Basic Biomechanics

by Jim Bison

Early Winter 2002

Biomechanics definition: The field of study that applies the principles of mechanics to the analysis of biological structures. Primarily, biomechanics studies the motion of living systems and the internal and external forces that cause or influence the movements.

I know what you’re thinking……Can you really use the word “basic” with “biomechanics”? Isn’t that an oxymoron? How can a rocket science like biomechanics ever be “basic”? Well I think over the years in ski teaching, biomechanics has gotten a bad rap. All that stuff about vector angles and such, and all we want to do is help folks ski better! Well truth is, a little knowledge of biomechanics can go a long way towards being able to determine the root cause rather than just a symptom of our own or our student’s “inefficient” movements. There is great information in the Alpine Technical Manual (see pages 62 & 63 Appendix D) and in the Core Concepts manual (see pages 17 – 20 Anatomy 101) It’s imperative that you read this information, understanding of it will greatly enhance you’re ability to apply biomechanics to skiing.

Let’s take this statement (taken from the PSIA-RM website) “A balanced, neutral stance is a prerequisite to applying other skills.” OK, sounds familiar? We’ve all heard that balance and stance is the most important thing, but why? Why is it a prerequisite to all other skill movements? Why can’t I carve a clean turn while being over flexed? Why can’t I ride steep terrain from the back seat? The answer lies in our old friend biomechanics. Our skeleton is designed in such a way that we can “align our bones” in order to hold ourselves upright with a minimal use of muscular effort. This frees up our muscles for other uses, such a lifting a beer glass or kicking the dog. If we walked around bent over at the waist, ankles straight, knees flexed, our muscles would tire very quickly. Same thing in snowsports.

Take for example the beginner student; at first they are fighting for balance, trying to find an aligned stance in an effort to remain upright. Your goal as their coach is to help them find a neutral, balanced stance by directing their attention to specific joints that they need to flex or extend in order to “line up” their skeletal structure! And when your students find their neutral stance they will say ahh…this is easy, now what? And you say; “now you can learn to turn in order to control your speed so you don’t run into the lodge! Basically, if the bones aren’t holding you up then you’re muscles are, and if you’re muscles are busy just holding you up, how can you expect them to make the small precise movements needed for tipping and turning the skis/board? Well you can’t, and the result is large gross movements used to edge and turn resulting in those dreaded “inefficient” movements that we all know are out there. That’s why a neutral stance in a prerequisite to applying other skills.

So how does one find a neutral stance? Take a look at the diagram with the stick man to see all the ways the joints can flex in combination together. See the neutral stance? (#2) Can you see how the skeleton could be in alignment even though all you see is a stick man? It’s pretty much common sense in a straight run, but what happens when you start turning, adding all these other external forces like inertia and centripetal force? This is where things could get tricky if you let them. Whenever we are in motion there exists a “line of action”. This “line of action” is one that we set up with our bodies to balance against external forces. While standing, the line of action runs vertically from the arch of our foot through the hips, shoulders and head. See it in the stick man? This is because the only force that we experience when standing still is gravity, which pulls straight down on us. Now at the apex of the turn (in the shaping phase) where forces are pulling us to the outside, we need to align our skeleton in order to balance against (or move with) this pull. This line of action will run from the outside foot, through the outside leg and hip at which point it crosses over to the inside half of the body.. Since centrifugal force is pulling us to the outside of the turn we need to align our skeleton over this force, which puts us and our line of action at an incline. (See figure 2) You can set up a strong line of action or a weak line of   action depending on how you align your skeleton. Whenever joints are constantly over flexed, there is a weak line of action. Whenever there is a constant twisting or contorting within the torso, there is a weak line of action. And when there is a weak line of action the muscles are used mainly to hold oneself upright and cannot be used to: #1. Move the ankles from side to side to finely edge the skis. #2. Rotate the femur in the hip socket to finely turn the skis and #3. Flex and extend the ankles, knees and hips and spine to smoothly glide over uneven terrain.

So you see, it is pretty basic. By finding a neutral stance while straight running, we have a starting point, from there we can set up a strong line of action while turning. If we can find this strong line of action on both sides in each turn then we’re halfway there. Bottom line is this: dysfunctional skeletal alignment overuses muscles, which creates tension throughout the body and simply “locks you up”. Conversely, functional skeletal alignment allows for muscular efficiency, freedom of motion and just plain more fun!