Buzz
This article is part of Find Your Fit Tech, Mytour's guide to purchasing fitness wearables. I explore challenging questions about whether these devices truly enhance health, how to choose the right one, and how to maximize the insights they provide.
The fitness community generally uses the term “Zone 2” to refer to the moderate-intensity cardio that is essential for regular exercise. In this zone, your effort level is sufficient to increase your breathing rate but still allows for conversation. You conclude a Zone 2 workout based on time, not because you’re completely drained.
However, there’s no consensus on the exact heart rate range that defines Zone 2, leading to differing opinions.
Understanding Zone 2 Training
As previously mentioned, the term “zone 2” originates from heart rate-based training. To train using heart rate, you can use a wristwatch equipped with an optical heart rate sensor (the green light on the back) or a chest strap synced to your watch or phone (chest straps are more precise, and I suggest a reliable $25 option here).
Heart rate training involves maintaining your heart rate within a specific “zone” to achieve your workout goals. Most popular systems categorize heart rate into five zones. Zone 1 is for rest or recovery; zone 2 is for low-intensity cardio; and zones 3, 4, and 5 are for higher-intensity efforts, typically performed in short bursts with recovery periods in zone 1 or 2. (For a more in-depth explanation of the zone system, check here.) While zone 2 is currently popular, the other zones remain valuable. Personally, I believe zone 3 is underappreciated, and a combination of zones 2 and 3 might be more beneficial for steady cardio than focusing solely on zone 2. But that’s a discussion for another day.
Heart rate zones are typically calculated as percentages of your maximum heart rate. For instance, when I configure my Apple Watch for zone 2 during runs, it targets a heart rate between 60% and 70% of my maximum. Even at a relaxed pace, I often surpass this limit. Conversely, on a Peloton bike, my heart rate frequently stays in zone 1 despite feeling like I’m exerting a zone 2 effort. This discrepancy arises because Peloton defines zone 2 as 65% to 75% of maximum heart rate.
So, who’s correct? Essentially, everyone. The term “zone 2” lacks scientifically defined boundaries, allowing anyone to divide heart rate zones as they see fit. (Keep an eye out for my innovative eight-zone system, launching once I figure out how to monetize it!) If you use multiple devices or discuss heart rate training with someone using a different system, understanding these variations is crucial.
What Percentage of Heart Rate Defines Zone 2?
Let’s explore some of the leading wearables and fitness systems that utilize a five-zone heart rate model or something similar.
First, it’s crucial to understand that most (though not all) of these percentages are derived from your maximum heart rate. Determining your max heart rate requires a real-world test, not just relying on a formula. For instance, one formula estimates my max heart rate at 178 bpm, while another suggests 169 bpm. In reality, I’ve recorded up to 207 bpm during runs and 198 bpm on a spin bike. (Interestingly, your max heart rate can vary depending on the type of cardio. For example, swimming might result in a lower max heart rate since being horizontal makes it easier for your heart to circulate blood.)
Other systems also exist. “Heart rate reserve” (HRR) involves calculating the difference between your max and resting heart rate (rather than max and zero) and using that as a baseline. Some devices estimate benchmarks like your lactate threshold and use that to define zones.
Here are the zone 2 percentages from various popular wearables, along with what they are based on:
Apple Watch: Zone 2 is defined as 60-70% of your heart rate reserve. Your “resting” heart rate is either set to 72 or automatically detected by the watch, while your maximum is calculated using the 220-age formula. (You also have the option to manually adjust the zones.)
Fitbit: Instead of “zone 2,” Fitbit uses a "moderate" zone (previously called “fat burn”), ranging from 40% to 59% of your heart rate reserve. Your max heart rate is determined by the "220 minus age" formula, and your resting heart rate is measured by the device. Manual adjustments for max heart rate and zones are available.
Garmin: The definition of zone 2 varies based on your device and settings. As a percentage of max heart rate, it’s 73-81%. For heart rate reserve, it’s 65-75%. If using lactate threshold heart rate (automatically detected by the watch, typically between zones 4 and 5), it’s 79-88%. These percentages may not align across systems, meaning a heart rate in zone 2 on one system could fall into zone 3 on another. Manual customization of max heart rate and zones is also possible.
Several other fitness platforms have their own definitions for heart rate zones. Here are a few examples:
Orangetheory: Named after the “orange” zone it emphasizes during workouts, its equivalent of zone 2 is the “blue” zone, set at 61% to 70% of max heart rate. Max heart rate is calculated using an “industry standard formula” (208 minus 0.7 times your age). After 20 classes, an algorithm adjusts your max heart rate.
Peloton defines heart rate zone 2 (distinct from Power Zone 2) as 65% to 75% of your max heart rate. The default max is 220 minus your age, but you can manually adjust it in settings.
The American College of Sports Medicine defines “light” training (its version of zone 2) as 57% to 63% of max heart rate, while “moderate” training is 64% to 76%.
How do you determine which benchmark to follow?
Instead of fixating on specific numbers, focus on the overall goal of your training and the outcomes you aim to achieve.
If your goal is to enhance endurance through low-intensity cardio or accumulate time in this zone for weight loss, the exact heart rate number isn’t critical. What’s important is maintaining an effort level that allows you to exercise for extended periods without exhaustion, while ensuring you’re not underworking either.
In short, while your device’s heart rate metrics can serve as a helpful guide, it’s essential to balance them with a practical assessment known as “perceived exertion” in fitness terms. For a measurable target, you can use a 1-to-10 scale (RPE, or rating of perceived exertion) and aim for a score of around 3 to 4.
With time, you’ll recognize the heart rate range that aligns with your desired effort level. For instance, I’ve observed that a heart rate in the 150s indicates a solid “zone 2” jogging pace. If it climbs into the 160s early in a run, it’s likely too intense for my goal—but reaching 160 at the end of a long, hot run is acceptable. (This variation, known as cardiac drift, occurs due to factors like temperature and workout duration.)
In the end, the most reliable approach to using heart rate for exercise intensity is to first define your desired effort level, then use heart rate as a tool to consistently achieve it. If there were a universally accurate and easy-to-determine number, all devices and platforms would have adopted it by now. So, trust your body’s signals over your watch’s data.
