Habets B, Smits HW, Backx FJG, van Cingel REH, Huisstede BMA. Hip muscle strength in middle-aged recreational male athletes with midportion Achilles tendinopathy: A cross-sectional study. Phys Ther Sport, 2017, 25:55-61.

The purpose of this study was to determine the relationship between hip strength tested isometrically, as well as single leg squat performance, and Achilles tendinitis in middle-aged, male runners. Twelve symptomatic runners were studied along with 12 age-matched control subjects. For the symptomatic subjects, both the injured and non-injured legs were tested.  The isometric tests of three hip motions (extension, abduction, and external rotation) showed deficits ranging from 28% to 34% for the injured leg compared to the control group. This provides evidence, consistent with previous studies, that hip strength deficits can cause a variety of tissue dysfunction and symptoms throughout the lower extremity.

Of interest is the fact that the strength in the uninjured hip was decreased compared to the control group, and just about as weak as the injured leg. This raises the question: Why only one side of Achilles tendonitis? The answer would be difficult to determine, but the results suggest that there are factors other than decreased isometric hip strength that can lead to Achilles tendinitis, although the strength deficit may be the primary cause.  Also, the single leg squat functional test did not show a significant difference between the control group, the non-injured limb, and the injured limb. Since a single leg squat is a functional test that requires posterior-lateral hip strength, the reduced strength and the equal squat performance are difficult to reconcile. It is possible that the rating criteria used to assign a “good, fair, or poor” to the squat performance might have inherent flaws.

Nevertheless, this study and others have shown a definite relationship between reduced hip strength and overuse injuries of the lower extremity. Hip strength is not the only potential cause, but certainly high on the list of “probable suspects.” This is gratifying confirmation of a “causative” article written by Dr. Gary Gray about 30 years ago. The title of the article was: The Achilles Hip. At the time the article was written, very few in the movement industry could appreciate Gary’s insight into the causes of Achilles tendinitis. The body is an integrated system assembled to complete a task. If the task is running, the entire lower extremity, trunk, and arms play important roles in successfully moving someone across the land surface. If one part of the system is functioning at a sub-optimal level, the other parts of the system will have to do more. Sometimes that “more” can create tissue damage and symptoms.

Why does this evidence matter to us? The hip weakness that is the cause, can become the cure if the training program restores the hip strength in a way that allows beneficial, but not excessive, stress to be experienced by the Achilles tendon.  The Principles of Applied Functional Science® would mandate a Strategy that provides hip strengthening in a weight bearing position. The hip is integrated with the knee, ankle, and foot. Not isolated by lying or sitting on a table. Stress to the Achilles tendon is limited initially by the selection of hip strengthening movements that protect the tendon. The movements are gradually tweaked so that the tissue stress is increased in a controlled manner. As the tissue heals and symptoms resolve, the activity itself (running in this study) can become what Gary Gray described three decades ago: the Causative Cure!