Why ski logic is backwards

July 7, 2017

 

I love the podiatry profession within which I work. It is still a relatively young profession which means there are many areas within it to explore and research, define and learn. The pod community is also quite small, so people know each other and are able to share knowledge. Focusing our knowledge on the feet and the lower limb allows us to really provide expertise for our clients and provide specialised advice. The parameters of podiatry are startlingly broad. From High-Risk podiatrists who work with people who have diabetic foot ulcers, managed successfully in multidisciplinary teams which include orthopaedic and vascular surgeons, endocrinologists, dietitians, diabetes educators, psychologists, pedorthists and the list can go on. To the other end of the podiatry spectrum where we have sports podiatry, which varies from working with the clients who have injuries or painful feet from social sports all the way to elite athletes. Did you know it was a podiatrist who wrote the Olympic guidelines for dealing with lower limb injuries at the games? 

 

Lately when I've been talking to fellow sports podiatrists, it has really reinforced to me how different ski podiatry biomechanics are to regular sports podiatry biomechanics. It's almost like you have to throw your understanding of foot alignment and function out the window when it comes to how it all works in a ski boot. 

 

Perhaps this is because skiing is a rare sport that relies so heavily on equipment? Perhaps it's because the foot is held in a midstance position for hours on end without being able to go through a full range of movement, like it can when walking or running? Cycling is a sport that also relies on equipment and holds the foot in a semi-fixed position. But it allows much more motion at the ankle, and the forces going through the foot get a break between the cyclist being seated and standing. Golf is another midstance foot position sport, but after you've taken your shot you get to walk along the fairway and the foot gets relief from static ground reaction forces via the full range of motion of a walking gait. So skiing is a very odd sport that health practitioners don't get to work with very often, and we're certainly not taught how to manage it at university. 

 

So how do we learn about it? Experience is great, but we have to start somewhere. Research is a good place to start. The most prominent research article that is found when searching for ski biomechanics is James Mcintyre's Clinical Biomechanics of Skiing - a thorough breakdown of what the body's movements are when skiing. The biggest problem with this article is that it was printed in 1988. Ski equipment has skyrocketed far away from this since it was written. With the dramatic shift away from straight skis in the 1990's to parabolic, then carve skis, changes in boots have occurred to follow the changing mechanics required to control and turn skis. And because we know equipment is so influential and critical in skiing, the biomechanics of skiing have changed dramatically. 

 

 Figure1. Check out this excellent pic from Macintyre's 1988 Clinical Biomechanics of skiing, outlining counter-rotation when anticipating the next turn.

 

Boots have gotten slightly softer over the past 15 to 20 years in their flex, allowing skiers to have more control over the sagittal plane balance (fore-aft, or ankle and knee flexion). This has meant skiers can have more finesse when loading different parts of the ski through a turn, which has also influenced flex patterns of skis. Changing flex patterns in skis changes the way you balance and control your skis - this influences optimal position and movement patterns which then comes full circle to impact boot design.

 

Professor Erich Müller, Head of the Department of Sport and Exercise Science and the Christian Doppler Laboratory of Biomechanics in Skiing at Salzburg University is someone you should be looking out for if you want to understand how the body moves in skiing now. Salzburg University is a prominent site of alpine ski research and works with Atomic in developing equipment, based on research results.

 

Dr Tonje Wåle Flørenes, of the Oslo Sports Trauma Research Center, published a research paper in the British Journal of Sports Medicine that identified knees were overwhelmingly the most common injured site for World Cup alpine skiers. Within the results more women suffered knee injuries than men. Another research article showed that the most common movements to cause anterior cruciate ligament damage in the knee was when the inside edge of the ski catches, forcing the leg to be internally rotated and the knee to go into a valgus position (knock-knee). 

 

Macintyre identified in 1988 that the foot needs a certain degree of pronatory movement (rolling in of the arch/ankle) to release and initiate ski turns. From what I've read and experienced when boot fitting, this still remains true today, but excessive pronation in a ski boot leads to loss of energy and lack of ski control, not to mention splaying of the foot which can cause pain along the outside of the foot, as well as foot cramps and numbness. Over pronation also leads to internal rotation of the tibia and increased valgus at the knee - the exact position identified as causing anterior cruciate ligament damage or rupture.

 

So whilst a certain degree of pronation is needed, the foot functions best in a neutral foot position with good arch support. Allowing for a certain level of pronation is very different to rigidly supporting the foot in a pronated position. Experience has shown me to cast ski orthoses with a higher arch than regular sports orthoses. But the trick here is to not have a rigid orthotic device, it needs to be softer than running orthoses, because remember, there is a stiff, plastic boot involved, holding your foot and ankle in position too. The foot does not like being rigidly blocked up under the arch in a ski boot. Oh the pain! But it does love nice, high support with a flexible arch. Oh the sweet, sweet comfort!

 

This is not the way functional sports orthoses are made. They are designed to alter your foot mechanics, which often requires a rigid device so that it can assert a level of control. It is in a running shoe, not a rigid plastic shell so it needs to have much more integrity within itself because it cannot rely on the shoe to hold the ankle in position. These sports orthoses work in a shoe, despite being rigid, because your foot is going through a full range of movements allowing changes in location of force and no ground reaction forces when swinging through the air between steps. Plus the centre of gravity in a walking/running gait moves in the opposite direction to what it does in a skiing. Way to confuse a podiatrist!

Figure 2. Opposites: Centre of gravity (or line of pressure) runs from heel to toe in running. In skiing it goes from toe to heel.

 

Knowing the body and how it functions in everyday life is not enough to provide you with a performance and fitted ski boot that can take your skiing to the next level. Whether your goals are to cruise the mountain comfortably all day, or to improve your ski technique, you need to be fitted by someone who understands how the foot functions in a ski boot. A podiatrist with bootfitting skills is a good place to start. Knowledge of the role equipment plays in skiing, whether your symptoms are from technique, ill-fitting boots or the wrong skis, as well as knowing how your foot should be stabilised in the boot is vital in ensuring your improved performance, comfort and reduced risk of injuries on the hill.

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