The physics of heeled shoes. (or, “Using Newton’s Laws to determine sole pressure.”)
Did you know that a 110 lb. woman wearing stiletto high heel shoes puts a lot more pressure on the ground than a 6,000lb elephant?
First lets begin with Newton’s laws of motion. They are three physical laws that form the basis for classical mechanics. They describe the relationship between the forces acting on a body and its motion due to those forces. They are summarized as follows:
- First law: The velocity of a body remains constant unless the body is acted upon by an external force. Meaning that a body stays at rest or in motion unless forced to do otherwise.
- Second law: The acceleration of a body is parallel and directly proportional to the net force F and inversely proportional to the mass m, i.e., F = ma.
- Third law: The mutual forces of action and reaction between two bodies are equal, opposite and collinear.
Now, we all know these laws well but here is something a little different today. Today we have lovely Dr. Deborah Berebichez the first Mexican woman at the Stanford University graduating with a doctorate in physics. Here she gives a simple dialogue of the application of these 3 laws to footwear.
In her PhD dissertation physicist Berebichez developed a new method for electromagnetic waves to focus with extreme accuracy in space and time. Berebichez is currently researching at the Courant Institute of Mathematical Sciences of New York University .
Our point ? This is a brilliant woman and so when she speaks about the physics of high heeled shoes, you should listen. 5 inches is the max ladies (oy vay !)
h(max)=Q (12 + (3s/8))
but remember, this the maximum height to stay stable and not risk falling over. It has nothing to do with the risk of pain and pathology to the body that will occur over time ! But that is another mathematical equation that might be best suited for our other favorite fellow-geek and mathemetician Garth Sunden @ Geek Logik who can figure out any formula for anything you wish to assess (for example, “What are my chances in scoring a date with a girl at a bar? click here).
Watch her video attached here to learn about Newton’s 3 laws and how they apply to shoes and heel height. It is great stuff ! It is important to note that even in the highest of women’s heeled shoes heel strike still occurs first (although it is softened as heel height increases……don’t bother asking us how we know this please), hence Berebichez’s point on heel pressure stands correct but somewhat muted. Heel strike does not however necessarily mean true impact. We encourage our patients to note the difference between heel impact and contact. Just because in normal walking gait (running can be different) the parameters dictate heel strike it does not have to be a long latent heavy impact period. Heel strike and impact should not be accentuated, heavy or prolonged. Many gait pathologies can occur when it is significant because the forces move up into the organism, for example increased knee extension or longer duration of the rear foot inversion phase and thus supination foot phase. Rather, begin to focus the thought more on heel contact (sort of a quick kiss as opposed to a long drawn out French-kiss necking session) and the subsequent and immediate soft gradual transition into the full foot loading phases. In otherwords, finesse the heel contact phase. Perhaps if runners had always looked at heel strike this way we would never have seen such a major intellectual epiphany towards midfoot and forefoot strike being the answer and heel strike being the black plague of all things gait/running related. So, at this moment, while it is still fresh in your mind, get up from your chair and walk and feel the difference between kissing the heel on the ground and a major heel-floor make-out session ! You may immediately note the woes of your ways. You may begin to make walking a more conscious finessed movement while in the process begin to note that walking should be soft and fluid, almost an art form or conscious zen-like meditative act where constant awareness is key.
For those new to gait talk and running, remember that walking gait does dictate this heel strike phase where as in proper running this phase is absent when unshod and most of the research is leaning towards this absence when shod as well (hence the minimialist shoe trend of today).
To put a cap on this talk, we would like to say that these are our kinda people ! Geeks rule ! (but then there are these kinds of people here (Las Vegas high heel shoe race, for those of you who don’t want to link elsewhere) that need to have their heads checked a little…… have they not hear Dr. B’s lecture on heels ?)
Shawn and Ivo…… The Gait Geeks, the guys you beat up in grade school, and now the kinds of geeks you gravitate to for intellectual stimulation. How ironic huh ? Who’s your daddy now !