In my last post, I erroneously stated that the sole turns inward, towards the center of the body, in eversion. I meant to state that the sole turns outward, away from the center of the body, in eversion.

I have revised the paragraph in my post so it reads correctly.

In order for the torso and Center of Mass to stack vertically over the ball of the foot, the sole of the foot must turn outward, away from the center the the body. This is called eversion. It is enabled by the joint that lies below the ankle called the sub-talar joint. The sub-talar joint is tied to the tibia where it acts as a torque converter. When the foot everts or inverts, the sub-talar joint translates this on an approximately 1:1 ratio into internal or external vertical axial rotation of the leg.

I apologize for any confusion this may have caused.


  1. Thanks for these clarifications. Honestly I think keeping language as simple yet as close to possible remaining accurate from a medical and functional language is the way to go if ideas such as this are to be shared amongst the greatest possible audience. I agree with what I think is the central theme to much of your writing. That the unfortunate tendency of equipment design to not take into account the body’s design to accomplish the tasks required of it in performing the sports is clearly not limited to ski boots though this was your starting point. On another topic many of the same modification needs I see being discussed or debated in this blog exist for other activities and in my world most frequently in hockey skates. Unfortunately the issue that I face most often is a traditionalist viewpoint about foot containment (restriction) or comfort versus function or even a misunderstanding of how the movements of the body need to be transmitted by the player to the ice surface. This is promulgated often simply because the size of the sport here is so large that viewpoints and ideas opposing or different from the norm are very difficult to promote. Honestly it is the same problem in skiing x10. There’s a little of the lighting one candle instead of cursing the darkness syndrome at work here. This forum has been instrumental for me in forming my own opinions though certainly my life experience as a skier taught me that the design concept or guru of the moment if not backed by science is often just another marketing ploy by manufacturers. Certainly have been a lot of counterproductive or dead end designs as a result. You are to be congratulated on not letting your frustration with this to flow over into your commentary too much and I continue to enjoy your editorship of this massively educational site.

  2. Actually you had it correct the first time, however it depends upon the readers interpretation.
    In eversion the motion in the frontal plane is towards the mid line – the medial aspect moves plantarly on the frontal plane axis and the lateral side moves dorsally on the axis…

    1. I agree. I am trying to frame things so the average reader can envision and understand them. The ingrained mental model in the ski industry is one of static, neutral foot (non)function predicated on any and all pronation being detrimental or, at least, more than small amount of pronation being detrimental. This mental model skirts the real issue which is the amount of adduction of the leg and eversion of the STJ required to stack COM over the 1st MPJ and the associated coupled vertical external axial rotation of the leg. I would prefer to speak in terms of eversion only and not even pronation.

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