A linear relationship?

A quick update on the throwing research: I’m still waiting on the data. Getting each throw ready for analysis requires someone to go through the manual process of tagging which marker is the inside of the elbow, which is the heel, etc. For thirty or so markers. For about seventy throws per participant. Then they need to write and run a bunch of macros to pull out the stuff I’m interested in – spin, speed, how many degrees the wrist snaps, how much the shoulders turn, and about thirty other things.

You get the idea – the guys in the lab are facing a long task to get all the data organised before I can even start analysing it properly. And since the raw data can only be analysed on their system, there’s not much I can do to help.

But in the meantime, there’s something interesting I wanted to talk about. We found, when doing a couple of on-the-fly reconstructions during testing (and some back-of-the-envelope calculations) that the spin on the disc is pretty much linearly correlated to the velocity of the throw – i.e. your hucks have much more spin than your short passes. This research found the same thing (and gives, at least until we get our full data, a great deal more confidence in the result). I find it really interesting.

If spin is generated by actively snapping, using the muscles of your wrist, it shouldn’t matter too much what speed you’re moving the disc at. You should always be able to apply the same sort of snap, regardless of speed (though not regardless of acceleration).

On the other hand, if wrist-snap is created by a sudden deceleration of your arm, while simply allowing the wrist to carry on, then it would indeed seem as if a more high-speed throw would result in a sharper deceleration and thus more spin.

Or could it be to do with  the acceleration of the arm/disc just before the snap? Imagine that the muscles of the wrist are fighting hard to maintain a fairly neutral position while being pulled back by the inertia of the disc under acceleration, and then that acceleration suddenly ceases. That would create a much stronger snap than the muscles/tendons could achieve without a resistance to push against. [With your hand flat on the desk, try tapping a finger as hard as you can – and then try resisting your finger-tap with the other hand and suddenly letting go. It’s very different. I just did it and bruised my finger from hitting the desk too hard…]

But why would the acceleration be stronger for a long throw than a short one? Surely the point about a longer throw is that it has a similar acceleration, but over a longer throwing-motion, after a bigger backswing?

If not – if our short throws are generally accelerating less aggressively than our hucks – then we could all have vastly quicker releases on short throws by accelerating harder and having an even shorter throwing motion. There has to be an advantage in that for beating a mark or hitting a receiver earlier. Whatever our maximum comfortable acceleration is, determined by our strength and technique, shouldn’t we be somewhere near it on the majority of throws?

Or is the wrist only a bit-part player? Perhaps the disc is simply spinning off the fingers as you let go – which would tally very nicely with the data, in some ways. The speed – and hence the sharpness of the deceleration – would probably affect the spin in a linear way in this scenario.

Honestly, I don’t know. I personally expect that more than one of these things will contribute to the overall spin – certainly I can throw very short throws with just the wrist, but I can really feel the disc snap off the index finger when I throw a full-power backhand too. My coaching focus is generally on fighting to keep the wrist fairly neutral and using the resistance (like that finger-tapping exercise) created by the disc’s inertia to generate a quick snap when you run out of arm and stop accelerating. But so far, I can’t say for certain. Add your own thoughts below, of course…

What’s great is that sometime soon I’ll get some nice 400 frames/second data. We’ll see how many degrees the wrist actually snaps through impact, and how fast, and how that correlates with the amount of spin. We’ll see whether the disc then increases spin as it comes off the fingers too. We’ll know both the velocity and acceleration of the disc, wrist, and arm at 400fps through the release, for both short throws and long. We’ll see the differences in technique between people who get more spin and those who get less. We’ll see the differences when someone is told to throw for maximum spin instead of maximum velocity.

That’s pretty exciting, I think.