What are zone minutes on a Fitbit device?

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If you have a Fitbit or use the Fitbit app with a compatible device like a Pixel watch, you’ve probably seen “zone minutes” or “active zone minutes” pop up on your screen as a metric the app thinks you should pay attention to. So what exactly are zone minutes, and how do they compare to other ways of measuring exercise, like steps?

Zone minutes refer to U.S. physical activity guidelines

Before we get into how zone minutes are measured, I think it’s most useful to look at why we count minutes in the first place. Fitbit’s goal here is pretty good: They’re trying to give you an automated way to check if you’re following public health guidelines for exercise, such as World Health Organization exercise recommendationsand Physical Activity Guidelines for Americans (which, conveniently, use the same numbers).

As I explain hereThese guidelines state that we should all exercise at least 150 minutes a week. “Moderate” exercise counts toward the guidelines, which includes activities like walking and housework.

The guidelines also say that if you do “vigorous” exercise, such as running, you only need 75 minutes to meet the guidelines. Another way to think about these numbers is to treat vigorous exercise as counting double. If you did 100 minutes of moderate exercise (such as walking), you only need 25 minutes of vigorous exercise to hit your weekly goal.

And while 150 minutes is a goal, it’s really a beginner’s goal. The U.S. and World Health Organization guidelines say that if you can hit 150 minutes without a problem, you should set a goal of 300 minutes. In general, more exercise is better (within reason), so it’s a good idea to track how many minutes of exercise you’ve done this week. Fitbit tracks it for you.

Zone minutes are detected based on your heart rate

Now we can talk about where zone minutes come from and why they’re called “zone” minutes. Your Fitbit (or compatible gadget) can measure your heart rate pretty easily, so the app simply marks you as having completed a “zone minute” whenever your heart rate seems to be in the zone that suggests you’re exercising.

There are many ways to divide your heart rate into zones, and Here is a list of the most popular schemesFitbit likes to use a system where instead of numbers, your heart rate can be at rest or at one of the following these zones:

• 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 (each minute here is one minute in the zone)

• Intensive or “cardio”: 60% to 84% of your heart rate reserve or 70% to 84% of your maximum heart rate (every minute counts double here)

• Peak: 85% or more, according to both indicators (every minute here is counted with the same intensity)

To be clear, the guidelines for physical activity are: NO based on heart rate, but based on another measurement called METs. In the MET system, walking is always moderate, and running is always vigorous. (More about this system Here.) On the other hand, with the “zone minutes” system, an experienced runner may find that running is so easy for him that his heart rate stays in the moderate zone.

So zone minutes are not perfect they fit the guidelines, but they’ll get you close without having to ask you what you’re doing or for how long. Your gadget counts the minutes, and at the end of the week you can see if you’ve beaten your 150-minute goal (or whatever it is). For example, my app tells me I logged 349 minutes in the zone last week. Great! And I didn’t have to do anything to count them.

If your zone minutes don’t make sense, check your heart rate settings

Here’s my main complaint about zone minutes: They only make sense if the zones are set correctly. By default, Fitbit calculates your heart rate zones based on what your maximum heart rate is likely to be. And as I explained earlier, no formula can accurately determine what your maximum heart rate isIt is very common for these calculations to be off by 10 or more beats in any direction, which throws the zones off.

So go into your app and check the zone minutes you’ve earned each day. Are you getting “moderate” zone minutes when you’re walking or doing light exercise, and “vigorous” zone minutes when you’re running or doing something strenuous? If so, your zones are probably accurate enough that you can assume they’re giving you a reasonable estimate of how much exercise you’re doing.

But if you’re getting “vigorous” minutes from walking or “moderate” minutes from heavy exercise, you might want to adjust your zones. Tap your profile picture in the FItbit app, then choose Fitbit SettingsThen PulseThen Heart rate zonesand check the box Custom Maximum Heart Rate.

This will allow you to manually enter your maximum heart rate. If you’ve done a field test of your maximum heart rate, use that. Otherwise, enter the highest number you saw during a hard workout. If you haven’t been doing a lot of exertion but your zones seem very inaccurate, you can experiment with entering different numbers and see how that affects your zones. As long as you’re getting moderate minutes during moderate exercise and intense or peak minutes during harder exercise, you’ll have a useful metric to track how active you’re being.