The soleus muscles are part of the group of muscles that move the foot and ankle. The soleus muscles and gastrocnemius muscles are good friends and even better working partners. Their tendinous attachment to the calcaneus (heel bone) form the very strong Achilles tendon. Soleus is sometimes referred to as the second heart, as the contractions of this muscle play an important role in helping blood get back to the heart. (source: Yoganatomy)