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A healthy dose of cardio is an important part of your exercise routine, and for a lot of us, “zone 2” cardio is going to make up a big chunk of that. Low-intensity cardio—sometimes called LISS or “zone 2”—used to be an underrated form of exercise. It’s super trendy now, after spending years on the sidelines while HIIT and lifting-only routines ran the field. But what is zone 2 cardio, exactly? How can you make sure you’re doing it right? And is it really so bad if your heart rate drifts into zone 3?
What is zone 2 training?
Zone 2 training is cardio done at a steady, low intensity. It has benefits for aerobic training (so you can run faster), anaerobic training (helping you to recover faster between reps and sets, or between intervals), and it’s also an efficient, low-fatigue way to burn calories.
“Zone 2” is a term drawn from the five-zone system of heart rate training, and the same concept is also known by other names and metrics. To runners, it is “easy pace” or “long slow distance pace.” To cyclists, it corresponds to zones 2 and 3 of a seven-zone system of mechanical power. In other sports, like swimming and rowing, it’s often just called “easy” or “low-intensity” exercise.
All that said, there is no official definition of zone 2, and different devices won’t necessarily agree with each other. The same heart rate might be “zone 2” on one device and “zone 3” on another. So please take the following with a grain of salt.
The hallmark of zone 2 training is that it’s relatively slow and that it’s done at a steady pace. You’ll be aiming for a heart rate of around 70%, but that doesn’t mean doing intervals at 90% and then resting at 50%. It means holding that 70% level the whole time you’re exercising. You can do zone 2 cardio with any steady, repetitive movement. Popular methods are running, cycling, swimming, rowing, brisk walking, fast hiking, or churning away on the elliptical. (Walking can count if you’re new to exercise; as you get fitter, you’ll probably need to choose a slightly harder form of exercise.)
To be clear, it’s still work—it’s not the same as sitting around resting—but it should feel like you could keep going forever if you wanted to. You don’t stop a zone 2 session when you get tired, you stop it because you set out for a 30- or 45- or 60-minute session, and your time is up.
What are the benefits of zone 2 cardio?
Zone 2 work builds your aerobic base. When you do cardio at this kind of easy pace, your body adapts to get more efficient at it. These adaptations are great for your health as well as your cardio fitness. You grow more capillaries (tiny blood vessels) to get oxygen and nutrients to your muscles more efficiently. You get more mitochondria in each muscle cell (you have thousands of mitochondria powering each cell) and you produce more of the enzymes that turn fuel from food into usable energy. Your heart and your lungs get more efficient at taking in oxygen and moving blood to your muscles, and your muscles become able to store more carbohydrates (in a form called glycogen) so that more of the carbs you eat are at the ready when you start a run or ride.
For runners, your zone 2 work, often called “easy pace,” should make up most (some say 80%) of your weekly mileage. The fitness you build doing easy running is what allows you to benefit from, and recover from, harder efforts like interval training.
For people whose main sport is more strength oriented (meatheads like myself), zone 2 cardio strengthens the same body systems that help us recover between sets, and even between reps. It increases our work capacity, letting us get more work done in total. As long as you’re eating enough, adding cardio into your routine should make you able to do more work in the gym, not less. (And no, cardio does not kill your gains.)
And for people who are just exercising for health, zone 2 cardio is the perfect “moderate” exercise we’re all supposed to get at least 150 minutes of per week. It’s heart-healthy, and even people with medical conditions that limit their ability to exercise can often do low intensity cardio safely. (Ask your doctor to be sure, of course.)
Importantly, zone 2 training is very low fatigue. More time-efficient forms of cardio and conditioning like HIIT, hill sprints, or CrossFit WODs are great for your aerobic fitness, but those workouts have to be high intensity to work, and you’ll be pooped afterward. They’re great in small doses, but they kind of have to be in small doses.
By contrast, easy pace work is basically free. You can work up to doing an easy zone 2 session every day, in addition to your regular training, and feel fine. Once you’re used to it, you can do zone 2 work on your “rest” days without defeating the purpose of a rest day. As long as you have the time for it, it’s like a cheat code for aerobic gains.
How do you know when you’re in zone 2?
Technically, zone 2 is defined in terms of heart rate, and the idea is that you glance at your watch and see whether you’re in zone 2 or not. (There are five zones, with zone 5 being the hardest, so zone 2 is the second-easiest). But even though “zone 2” is defined in terms of heart rate, there are so many caveats to determining your max and deciding on the zone boundaries that I don’t recommend that beginners calculate it from heart rate percentages at first. Unless you’ve actually gotten your heart rate up to a maximum effort level, and know what that number is, you don’t really know your max heart rate.
So if you’re a beginner, the best way to know if you’re in zone 2 is to ignore your watch and instead pay attention to your effort, and how it feels. On a scale from 0 to 10, where 0 is nothing and 10 is all-out sprinting, low intensity cardio is about a 3 to 5. You’re working, but not very hard. If your breath starts to get ragged, or if you feel like you’re getting pretty damn tired and you can’t wait for this to end, you’re probably somewhere 7+ and definitely going too hard for a zone 2 workout.
A zone 2 pace is conversational, and it’s sometimes described with a “talk test.” If you could tell your friend about your day while you’re exercising, you’re probably around the right level. That doesn’t mean spitting out a few words here and there, but speaking in full sentences without feeling out of breath. If you find yourself stopping to catch your breath or if you feel like you need to take break, you’re going too hard. (That said, some of zone 3 is also within that conversational zone, but it’s okay—zone 3 is still good for you.)
That said, it shouldn’t feel too easy—zone 2 is more like a brisk walk or easy jog than a leisurely stroll. If you stop, you should feel like you took a break from something. It should take a little work and focus to keep up the pace.
How do I find my zone 2?
Before you start, there’s a big caveat. Zone 2 is based on heart rate zones, and to set your zones correctly, you need an accurate max heart rate. Finding your max is a trickier task than you might expect, so you have my permission to skip this section completely, and scroll down to “How do you know when you’re in zone 2?” which will teach you how to get into zone 2 by feel, no heart rate monitor needed.
With that out of the way, I’ll explain how exactly to find your zone 2, if you want to do it by the book. There are two steps: finding your max heart rate, and then setting your zones based on that heart rate.
Find your max heart rate
Your maximum heart rate is defined as, literally, the fastest your heart can beat. (Sometimes people assume this is a guideline, that you should keep your heart rate under this number. Nope—if your heart rate is higher than the number you thought was your max, that just tells you that number was not your max.) Here are some different ways to find your max heart rate:
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A max heart rate field test (best for people with healthy hearts and some pain tolerance): There are a few ways of doing this, but basically you’re going to try to push your heart rate to its absolute max, and see what that number is. The most common way is to find a long, steep hill, and run up it three times, really sprinting hard on the last one. The number you see at the end is a good estimate of your max. Obviously, don’t do this if you’ve been told you shouldn’t exercise at high intensity.
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Your personal history (best for athletes who have experience using a HR monitor): If you’ve done high intensity exercise in the past, especially killer efforts that left you collapsed on the floor, the highest number you’ve ever seen on your watch or heart rate monitor is probably your max, or close to it. A 5K race or an FTP test will often get you close, if you really pushed yourself the whole way.
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Estimating based on easy exercise (best for non-athletes who have experience using a HR monitor): If you have a sense of what heart rate you see when you’re exercising at a steady, conversational pace, multiply the highest number you would consider conversational by 1.25 to find a number that you can use as your max. This is my own method, but it’s based on studies that have found the top of conversational pace to be around 77-79% of max. This isn’t as good as a field test, but for many people it will give a better result than the formula below.
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A formula. I don’t recommend using a formula if you have the option of using either of the first two real-world options above. Using a formula to get your max heart rate is like asking ChatGPT for your shoe size. It will give a plausible guess, but it could easily be very, very wrong. Anyway, the easiest formula is to subtract your age from 220. (There are other formulas, but honestly they all have serious inaccuracies. I wouldn’t worry about whether any one of them is “better” than the others. They all suck.)
I have more here on why max heart rate formulas are pretty much all wrong, but that’s beside the point for the moment. If you know your max heart rate, you can proceed to the next step.
Use a percentage of your max as your “zone 2”
Once you know your max heart rate (or have an estimate you’re willing to work with), multiply to get the upper and lower boundaries of zone 2. Multiply by what? Well, there’s more than one opinion out there about what zone 2 should be.
If you use a smartwatch or other device, go into the settings and set a custom heart rate (all the major brands can do this—check the instructions to find out where this setting lives.) The zones will usually populate automatically.
As I’ve written before, every device has a different idea of what should count as zone 2. If you’d like me to be the tiebreaker, I’d go with 60% to 75% of your max heart rate. So, multiply your estimated max heart rate by 0.6 to get the lower end of that zone, and 0.75 to get the higher end. For example, if your max heart rate is 200, your zone 2 is 120 to 150 beats per minute. If your max heart rate is 175, your zone 2 would be 105 to 132.
What happens if I can’t stay in zone 2?
I have good news for you: zone 3 has almost all the same benefits as zone 2. Don’t view the top of zone 2 as a barrier thou shalt not cross; it’s just a way of dividing easier exercise (zone 2) from medium intensity (zone 3). The more exercise you do, the more of it should stay in zone 2. Otherwise you could find yourself building up fatigue. After a zone 2 cardio session, you should feel good. You should feel like you totally could have done more, but you’re saving some energy for tomorrow.
So if you have a hard time staying in zone 2, don’t beat yourself up about it. Just try to keep your effort level low, on average, so you’re still fresh for the next workout. As you get fitter, you’ll find it easier to stay in zone 2.
How to run in zone 2
Runners often have trouble with this, because the dividing line between walking and running is sometimes too high to maintain an easy pace while you’re running, if you’re a beginner. The next best thing is to jog as slow as you can, and when you start to feel out of breath, switch to a brisk walk. For some people, a brisk walk for the whole session is a perfect zone 2 workout. As you get more fit, easy jogging will become possible.
Here’s a real world example of how to keep a zone 2 pace: if I’m heading out for an easy run, I start at a nice chill jogging pace. But I live in a hilly neighborhood, so pretty soon I’ll be chugging up a hill and notice my breathing getting heavier. At this point, if my heart rate is getting higher than I’d like for this workout, I switch to a power walk. Jogging the flats and walking the uphills is a great way to keep your effort level steady, instead of accidentally turning your easy jog into a hill sprint workout.
How to cycle in zone 2
Cyclists often measure their training in a seven-zone system that is based on how much power, in a physics sense, you are putting into the gears of your bike. These are called Coggan power zones, and bike training systems like Zwift and Peloton use the same basic idea. To calibrate these zones, you’ll take an FTP (functional threshold power) test—basically, a 20-minute race against yourself. From there, you (or your training app) calculates wattage numbers for your zones.
Zones 2 and 3 in this system usually correspond to our “zone 2” cardio. (Your heart rate at the end of an FTP test will be pretty close to your max heart rate, by the way, if you really went all-out.) If you train with both a heart rate monitor and a bike power meter, don’t worry if they don’t match exactly. A ride in power zones 2 and 3 will meet your low-intensity cardio needs, even if your heart rate starts in zone 1 and spikes into zone 3 by the end.
For other forms of cardio, go by feel, or by heart rate if you truly know your heart rate percentages. When you’re on the elliptical or the rower or the airbike, you should feel like you could carry on a conversation easily, and stop because time is up rather than because you’re running out of gas.
