boot-fitter

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.

 

PRONATION: FORCES IN THE FEET – PART 2

Before I can discuss the role of pronation in enabling a skier to develop a dynamically tensioned base of support, I need to clarify the implications of a neutral foot.

The 2 big buzz words in boot-fitting are neutral foot and neutral alignment meaning that the knees track straight forward during ankle flexion.

The ankle complex consists of two major joints. The base of the tibia forms a joint with a bone called the talus. The resulting joint is called the tibial-talar joint, commonly referred to simply as the ankle joint. A second joint below the talus is the sub-talar joint. This joint underlies the tibial-talar joint. It allows the foot to rotate about its long axis in eversion and inversion. The tibial-talar joint is the joint that flexes the foot in plantar-flexion (toes move away from the shin) and dorsi-flexion (toes move closer to the shin).

TT -STJ

Due to the confusion and misinformation that has arisen surrounding pronation, a common perception exists that anything other than flexion of the ankle is abnormal and problematic. The solution is footbeds that are claimed to maintain the foot in a neutral axis and alignment procedures typically follow that are claimed to correct abnormal tracking of the knees and ensure that they move straight ahead on a neutral axis when the ankle joint is flexed.

None of these positions are supported in sound principles of biomechanics. But I will save further discussion of this issue for a future post. The image below shows the same neutral configuration of the feet in bipedal neutral stance as my last post. In this image I show the straight ahead (neutral) excursion trajectories of Centre of Mass and Centre of Pressure in each foot. I also show the axis of the ankle joint as square (at right angles) to the excursion trajectories. This does not happen in reality. But in order to differentiate between neutral Sub-Talar Joint and pronation I need to indulge the neutral camp.

Neutral axis

The limits of the Base of Support that define what is called the sway zone is shown in grey. Because of the large area of the Base of Support at one time or another some formulators of ski methodologies have advocated a wide track stance with  weight and steering on both skis because it is more stable than a narrow stance where the weight is predominantly on the outside ski of a turn. In fact, as I will show in future posts, a wide track stance is not only highly unstable, it precludes the ability to develop a dynamically tensioned base of support on which to move from one foot to another foot.

THE MYTH OF PRONATION AND THE COLLAPSING ARCH

If you purchased a pair of ski boots or had work done by a boot-fitter you may have been told that your feet pronate and that this will cause your arch leg to collapse creating a myriad of problems including a lack of control and especially an inability to effectively transfer energy. You may have also been told that your foot functions best in skiing when it is immobilized, preferably in a neutral position, one that completely prevents pronation. All of the preceding are myths. But more than simply being untrue, they are potentially dangerous. ‘Pronation is bad’ is nothing more than a good story; one that most people buy into simply because they have no idea of what pronation is. So they tend to assume that the store clerk or boot-fitter actually knows what they are talking about.

When I first started modifying ski boots in 1973 in an attempt to help my own skiing I bought into the pronation is bad story after reading an article in a running magazine about how over-pronation (an invented term) was causing injuries in runners. The article implied that the human feet, far from being a marvel of complex engineering, are riff with problems like ‘pronation‘  that require corrective devices such as footbeds or prescription orthotics to make feet function properly. This made sense to me at the time, but only because of what I didn’t know. After reading the story in the running magazine, I had what I thought was an epiphany; ‘If foot defects can cause a myriad problems in running, imagine what havoc they must be wreaking in skiing’. Thinking I was on to something, I had prescription orthotics made for my wife and myself by a sports podiatrist. Later, I began making custom footbeds for ski boots. In the 1970s, I was one of the few boot-fitters in world making custom footbeds. And while the response of the majority of skiers I made them for was overwhelmingly positive there was one problem, my own custom footbeds didn’t work for me. In fact, footbeds and prescription orthotics made skiing much more difficult for me than insoles with no arch support. Unfortunately, the pronation is bad story caught on. Soon the evils of over-pronation morphed into the evils of pronation period; any and all pronation was bad and should be stopped or at least greatly restricted.

As Mark Twain quipped, “It ain’t what you know that gets you into trouble. It’s what you know for sure that just ain’t so”. For the past 30 years most of the world has known for sure that pronation is bad. Now a study published this month (1) confirms what I and others have maintained for years, not only is pronation not a predisposition to injury but there are significantly less injuries in those whose feet pronate.

Far from being a bad thing in skiing, pronation is the key to setting up the over-centre mechanism that makes the forces of skiing work for you instead of against you. So what is pronation?

In future posts I will explain what pronation is and why it is essential to sound ski technique and the ability to balance on the outside ski.


1.  British Journal of Sports Medicine (http://bjsm.bmj.com/content/early/2013/06/12/bjsports-2013-092202.abstract?sid=3e90eba8-f3ca-46f7-88e0-d8a28f83b729)

Sources of the story on the Danish study include:

A Popular Myth About Running Injuries – New York Times
http://well.blogs.nytimes.com/2013/06/26/the-myth-of-pronation-and-running-injuries/?_r=1

Speciality running shoes may not reduce injuries – Health – CBC
http://www.cbc.ca/news/health/story/2013/06/27/running-shoes-injuries.html

KNEE INJURIES – PART 2

When I started skiing in 1970, the buzz was all about the new safety bindings. Debates raged in magazines and ski shops over which binding was the best as in the safest. After years of skiing being perceived as dangerous because of the incidence of broken legs, a new era had arrived with the introduction of a generation of sophisticated bindings. This created the perception that it was finally safe to go out play on the ski hills. But as the sound of snapping leg bones faded into the background it was replaced by an even grimmer sound; the popping of knee ligaments, in particular, torn ACLs. Before the introduction of the rigid plastic ski boot, few skiers had ever heard of an ACL. That was about to change.

It was about the time that I started working with National Ski Team members in 1977 that I began to hear of racers suffering knee injuries. Knee injuries seemed to start with a trickle. I can’t even recall hearing of a recreational skier suffering one. Like most skiers, I believed that the new bindings had addressed the injury issue. Even after knee injuries started to increase in frequency I thought it only a matter of time before refinements would be made to ski bindings and that this would be the end of them. As the popping of ligaments got more frequent, panic seemed to set in in the industry. Skiing had entered a period of vigorous growth. The last thing it needed was a good news, bad news story as in, “The good news is that the rigid plastic boot has made skiing easier. Now for the bad news…..”. As best I can recall, it was around 1980 that a team of spanish orthopaedic surgeons published a study linking the introduction of the rigid plastic boot to knee injuries noting that the incidence appeared to be rising in lock-step with sales of the boot. A classic problem-solving strategy is to go back to the time when a problem first emerged and look for anything that changed. In this case, the most significant change was in the boot. Meantime, those with expertise in biomechanics were pointing out that by stiffening the ankle the boot was sending the forces of skiing upward to the relatively weak knee.

In retrospect, it seemed like it should have been obvious that encasing the foot within what amounts to an orthopedic splint would act to transfer force up the leg. It’s ironic, if not erroneous, that the industry, even today, talks about the boot transferring energy to the ski as if this were the end game of skiing. The reality is that unless the ski industry has repealed Newton’s Third Law (which is doubtful), if a skier were to transfer energy to anything through the boot it would be through the stack of equipment between the sole of the boot to the source of Ground (or Snow) Reaction Force at the snow. This being the case, according Newton’s Third Law which states; “For every action there is an equal and opposite reaction”, the snow will transfer an equal amount of energy through the stack of equipment back up the skier’s leg to the knee. The issues are way more complex than a simple transfer of energy. But I will start with the simple and obvious then build from here.

The question is, “Given the established reputation of skiing as being a dangerous sport prior to the introduction of the rigid plastic ski boot and the fact that skis attached to the foot and leg act as force multipliers, did anyone consider the implications of trying to immobilize the foot and leg within a rigid plastic ski boot?”