PRONATION 101


The mere mention of the word pronation in skiing evokes images of arches collapsing, ski edges sliding away and skiers careening out of control.  Of all the information that exists in skiing today, that pronation is somehow detrimental to sound ski technique is not merely wrong, it is seriously wrong. The problem is that pronation has been so thoroughly vilified that it has become synonymous with bad. Pronation is bad to the point where when skiers see the word pronation they stop paying attention. Once they see the word pronation they assume that any discussion that follows will confirm what they already know or, at least, what they think they know; that any and all pronation in skiing is bad and must be prevented at all costs.

The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge.
― Stephen Hawking

You have probably assumed that there is solid science and studies to support the idea that pronation is detrimental in skiing. There aren’t any that I am aware of. Nor, do I believe it possible to support such a position with sound  principles of science, let alone properly done studies. If anyone knows of such studies please pass them along to me.

So how did we get to where we are today? As far as I have been able to ascertain, pronation became synonymous with injuries and adverse effects on the lower limbs when jogging took off took off in the ’70s. Jogging defined a new category of running with a perceived need for special shoes. Prior to the introduction of jogging and jogging shoes, running was typically done in basic training flats. One of the characteristics of jogging shoes is an elevated heel to forefoot ramp known as drop. The ramp of the shoe sole typically has a 12 mm drop compared to a zero mm drop for training flats. Elevating the heel can have the effect of lengthening the stride which can cause joggers to overextend the lead foot, accelerate the swing phase and strike the ground with the heel.

Heel striking with the lead foot extended using shoes with 8-12 mm heel drop and flared heels can cause over-pronation in which the hind-foot rolls inward excessively compared to what happens in the full foot strike pattern typical of barefoot. Although the shoe was the source of over-pronation the solution came in the form arch supports and orthotics  prescribed to retard or control excessive pronation. With running in a rapid growth curve and the incidence of associated injuries increasing, excessive pronation as a cause or contributor to injuries morphed into an any and all pronation is bad mentality.

It was about the time that jogging was taking off that I started to modify ski boots. I was looking for a solution that would give skiers the edge (literally!). When I read an article in Runner’s World on running injuries and orthotics I thought that I had found the magic bullet. I started making custom moulded footbeds for skiers feet. I believe that I was one of the few in the world who was making custom footbeds for skiers at that time. So I was something of a pioneer. A lot of skiers swore by my footbeds. But in the late ’80s as my knowledge of the mechanics, biomechanics and physics of skiing grew, I began to see that supporting  the arch of a skier had the potential to compromise balance and control although I wasn’t sure exactly why. Today, I actively take steps to ensure that nothing under the arch of the foot acts to support it in ski boots and ice skates.

So what is pronation? First off, pronation is associated with forms of human locomotion that involve moving from one dynamically balanced base of support to another dynamically balanced base of support. Although humans are bipeds, supporting the body on one limb is referred to as monopedal function. Monopedal function is infinitely more complex than quiet erect standing in bipedal function. In bipedal function the base of support is large  compared to that associated with monopedal function. In bipedal function, the joint of the ankle (the sub-talar joint or STJ) that allows the foot to rotate about its long axis is in a neutral or close to neutral position. A neutral position means that the sole of the foot is neither inverted (turned towards the transverse centre of the body) or everted (turned way from the transverse centre line of the body). The foot can rotate approximately 30 degrees in inversion and 20 degrees in eversion. When the lower limb is unloaded (ergo – off the ground) it is maximally supinated.

Here is what Robert G Colborne, Ph.D in functional anatomy with expertise in the human lower limb, particularly as it relates to walking and other forms of human locomotion, said in 1991 in a memo to me about pronation. “When one shifts to monopedal stance, the base of support is greatly reduced, and balance over the supporting foot is controlled by postural responses through the musculature. The absolute weight borne by the foot is increased, and the arches are compressed. They are supported by the tendons of the same muscles acting to control medial and lateral displacement of the body over the foot. Tibialis posterior supports the medial arch and counteracts lateral displacement of the body by producing an inversion moment and transferring pressure to the lateral aside of the foot. Peroneus longus supports the lateral arch, and produces an eversion moment, increasing pressure on the medial side of the foot to counteract medial displacement. The intrinsic muscles of the foot act to limit the compression of the arches of the foot, by working collectively as a truss. They act further to stabilize the metatarsal heads and the toes, and to complement the activity of the long flexors of the toes.”

Does this sound like the arches are collapsing and the foot failing? Hardly. In skiing, the medial side of the outside foot of a turn is the inside edge aspect. If pronation drives the forces into the turn is this something that we want to stop? Hardly. In skiing we don’t want the outside foot of a turn to simply pronate. We want the outside foot of a turn to pronate maximally within normal limits.

So why is pronation important in skiing? Dr. Colborne again, “Medial movement of the Centre of Pressure of the foot is crucial to skiing, given that a ski turns in response to forces applied to its medial edge.”

In the image below the skeleton runner is about to make ground contact with the right foot. In the current position the foot is unloaded (off the ground) and maximally supinated. What has to happen when the foot contacts the ground on its (outside) border? This is will be the subject of my next post.

Run Right