Where does Fitbit get its data for calories burned during various workouts?

[ColossalWhale]

Whenever I manually log an exercise, Fitbit seems to give me some unreasonably high number for calories burned and I always have to adjust it.

There are plenty of studies for how many calories are burned for typical exercises, but, for example, Fitibt will claim that 1 hour of weight training is 300 calories. However, Harvard Medical studies show that you burn on average 180 calories per hour in weight training.

I'm just wondering where does Fitbit source this information from and why does it seem so much higher than most published data out there?

[yayuhz]

It is based on your heartrate, weight, height, age and gender. Obviously, results for exercise vary based on the person, it just gives you an estimate. However, lifting with enough intensity can raise your heart rate to the "fat burning zone" and help you burn more calories. My average heart rate throughout my lifting sessions stays above 110.

[Dominique]

As @yayuhz says: big difference between 20-something 250 lbs / 6’5" male and older, petite female. The generic estimate you saw is for some unknown average person. Secondly, Fitbit includes BMR calories, whereas the estimates you see are usually only for the activity itself. Thirdly, "weight training" is also a generic describer: big difference between something like crossfit (which has a large cardio component) and powerlifting (which is primarily anaerobic).

Unless you spend a very high amount of time doing formal physical exercise (like 2-3 hours everyday), what you burn during that formal exercise won’t have that much of an impact on your total daily energy expenditure, and whatever Fitbit would overestimate during formal exercise may be offset by it understimating your expenditure during the rest of the day. If you are interested in calories burned for weight management purposes, what matters are the total calories burned during the entire day, not so much calories burned during one particular workout.

[WavyDavey]

The beauty of HR enabled fitbits are they take actual exertion rates instead of an estimation of a chart. Sometimes an hour of weights burns 250 calories, sometimes it's double that. 

[emili]

For me, lifting does not burn a ton of calories unless I do a farmers walk or something more aerobic, so my fitbit registers lifting even lower than the study you cited. I have a slower heart to begin with so unless I am really moving, it doesn't speed up to fat burn for 90% of my lifting time. I am also not lifting too heavy for me so the exertion it captures is pretty accurate for what I am doing. If you have an HR tracker, I would go with the estimate it is giving you for the activity. Even if it is too high, it will always be too high so you will have consistency in your calorie tracking. At the end, that's what you are going for.. consistency.

[HokieHoo]

@Dominique What do you mean by "formal physical exercise"? I walk and play tennis and both have an impact on my total daily expenditure.

[phatbitzr]

I tried manually entering skiing as an activity with the total amount of time I was outdoors.  It gave me an insanely high calorie count.  I assume it thinks I was skiing non-stop the whole time.  I eventually entered the estimated calorie count from my ski tracking app (which is based on GPS data of time on slope) and it came within 100 calories (1100 vs 1200 on the fitbit) of what my calorie expenditure purely based on fitbit's measurement of my heartrate.

Why can't they combine the manually entered exercise with the heart rate data and produce a more accurate result.