Buzz
If you're using a Fitbit or a compatible device like the Pixel Watch, you've likely encountered 'zone minutes' or 'active zone minutes.' But what do these terms really mean, and how do they compare to other fitness metrics like steps? Let’s explore.
Zone minutes are linked to the U.S. Physical Activity Guidelines, offering a way to monitor how well your physical activity aligns with recommended health benchmarks.
Before understanding how zone minutes are measured, it’s helpful to understand why we track minutes in the first place. Fitbit aims to give users an automated tool to track whether they’re meeting global exercise standards, such as the World Health Organization’s recommendations and the Physical Activity Guidelines for Americans, which use identical benchmarks.
As I mentioned earlier, these guidelines recommend that everyone aim for at least 150 minutes of moderate exercise each week. Activities such as walking and household chores count towards this total.
The guidelines also state that if you're engaging in 'vigorous' exercise, like running, you only need 75 minutes to meet the target. Another way to look at it is that vigorous exercise counts as double; for instance, if you've done 100 minutes of moderate activity (like walking), only 25 minutes of vigorous exercise are needed to hit your weekly goal.
While 150 minutes is a baseline, it's not the maximum target. Both U.S. and World Health Organization guidelines suggest that if you're hitting 150 minutes comfortably, you should aim for 300 minutes. In general, more exercise is better (within reasonable limits), so it's helpful to track how many minutes you've worked out each week. Fitbit can assist in tracking this for you.
Zone minutes are identified based on your heart rate.
Now let's explore where zone minutes originate and why they're called 'zone' minutes. Your Fitbit (or compatible device) can easily monitor your heart rate, and the app logs a 'zone minute' whenever your heart rate enters a range that indicates you're exercising.
There are various methods for categorizing heart rates into zones, and I have outlined the most popular systems here. Fitbit uses a system where your heart rate is classified into one of these categories, instead of just numbers: it can either be at rest or in one of these zones:
Moderate or 'fat burn': 40% to 59% of your heart rate reserve, or 50% to 69% of your maximum heart rate, depending on your device (each minute here counts as one zone minute)
Vigorous or 'cardio': 60% to 84% of your heart rate reserve, or 70% to 84% of your maximum heart rate (each minute here counts as double)
Peak: 85% or higher, based on either measurement (each minute here is counted like vigorous exercise)
To clarify, the Physical Activity Guidelines are not based on heart rate, but rather on METs (Metabolic Equivalent of Task). In the MET system, walking is always considered moderate, and jogging is always considered vigorous. (You can read more about that system here.) However, in the 'zone minutes' system, a seasoned runner may find jogging so easy that their heart rate stays in the moderate zone.
Thus, while zone minutes may not perfectly align with the guidelines, they offer a close approximation without needing to ask you about the specifics of your activity or its duration. Your device counts the minutes, and by the week's end, you can check whether you've surpassed your 150-minute target (or whatever your goal is). For instance, my app tells me I logged 349 zone minutes last week. Awesome! And I didn’t need to do anything to track them.
If the zone minutes don’t seem right, review your heart rate settings.
One of my main issues with zone minutes is that they only make sense if your zones are set up correctly. Fitbit, by default, determines your heart rate zones based on an estimated maximum heart rate, but as I’ve pointed out before, no formula can precisely determine your actual maximum heart rate. These calculations can often be off by 10 or more beats, which can throw off your zone readings.
Take a moment to review your zone minutes in the app. Are you getting ‘moderate’ zone minutes for light activities like walking and ‘vigorous’ minutes for intense exercises such as jogging? If yes, your zones are likely accurate, and you can trust they’re providing a good estimate of your exercise levels.
However, if you're receiving 'vigorous' minutes from walking or 'moderate' minutes from intense activities, it may be time to adjust your zones. Head to your profile in the Fitbit app, then select Fitbit Settings, Heart Rate, and Heart Rate Zones. From there, check the box for Custom Max Heart Rate.
This will allow you to manually enter a maximum heart rate. If you've done a max heart rate test, use that value. If not, enter the highest number you've observed during a tough workout. If your zones still seem way off, you can experiment with different numbers to see how they affect your zone readings. The goal is to ensure you’re hitting moderate minutes for moderate exercise and vigorous or peak minutes for harder activities, which will give you accurate metrics to track your activity levels.
