Swing for it#

Wed, 13 Dec 2006 18:57:28 +0000

I spent an hour or so after work googling for gait analysis papers and watching skating videos in freeze-frame, while preparing a first cut of my long-threatened article on armswing - which was going to say something like "still don't understand, here are some hypotheses about what might be happening". Then I skated home, and - somehow I must have internalised something, because I had a natural two-arm swing for the whole 5k and was barely even thinking about it. From the little I could tell by looking at my shadow it was quite respectable too.

[[Once upon a time => It don't mean a thing/if it aint got that (arm)swing]], I wrote

Note to the "unlock the power of gravity" people: there's no net gain on the action-reaction principle from throwing your arm away from your body behind you. Unless you sever it while doing so, sooner or later it will reach the end of its travel and have to be brought back. So, we're probably looking for some mechanism that makes it sufficiently worthwhile to get that extra oomph at a certain part of the push that losing it again at some other part of the cycle is a price worth paying.

which I now believe, surprisingly enough, is exactly what happens - though it's the lateral component that's important. Swing your arms left (left arm back and outward, right arm forward and inwards) to impart a rightwards force to the torso at the same time as pushing with the right foot. This will counteract the leftward movement of the torso due to pushing, so that you get a longer time to push before your leg straightens. So it doesn't matter that there's no direct energy gain from swinging your arms one way and then back again, what matters is that when you're swinging them one way it gives you longer to put force down with the leg.

Secondary issues:

• side-to-side armswing: conventional wisdom has it as a no-no. I'm going to postulate that this is for reasons of (1) aerodynamics, (2) keeping the upper back still, (3) sociability (it's nice not to smack your fellow skaters in the side of the head too often).
• weight transfer: starting the armswing (from the "one arm forward, one back" position) when the glide turns into a push gives you a nice sideways kick which is exactly what you need to get onto your inside edge.
• what I said [[the other week=> Disarmament]] about keeping elbows tucked in was the tipping point in making the motion natural for me. The real reason for this could be aerodynamics again, possibly, but what it's done for me is reduce the number of degrees of freedom in my armwave so that it flows better.
• this is all about armswing at steady speed. Haven't thought about acceleration at all

Now that I think I've worked it out (ICBW, quite easily) it all seems bloody obvious, of course. It probably is.