Does Garmin use Firstbeat calorie calc method when biking w/ a powermeter paired?

Hi all,

I am curious whether Fenix 5X has the same bug (feature?) as Fenix 3 HR has.

The calorie calculation of Fenix watches, both of the members of F3 and F5 families, uses the Firstbeat method as a general rule. But when you have a powermeter paired, F3HR calculates the calories burnt as being equal to the work done in kJ.

See some of my posts about it:

Just as a simple example why the 2nd gen Firstbeat method is better. Imagine you are climbing a hill with pretty high HR. Then you are at the top, some seconds later you still have high HR, but you are coasting down with a cadence of zero, so with a power of zero. Your calorie number does not change at all for minutes and minutes, even if your heart rate is being still at an elevated level.

I reported it to both Garmin support and F3 (HR) beta team, but no reaction at all. Some month later, which was 3 weeks ago I reported it to a user HermanB, who is a Firstbeat associate and present here for a while.

First he seemed to be a bit shocked and his first reaction was that I must have been wrong, he assumed that Firstbeat method had to be used always by newer Garmin watches including F3 family. He asked some time to discuss it first with his colleagues and later presumably with Garmin, but since this issue could have been checked within 3 weeks, I gave up. I dont believe I will get any clear confirmation and I dont think I will receive any help from Firstbeat guys to make Garmin fix it for F3 families.

So to cut a long story short: is there anybody het who has both a F5/5S/5X and a powermeter paired, and realized how his watch calculates calories when biking?

If not, can you please simply make a short test?

1. Bike or indoor bike app has to be started.

2. Powermeter has to be connected

3. Then please pedal backwards in order to generate zero power, but make your HR increase.

If your calories is not increasing then F5 family works the same way as F3 family.

Thanks for your help.


  • From a purely logical standpoint, it doesn’t seem like there would be a universal standard relationship between watts output per calorie consumed. I would imagine I burn more calories per watt produced than Chris Froome since my “engine” is far less efficient.

    Does Garmin use some sort of “efficiency factor” or just X Watts = Y calories burned?
  • From a purely logical standpoint, it doesn’t seem like there would be a universal standard relationship between watts output per calorie consumed.

    From another purely logical standpoint, it doesn't seem like there would be a universal standard relationship between heartbeats and calories consumed.

    As an example, a lot of runners are doing low heart rate running where they train themselves to be able to run faster at the same, low heart rate. The improvements are often 50-100% in speed. Granted, some of the explanation may be that they get more efficient. But the general explanation is that they become able to burn more fat, and the body can run on fat at a lower heart rate. How would a heart rate based calorie calculation know this?

    So to me, this is not a question of picking the correct method. It is a question of picking the least incorrect method. And neither my logical standpoint nor your logical standpoint brings us closer to that.
  • As I wrote it seems that the best method, or at least the one among those used by sport watches, is "Firstbeat method called EEHR+RespR+ON/OFF"

    Therefore it uses not just HR data, but the respiration ratio (HRV data are needed) and a third element you can find more about on Firstbeat site.
  • @Tiszful_A_Visztula, thanks so much for your info.
  • In the last 4-5 weeks I used my Fenix 3 HR without a paired powermeter, while my 910XT was always with me and my Powertap was paired with it.

    So I collected around half a dozen ride files where my Fenix 3 HR was able to use the Firstbeat calorie calculation method, but at the same time I did not have to sacrifice my power track (I mean I could add the power data from my 910XT), so using the average power I could calculate the calorie in the same way as Fenix 3/3HR/5/5S/5X calculates it from the work data.

    The difference between the Firstbeat Fenix method and the work based Fenix method was between 20.3% and 32.8%. Always the energy expenditure data coming from the Firstbeat method were the higher ones.

    So either the Firstbeat method is not realiable at all, or as I dared to say earlier the work based energy expenditure data were totally of poor quality.

    I guess there were no results of the discussion between Firstbeat people and Garmin people, because I got no feedback related any change in the approach that Garmin uses in its energy expenditure estimation.
  • This issue, confirmed by HermanB as something interesting that he had not known, and as something not even Firstbeat physiologyst had been aware of before my findings, is still open. Investigation did not result in a fix by Garmin.
  • FYKI the most accurate method of calories calculation is HRV-RR-On/Off by Firstbeat (2nd Gen Firstbeat model), the 2nd best is the one using power data , then the one which only uses HR data, but not HRV (Firstbeat 1st Gen model)

    I guess somebody at Garmin properly decided to use power data instead of HR data for calories calculation, but it had been before Garmin bought the most accurate method from Firstbeat, and everybody at Garmin forgot to modify the priority order of Fenix watches when the HRV-RR-On/Off was developed by Firstbeat and bought by Garmin.