When you think of shock absorption in a car, the above picture might be what you imagine. A series of springs and rods that can take force from one direction and transfer it into another structure. But what if I asked you to describe the shock absorber of the foot? Some people think of the cushion in running shoes, others picture the heel bone transferring the shock, and yet others think about insoles. While all of these things can contribute some shock absorption to the big picture, the biggest shock absorber of the body is actually FOOT PRONATION!
But Dr. Sandy, no…that can’t be right! All I hear about is being careful not to pronate when I run or that some people need special shoes so they don’t pronate too much. Why would I want to pronate on purpose?!
Well, the answer to that lies in drawing a distinction between normal pronation and over-pronation. If the foot didn’t pronate at all, we would never be able to land our foot on the ground in preparation for pushing-off. We would all walk around with rigid levers on our feet… CLUNK, CLUNK, CLUNKETY-CLUNK like robots. We won’t get into the issue of over-pronation in this article, but let’s dive a bit further into the normal, healthy pronation of the foot.
Shock is absorbed when the rapid pronation of the foot is controlled by the posterior tibialis muscle. This muscle functions in an eccentric contraction (slowing down the elongation of the muscle). This careful control by the posterior tibialis allows the medial longitudinal arch of the foot to be gently lowered to the ground as opposed to letting it slap the ground.
Four common problems affecting pronation:
1. Joint fixation in the lumbar spine (the nerve flow to posterior tibialis comes from the nerve exiting the spine at L4/L5 in the low back).
2. Disc herniation in the lumbar spine, for the same reason as in #1.
3. Joint fixation between any of the 26 bones in the foot.
4. Adhesion in the tibialis posterior muscle itself, as a result of overuse of poor biomechanics.
If you are on your feet a lot and would like to make sure you’re achieving healthy shock absorption, please call us at 510-465-2342 to setup an appointment.