantaris muscles combine to form the Achilles tendon, the thickest and strongest tendon in the human body.
The soleus is a wide, flat muscle found in the calf. It is located deep in the gastrocnemius muscle and superficial to the tibialis posterior. The soleus arises from origins on the posterior head and shaft of the fibula and a thin band on the posterior tibia between the origins of the popliteus and flexor digitorum longus muscles. From its origins, it descends the calf and gradually tapers as it approaches and joins the calcaneal (Achilles) tendon. The calcaneal tendon crosses the ankle joint posterior to the tibia and talus to insert on the posterior surface of the calcaneus bone.
The soleus muscle contracts to draw its insertion on the calcaneus posteriorly and superiorly toward the posterior fibula and tibia. It plantar flexes the foot at the ankle, pointing the toe. Plantarflexion is an important part of many movements of the leg, such as running, walking, and jumping, as it uses the length of the foot to lift and push the body forward.