Heart rate zone limits increased from Blaze to Sense 2

[LF5]

I recently got a Sense 2 after using a Blaze watch for almost seven years. I try to keep in the "vigorous" zone when I work out on my elliptical and slow down when it gets into the peak zone. After updating the Fitbit app, the first time I did the workout with Sense 2, the average HR that used to be in the "vigorous" zone with Blaze was now only in the "moderate" zone. I checked the history of workouts using Blaze, and the heart rate zone limits all increased by 9 bmp, from 100 for the lower "vigorous" limit using Blaze to 109 using Sense 2. After I saw that, the next few times I increased my peddling rate and got an average heart rate of 123, which used to be in the "peak" range with Blaze but now is midway in the "vigorous" range on Sense 2. My resting heart rate is about the same as it always was, (about 58 - 60 bpm), and I'm almost a year older than the last time I updated the app, so those two factors couldn't have affected the calculations used to set zones boundaries.

So I'm wondering if there are other metrics used by the app besides RHR and age that go into calculating the HR zones that were not available with the Blaze such as O2 saturation and HRV on Sense 2, or if there's some other reason for the increases in the zone boundaries.

[LZeeW · Accepted solution]

@LF5   The Blaze gives active minutes and the Sense 2 gives active zone minutes.  They use entirely different equations to calculate zones.  Active minutes are no longer used as a measurement of physical activity.

[LF5]

Thanks for your answer. I guess I have to step up my peddling rate on the elliptical to keep in the "vigorous" range (which I believe used to be called the "cardio" range).

[LZeeW]

@LF5   No need to do that.  Comparing active minutes to active zone minutes is like comparing apples to oranges.  The active zone minute heart rate zones are set to be consistent with current CDC/WHO activity recommendations.  The CDC activity recommendations are a minimum of 150 minutes per week of moderate activity or 75 minutes per week of vigorous activity or a combination of the two.  Notice how you get 2x the number of minutes in the vigorous and peak zones, compared to 1x the number of minutes in the moderate zone.