the powertap data is POWER= very accurate KJ measurements
kj is roughly equal to kcal.
Dude. If your powertap told you how many kcal you burned based only on the power you expend to turn the pedals then the value will be off by a VERY large percentage. I certainly hope you're not trying to tell me that your body doesn't burn calories generating heat, etc, and that there is no need to take this into account.
Here's the deal, without HR data, your PT has to solve the following problem to get total calorie expenditure:
Calories expended to do mechanical work over time at the rear wheel hub (about 10-15% of your body's total calorie expenditure)
Account for "other" calories expended by your body, in the form of heat, work done on other parts of your body (a la out of saddle sprints where you move your torso), biological processes etc. (about 85-90% of your body's total calorie expenditure)
My point is simply that the PT isn't some gold standard for measuring calorie expenditure because it is extrapolating the 85-90% based on the 10-15%.
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