Buzz
Low-intensity cardio, also known as LISS or 'zone 2,' was once an overlooked form of exercise but is now making a resurgence after years of being overshadowed by HIIT and strength-based routines. So, what is zone 2 cardio? How can you be sure you're performing it properly? And does it really matter if your heart rate occasionally drifts into zone 3?
What defines zone 2 training?
Zone 2 training involves cardio performed at a consistent, low intensity. It provides benefits for both aerobic conditioning (helping you run faster) and anaerobic performance (assisting with faster recovery between reps and intervals), and is also an efficient, low-fatigue method for burning calories.
"Zone 2" refers to a specific range within the five-zone heart rate training system, though it’s known by different names in various sports. For runners, it’s often referred to as “easy pace” or “long slow distance pace.” In cycling, it aligns with zones 2 and 3 of a seven-zone mechanical power system. Other sports, like swimming and rowing, tend to label it simply as “easy” or “low-intensity” exercise.
That said, there isn’t a universally accepted definition of zone 2, and devices may not always match up. For example, the same heart rate could be labeled as "zone 2" on one device but "zone 3" on another. So, take the following information with a pinch of salt.
The key feature of zone 2 training is its steady and relatively slow pace. You’ll target about 70% of your maximum heart rate, which means maintaining that intensity for the entire session, without fluctuating between high-intensity intervals and recovery. Popular forms of zone 2 cardio include running, cycling, swimming, rowing, brisk walking, hiking, or using the elliptical. Beginners can start with walking, but as you build fitness, you'll likely need to engage in more challenging activities.
To be clear, zone 2 is still considered work—it’s not like lounging around. However, it should feel sustainable, as though you could keep going indefinitely if you chose to. A zone 2 session doesn’t end because you’re exhausted; it ends because you’ve completed the time you set for yourself—whether that’s 30, 45, or 60 minutes.
How can I determine my zone 2?
I'll give you the quick answer, but keep in mind that there are some important caveats, which I’ll address in more detail later. Consider this formula as providing rough estimates, and then I'll explain how to personalize it for your actual body, which may not align with the standard formulas. There are two main steps:
Determine your maximum heart rate
Your maximum heart rate is essentially the fastest your heart can beat. (Some people mistakenly think this is a target to stay under. Not the case—if your heart rate exceeds the number you thought was your max, that simply means it wasn't your max after all.) Here are some ways to figure out your max heart rate:
Max heart rate field test (ideal for those with healthy hearts and tolerance for discomfort): There are several methods, but the basic idea is to push your heart rate to its limit and see the result. A common approach is to find a steep hill and run up it three times, sprinting at full intensity on the final run. The highest number you hit will be a solid estimate of your max. Don’t attempt this if you've been advised to avoid high-intensity exercise.
Your personal experience (best for athletes familiar with using a heart rate monitor): If you've previously done high-intensity exercise, particularly intense efforts that left you wiped out, the highest reading you’ve seen on your watch or heart rate monitor is probably your max, or very close. A 5K race or an FTP test can also get you pretty close, especially if you pushed yourself the whole way.
Estimating from light exercise (best for non-athletes with some experience using a heart rate monitor): If you have an idea of the heart rate you hit during easy, conversational exercise, multiply the highest number you’d consider “conversational” by 1.25. This is based on studies showing conversational pace is around 77-79% of max. It’s not as accurate as a field test, but it can be better than the formula below for many people.
A formula: I strongly discourage using a formula if you have the option to use one of the real-world methods above. Relying on a formula to determine your max heart rate is like asking for your shoe size—it may give a reasonable guess, but it’s likely to be way off. The most common formula is to subtract your age from 220. (There are other formulas, but all of them have significant flaws. Don’t worry about which one is 'better'—they all have issues.)
I have additional details here about why most max heart rate formulas are flawed, but for now, let's move past that. If you already know your max heart rate, you can move on to the next step.
Use a percentage of your maximum heart rate to define your 'zone 2.'
Once you have your max heart rate (or a reliable estimate), multiply it to find the upper and lower limits of zone 2. How do you decide on the right percentage? There’s more than one school of thought on where zone 2 should be.
If you're using a smartwatch or another heart rate monitoring device, head into the settings and set a custom heart rate zone (most major brands offer this—check your user manual to see where this option is). The zones will typically be set up automatically.
As mentioned before, every device has its own interpretation of what constitutes zone 2. If you're looking for my recommendation, I’d suggest going with 60% to 75% of your max heart rate. To find the boundaries, multiply your max heart rate by 0.6 for the lower limit, and by 0.75 for the upper limit. For instance, if your max heart rate is 200, your zone 2 would range from 120 to 150 beats per minute. If your max heart rate is 175, your zone 2 would fall between 105 and 132 bpm.
What advantages does zone 2 cardio provide?
Zone 2 training is essential for building your aerobic base. By exercising at this easy pace, your body adapts by developing more capillaries (tiny blood vessels), improving the efficiency of oxygen and nutrient delivery to your muscles. You also gain more mitochondria per muscle cell to provide energy and increase the production of enzymes that convert food into usable energy. As a result, your heart and lungs become better at absorbing oxygen and circulating blood, while your muscles store more carbohydrates in the form of glycogen for faster energy use during physical activity.
For runners, the majority of your training, often referred to as 'easy pace' or zone 2, should comprise most of your weekly mileage—some say up to 80%. The fitness gained from this easy running is the foundation that supports your ability to handle, and recover from, more intense exercises like interval training.
For those focused on strength training (like myself), zone 2 cardio improves the same systems that enhance recovery between sets and even reps. It boosts your overall work capacity, allowing you to get more done. As long as you consume enough fuel, adding cardio to your routine can help you perform better in the gym, rather than hinder it. (And no, cardio does not destroy your gains.)
For those exercising primarily for health, zone 2 cardio provides the ideal 'moderate' activity that we're all encouraged to do for at least 150 minutes each week. It's great for heart health, and people with medical conditions that might limit their exercise can often safely engage in low-intensity cardio. (Always check with your doctor first, of course.)
An important aspect of zone 2 training is its very low-fatigue nature. Although more time-demanding cardio activities like HIIT, hill sprints, or CrossFit WODs are excellent for boosting aerobic fitness, they require high intensity, and you'll likely feel exhausted afterward. These workouts work best in smaller doses, as they're inherently designed to be intense.
In contrast, easy pace work is essentially free. You can gradually build up to doing a zone 2 session every day, alongside your usual training, and still feel fine. Once you're accustomed to it, you can incorporate zone 2 work into your 'rest' days without undermining the recovery purpose of those days. As long as you have the time, it's like unlocking a cheat code for improving your aerobic capacity.
How can you tell when you're in zone 2?
The most reliable way to know you're in zone 2 is to focus on your effort level and how it feels. While 'zone 2' is often defined by heart rate, there are so many variables in calculating your maximum heart rate and zone boundaries that it's not ideal for beginners to rely on heart rate percentages initially. Unless you’ve actually pushed yourself to your maximum effort and know your top heart rate, you don't truly know your max heart rate.
Instead, let's focus on how it should feel. On a scale from 0 to 10, where 0 means no effort and 10 is full sprinting, low-intensity cardio typically falls between 3 to 5. You’re working, but it's not overly taxing. If your breathing becomes ragged or you feel overly fatigued, wishing the session would end, you're likely past a 7+ and pushing too hard for a zone 2 workout.
A zone 2 pace is conversational, often referred to as the 'talk test.' If you can chat with a friend about your day while exercising, you're likely at the right intensity. This doesn’t mean only uttering a few words, but being able to speak in full sentences without gasping for air. If you find yourself stopping to catch your breath or needing a break, you're likely pushing too hard. (That said, part of zone 3 falls within this conversational range, but that's okay—zone 3 is still beneficial.)
That being said, zone 2 shouldn't feel too easy—it should be more like a brisk walk or an easy jog, not a slow, relaxed stroll. When you stop, you should feel like you've taken a break from something. It takes a bit of effort and concentration to maintain that pace.
Running
Runners often struggle with this because the gap between walking and running can be too wide to sustain an easy pace, especially for beginners. The best alternative is to jog as slowly as you can, and if you feel winded, switch to a brisk walk. For some, a brisk walk throughout the entire session might be a perfect zone 2 workout. Over time, as your fitness improves, easy jogging will become more manageable.
Here’s a real-world example of how to maintain a zone 2 pace: if I’m going for an easy run, I start with a relaxed jog. But since I live in a hilly area, I quickly find myself running uphill, and my breathing starts to intensify. If my heart rate climbs higher than I want for this workout, I switch to a power walk. Jogging the flat stretches and walking up the hills is an excellent strategy to keep your effort level consistent, rather than unintentionally turning your easy jog into a hill sprint.
Cycling
Cyclists typically track their training using a seven-zone system based on the amount of power, in a physics sense, being applied to the gears of the bike. These are known as Coggan power zones, and platforms like Zwift and Peloton follow this same general framework. To establish these zones, you’ll need to take an FTP (functional threshold power) test, essentially a 20-minute race against yourself. From this test, you (or your training app) can then determine the wattage numbers that correspond to your various zones.
In this system, zones 2 and 3 typically align with what we think of as ‘zone 2’ cardio. (By the way, your heart rate at the end of an FTP test will be very close to your maximum heart rate, assuming you really gave it your all.) If you use both a heart rate monitor and a power meter on your bike, don’t be concerned if they don’t align perfectly. Riding in power zones 2 and 3 will still fulfill your low-intensity cardio requirements, even if your heart rate starts in zone 1 and climbs into zone 3 by the end of the session.
Other cardio
For different types of cardio, rely on how it feels or use heart rate if you are familiar with your heart rate zones. Whether you’re on the elliptical, rower, or airbike, you should be able to maintain a conversation without issue and stop when your allotted time is up, rather than because you’re running low on energy.
