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Comment by nicpottier | Hacker News Reader

I don't know about GP, but I'm an aggressive skier and very, very rarely hit my head. I have maybe a dozen falls a season, wear a helmet and am not colliding with anything. This is a silly comparison.

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It's sort of silly but it's sort of not. The evidence suggests that a few really big hits doesn't do it, it's repeated medium sized head traumas that does. (ie: it happens to line men more frequently out of footballers) Quantifying the size of that head trauma is really key. Does it have to be a "hit?" I mean repeatedly hitting mogul runs put shock on your whole body, you may not hit your head but you're absorbing that up and down shock and moving side to side fairly abruptly; more so that you do just running around and your brain absolutely experiences some amount of that. Age might have a factor too, age when this trauma or shock happen.

I ski and snowboard and I'm not planning on stopping, I think the benefits outweigh the risks. I'd say that about most sports but I'm not about to let either of my kids play football or box.

We need to study this stuff a lot more.

A sub-concussion doesn't require that you hit your head. It simply requires a g-force event -- like skiing quickly over rough terrain -- that shakes the brain around, building up the scar tissue that we know as CTE. Offensive linesmen engage with the opponent via their body/arms, seldom hitting with their head, but that rapid g-force of the body stopping is enough.

Again, someone studied football players because the impact is obvious. As it reaches out, players in even relatively low-g sports like soccer are being found with CTE.

Having played the game for years, I can assure you the impact being generated on the line is very real. These folks do interact with their body/arms, but head on head contact is a very real part of the game, and that is the part that really affects the brain.

And the part of soccer that seems to cause concern is heading the ball, not the running around part.

Comparing helmet to helmet impacts to skiing over rough terrain feels like a real stretch here.

And the part of soccer that seems to cause concern is heading the ball

But we don't know what the concern is in soccer. Heading is immediately looked at because it's an impact, but the actual cause may be something altogether different.

I mentioned the g forces measured in skiing elsewhere. They are absolutely in the range of subconcussion.

Maybe the aggressive compressions of slalom cause the brain to bounce around a bit? In any case, I'm sure it's much less than the sudden stops caused by running into a 300 pound lineman.

The Earth weighs a good deal more than a 300lb lineman, and it's the Earth that skiiers are repeatedly running into while carrying an enormous amount of inertia.

Have you ever been skiing? It's your feet that are running into the earth, and hardly even that - they're skating smoothly over it unless you really mess up. On good mogul run,your head hardly moves off a straight line while your legs and hips adjust to keep your skis moving smoothly. In a similar comparison, walking does not produce head trauma.

I've been skiing plenty of times. Runs where I'm at a high rate of speed and hitting countless variation changes (not moguls, just normal skiing) and my head is shaking so much that my vision is blurry. Landing a jump at best (when you absorb with your legs) is a 19G+ event. Every minor mistake in absorbing can tenfold increase that. Walking is not a relevant comparison.

We evolved to walk with a limited brain suspension that just wasn't adapted for 100kph wax shoe runs.

That's the forward component of the velocity vs the component that's normal to the ground, though - the collision with the Earth is much lower speed than the lateral motion (sliding along the surface after the fall). If you're skiing aggressively, you're frequently quite close to the ground, and a fall is frequently where you end up grazing it because you lean further than the centripital force can maintain. You fall a much shorter distance toward the Earth than a timid skier does.

If you're skiing at the level I'm talking about, falls are probably not that frequent, though.

In my earlier comment I was talking more about the explosive vertical compression-expansion cycle that characterizes skiing really hard with very tight turns on short radius skis. Those are much less violent than hitting a lineman though.

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