The Achilles tendon runs down the back of the lower leg. This tissue connects the calf muscle to the heel bone. It facilitates walking by helping to raise the heel off the ground. Two common issues that occur concerning the Achilles tendon are Achilles tendonitis and Achilles tendonosis. These are overuse disorders caused by a sudden increase in repetitive activity involving the Achilles tendon. This type of activity puts too much stress on the tendon too quickly, leading to injury of the tendon fibers.