BMR calories burnt.

[Wilderbeast]

Hi guys!

Got my Fitbit charge 3 yesterday after finally starting the healthy eating and exercise lifestyle two or so weeks ago. Made a lot of progress so far and I am a happy chap!

Question though, how does the Fitbit count calories burnt? Apparently during my 30 minute stationary bike workout yesterday (using the spinning exercise option on the charge 3) I managed to burn 504 calories. This seems quite high but I am a 22.4 stone man, 6ft 3 tall and I am 28 years of age. Does this sound right to you guys?

also, just being alive with average movement my Fitbit tells me I am burning around 2600-2900 calories per day with BMR. I have done several tests on my heart rate (fingers on the wrist) and it is crazy accurate with what my Fitbit is picking up, maybe 1 or 2 beats per minute under or over but mostly it is accurate.

Thanks guys!

[Baltoscott]

Welcome to the forums @Wilderbeast. 

Fitbit calculates calories burnt based in part on heart rate, in part on the exercise you choose when you start an activity, in part on how much movement it detects, and in (large) part on how big you are.  

Many users think it overestimates calorie burn for exercise. In my experience, that seemed to be true when I was overweight, but it seems closer to other measures now that I’m in a normal BMI range.  I like to compare what Fitbit says to this body weight planner as a ‘second opinion.’ https://www.niddk.nih.gov/bwp  Plug in your numbers and see what it says for you.

I looked at your profile and it looks like you are already losing weight, so you are off to a good start.  Keep at it.

[JohnnyRow · Accepted solution]

BMR is not "with average movement".  It is more like if you just lie  motionless in bed all day long.  Some people seem to think you are either at your BMR or actively exercising.  Any normal daily movement gets you well above BMR, even if not actively "exercising".  If you want to see what Fitbit is using as your BMR, look at you calorie burn graph overnight when asleep, or even better since just got Fitbit, look back a few days ago before you had Fitbit.  It will show the same calorie burn for every day back in the past - that is your BMR.

504 calories burned in 30 minutes is quite a bit, but certainly could be reasonable for a big guy if you were working hard and had your heart rate up.

[Wilderbeast]

That makes sense. Thank you very much for the information. I checked on multiple online calculators how much a man of my height and weight should burn (using the same exercises and roughly same intensity, including the BHF calculator) and they are all coming back with similar numbers that the Fitbit gave me so I am pretty happy with the numbers now. Taking it all with a pinch of salt of course :D.

[emili]

@Wilderbeast AND you are losing weight and becoming a healthier you. All great things. Let your little buddy do its thing in helping you achieve your goals and you.. keep up the good work and get those goals. 

[Wilderbeast]

Thank you for the motivation. Down 3lbs as of today, going to hit below 22 stone soon (fingers crossed)!

[Heybales]

Biking is one of those workouts that could be measured almost exactly for calorie burn, within 3% easily.

With a power meter.

Because calories is energy and watts is energy, it's merely the conversion.

https://www.welovecycling.com/wide/2020/05/14/how-to-convert-watts-into-calories-burned-on-the-bike/

508 calories in 30 min would imply you averaged 280 watts the entire time.

That is enormous - no way around it.

If you just started 2 weeks ago - you also didn't accomplish that sad to say.

https://www.roadbikerider.com/average-wattage-cycling/

As comment above says - this is where the formula for calories from HR can fail you - at the start of getting fit and still being overweight.

If this bike happens to give you avg watts - you can now log that workout activity manually and replace the inflated Fitbit figures.

Those workouts will help you get fit though aerobically, and while not tearing up your joints yet!

Keep up the good work.

But for keeping to the goal of losing fat weight by eating less than you burn - that is one burn that will need to be adjusted.

[JohnnyRow]

@Heybales   However, isn't it true that a power meter would measure just the work put into the bike.  The heat generated by the rider is still calories burned, but not energy put into the power meter; likewise for rider inefficiencies, and how about energy put into overcoming air resistance?

[Heybales]

The PM does - that covers all resistance to move forward, air, tire, ect.

The formula already takes into account the low 24% efficiency for human calories turned into that energy, rest is indeed lost through heat.

It does NOT take into account the BMR level burn going on at the same time. So probably 50 calories in this case for 30 min.

I'd read the first link. It is well known in cycling world and research studies that formula is going to be your almost total calorie burn for that chunk of time, missing BMR.

You stand up and balance, you are putting that energy into the power meter reading, you grip and pull on the bars more, that's energy going into the PM.