How and how well does the Nike+iPod Sport Kit calculate distance?
January 5, 2007 1:58 PM   Subscribe

How and how well does the Nike+iPod Sport Kit calculate distance?

I just bought the Nike+iPod Sport Kit because it's something I've had my eye on for a while and I had a soon-to-expire coupon. Before I take it out of the box, though, I want to know how well it calculates distance. I've read some good things about it, for example here (+ .02-.05 miles) and here. However, I still have some reservations based on the nature of the device itself.

Is the sensor (the doodad that goes in the shoe) a traditional pedometer-style accelerometer or a more sophisticated version? I ask because the difference could be important. Traditional pedometers measure up-and-down motion, counting each as a "step." They then multiply the number of steps by the average distance of each step (as entered by the user) to find the distance traveled. The problem with this, it seems to me, is that when running I tend to have different types of steps. On uphills, for example, I shorten my stride, while I try to let it all out on the downhill. The traditional pedometer would measure each kind of step as the same distance. It would seem to be more accurate if, instead of counting up-and-down motions, the accelerometer were to measure forward-and-back motion.

There are two ways the problem I just mentioned might not manifest itself. One is that the difference in my step types could be too small to make any serious difference over the kind of runs I do (<10k usually). The other is that the distance I add per step going downhill just about balances out the distance I subtract per step going uphill. (Seems less likely to me.)

My questions for the hive mind are thus several: Does the problem with pedometers I suggested hold any water? How does the Nike+iPod kit measure distance: (#steps)*(distance per step), or is it something a little more sophisticated? Have you encountered distance-measuring problems with your Nike+iPod and if so, how much was it off by?

Thanks in advance!
posted by dondiego87 to Sports, Hobbies, & Recreation (9 answers total) 2 users marked this as a favorite
I researched the device a couple of months ago, and I concluded that it must be some sort of conventional pedometer. It does not use GPS.

I saw references to your possibly having to calibrate it, which I interpreted as: it's calibrated to an average step length. If you are anal, then recalibrate it for your own stride.

I'd like to hear from someone who has calibrated one. The process that you have to go through should make it clear whether the device is a standard pedometer or not.

Oh, the other clue that it's a conventional pedometer is that you have to position is very precisely in your shoe regarding front-back alignment. That indicates to me that it contains some sort of mechanical motion detector: if the device is out of alignment, it won't detect forward/back motion.
posted by tippiedog at 3:04 PM on January 5, 2007

By the way, I decided not to buy one. I can get a mechanical pedometer for a few bucks. Not interested in that.
posted by tippiedog at 3:04 PM on January 5, 2007

According to the patents in the front of the manual, the technology is from a company called Fitsense. It looks like they used to sell the product themselves before licensing it to Nike. They claim that it can handle different stride lengths.

tippiedog, to calibrate it, you pick a distance (like a mile) and then run that distance and tell it when you're done.

(I got one for Christmas but it's not running weather yet.)
posted by smackfu at 3:24 PM on January 5, 2007

Actually, according to this post on Podophile:
Apple’s FAQ states that “a sensitive piezoelectric accelerometer monitors your footstrike when you walk or run and determines the amount of time your foot spent on the ground. This contact time is directly related to your pace.”
So it's not exactly like a traditional mechanical pedometer, and my own personal use bears that out. I bought one of the traditional ones and tried to use it for running, but the results were wildly inaccurate. You had to calibrate it before you did anything and I just couldn't find a setting that mimicked my average stride length.

After the pedometer debacle, I'd resorted to using Google Pedometer to measure my distances. In November I got the Nike+ and headed out for my 5K route with no calibration. The voice feedback told me I was finished within about 50 feet of the finish line, which is way better than I expected. All my subsequent runs have been similarly spot-on. And yeah, while you need to orient the device properly (front-to-back, not upside-down, as horizontal as possible), my experience is that you don't have to be too precise about it. Me, I just attached the thing to my shoelaces.
posted by web-goddess at 3:28 PM on January 5, 2007

Yep, it's a fancy auto-pace-adjusting pedometer. Here's the Apple technical FAQ.
posted by trevyn at 3:43 PM on January 5, 2007

I use mine on the treadmill (why? makes no sense, I know, but there you go) and it's not accurate at all, but then I haven't calibrated it yet. I do recommend one of these ShoePouches (or similar) if you don't want to get the special Nike shoes.
posted by pyjammy at 4:12 PM on January 5, 2007

I've been using mine for about 6 months. If you don't change your pace, hence changing you gate- you'll be fine.

However, if your training includes changing pace (running faster/slower), you get about a 10% error rate. Note: this sucks when you're training over perhaps an 8 mile course, and because your ipod thinks you only ran 7.1 miles, your pace and overall performance is poor.

If you keep your pace even, and change the distance, it's worth the money spent.

I don't have Nike shoes, it just bought one of those shoelace wallets for $5- works fine.
posted by rryan at 5:05 PM on January 5, 2007

if your training includes changing pace (running faster/slower), you get about a 10% error rate

bought one of those shoelace wallets for $5- works fine

posted by trevyn at 2:14 AM on January 6, 2007

For those that don't want to use the shoe pouch, I took a chance and cut a sensor-sized hole in the foam of my sneaker with an exacto knife. I tried it first on an old crappy pair of sneakers to see if it would work and when it did, I did the same again on my newer pair. Fits perfectly.

As for accuracy, I did two runs this week, both the exact same distance and my first reading was 2.8 miles and my second 2.73. Close enough I thought. But I just went to Google Pedometer to check and it said the actual distance was 2.5 miles. I guess I'll try calibrating.
posted by gfrobe at 2:59 AM on January 6, 2007

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