Why heart rate zones on Fitbit devices are lower than general standard?

[Kat610]

Hi

Does anyone know why the heart rates zones on the Fitbit are lower than the general standard everywhere else? E.g. the fat burning zone on Fitbit is set from 50% of your max heart rate, whereas everywhere else sets it at about 70% of your max hr?? 

Kat

Moderator Edit: Clarified subject

[JohnnyRow]

1)  As for other places using 70% max heart rate as start of fat-burn zone, I suspect you are thinking of arobic zone starting at 70% of max heart rate, rather than fat-burn zone.

However, Fitbit does not use that anymore anyway.

2)  Fitbit's % of max heart rate was dropped a few years ago and is now used only on a few of the older devices.  The Versa 3 uses a more complicated formula that takes into account your resting heart rate.

What you referred to as the "general standard" is actually a less accurate simplified version that doles not take into account one's resting heart rate.

[t.parker]

@Kat610 Fitbit zones are jusy it - Fitbit zones. There is no equivalent of that anywhere else. Other platforms use rather established models like Coggan's 5-zone model. The Fat Burn zone is also rather Fitbit's idea and at best may be compared to recovery/low-aerobic zones of other HR zone models (well... not exactly). As @JohnnyRow already mentioned, newer devices use different formula to calculate zones as they use Heart Rate Reserve rather than MaxHR. HRR is MaxHR - RHR. In general, the formula is (HRR x Z%) + RHR. The Fat Burn Zone starts at 40% of HRR. My HRR is 150bpm (max 192 and RHR is 42) so this gives 40% of HRR = 60 and add RHR, which results in 102bpm. This is where my FB zone starts. This is roughly 53% of MaxHR. It's way below my warm up/recovery zones in other HR zone models though (Coggan's model's warm-up/recovery using LTHR% starts at 115bpm for me).

EDIT: I just realized the calculation above uses artificially inflated MaxHR (I don't use 220 - age, I have different way of setting up my zones and use custom MaxHR). But if I used 220bpm-43yo that would set my MaxHR to 177 and HRR to 135. Then my FatBurn would start at 96bpm.

I have a theory that Fitbit just set a lower band for zones so it is easier for users to achieve zone minutes or simply to get a credit for lower intensity activity (users don't like to see Below Zones) and since Fitbit isn't made as a training device it is a possibility that the company wanted to make a Fat Burn zone a low hanging fruit. See that majority of users are not athletes and many mostly walk.