Originally Posted by
njkayaker
Referring to the units is confusing.
It might be less confusing to refer to the thing being measured ("power output" and "calories burned").
Since humans don't convert "calories burned" into "power output" with 100% efficiency, the two won't be the same ("calories burned" will be larger).
Power and calories
There's been some other threads about calorie calculations using a power meter.
There have been many tests / reviews with 2, 3, or 4 different power meters on the same bike. They usually match up very well, often within 5% of each other. So I think the power meters are quite accurate. Different software rounds and smooths the data with different formulas, so the totals for the ride are usually a little different.
Lab tests measuring CO2 output, etc, can calculate calories burned quite accurately.
From this article
"convert watts to calories"
The efficiency of
calories to useful work is around
20% to 25%. The other 75% to 80% is wasted heat!
One joule is defined as one watt per second. One (kilo)calorie is 4.18 kilojoules.
Then, since the conversion to useful work is about 1/4 (25%), calories burned are pretty close to kilojoules. No math needed. This is a lot more accurate than estimating using heart rate, or road speed & elevation.