The soleus muscle is a powerful muscle in the back of the leg that runs from just below the knee to the heel. It is similar to the gastrocnemius muscle, but instead of assisting in running and jumping, it assists in walking and standing. It is also responsible to flexing the foot to point the toes downward.
Together, the soleus muscle and the gastrocnemius muscle form the calf. They join onto the tendon at the bottom of the leg called the Achilles or calcaneal tendon, which is the thickest and strongest tendon in the human body.