Hello fellow skiers!
It’s been a while since my last post. In the last few days I have moved to Idre and have been getting myself organised for the season (still don’t have internet – relying on Idre’s free wifi). I’ve had a few days back on skis and am looking forward to the season!
In this post, I want to talk about balance. I think everyone can appreciate the importance of balance in skiing, but what is good balance in skiing?
What is balance?
A basic understanding of physics is necessary to understand the concept of balance. I promise that I will try to keep the mechanical engineer in me under control and keep things as simple as possible!
When you sit on a see-saw, gravity acts on your mass to make the see-saw rotate. Such a rotational force is called a moment.
An object is balanced if the moments acting on it are balanced. For example, two people of equal weight, each sitting on one end of the see-saw, create equal but opposing moments, which balance each other out and the see-saw is balanced.
Now consider a stationary object. I am going to go ahead and assume that you are familiar with the concept of an object’s centre of mass.
The vertical line that passes through an object’s centre of mass is called the line of gravity. The moments acting on the object are balanced if the line of gravity passes through the object’s base of support. If the line of gravity moves outside the base of support, the moments are no longer balanced and the object topples.
For example, imagine trying to get a sharp pencil to balance on its point on a table. If you could position the pencil’s centre of mass directly over the point (base of support), you could theoretically get it to balance. The more likely outcome is that the pencil’s line of gravity will be outside the tiny base of support, creating an unbalanced moment which will make the pencil topple.
What is balance in skiing?
Things become a bit more complicated in skiing because there are additional forces to consider, primarily the centripetal (turning) force generated by steering the skis. All you really need to know is that to remain balanced in a turn, you must incline into the turn as you do on a bicycle.
When we are inclined, gravity acts on our mass, creating a moment that acts to make us topple to the inside of the turn. The turning force acts laterally against our base of support, creating a moment that acts in the opposite direction to that created by gravity. By inclining the right amount, we are able to balance these opposing moments so that we will not topple, just like the see-saw.
For simplicity’s sake, I usually refer to balance in skiing as when our mass (body) is supported by our base of support (skis).
Balance as a skill
Up until now, I’ve been talked about balance as a state in which the moments acting on us are balanced or in which our mass is supported by our base of support.
However, skiers are capable of manipulating the mass and the base of support. It is therefore useful to view balance in skiing as a skill – the ability to manipulate the mass and the base of support to remain balanced.
So is balance in skiing simply the ability to not fall?
Unfortunately, this definition of balance in skiing is trivial for everyone except beginners, for whom toppling is more of an issue.
Skis give you a relatively large base of support, which means that the centre of mass must move a long way to be outside the base of support to result in toppling (especially in the fore/aft direction).
So what determines good balance in skiing?
Good balance in skiing enables us to ski efficiently, with minimal effort and energy expenditure and must therefore take biomechanics into consideration.
Centre of pressure
When a glass rests on a table, gravity acts on the glass’ centre of mass along the line of gravity. The point where the line of gravity intersects the base of the glass is called the centre of pressure. An object’s centre of pressure lies directly below its centre of mass.
If you could position the point of a sharp pencil under the glass’ centre of pressure, the moments acting on the glass would be balanced and the glass would be balanced on the pencil.
When we ski, we need to account for the turning force. Imagine trying to do balance a glass on a pencil while in a car driving around a circular track. Again, all we really need to understand is that if we incline the pencil and the glass the right amount, the point of the pencil will remain at the glass’ centre of pressure and the glass will balance on the pencil.
In skiing, the term balance is often used to refer to one’s centre of pressure.
So where should we balance?
We ski efficiently when minimal muscular effort is required to make the movements involved in skiing.
Good balance is crucial to biomechanical efficiency. If our balance is not good (but not so bad to make us fall), we must recruit muscles to help keep us upright. This diminishes the muscles’ capacity to make the movements involved in skiing.
In thinking about where we should balance for efficient skiing, it is useful to think of our balance in two directions – fore/aft (forwards and backwards) and laterally.
Imagine betting your house on one throw at a dartboard. To keep your house, all you have to do is hit the board. Miss, and you’re sleeping on your buddy’s couch. Unless you deliberately compensate for a known bias, you would aim for the bullseye, since this maximises the distance by which you can miss the bullseye and still hit the board.
Our fore/aft balance is similar. standing (not on skis) with your balance halfway along the length of your foot maximises the distance your centre of mass can move (in the fore/aft direction) before you topple.
However this is not the full story. The weight of our body is transferred to our foot via the ankle joint. The strongest position to balance is directly below this point, on the heel. If our balance is in front of this point, a moment is created that acts to close our ankle joint and we must recruit the muscles around the ankle – in the foot and the calf – to counteract this moment.
To experience this, stand with your heels on a step and the front half of your foot overhanging. You should feel the step supporting your weight through the heel. Now, stand on your forefoot with your heels overhanging. Now, you should feel your weight pushing your unsupported heel down. If you try to keep your foot horizontal, you should feel the muscular effort required.
The optimal place to balance must therefore lie somewhere between the middle of the foot and the heel.
The exact location is impossible to say and must be determined through experimentation – figuring out what gives you the best combination of balance, strength and mobility.
When we stand normally (with our body perpendicular to the ground), we want our balance to be halfway between our feet with half our weight on each foot (remember the dartboard!). Furthermore, if our balance shifts laterally from this point, one leg supports more weight than the other and therefore must work harder.
When we ski however, our body is rarely perpendicular to the slope due to the fact that we are on a slope and that we need to incline into the turn to stay balanced. As a result, one leg is longer than the other.
When we are inclined in a turn, our outside leg is longer than our inside leg. A long leg is much stronger than a bent leg. Imagine doing weighted squats and taking a break without racking the bar. Would you rest in a standing position or with your thighs parallel to the floor? Hopefully the answer is obvious. If it’s not, give it a try!
We therefore want to balance towards the outside leg.
Again, the exact location of our centre of pressure must be determined through experimentation – figuring out what gives the best blend of balance, strength and mobility.
I hope you’ve made it this far and I apologise for all the physics but it is important to understand balance in skiing and I will be referring back to many of these concepts in future posts.
Interested in skiing with me?
If you are interested in joining me for some on-snow coaching and you are able to make it to Idre Fjäll in Sweden, you can book a session with me through the Idre Fjäll Ski School. Just be sure to ask for James Nunn!
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