Watts watts watts!
If you do a trainer ride one day at a constant 100 W for an hour, and the next day do the exact same ride but have a higher average HR (you're sick, or it's hot out, your job has you stressed, or whatever), do you think you burned significantly more calories?
If you're using watts as the primary metric for calories, the only variable or fudge factor is how efficiently your body converts caloric energy to physical work (typically around 25% efficiency). If you use HR, you're using whatever convoluted algorithm they have to get some caloric information.
Basically, if you use power, the only operation is convert watts to calories (exact calculation, no guessing!), and then divide that number by your efficiency (a best guess based on experimental data from other athletes).
If you use heart rate, the operation is take heart rate --> put into black box strava or wahoo or myfitness pal created (all of which will differ) --> get calories.
Unfortunately I couldn't find any scholarly research on how much efficiency varies throughout the population, but perhaps one of our esteemed members can enlighten us.
If you do a trainer ride one day at a constant 100 W for an hour, and the next day do the exact same ride but have a higher average HR (you're sick, or it's hot out, your job has you stressed, or whatever), do you think you burned significantly more calories?
If you're using watts as the primary metric for calories, the only variable or fudge factor is how efficiently your body converts caloric energy to physical work (typically around 25% efficiency). If you use HR, you're using whatever convoluted algorithm they have to get some caloric information.
Basically, if you use power, the only operation is convert watts to calories (exact calculation, no guessing!), and then divide that number by your efficiency (a best guess based on experimental data from other athletes).
If you use heart rate, the operation is take heart rate --> put into black box strava or wahoo or myfitness pal created (all of which will differ) --> get calories.
Unfortunately I couldn't find any scholarly research on how much efficiency varies throughout the population, but perhaps one of our esteemed members can enlighten us.