Achilles tendonitis is a common condition. The Achilles is the largest tendon in the body. Achilles tendonitis occurs when the large tendon that runs from the calf to the heel bone becomes irritated and inflamed. The Achilles tendon can withstand great stress; however, it is particularly prone to develop inflammation, resulting in Achilles tendon pain. This pain most often occurs due to overuse and degeneration. Certain athletes, such as long distance runners and sprinters are at increased risk for Achilles tendonitis and even an Achilles rupture.