While the Achilles tendon may be injured in several different locations, one of the worst running injuries occurs when the Achilles is damaged directly at its attachment on the heel. With this injury, you feel pain directly on the back of the heel, particularly if you press at the point where the Achilles tendon attaches to the heel bone. Referred to as an insertional Achilles tendinitis, this type of Achilles injury is notoriously difficult to treat.
In a study evaluating the success rate associated with conventional eccentric exercises, only 32 percent of athletes presenting with insertional Achilles tendinitis improved over a 12-week training period. This compares to the 80–90 percent success rate when the same exercises are used to treat non-insertional Achilles injuries. This frustrating injury is more likely to occur in high-arched, inflexible runners, particularly if they possess a Haglund’s deformity.
illustration courtesy Thomas Michaud
Until recently, researchers believed the biomechanical cause for the development of insertional Achilles tendinitis was pretty simple: Excessive running causes the Achilles tendon to break down on the back portion of the Achilles attachment, where pulling forces are the greatest. While this makes perfect sense, recent research has shown that just the opposite is true: The Achilles tendon almost always breaks down in the forward section of the tendon, where pulling forces are the lowest.
By placing strain gauges inside different sections of the Achilles tendons and then loading the tendons with the ankle positioned in a variety of angles, researchers from the University of North Carolina discovered that the back portion of the Achilles tendon is exposed to far greater amounts of strain (particularly when the ankle was moved upward) while the forward section of the tendon, which is the section most frequently damaged with insertional tendinitis, was exposed to very low loads. The authors of the study suggest that the lack of stress on the forward aspect of the Achilles tendon (which they referred to as a tension shielding effect) may cause that section to weaken and eventually fail.
The treatment of an Achilles insertional tendinitis should thus be to strengthen the forward-most aspect of the tendon (after rest has reduced swelling in the sheath around the tendon). This can be accomplished by performing a series of eccentric load exercises through a partial range of motion. It is particularly important to exercise the Achilles tendon with the ankle pointing down as far as possible (i.e., standing way up on tiptoes), because this position places greater amounts of load on the more frequently damaged forward portion of the tendon.