Do NOT ignore the soleus... This is one of the most important exercises for your lower leg. Training this way strengthens a muscle called the soleus, which sits underneath the calf. It plays a huge role in preventing ankle injuries, Achilles pain, and even plantar fasciitis. Here is how it works. When you do a standard calf raise with straight legs, you are training the gastrocnemius, the large outer muscle. When you bend your knees slightly, the soleus takes over and handles the same ankle move