The Achilles tendon is the largest tendon in the body. It connects your calf muscles to your heel bone and is used when you walk, run, and jump.
Although the Achilles tendon can withstand great stresses from running and jumping, it is also prone to tendinitis, a condition associated with overuse and degeneration.
Simply defined, tendinitis is inflammation of a tendon. Inflammation is the body’s natural response to injury or disease, and often causes swelling, pain, or irritation. There are two types of Achilles tendinitis, based upon which part of the tendon is inflamed.
Noninsertional Achilles Tendinitis
In noninsertional Achilles tendinitis, fibers in the middle portion of the tendon have begun to break down with tiny tears (degenerate), swell, and thicken.
Tendinitis of the middle portion of the tendon more commonly affects younger, active people.
Insertional Achilles Tendinitis
Insertional Achilles tendinitis involves the lower portion of the heel, where the tendon attaches (inserts) to the heel bone.
In both noninsertional and insertional Achilles tendinitis, damaged tendon fibers may also calcify (harden). Bone spurs (extra bone growth) often form with insertional Achilles tendinitis.
Tendinitis that affects the insertion of the tendon can occur at any time, even in patients who are not active.
Achilles tendinitis is typically not related to a specific injury. The problem results from repetitive stress to the tendon. This often happens when we push our bodies to do too much, too soon, but other factors can make it more likely to develop tendinitis, including:
- Sudden increase in the amount or intensity of exercise activity—for example, increasing the distance you run every day by a few miles without giving your body a chance to adjust to the new distance
- Tight calf muscles—Having tight calf muscles and suddenly starting an aggressive exercise program can put extra stress on the Achilles tendon
- Bone spur—Extra bone growth where the Achilles tendon attaches to the heel bone can rub against the tendon and cause pain