What is Achilles Tendonitis or Tendinopathy? Achilles Tendonitis or Tendinopathy is a condition that causes pain, swelling, stiffness and weakness of the achilles tendon. The achilles is the tendon formed as the gastrocnemius and soleus (calf muscle) and joins to insert on to the heel bone. It is often seen in conjunction with Plantar Fasciitis pain in the heel....... Click The Button To Continue Reading. in Healthwith achilles-tendonitisby 5 users