BMR & Total Calories Burned

[HockeyGrl]

Since we cannot enter an actual BMR (even though some of us have had it actually measured), I played around with my data until the Fitbit Versa BMR matched my actual BMR. Anyway, if I subtract calories burned per the BPM/heart rate data from total calories burned for the day, shouldn't it always be the same number, i.e. BMR? Mine ranged from 1670 to 2000! What am I missing? 

[JohnnyRow]

I would think a big problem with that approach would be knowing exactly what number to subtract from the total.  How do you know how many calories you are burning above your BMR?

[HockeyGrl]

Q: How do you know how many calories you are burning above your BMR?

A: I am using the calories burned from the heart rate field to determine the calories burned above my BMR. The heart rate field shows 3 exercise zones and calories. Isn't that what that calorie number means? Perhaps this is where I am mis-calculating. 

[JohnnyRow]

I'm not sure how you would read calories burned.  For instance are you just looking at minutes in fat burn, cardio, and peak zones? And remember you have to consider throughout full day, not just during workouts.  Some people think of being either in a workout or at BMR, but any normal activity throughout the day is somewhat above BMR.

[HockeyGrl]

Q: How are you reading calories burned?

A: I am reading the calories from this screen shot. However, as you pointed out that includes BMR burned. Seems like the math should be easy: total calories=BMR+calories burned exercising. I thought Fitbit could display calories burned exercising, which when added to my BMR would (within 5%) = total burned for the day. I am super curious about the calories I burn throughout the day above BMR.

[JohnnyRow · Accepted solution]

I see that screen and understand your logic.

I don't know if this could explain it all, but here's a likely explanation for part of the discrepancy, or I expect for most or all of it:

As I think I mentioned before, the whole day is not spent at either BMR or in exercise zones.

Fitbit's lowest exercise zone, fat burning, start at 50% of your max HR, calculated as 220-age.  For a 40 year old, that would be 90 beats per minute.  So anything below that does not count as calories burned in exercise zones.

Say you are walking around with a heart rate of 80.  You are below exercise zones but are still burning many more calories than you would be lying in bed at your BMR.  So for any time between your BMR and 90 bpm, calories above BMR are not included in exercise zone.

You probably do realize you can just subtract your BMR from total calories burned to get calories above BMR, but I realize you are trying to understand the numbers.

If you want to take the effort to examine the numbers more in-depth, I find it helpful to look at the fitbit.com dashboard.

Logged into your Fitbit account in fitbit.com in a web browser, click 'Dashboard' near top right of screen.  Then look for a wide graph with 2 drop-down menus at right.  Choose 'Daily' and calories (or heart rate).  Then by dragging cursor along the graph, your can read out your calorie burn in 15 minute intervals, or hearty rate at 5 minute intervals.  You can see exactly when you burned how many calories, and note all the time calories burned above BMR but below 50% of max heart rate.

[HockeyGrl]

Just a quick thank you. Much appreciate your patience and detailed replies.