THE DREADED DIAGNOSIS: PRONATION


You may have been told by a boot-fitter or even a ski pro or coach that your feet pronate and that this will make it difficult, if not impossible, for you to hold an edge and/or control your skis. Or you may have overheard a boot-fitter run through a pronation diagnostic drill with a customer having a boot fit and/or alignment session. It goes something like this.

Boot-fitter to customer: Now stand with the weight even on both feet and flex your boots. Oh yes, I see your problem. Look down at your knees when you flex forward. See what happens. Your knees move towards each other. This explains why you are having so much trouble skiing. Your feet are pronating.

Customer, fearing their situation is terminal: Is this bad? Is there any hope? Can you help me?

Boot-fitter:  Yes, pronation is very bad. But don’t worry. I can help you. A pair of custom footbeds and an alignment job and you will be a World Cup star.

Customer: Wow! Sign me up!

It all sounds good. But there’s one small problem……. OK, it’s a big problem. Standing on two feet and flexing ski boots has nothing to do with skiing. In fact, it has nothing to do with the normal function of the lower limbs (ergo – the legs). The boot-fitter may not realize it, but the boot-flex procedure is something of a con, a sleight of hand. The basic balance strategy of the body when standing erect on two feet is to maintain position Centre of Mass slightly in front of the ankle joint so that gravity tends to disturb balance and cause a forward fall by causing the ankle to flex forward. This tendency is opposed by muscles in back of the leg starting with the soleus.

The soleus is an extensor muscle. It’s job is to extend or plantarflex the ankle so that the forefoot is pushed down; towards the floor. This pushes Centre of Mass backward, against the force of gravity to the isometric contraction position.

The foot is configured for standing on one foot so that gravity will tend to cause the foot to evert or pronate. Eversion is the turning of the sole of the foot away from the centre of the body. The tendency of gravity to cause the foot to evert or pronate is opposed by a group of muscles that I refer to as the inverter sling. Here’s the kicker. The inverter muscles of the everter sling are also extensors.

Think of the front of the boot cuff as a resister of forward ankle flexion. Guess what happens when the resistance of the boot cuff starts to support your weight when you flex forward and your shins press against the front of the shaft? Your hard working extensor muscles start to go on vacation because there is less and less for work for them to do. Since the inverters have also turned off, guess what happens next? The feet relax and fall inward in a quasi-pronation movement. It’s not the same as functional pronation. The knees turn inward towards each other more than they would when the extensors and inverters are in isometric contraction. There’s nothing wrong with your feet. It is just that muscles only do their job when they have something to do. Things are not really what they appear to be. But the illusion sells footbeds and alignment programs.

 

2 comments

  1. Thanks for the explanation Dave,. I also just read pronation 101.4. Look forward to the video. Do you think Ligety / Shiffron ski boots are designed correctly to let them do what they do ? Or do you think they can do what they do even though the ski boots
    may not be ideally designed? Just curious about that.

    1. With regard the the boots of those such as Shiffrin, Ligety and others who move differently from their competition I suspect it is a combination of having the right stuff as in the right feet and having made the connection with the right feel in their formative skiing years. By the right feet I mean compact, stiff, tight feet that do not change shape much under load and slender legs. Without even seeing their legs and feet, I am confident that Vonn, Shiffrin and Ligety all fit this description. This being the case, it becomes a matter of those with the right feet whose feel and movements were programmed early in skiing of rising to the top because they ski with greater efficiency. I am not saying that they don’t have athletic talent. Clearly they do. But in a number of skiers of equal athletic ability those with the right feet and legs will have a clear advantage. Are the boots of Vonn, Shiffrin and Ligety modified to let them ski? Possibly. They can probably ski pretty well in any boot right out of the box. But once a skier knows what a boot should feel like (I sure do) they will sense issues and do something about it. My best friend here is a sharp knife. For a few years Kathy Kreiner lived next to me. Of course, we talked about ski boots. She told me that when she trained with Ignemar Stennmark he fiddled with his boots for 15 or 20 minutes before he started training. He would adjust his buckles, make a few turns, stop then re-adjust them. She said he always started off making very precise slow turns as if he was trying to connect with the feel of the pressure on his skis.

      Here’s a quote from my US Patent No. 5,265,350. The patent is specifically about boot structures that let a skier move between bipedal and monopedal (pronated) stances. The excerpt speaks to what happens in most skiers.

      Problems arise when the foot is attempting a transition from a state of bipedal stance to monopedal stance. If the transition to monopedal stance or function can be completed without interference from the structures of the ski boot, all is fine and well. However, if the transition is allowed to proceed to a point where the mechanics associated with the monopedal function can establish significant horizontal forces, and the further movement of the foot is blocked before the transition can be completed, the skier will experience pain and discomfort at the points where the inner aspect of the foot bears against the structures of the footwear. This is the situation experienced by a majority of the skiers with prior art footwear. It is at this point where arch supports, if employed, also begin to cause discomfort. It should be noted that it is the normal tendency of the foot to pronate when weight bearing on one foot.

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