What Are “zone Minutes” and Why Does Fitbit Sometimes Double Them?
If you have a Fitbit or use the Fitbit app with a compatible device, such as a Pixel watch, you’ve probably seen “minutes in zone” or “minutes in active zone” pop up on your screen as a metric that the app thinks you’re worth. pay attention. So what are zone minutes and how do they compare to other ways of measuring exercise, such as steps?
Zone Minutes meet US physical activity guidelines.
Before we get into how zone minutes are measured, I think it’s most helpful to look at why we count minutes in the first place. Fitbit’s goal is actually pretty clear: They’re trying to provide you with an automated way to see if you’re meeting public health guidelines for exercise, such as the World Health Organization’s exercise guidelines and the Physical Activity Guidelines for Americans (which, conveniently, use those same numbers).
As I explain here , these guidelines say we should all get at least 150 minutes of exercise per week. The recommendation considers “moderate” physical activity, which includes activities such as walking and housework.
The guidelines also say that if you do “intense” exercise, such as running, you’ll only need 75 minutes to meet the guidelines. Another way to think about these numbers is that vigorous exercise produces double the benefits. If you’ve completed 100 minutes of moderate exercise (such as walking), you’ll only need 25 minutes of vigorous exercise to reach your weekly goal.
And while 150 minutes is a goal, it’s really just an entry-level goal. US and World Health Organization guidelines say that if you do well at 150 minutes of exercise, you should aim for the 300-minute goal. In general, the more exercise the better (within reason), so it’s useful to keep track of how many minutes you’ve exercised this week. Fitbit tracks this for you.
Zone minutes are determined based on your heart rate.
Now we can talk about where zone minutes come from and why they are called “zone minutes”. Your Fitbit (or compatible gadget) can measure your heart rate quite easily, so the app simply marks you as having passed a “zone minute” every time your heart rate appears to be in a zone that suggests you’re exercising.
There are many ways to divide your heart rate into zones, and here I provide a summary of the most common patterns . Fitbit likes to use a system where instead of numbers, your heart rate can be at rest or in one of these zones :
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Moderate or “Fat Burning” : 40% to 59% of your heart rate reserve or 50% to 69% of your maximum heart rate, depending on your device (every minute here earns you a one minute zone)
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Vigorous or “cardio” : 60% to 84% of your heart rate reserve or 70 to 84% of your maximum heart rate (every minute counts double here).
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Peak : 85% or more on any metric (here every minute is considered energetic).
To be completely clear: Physical activity recommendations are not based on heart rate, but on another measurement called MET. In the MET system, walking is always moderate and jogging is always vigorous. (More about this system here .) On the other hand, with a “minute zone” system, an experienced runner may find that running is so easy for them that their heart rate remains in the moderate zone.
So the zone minutes aren’t perfectly in line with the guidelines, but they will get you pretty close without asking what you’re doing or for how long. Your gadget will count your minutes, and at the end of the week you’ll be able to see if you’ve surpassed your 150-minute (or whatever) goal. For example, my app tells me that I logged 349 minutes in the zone last week. Big! And I didn’t have to do anything to count them.
If zone minutes don’t make sense, check your heart rate settings.
Here’s my main complaint about zone minutes: they only make sense if your zones are set up correctly. By default, Fitbit calculates heart rate zones based on your estimated maximum heart rate. And, as I explained earlier, no formula can tell you exactly what your maximum heart rate actually is . Very often these calculations are off by 10 or more strokes in any direction, messing up your zones.
So, go to your app and see how many zone minutes you earn every day. Do you get “moderate” zone minutes when you’re walking or doing light exercise, and “vigorous” zone minutes for running or doing something strenuous? If so, then your zones are probably close enough to accurate that you can assume they give you a reasonable estimate of how much exercise you’re getting.
But if you get “vigorous” minutes from walking or “moderate” minutes from strenuous exercise, you may want to adjust your zones. Tap your profile picture in the FItbit app, then select Fitbit Settings , then Heart Rate , then Heart Rate Zones, and check the Custom Max Heart Rate box.
This will allow you to manually enter your maximum heart rate. If you have performed a maximum heart rate field test, use that. Otherwise, enter the highest number you saw during a hard workout. If you haven’t put in any serious effort but your zones don’t seem right, you can experiment with entering different numbers and see how it affects your zones. As long as you get moderate minutes when doing moderate exercise and intense or peak minutes when doing heavier exercise, you get useful metrics for tracking your activity.