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. 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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