calories burned errors - tracked activity cals burned vs logged activity cals burned

[Steves70119]

I've noticed a strange occurrence that I'm sure has been noticed before by someone but I cant see it mentioned here so I'm gonna post this. Bear with me as it takes a bit to explain properly. Everyone seems to acknowledge that most activity trackers are not reliable to use for number of calories burned for walking or treadmills, if u use the actual activity tracking aspect of the tracker. Most calculate calorie burn too high, some calculate too low. That seems to be generally accepted. Whats puzzling to me is that if I go into my fitbit app and then manually "add" the same activity as a "logged" activity, starting at the same time, for the same amount of time and for the same distance, the calorie burn number that the fitbit app then generates is much closer to the number that every other calorie burn calculator available generates. And since i used the same start time for the "logged" activity, the fitbit app replaces the numbers (both steps and calories burned) in my daily totals with the closer to correct numbers in the daily total on the dashboard. This doesnt affect my BMR which is the same in both cases. So i know that if i add a "logged" activity that mirrors any "tracked" activities, the calories burned will be adjusted by the fitbit app to be more realistic. Of course this is a PITA to do, so after several days of testing I've found that I can pretty accurately calculate that any calories over my BMR the fitbit app tells me I've burned, if the fitbit is calculating burn using activity tracking (and i dont go in and "log" a "mirrored" activity) can be cut in half and that is a close to accurate number for calories burned for physical activities. This 50% factor works for my activities which are mostly walking based (walk, treadmill). The correction factor may be different for other activities.
The most curious part to me is that the fitbit can obviously calculate a closer to correct number for calories burned walking because when I manually "log" the activity, the calorie burn number is pretty near accurate when compared to other calculators available (and yes these other calculators ask for factors like age, weight and pace, so they are fairly reliable). Why, then, is the number of calories so far off when the app does the original calculation using the activity tracking? And this has nothing to do with the numbers for my BMR. I will illustrate with screenshots.
Yesterday i "tracked" a couple of walking sessions. Today i went back to yesterday's dashboard. it said i had

21,298 steps, 9.84 miles, burned 4,432 calories, 137 zone minutes.

This was before i mirror "logged" any activities. So to illustrate the phenomenon i'm talking about, I'll use a walk I took at 10:33am yesterday. The fitbit app tracked me starting at 10:33am, walking for 1:22:51 min, for 3.23 mi.. The app calculated i burned 673 calories. Then I went in and "mirror logged" that same activity. I manually logged an exercise session, "walking", started it at 10:33 am yesterday, for 1:23:00 min, 3.3 miles (actually 9 seconds more and .07 miles further than the tracked activity). for this manually logged activity the fitbit app calculated only 328 calorie burned. The app also adjusted my daily totals on my dashboard for the day since the app was now using the logged activity numbers instead of the tracked activity numbers. Now my dashboard for yesterday had:

21,326 steps, 9.89 miles, 4087 calories burned, 137 zone minutes. The calorie burn number for the day was 345 less, the actual difference between the number of calories burned calculated by tracked activity vs number of calories burned calculated by "mirror" logged activity.

If fitbit knows more accurate calculation methods for calories burned

why dont they implement them all the time? This is pretty stupid. And i know that fitbit isn't the only tracker company with this problem. And I know the engineers in these companies are smarter than me. What’s the problem?

I hope i've explained this in an understandable way. Any questions or useful comments about this info is welcomed. I do expect a fitbit rep to respond with a pat answer that doesnt really address the problem or answer the main question. But I did wanna post this info. Thanks for getting this far.

I like the fitbit because the charge 5 I have is an inexpensive device that assists me in tracking my vitals and activity. And now that I've figured out this calculation error I can use the info more correctly. So I use the tracker and accept its shortcomings.

 

[JohnnyRow]

Do you realize that when you manually log a walk, your measured heart rate gets overridden/ignored?

So basically you are starting with the premise that you can get more accurate calorie calorie burn by ignoring your heart rate, basically better result by using less data.  If that's the way you prefer to go, that's your option.

[Steves70119]

Yes I realize that. If the calculation using less data is closer to correct, then that is what I want to use. Are u saying that the fitbit burn rate using the activity tracker is closer to correct? I use Fitbit in conjunction with a calorie counter, Loseit! If i just use fitbit's burn rate from the activity, the fitbit way over calculates the burn rate. When i use the burn rate from the logged activities instead, my corresponding weight loss (or gain after Turkey day) all fall right in line. The proof of the over calculating is in the weight loss or gain. If i would use the initial fitbit burn rate from the activity I would be misled as to how many calories i burned/calories i could consume based on burn and still be on target weight wise. To lose 1 lb a week u need to burn 3500 more calories than u consume that week. That formula doesnt work if u use fotbit's non-adjusted burn numbers.That's only because the fitbit is overestimating the burn. But fitbit isn't alone with that problem. It seems most trackers have a similar problem

[t.parker]

@Steves70119 neither is correct. You're just lucky you fall into the statistical range of automatic calculation. Those are usually designed to provide lower caloric output due to a lack of data. That's it. It looks correct for you, but won't for somebody else. It's all estimate. There is no way without a dedicated device to know energy expenditure and the closest to reality are power meters.

For me, Fitbit overestimates calories during walking or weight training. Walking for some reason registers a few beats higher HR than real (I experienced that on several models) and this is enough to inflate energy output. With weight training, it's a different story and usually, I don't include that into any calorie burn (0kcal). Using heart rate is probably the next method after power meters that provide some level of accuracy but under certain conditions:

- it uses realistic data

- it takes into account your fitness level (lower HR doesn't mean burning fewer calories, it's all physics)

- it uses accurate HR (and that IMHO can be achieved probably only with a chest strap)

In other words, the best estimate you may get from longer steady-state cardio is when your HR is relatively steady. It's still going to be an estimate but closer to reality.

Fitbit, when using HR may as underestimate as well as overestimate energy. This is because the response of the heart is delayed which will affect average HR and judgment of effort. I will give you two examples from one of my workouts.

Here are four intervals of different intensity showing the relation between the power, HR and kcal:

Since we don't know Fitbit's algorithms for estimating the kcal using HR and Fitbit has no suitable viewing tools to select regions I used the Runtastic tool which is considered a pretty good running estimator.

Walking (last chart) shows that when entered manually, Fitbit underestimates that walk 4 times compared to the power meter. That definitely would support weight loss but the number of people who will find it accurate is rather limited.

So above you can see kcal calculated using HR, power and using Log Previous in Fitbit. The last interval is very low-power walking. Guess, which estimate is closest to reality? Not the lowest but the one coming from the power meter. It is still not perfectly accurate but it's the closest you can get without dedicated lab equipment.

I believe that Fitbit, when activity is logged manually, uses MET and assumes the lowest intensity because for people who count calories it is safer to underestimate rather than overestimate. The HR however is kind of a wild estimate because it depends on many factors.

If you look at energy (yellow) and HR (red) when I already exert the energy that my interval targets my HR still has to catch up and it takes time. This affects the overall average later. Let's consider two points of the second interval. Two data points of equal power but different HR:

1) TIME: 18:25, PWR: 181W, HR: 176BPM, KCAL(PWR): 0.181kcal, KCAL(HR): 0.3kcal

2) TIME: 19:20, PWR: 181W, HR: 153BPM, KCAL(PWR): 0.181kcal, KCAL(HR): 0.25kcal

The same power for a 1sec period, two different HR readings but the same real energy expenditure.

As you can see, every method has pitfalls and it's not so simple to estimate HR. If you find MET-based estimates working for you then you should use them. Remember that no matter what you use, it's only an estimate.

[Steves70119]

@t.parker Thanks for the great info and illustrations. Yes, currently using an estimate based on MET numbers does seem to work best for me. I've found that based on those numbers if my calorie intake is above recommended levels or below recommended levels those numbers are fairly well reflected in weight gain or loss to within about .5 pound which is close enough to progress with.

I'm curious since u acknowledge the shortfalls involved in any single method of tracking calorie burn what u use the fitbit to track for your own purposes. Also is there a way to tell the fitbit to not include the data from any particular activity/time period in its daily totals as per "With weight training, it's a different story and usually, I don't include that into any calorie burn (0kcal)." Or r u just not using the daily tallies to begin with, just using parts of the data?

Thanks again.

[t.parker]

@Steves70119 in general I have my own method that works for me.

- I track calories only from power meters so that includes only running, cycling and indoor rowing with PM5.

- I ignore calories from walking or weight training. Walking because I hardly burn anything doing it and weight training because the time of work (sets) comparing to rest between sets is too short to matter (and with HR that would be very inaccurate).

- I know my BMR and estimated TDEE

- Eventually, I combine elements together and of it doesn't work I reduce my estimates. Trial error.

If I want to cut weight, I add more easy aerobic steady-state cardio that is supposed to help me with achieving deficit. Basically, I decide that I want to run with steady 190W or cycle with 175W and just do it. For cutting weight I estimate my daily calories burnt as BMR + active calories from those activities. I don't care what Fitbit or Garmin show but I understand basics of what and why they show.