Zone Minutes and Heart Rate Zones

[SunsetRunner]

There seems to be an issue with zone minutes and associated heart rate zones. In the good old days, before zone minutes caused confusion, I used to get lots of active minutes. Now, very low or no zone minutes. Based on everything I read moderate exercise falls between 50% and 70% of max HR. For me, max HR is 157. Therefore moderate activity falls between 78.5 and 109.9 BPM. So, would you not expect to get minutes for any activity in that range? Apparently not in the view of Fitbit! Having set-up my Charge 4 my fat burn zone is 106 to 123 BPM. As one only gets zone minutes in the fat burn zone, or above, I now only get minutes from 106 BPM or higher. So, I could do 150 minutes of moderate exercise and get no zone minutes. To get zone minutes I have to exercise at vigourous activity levels. Surely that cannot be correct! On 28th May the Fitbit dashboard, which still shows active minutes, showed 80 active minutes. My Charge 4 gave me 4 zone minutes. Something terribly wrong there!

[Rich_Laue]

Hi @SunsetRunner please see What are Active Zone Minutes or active minutes on my Fitbit device?

Or page 40 of your user manual that will be found in Fitbit help.

[SunsetRunner]

Hi Rich - thank you for responding.

I have read that article a number of times and fully understand the concept of Active Zone Minutes and Active Minutes. That really isn't the issue!

My point is, the bottom HR number of the fat burning zone, automatically set by the device, is 106 BPM. This is equivalent to 67% of my MHR. So in order to get any active zone minutes I have to exercise in excess of that number. As 70% of my MHR, upper threshold for moderate exercise as suggested by many organisations, including the AHA, is 109.9 BPM I need to exercise near to, or at, intensive levels (70% MHR to 85% MHR) before accruing minutes. That cannot be correct, in fact it is demoralising. This goes against the Fitbit mantra of encouraging people to do exercise.

It seems that the logic underpinning Active Zone Minutes is flawed. The device triggers active zone minutes at the lower end of the fat burning zone. For my partner and I, and probably many others, this is too high. The threshold needs to be set at 50% of the users max HR so 1 active zone minute is awarded per minute spent exercising at the moderate level. Similarly, the threshold for the award of 2 for 1 minutes should be set at >70% of the users max HR. To do anything different places Fitbit at odds with a large part of the medical advice from organisations as the AHA, Mayo Clinic and WHO.

[SunsetRunner]

Hi Rich

Please see my previous response and advise. Will Fitbit respond? Or. Is it all too difficult?

Best

Ray

[LZeeW · Accepted solution]

@SunsetRunner   The conventional heart rate zones (220 - age) only use age when calculating heart rate zones.  The equation that Fitbit uses in the active zone minute calculation is the Karvonen formula.  It is felt to be more accurate when calculating heart rate training zones because it uses age and resting heart rate to calculate heart rate zones.  This is also known as the Heart Rate Reserve (HRR) method.  

The Mayo Clinic does recognize HRR.  Scroll to about halfway down this article: Exercise Intensity: How to measure it - Mayo Clinic 

Using the 220 - age method can put many users in the 50% MPHR with minimal levels of activity, a far cry from moderate activity.  When it comes to exercise and training, I think the AHA and WHO are a little behind the times when it comes to current concepts in exercise training.

[SunsetRunner]

Ah ha! Now it makes sense.

Thank you for the link to the very informative document. I now know why the zones are different.

I've done the sums and my zones are now within a few beats of those on Fitbit. That's almost certainly down to the fact I used a morning resting heart rate of 65 whereas Fitbit uses a slightly different number.

Thanks again

Ray

[Asdffgg]

I am using a Versa Lite. It uses active minutes.  Fitbit calculates active minutes by figuring out how many Mets you are doing.  That is also an estimate.

I wanted to change my fitbit cardio and peak zones to match my Karvonen moderate zone.  But I also needed to know how many minutes I am above the Karvonen moderate zone so I can calculate those calories.

I had to assign a custom max heart rate of 184 bpm (normally 159) so the new fitbit cardio lower limit would be the top of the Karvonen moderate level I customized by creating a custom zone.

So now my custom Karvonen moderate zone is 108 to 127 (NOT 79 to 109)

and anything above 128 bpm would show up in my cardio and peak minutes which is vigorous.

Now I can calculate my calorie burns accurately using the exercise calories determined by my real life BMR test.  It took ten minutes that I did in a dietician's office.

I burn 165/:30min. calories at moderate intensity (50% to 69%), 330/:30min at high intensity (anything over 128bpm)  And if I was doing interval, high-mod-high, it would be 1.5 x 165 calories.

I hope this made sense.  The fitbit fat burn, cardio and peak zones are too low.  They are based on 220-age = X and then multiply X by the percentage for the zones. 79 to 109bpm  50-69% MHR moderate (fat burn).  111 to 134 bpm, 70% to 85% vigorous (cardio)

But Karovnen method takes into consideration heart rate reserve using your resting heart rate. 

max HR - resting heart rate = X,  multiply X by percentage you want + resting heart rate.

So now my moderate exercise is 108-127 (fat burn)

and vigorous anything over 128 (cardio and peak)

and this actually feels more like what is meant by moderate.

The trick was just getting the fitbit zones to match the new formula.  If there was a watch or chest strap that I could edit these values, I would buy it instead.  As it is now, I have to edit the exercise type, calories burned, intensity zones and sometimes the time when I forget to shut it off after exercising.

Fitbit, help us!

[LZeeW]

@Asdffgg   According to the Fitbit Blog , zone minutes are coming to the Ionic and Versa Family.  But I have no idea when it is coming.

[JWThorne]

This entirely negates moderate exercise.

It basically makes it so a walk doesn't "count". Karvonen basically only recognizes jogging and more intense exercises and entirely ignores that the energy output necessary for a 2 mile walk and a 2 mile jog are quite similar. 

[Mytym4fun]

As an alternative, I had to set my custom maximum heart rate lower (-11) in the Android app to make the Android app's heart rate zones somewhat match the Windows 10 app's heart rate zones, which were more on point to the Mayo Clinic's method.  It's not perfect but at least I am not required to exercise using a 20 year old's HR zones.  It took me a while to figure out the Windows app didn't update my tracker's settings.