Soleus

The soleus is a broad, flat skeletal muscle located in the superficial posterior compartment of the leg, deep to the gastrocnemius. Together with the gastrocnemius, it forms the triceps surae muscle group.

The soleus lies deep to the gastrocnemius in the posterior leg compartment. It originates from the soleal line of the tibia and the posterior surface of the fibular head, and joins the gastrocnemius to insert via the calcaneal (Achilles) tendon on the heel.

The soleus is a powerful plantarflexor of the foot at the ankle joint, and unlike the gastrocnemius, it acts independently of knee position. It also plays an important role in maintaining upright posture and propelling the body forward during walking and running.

The soleus may be involved in Achilles tendon pathology, calf strain injuries, and deep vein thrombosis given its proximity to deep venous structures. It is also a muscle commonly involved in exercise-related compartment syndrome of the posterior leg.

The soleus is a wide, flat, pennate muscle with a broad attachment spanning the tibia and fibula. On cross-section imaging it appears as a large muscle mass deep to the gastrocnemius, contributing to the prominent bulk of the calf.