The Achilles tendon connects the gastrocnemius and soleus calf muscles to the back of the heel bone. Under too much stress, the tendon can tighten and become inflamed. This inflammation is what is known as Achilles tendinitis. It is characterized by dull or sharp pain along the back of the tendon, usually near the heel. Achilles tendonitis also can cause limited ankle flexibility, redness, and heat in the area. One of the most common causes of Achilles tendonitis in runners is tight or tired calf muscles—this places too much of the stress of running on the Achilles tendon. To prevent tight or tired calf muscles, runners should be sure to properly stretch, increase mileage slowly, and avoid overtraining. Running on hills and wearing inflexible shoes also can lead to Achilles tendinitis. The former places more stress on the Achilles tendon than other types of running and the latter forces the Achilles tendon to twist. People who experience any pain in the Achilles tendon should immediately stop running. Ibuprofen and ice can help to reduce the inflammation and pain. If the injury doesn’t respond to self-treatment within two weeks, however, physical therapy may be necessary. Once the pain and swelling subside, a physical therapist may develop a custom return-to-running exercise program, which might include stretches to increase the flexibility of the tendon and exercises to strengthen the feet, calves, and shins. He or she also may recommend alternative, non-weight-bearing exercises such as swimming and bicycling in low gear.