run4life

Losing Weight by Running

Introduction

I purchased a Nike + iPod Sport Kit to track the distance and monitor the speed of my runs.  The ability to track distance gives me the freedom to spontaneously run wherever I want and still keep track of the distance travelled.  The ability to monitor my speed allows me to easily pace myself during training runs or races.  Btw, I don't have Nike shoes, so I bought a Shoe Pouch for the iPod sensor.

The iPod has the advantage over GPS devices in that it is much less expensive, much smaller, and does not rely on satellite visibility.  On the other hand, it may be less accurate. Nike says:

"The Nike + iPod system measures the distance traveled by most runners and walkers to over a 90 percent degree of accuracy, right out of the box. You can calibrate the system to your stride for increased accuracy."

This web page documents my finding with regards to iPod accuracy.

iPod vs. Track

Date Track Distance iPod Error Calibration Type
1/12/2007 MHS 400 430 7.50% uncalibrated walking
1/12/2007 MHS 400 400 0.00% uncalibrated running
1/12/2007 MHS 400 400 0.00% 400 m - 1/12/07 walking
1/12/2007 MHS 400 400 0.00% 400 m - 1/12/07 running
1/14/2007 MHS 1600 1700 6.25% 400 m - 1/12/07 walking
1/14/2007 MHS 1600 1720 7.50% 400 m - 1/12/07 running
1/14/2007 MHS 1600 1610 0.63% 1600 m - 1/14/07 walking
1/14/2007 MHS 1600 1600 0.00% 1600 m - 1/14/07 running

Notes:

  1. Distances are in meters.
  2. When set to kilometers, the iPod's display resolution is two decimal places or 10 meters (e.g., 0.39 km, 0.40 km, 0.41 km, ...) (10/400 = 2.5%).  I should probably use at least 1600 m (10/1600 - 0.625%) for all tests.  This begs the question, what is the internal measurement resolution of the iPod?  I suppose ṭhe display resolution may be the limiting factor in the device's accuracy at shorter distances.  This also makes me wonder if a longer calibration period would be beneficial.
  3. The 1600 m calibration numbers are good, but I don't think I can conclude much from 2 data points.  I need to get some more data... Also, it will be intetesting to determine how much the accuracy depends on the distance travelled relative to the calibration distance.  Similarly, the relation between accuracy and pace would be interesting to measure.

iPod vs. Race Course

Date

Race

Distance

iPod

Error

Calibration

Pace

2/24/07

RFD 5K

3.11

3.03

-2.57%

1600 m - 1/14/07

9:24

3/10/07

MJ 8K

4.97

4.89

-1.6%

1600 m - 1/14/07

9:43

3/24/07

RFL 5K

3.11

2.94

-5.5 %

1600 m - 1/14/07

9.20

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

iPod vs. Treadmill

Date Treadmill Distance iPod Error Calibration Type Comments
1/10/2007 3 3.1 3.33 7.42% uncalibrated running
1/10/2007 3 3.1 3.35 8.06% uncalibrated running
1/15/2007 3 1.77 1.8 1.69% 1/14/2007 walking
2/22/2007 3 3.1 3.44 10.97% 1/14/2007 running
2/23/2007 3 4.55 5.01 10.11% 1/14/2007 running hills
2/24/2007 3 3.1 3.39 9.35% 1/14/2007 running
2/25/2007 3 4.49 5 11.36% 1/14/2007 running

Notes:

  1. Distances are in miles.

Things to Test

  • How does accuracy vary with pace? 
  • How does accuracy vary with incline?
  • How does accuracy vary with distance run?
  • Is there any benefit to using more than a 1600 m calibration.
  • Does calibration pace matter?
  • Is the sensor sensitive to temperature?