Originally Posted by
Hermes
Since I got my power meter, it is interesting to see how much energy (Kjoules) I produce on a ride. I always knew that most of the HR / speed devices were inaccurate and overstated the calories but what was slightly surprising was the amount. Generally, on a hard 3 hour ride I will burn approximately 500 calories an hour.
Here is a simple thought experiment. According to calculations derived from your power meter you say you are "burning" 500 calories per hour. Sit on your bike in the garage all day without turning the cranks. How many calories does the meter say you've burned? Zero. Does that sound right?
My point here is that a lot of people misinterpret the data they get from power meters. You burned 500 calories per hour generating the wattage measured by the power meter. But your body has an additional base metabolism that also has to be accounted for just to keep you alive. In other words your body is burning calories doing a lot of things that your power meter does not measure. So the power you produce won't equal the calories you burn; it is only one component.
Back to the thought experiment, you'd probably have "burned" 2400 calories just sitting there all day (YMMV). Translated to your own experience that would be an additional 100 calories per hour on top of the 500 you measured which is much more in line with many of the estimates you see from various sources.