This is another of my favorite muscles.  I like it because many of the muscles that have nicknames like pecs or lats are named from their original terminology.  Pecks for the pectoralis muscles.  Lats for the Latissimus Dorsi.  They sound like what they are called.  The calf is the exception.  Neither calf muscle sounds anything like the word calf.

The deepest muscle of the back of your lower leg is the soleus.  Its name comes from the Latin word for sandal.  It connects right below your knee to both bones in your lower leg.  It runs down the leg and connects to the Achilles tendon, which attaches to your heel. 

The soleus plantar flexes (like pointing the toes) the foot at the ankle.  It’s an important muscle in the human body because helps keep us upright.  When you stand up, if you didn’t have a soleus, you would start to sway forward from your ankle.  The soleus helps prevent this.  Three cheers for the soleus!!  Hip, hip, Hooray!  The body is so cool.

Even though the soleus does this for us other animals who walk on all fours also have soleus muscles.  But their soleus muscles are more intertwined with the other calf muscle. 

If you want to target the soleus when you stretch your calf muscles, you need to keep your knee bent.  This video will show you how.  (Note: In the picture, the soleus is on the right.  In the body it is underneath the calf muscle pictured on the left.)