Questions about heart rate accuracy.

[orpheus321]

I recently upgraded to a Versa 3 after my old Charge 2 finally gave up the ghost after years of good service. Since using the Versa 3 though I have become concerned about the accuracy of the heart rate readings. Although my daily activity levels have not changed it's clear from the screenshot that the readings between the two devices show huge differences: 

 You can see, to the day, when I switched devices. How can this discrepancy be explained, and which figures can I trust? 

[Guy_]

Hi @orpheus321 - unfortunately the Versa 3, or later, has a new technology heart rate sensor which is notorious for giving inaccurate readings during some exercises or repetitive movements. Your graph clearly demonstrates this.

[LZeeW · Accepted solution]

Hello @orpheus321 and welcome to the Community.  This discrepancy is fully explained by the fact that your Charge 2 awarded active minutes and the Versa 3 awards active zone minutes.  The heart rate thresholds for fat burn/cardio/peak active minutes and active zone minutes are completely different.

Fitbit's Help article, How do I track heart rate with my Fitbit device?, explains the difference in methodology.  The active minute fat burn zone starts at 50% of your maximum heart rate for your age.  The active zone minute fat burn zone is actually different between two people the same age, because the equation uses your resting heart rate.  The Help article gives an example of a 41 year old with a RHR of 74 bpm.  Wearing a Charge 2, the fat burn zone starts 88 bpm.  Wearing a Versa 3, it starts at 114 bpm.

It's true that different optical heart rate monitors have different accuracy.  You can judge your experience by looking at heart rate graphs for similar workouts on the two different devices.  Without additional information, this graph only clearly demonstrates the difference between tracking active minutes and active zone minutes.

[orpheus321]

Hi LZeeW,

Many thanks for your reply - very helpful. I think I've got my head around the different zone calculations and that certainly explains most of the dramatic change on the graph I posted. I do still have the impression though that the maximum heart rates are slightly lower with the Versa 3 than with the Charge 2 but I will try to monitor that using other metrics.