Just as with the Nike + iPod, I got the chance to try out a Polar RS800sd bought for the lab.

It consists of 3 main elements:
  • An ECG belt to get the heart rate through comfy textile electrodes.
  • A foot pod, measuring stride length and cadence, based on inertial sensors (accelerometer and maybe gyroscope).
  • The watch gathering wirelessly the information from the two above and connecting to a PC.
I went running in the park for 6.33km, again without pre-calibration. The watch told me 6.43km, not bad! Only 1.6% error, to be compared with 33% for the iPod gadget...
polar rs800sd
Technically, the main difference between these two apparently similar systems is the foot sensor. The iPod+Nike relies simply on a contact sensor that can't do much more than counting your steps. Therefore sensor calibration is crucial. I wouldn't mind calibrating the sensor once, but every pace change means recalibration! I guess Nike has never heard about interval training and that sort of things.
To test the limits of the Polar, I tried it walking instead of running, and it behaved very well, as I got a very similar error: 1.6% above. I guess I just need to calibrate it once to get near-perfect distance/speed estimation at any pace. I finally performed an ultimate test on the sensor: I ran on a treadmill :) . This tricked the sensor. Indeed, your actual speed is null, whereas your feet are moving. It displayed a 13km/h running speed when the treadmill was set on 15km/h (13.6% off).

You can use their software (PolarProTrainer) to upload your data, view the training calendar, running curves (speed, heart rate, cadence, altitude, ...), evaluate your training efficiency, and even program some exercices to be sent back to the watch. It seems to have loads of functionalities, but the look and feel is not great.

Some Adidas shoes have a placeholder for the sensor (just like the Nike for the iPod one). Better: some Adidas shirts have embeded ECG electrodes for a truly wearable sensing.

On the whole, the iPod+Nike is just a fashion gadget based on the Apple hype, whereas the Polar system (with or without Adidas) is really designed for training. And I swear I'm not paid to write that!

Ultra running sensor.