Monday, June 30, 2008

How Does Nike+ Work

So the first step in educating the world about Plus is explaining how the system works in the first place. First though I just want to issue this declaimer - I’m not a scientist, I don’t have a mechanical engineering degree, I’ve never owned a pocket protector or a lab coat, I get this strange clicking sound in my jaw occasionally that I can’t really figure out, and in general I’m not a certified expert on any of this. But chances are I know more about it than you and the evaluation was derived from several conversations with some of the developers. So as is the nature of the internet, if anyone wants to come in and nitpick and offer their own input on how the science behind the system works I’m open to correction…

In technical mumbo-jumbo Nike+ calculates pace using a one axis piezoelectric accelerometer that measures the brief pause between heel-strike and toe-off. I’ll spare you of a scientific evaluation of how an accelerometer works – mostly because I’m not that smart, but the basic premise is similar to how a Nintendo Wii. After determining these pauses it runs the data through a series of algorithms that determines if there is X amount of time between each midstance that means the average runner has traveled Y distance.

So in normal people speak it’s basically measuring how long your foot is off the ground when you’re in stride and using a formula to figure out how far a foot that’s off the ground for that amount of time should be going.

This is similar to a pedometer which is basically measuring how many steps you’re taking and using that as the main data point. But different in that it’s taking a more advanced method of determining stride length and foot strike to get to the numbers.

With all that said the basic measurements are still highly dependant on human input. A major portion of the equation is the stride of the “average runner”. Who is this average runner and how much like you are they? Damn fine question that I don’t have an answer to. Every runner is different – stride length, how long you’re in the “float phase”, foot strike, pace, etc., all make every runner a little different. So this “average runner” the device comes calibrated for is likely not you. Out of the box the device is calibrated for an 8 minute pace, so if you’re like me and you’re faster than that you’ll find that the feedback is slower than you’re going, if you have a shorter than average stride the device will read slower, and a dozen other variations of this basic premise.

This is why calibrating is such a big deal. Through calibration you’re able to tweak the formula to match your particular running style…

But I think that’s enough for now. I hope that was somewhat helpful. Next post I’ll go over calibration, how it’s done, and how it can be made more accurate.

1 comment:

chia said...

I thought it was super cool when I calibrated my 10 minute mile gait to be a 7 minute mile gait.

Funny how much further you go when you cheat the system!

Thanks for the technical dissertation on the inner workings f the Nike+ :-)