What exactly is Achilles Tendonitis, exactly? Achilles Tendonitis is the swelling of the Achilles tendon. The Achilles tendon, which is a large tendon that connects two major calf muscles (Gastrocnemius & soleus) to the back side of the heel bone, is called Achilles Tendonitis. Achilles Tendonitis, a sports-related injury that results from excessive exercise and jumping, is one of the most common. There are only a few tendons in the body that have low blood supply. "Watershed zones" are tendon…