Hirscher vs Kristoffersen Levi Slalom Analysis - Fore/Aft boot set up part 1 – Forward lean
Very interesting race!
This race was so close, but so many great aspects made it very interesting. I wanted to talk about how the two best slalom skiers in the world are so different, but with nearly the same time.
Hirscher and Kristofferson were so close in this race and it definitely could have gone either way. What fascinates me about these two is the complete difference in how they stand on their skis.
Their stances are very different, but showing similar times and results. In this analysis I want to break down how their stance and their boot set up, along with their personal bodies geometry, influence the way they ski and also why they are so different in this aspect. Both are aligning their Center Of Mass (COM) over their Base Of Support (BOS) perfectly at the right time in the turn, but with big differences in their vertical alignment.
I will go over, in a 3 part series, all the aspects of their stance and why they are different.
-Part 1 – boots and lower leg
-Part 2 – Knee and hip
-Part 3 – Torso and arms and how all three areas interact with each other to create a dynamic stance.
As you can see in the video Kristoffersen and Hirscher’s overall stance or posture are vastly different. Kristofferson has that more traditional forward bend at the hips, driving the hands forward and overall a much more aggressive stance that stays pretty much the same all the time, while Hirscher has a much more vertical spine, flexed ankles and overall casual posture that varies throughout the turn.
Why is this?
Let’s start with their body type and especially their lower legs. Hirscher is short and stocky, with a lot of mass around the calves, whereas Kristofferson is much skinnier with longer levers, but much less muscle around the legs and calves (and higher calves). These differences can greatly affect the overall stance.
Below I have made four diagrams looking at how the boot and lower leg interact with each other, and how the thickness of the lower leg can influence where the COM of the knee sits. (note the colored center of the legs is where the tibia bone tracks).
The only variable in this diagram is the thickness of the leg and the addition of the spoiler. Everything else is identical including the length of the leg to the knee, the angle of the foot sitting on the boot board, and the cuff is a constant.
As you can see all the COM of the three knees sit in vastly different areas with only one variable that has changed: The amount of muscle one has on their leg + a spoiler. This doesn't even consider the ramp angle of the boot board which have variances between brands, and actual forward lean between brands. Factoring in those other two create a myriad of variables that can greatly change where the COM of the knee sits.
For this example I wanted to keep it simple just to show how ones body type can greatly change the appearance and function of ones stance and actually show two skiers that are the best in the world with opposite body types exhibiting different stances.
The ankles and boot set up will greatly affect where the hips are, and also the torso but I will get into that in part 2 and part 3.
There are so many other variables that will affect where the COM of the knee sits and also the function of the ankle inside the boot that I have not covered in this article such as:
Ramp angle
Length of Tibia and Fibula
Ankle mobility in the dorsiflexion and plantar flexion range.
ROM of the subtalar joint in the eversion and inversion range.
That need to be all correctly measured and taken into consideration, but for simplicities sake I have just chosen to demonstrate the point with one variable that is prevalent and observable between the two athletes. All these other points I have stated would just be speculation and guessing without actually having a look at each athlete out of boots.
Part 2 coming soon!
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