Originally Posted by
FBinNY
Despite all the theories and math, converting distance, speed, climbing, etc to calories is only possible if you're looking for ballpark numbers. That's true even with a power meter.
There are too many variables, and while a power meter will address some of them such as varying wind drag, is can't address one big one, which is that human engines vary greatly in efficiency. So the calories needed to produce a given output (if it's measured correctly) will vary among people, and even in the same person with changes in temperature or other conditions.
So, rather than sweat trying to pin calories down precisely, accept them as a rough guideline based on simple formulas (or a power meter) and let the long term average things out for you.
Very true, and even kilojoules to calories is very ballpark, a few percent off in fact.
But using math again can put the ballpark into perspective. Our expected metabolic efficiency is given at 22% plus or minus 4%. So bottom line if some formula says "25 calories" it might really be 24 calories, or 26 calories. I think it's pretty useful for that level of precision, though it's true you'll never get an exact number this way.