Originally Posted by
Wesley36
The answer is that there is no way to calculate it based on HR. The estimations that you can find will vary wildly, as each is based on a whole series of assumptions that are designed to give an average for the population - not useful at all for calculating what a particular person burns with any kind of precision or accuracy.
This is generally true.
Firstbeat, a Finnish company, claims to have developed an algorithm that is much more accurate than the traditional HRM equations and that adapts to an athlete's performance as measured by GPS devices. It works by measuring the intervals between individual heartbeats and analyzing changes in them.
This white paper describes the technology (in general terms, since it's a trade secret). Firstbeat claims an error of 7-10% vs. direct calorimetry; for comparison, the indirect calorimetry done in many fitness testing labs has an error around 5% (according to the white paper).
I've noticed that my Garmin Edge 800 and Forerunner 620, which use Firstbeat's technology, produce calorie estimates that are much lower than other HRMs and that are comparable, for cycling, to estimates from stationary ergometers.