Muscle · Lower leg

Soleus

Musculus soleus

The broad, flat workhorse lying underneath the gastrocnemius. It only crosses the ankle, so unlike its partner it keeps working with the knee bent — which is most of standing, walking and running. It is built for endurance rather than speed: it is the muscle quietly holding you upright against the constant forward sway of the body over the foot, and it carries a huge share of the load through the Achilles. Because it is deep and rarely trained with the knee bent, it is often the part of the calf that has been missed when calf pain, Achilles pain or a stiff ankle keeps coming back.