Wednesday, July 13, 2011

A better way to measure cadence

I promise, this will be my last post about cadence for a while. But today I got to play with a new gadget, a foot pod for my Garmin Forerunner 305. It attaches to your shoe and syncs with your GPS trainer, allowing it to count your steps. I had been measuring cadence occasionally during runs by counting 30 steps of my right foot and seeing how long that takes -- if it takes 20 seconds, that means I'm running at a cadence of 180 steps per minute for both feet.

I had been wondering if I subconsciously was increasing my cadence during those spot-checks, so I borrowed Chad's foot pod while he was out of town. It took me a couple days to get it to work: I could find the menu on my Garmin that asked "do you own a foot pod," but I couldn't figure out how to activate the menu -- it wouldn't let me answer. Finally Marc pointed out that I needed to press "enter" in order to then make my yes/no answer. Bafflingly simple.

Anyways, the end result is that for the first time I have cadence data for the whole run. How did I do? I was taking this morning's run fairly easy -- about an 8:30 pace, in very hot, humid weather. The Garmin gives you cadence based on just the one foot, so instead of a number in the high 100s, mine was in the 80s and 90s. To hit my target cadence of 180 I'd need to register a 90 on Garmin. I ended up averaging 84 for the run, or about 168 when counting both feet. So my cadence isn't quite as fast as I had thought; my spot-checks probably overestimated my real cadence.

For each mile split, the cadence didn't change much, varying from 83 to 85. There was a slight trend to slow down over the course of the run, with my 85 in Mile 2 and 83s in Mile 6 and the last .35 miles.

One thing I had been hoping for with the foot pod was a smoother pace curve; typically with the Garmin the graph of my pace during the run is pretty much useless, looking something like this:

As you can see, it's pretty hard to tell from this graph whether I did better on Mile 2 or 3. I had thought this was due to GPS artifacts like trees blocking the satellite signal. Since the footpod isn't affected by trees, I thought the data might be cleaner. Below is the same graph for today's run:

While the vertical axis is slightly different, the result is the same: It's hard to tell how I did at all. It's just not very useful. That said, it's nice to have the cadence data. I'll keep using the foot pod over the next couple weeks until I have to give it back to Chad, then decide whether I want to spend the $50 for one of my own. Details of today's workout are below.

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