PRONATION – WHAT SHOULD IT FEEL LIKE?


Given the widespread confusion and misunderstanding surrounding pronation and it’s role in skiing that seems to exist I am going to provide some drills that will teach you how to assume a functionally pronated position.

Functional pronation is specific to monopedal (one-foot) stance especially as it relates to the ability to assume and move from one dynamically tensioned base of support to another. Once you have a feel for the functionally pronated monopedal position you can go through series of drills standing in your bare feet on a hard flat surface. Next you can stand in your ski boots starting in the boot shell after which you can add the liner with no insole followed by the liner with an insole or custom footbed. By using the feeling associated with standing in your bare feet on a hard, level, flat surface and then comparing the sensations to standing in your ski boots on a hard, level, flat surface you can experience for yourself how the various elements around and beneath the sole of your foot affect your ability to assume a functionally pronated position or even stand properly on two feet. As a prelude to providing drills on how to assume a functionally pronated monopedal stance, I will provide a brief history of the events that contributed to my current position on pronation, footbeds and insoles in general in skiing.

In my initial years of modifying ski boots I was a big proponent of footbeds. In those days, my work on ski boots was very much aligned with conventional views of immobilizing and supporting the foot and leg. But my disastrous experiences with Dave Murray got me rethinking this. By the time I began working with Steve Podborski, I was moving in a direction away from conventional thinking. In 1980, I had a huge breakthrough with a in-boot technology for which I was later awarded a patent. This was the turning point at which  severed any association I had with conventional thinking in ski boots and started fresh with a clean sheet of paper; one that did not include any premises on which existing ski boots are based.

By 1991, when Steve Podborski and I  initiated a research program to test my hypothesis on the mechanics, biomechanics and physics of skiing, my thinking was so far from convention that I insisted on retaining two scientists to provide oversight on the project. This included reviewing everything I put in writing but especially my patent. This process was intended to ensure that the principles I was using were both sound and correct. One of the scientist was G. Robert Colborne, Ph.D, an expert in the biomechanics of the human lower limbs. After reviewing my hypothesis, the initial impression of these scientists was that if it were correct it meant the whole world was wrong. Because I was in uncharted territory it was critical to me to have my findings confirmed before going forward. Once the wheels of a new technology are set in motion and significant money has been invested, it is hard to change direction, and especially to reverse direction. For this reason, we did a series of on snow studies in 1991 on Whistler’s glacier to confirm my hypothesis. I will provide details of the results in future posts.

The image below shows the model engaged in quiet standing Bipedal stance. The major muscles responsible for maintaining COP within the limits of the base of support in the feet in an upright posture or stance are being tensioned in eccentric contraction. There four positions of Centre of Mass in relation to the feet with weight distribution as follows from 1 to 4:

1. Centre of Mass is just in front of the base of the shin. The heel of each foot is carrying about 60-70% of the load. This represents the rearmost limit of Centre of Mass. Should CoM fall behind the base of the shin, a rearward fall will result.

2. Centre of Mass is in the proximate centre of the span of the longitudinal arch. The heel of each foot is carrying approximately 50% of the load. The balls of the feet are carrying the remaining 50% of the load. The ball of the great toe of each foot is carrying twice as much load as the other 4 balls the foot. This position represents the most stable and efficient form of bipedal stance.

3. Centre of Mass is approaching the balls of the feet. The eccentric contraction of the muscles that plantarflex (push down) the feet is increasing. The balls of the feet are carrying the remaining 60-70% of the load of each foot.

4. Centre of Mass is almost over the balls of the feet. The contraction of the muscles that plantarflex the feet has further increased. The muscles that push the toes down are now contracting forcefully, pushing the toes against the floor. This is the absolute forward limit of Centre of Mass in quiet standing. The toes act as a fail safe by pressing down onto the support surface in what is called the Reverse Windlass Mechanism. This mechanism tensions the forefoot into a rigid lever in preparation for propulsive phase of gait. At this point, almost all the weight is being carried on the balls of the feet and the toes. Should CoM pass the balls of the feet without evoking plantarflexion of the ankle, a forward fall will occur.

Screen Shot 2014-02-10 at 10.03.33 AMBIPEDAL DRILLS

These should be done in bare feet on a hard, flat, level surface. Start with the second position.

Drill 1. Stand erect with your feet a natural hip width apart and with a small angle of flexion at the knee joint. Release any tension from your body and allow your feet to settle onto the surface of the floor. Do not consciously apply force with your feet. Tune in to the pressures in your feet and buttocks. Sway back and forth slightly using only ankle flexion. Find the point at which the weight feels even between your heels and balls of your feet. You should feel slightly more pressure under the ball of your big toe than under the balls of your other toes. This is normal. Look down at your knees. They should be aligned straight ahead.

Drill 2. Using only the ankle joint, press down on the balls of your feet until you feel most of the weight on under your heels. Do not go too far. This is the limit of the rearward movement of C0P. At this point you are on the verge of a backward fall. Look down at your knees. They should be aligned straight ahead.

Drill 3. Using only the ankle joint, release the pressure under the balls of your feet until you feel more of the weight on the balls of feet than your heel. Look down at your knees. They should be aligned straight ahead.

Drill 4. Using only the ankle joint, release more pressure under the balls of your feet until you feel the weight pressing down hard on the balls of your feet and your toes. Do not go too far. This is the limit of the forward movement of C0P. At this point you are on the verge of a forward fall. Look down at your knees. They should be aligned straight ahead.

FUNCTIONAL PRONATION MONOPEDAL DRILL

1. Start from position 2 above.

2. Move your Centre of Mass slowly towards whichever one of your feet you most comfortable and confident with.

3. As you move towards one foot allow your ankle and leg to relax and roll inward, towards the L-R centre of your body.

4. When you feel the pressure strongly under the ball of your foot move, allow the ankle to relax and your Centre of Mass to move forward into position 3 above. As this happens lift the other foot off the floor. You will feel a pronounced change in the tension of the gluteus muscles in same side as your support foot in your buttocks. If your foot is functionally pronated you will feel most of the pressure under the ball of your foot.

Congratulations. You have achieved functional pronation and a dynamically tensioned base of support. Now try putting insoles and arch supports under your foot and feet. Do the same drills and see what happens.

2 comments

  1. very interesting ! Its also showing how little I knew about what pronation really is. In some ways it is almost the opposite of what I visualized earlier.

    1. Because of the publicity and misinformation pertaining to ‘contact pronation’ (ergo – excessive rolling inward of the heel at heel strike in running and jogging), the term pronation became associated with something bad. As a result, very few people including boot-fitters and ski pros have an understanding of what pronation is all about. I knew more than most people about pronation in 1991 when Robert Colborne, Ph.D. was retained to oversee my work on the development of a ski boot. But it was Dr. Bob that filled in the blanks and gave me a complete picture of what pronation is and why it is crucial to skiing. Over the next 3 or 4 posts the pronation picture should really start to come together. If you have done the drills you will have found that your knees continue to track straight ahead in all 4 positions of bipedal stance. In a future post I will provide a series of drills where your knees will track towards each other in bipedal stance and your feet appear to pronate. I will explain why this happens and especially why it happens on ski boots.

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