The “Z” angle: Hip extension should equal ankle dorsiflexion and vice versa
An intern we have had in the office for some time now was unaware of the role of adequate hip and ankle ranges of motion in the development of achilles tendonitis and plantar fasciopathy. While doing some research for another article, I had run across this article (referenced below) which exemplifies ankle dorsiflexion, hip extension and their role in achilles tendinopathy.
Dr Allen and I like to talk about something called the “Z” angle (see above). The angle is a line drawn parallel to the plane of the sole of the foot and the plane of the angle of the pelvis (or perpendicular to the spine), with a connecting line between the 2 ends. Ideally, the amount of hip extension should equal the amount of ankle dorsiflexion. Again, this is ideal rather than the norm. When one or both ranges are not adequate (10 degrees seems to be the clinical threshold, 15 or more ideal), then that motion must occur somewhere else, like the midfoot, forefoot, lumbar spine, etc.
Note in the photo above how the gent in black shorts and running shoes actually has very little of either. Look at the other photos to get the idea as well. Begin looking for this relationship in your patients and clients and seek to improve (if needed) as well as balance (if unequal) both. A lack of balance, or a deficit in one or the other seem responsible for many lower extremity ailments we encounter on a daily basis.
Kim S, Yu J. Changes of Gait Parameters and Lower Limb Dynamics in Recreational Runners with Achilles Tendinopathy. Journal of Sports Science & Medicine. 2015;14(2):284-289.
free full text: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4424456/