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Question on Active Zone Minute calculations
d_thomas02
Posts: 9,055 Member
Just bought a Charge HR 4 and I'm trying to understand the calculations the go into calculating Active Zone Minutes.
I've found the "help" documentation on the Fitbit site, https://help.fitbit.com/articles/en_US/Help_article/1565.htm, which states:
Which is fine as far as it goes. I plug my stats into the formula (61 years old with a resting heart rate of 64) and I get the following ranges;
Peak HR 145 159 bpm
Cardio HR 121 144 bpm
Fat Burn HR 102 120 bpm
Again, fine as far as it goes. The issue is that the Active Zone Minutes screen on my fitbit app are showing much higher zones.
My resting heart rate would have to be 74 bpm to get close to the 108 number that starts the Fat Burning Zone. And my Peak Zone starts at 100% of my Calculated Max Heart Rate, not 85% as it should.
Why the discrepancy from the published formula?
I've found the "help" documentation on the Fitbit site, https://help.fitbit.com/articles/en_US/Help_article/1565.htm, which states:
HOW DOES MY FITBIT DEVICE CALCULATE MY HEART-RATE ZONES?
The formula Fitbit uses to calculate your heart-rate zones is based on your device.
OpenCharge 4, Inspire 2, Ionic, Sense, and Versa series
Fitbit personalizes your heart-rate zones using your heart rate reserve, which is the difference between your maximum heart rate* and your resting heart rate (source).
Heart rate reserve is an indication of your overall cardiovascular fitness. While your maximum heart rate is generally determined by age, your resting heart rate can be lowered by increasing your fitness level. By lowering your resting heart rate, you can increase your heart rate reserve.
For example, if you are 45 years old and your resting heart rate is 74 bpm, here’s the math:
First, calculate your maximum heart rate and heart rate reserve.
Metric Calculation
Maximum Heart Rate 175 bpm
Common formula of 220 - age (45)
Heart Rate Reserve
Maximum heart rate - resting heart rate
Target Heart Rate Per Zone (Percentage of maximum heart rate × heart rate reserve) + resting heart rate
Next, use your heart rate reserve to calculate your personalized heart-rate zones.
Heart-Rate Zone Calculation
Fat Burn Zone 114 to 134 bpm
Bottom of zone: (0.4 × 101) + 74 = 114 bpm
Top of zone: (0.59 × 101 ) + 74 = 134 bpm
Cardio Zone
135 to 155 bpm
Bottom of zone: (0.6 × 101) + 74 = 135 bpm
Top of zone: (0.84 × 101) + 74 = 154 bpm
Peak Zone 156+ bpm
Bottom of zone: (.85 × 101) + 74 = 155 bpm
Top of zone: maximum heart rate
Note that you can see your personalized heart-rate zones on the Active Zone Minutes screen in the Fitbit app.
Which is fine as far as it goes. I plug my stats into the formula (61 years old with a resting heart rate of 64) and I get the following ranges;
Peak HR 145 159 bpm
Cardio HR 121 144 bpm
Fat Burn HR 102 120 bpm
Again, fine as far as it goes. The issue is that the Active Zone Minutes screen on my fitbit app are showing much higher zones.
My resting heart rate would have to be 74 bpm to get close to the 108 number that starts the Fat Burning Zone. And my Peak Zone starts at 100% of my Calculated Max Heart Rate, not 85% as it should.
Why the discrepancy from the published formula?
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Replies
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Ohhhh - that needs to be on Fitbit's forums under your device - sounds like a bug they need to know about.0
This discussion has been closed.