Originally posted by: spacejamz
Originally posted by: techs
Here's a good one. You put in your weight and the distance and it gives you the calories.
Calorie Counter
for my last 4.2M run (finished in 45 minutes), I get the following:
Polar heart rate monitor - 615 Calories
Nike+ kit - 586 Calories
Tread Mill Display - 603 calories (input my age/weight before run)
That site - 566 Calories
The Nike+, treadmill and site all measure mechanical energy usage and then use correlations based on age, weight etc. to predict your bodies calorie expenditure. The Polar uses a correlation between you heart rate, age, weight etc. to predict your calorie expenditure.
It's somewhat analogous to measuring your car engine's power consumption at the rear wheels (Nike etc.) and then compensating for drivetrain efficiency by taking a guess based on car type vs. measuring your engine RPM and comparing it to a typical torque/power curve for your car type (Polar).
On basic models Polar calculates expenditure based on gender, age and weight (OwnCal) and also includes VO2max and HRmax on the more advanced models (OwnCalS).
Scientific development and evaluation of the Polar OwnCal/OwnCalS
The above article outlines validation studies that compare the Polar predictions with results from gas analysers. The accuracy for men (it's more accurate if you're a woman) is around 1.6 kcal/min for less fit to moderately fit individuals using OwnCal and around 1.4 kcal/min for fit individuals using OwnCalS.
What does this mean for the different energy measures?
The accuracy over 45min translates to around +-63 kcal to +-72 kcal.
All of the above readings lie within this band around the Polar, so the others are all probably reasonably good estimates and you can draw no real conclusions about their accuracy relative to each other.