Sometimes there can be problems with the calorie algorithm being thrown off because of recording problems or profile settings. If you are seeing calorie differences on the app from workout to workout you may need to delete and reinstall it to reset the calorie algorithm. Also check your MapMy profile settings to make sure your profile height and weight are accurate. Profiles and activities without age, height, weight, gender, activity type, and duration data will not record calories correctly.
Typically calories are determined by age, height, weight, gender, intensity of the workout, distance travelled, and activity type. Heart rate does not currently factor into the equation, but will as the app grows. Our products calculate total burn, which includes caloric burn for both resting and active phases of activity. This means the calories you would normally burn simply by being alive are added to the amount of calories you would burn from whichever activity is chosen.
We have based our calorie count on established scientific research detailed in the Compendium of Physical Activities. This measures time spent at a specific exertion level and uses this as a multiplier (the corrected MET, see below) of your resting metabolic rate. Distance is not the sole factor of calories burned, you must also look at duration of activity as well. The resting metabolic rate is estimated from your height, weight, gender and general activity level through the Harris-Benedict equation. You can learn more about the theory behind this by visiting: https://sites.google.com/site/compendiumofphysicalactivities/corrected-mets.