Cardio fans have been all about Zone 2 training lately, but there’s another heart rate zone that you may want to pay more attention to: Zone 3 cardio.

To reach this challenging-but-doable heart rate range, you’ll have to push yourself a little harder than when you’re exercising in Zone 2. And that added effort means your endurance and stamina will grow over time. But is Zone 3 right for everyone? Here’s what you should know about Zone 3 training.

What Is Zone 3 Cardio?

“Zone 3 often equals race intensity,” says doctor and Peloton Instructor Dr. Charlotte Weidenbach. “It’s the sweet spot, meaning it shouldn’t exhaust the body too much but still leads to important physiological adaptations.” First, a quick refresher on what we mean when we talk about training in different cardio zones. The whole idea is based around the fact that as your level of effort increases in your cardio workouts, your heart rate goes up.

Using what’s known as your maximum heart rate, fitness experts sometimes categorize those efforts into five zones:

As you can see, to figure out where you fall in each zone, you first need to know your MHR. While it only provides a rough estimate, the simplest way to get your maximum heart rate is to subtract your age from 220, according to the American Heart Association. For a 32-year-old person, for example, a rough max heart rate estimate is 188. Then, you multiply that number by the upper and lower benchmarks for your zone. 

That means for that same 32-year-old, Zone 3 cardio would fall between:

You’ll likely start to feel fatigued and winded if you spend some significant time in this zone, but you should still be able to carry on a short conversation with a workout buddy. Zone 3 is considered to be a moderate intensity, according to the National Academy of Sports Medicine. Any number of cardio workouts can get you there, including brisk walking, jogging, cycling, pickleball, swimming, rowing, and more, according to the Centers for Disease Control and Prevention (CDC). It’s less about the type of workout and more about your level of intensity and effort (and therefore how fast your heart’s beating) that makes something a Zone 3 workout.

The Benefits of Zone 3 Cardio Training

There are benefits to any and all aerobic exercise, and no single zone is necessarily better than the others. “Individuals who want to improve their endurance should spend a lot of time in Zone 3, but it is not the holy grail, nor is any zone,” Dr. Charlotte says.

Still, Zone 3 has a few special perks all of its own.

It Helps Your Body Store Energy

Zone 3 training is more intense than a Zone 2 workout, so slower-burning fat doesn’t provide enough energy for that effort, Dr. Charlotte says. Instead, your body will naturally turn to carbohydrate stores for energy, in the form of glycogen in the muscles and liver. “If we train in Zone 3 and empty this storage, it is refilled in recovery between sessions,” she says.

After any form of exercise, your body changes to get used to that level of effort. “As the body adapts to higher demand, every Zone 3 session leads to more glycogen storage and therefore the ability to sustain the effort for longer,” Dr. Charlotte says. In other words, you’ll be able to store more energy and then put it to good use in longer workouts.

Of course, you’ll also need to refuel with carbs after Zone 3 training to make use of your newly improved glycogen storage capabilities. Doing so “signals the body to restore glycogen quickly and increase the amount of glycogen stored,” Dr. Charlotte says.

It Builds Endurance

In addition to storing more carbs that you can use for sustained energy,  “Zone 3 training improves oxygen consumption and lactate threshold,” Dr. Charlotte says. You’re asking your body to sustain a pretty high level of intensity during Zone 3 workouts, and if you can’t produce enough energy using oxygen alone, your anaerobic system will kick in to help. The more Zone 3 training you do, the more your body adapts to this stress, by improving the way your cells use oxygen, she explains. That means you’ll be able to last longer in your workouts before reaching this threshold—a good thing, because anaerobic efforts by definition can’t be sustained for long.

Over time, those adaptations build up to serious results: Tough workouts will slowly start to feel easier and you’ll be able to run, cycle, or swim longer before you hit the wall—helping you make progress toward your fitness goals.

It’s Doesn’t Take Too Long

Zone 3 training doesn’t require quite as much of a time commitment as lower or higher zones, both during and after a workout. For example, HIIT, because it’s so intense, “requires quite a bit of recovery time and can lead to overtraining,” Dr. Charlotte says. “Zone 2 training, on the other hand, needs to be done for longer durations, and therefore can seem boring,” she explains.

Zone 3 training is—of course—somewhere in the middle. “Zone 3 training is still intense, giving relatively quick, noticeable improvement in fitness, while [also] being less straining than HIIT,” she says.

It Improves Race Performance

More stored glycogen and improved oxygen consumption can already translate to race-day success. But Zone 3 cardio also causes some adaptations in muscle fibers that help you sustain longer efforts and get tired less quickly, Dr. Charlotte says. That’s a boon for racing and endurance workouts.

But Zone 3 workouts can also cause those same muscle fibers to produce less force, Dr. Charlotte explains. And that’s not necessarily great if your ultimate goal is to build strength. “This is the reason why it's basically impossible to be a top marathoner as well as the strongest person in the gym,” she says. “But if overall fitness is the goal, balance is key and a healthy mix of endurance and strength training will give optimal results.”

Zone 3 vs. Zone 2 Cardio

The big difference between these two steady-state cardio zones is intensity. Remember, when you’re doing Zone 2 cardio, you aim to be at 60 to 70 percent of your MHR, while when you’re doing Zone 3, you want to come in at 70 to 80 percent of your MHR.

In other words, on a scale of 1 to 10, Zone 2 will feel like a 3 or 4 effort, and Zone 3 a 5 or 6 effort, while Zone 4 will feel like a 7 or 8. As you can see, that’s pretty similar—and there is no one “best” zone for everyone. It’s all about your goals.

“I think the trend to talk so much about Zone 2 came from the fact that it improves fat metabolism, which is crucial for losing weight, but also for prevention of metabolic syndrome and many other common illnesses,” Dr. Charlotte says. “It also requires less recovery than Zone 3 training, and if an individual, even a beginner, trains a lot in Zone 2, it is very unlikely to cause overtraining or injuries,” she adds. 

That means pretty much anyone can safely do Zone 2 cardio. But a devoted Zone 3 routine requires a little more “consideration and expertise,” she says.

If this feels a little like whiplash after all the recent cheering for Zone 2, remember we’re not leaving Zone 2 behind entirely: “While a lot of people talked about all the amazing benefits of Zone 2 training, Zone 3 was spoken about less, even though it also offers great benefits,” Dr. Charlotte says. “Now that has turned, but it is important to know about and implement both Zone 2 and 3 in aerobic training.”

That’s why there’s no set amount of Zone 2 and Zone 3 training you need to see progress. Both can be considered moderate-intensity exercise, and most healthy adults need at least 150 minutes total of that kind of activity each week to stay healthy, per the CDC.

When to Use Zone 3 Training

Some running coaches and fitness experts consider Zone 3 a “no-man’s-land” or a “grey zone,” where progress actually stalls, despite the possible benefits above.

That’s typically because a lot of people accidentally end up in Zone 3 when they shouldn’t necessarily be hanging out there. For example, if you’re trying to log an easy run, you should be in Zone 2. If you’re trying to really push your pace, you probably want to be in Zone 4. If you end up muddling through lots of Zone 3 instead, you won’t reap the benefits of slow-and-steady mileage or harder, faster efforts.

This training strategy will vary from person to person depending on your fitness level and goals. And it doesn’t mean Zone 3 cardio itself is inherently bad; it just means sticking to your training plan is better.

How to Start Zone 3 Training

Ready to give Zone 3 cardio a try? The first step is figuring out your unique Zone 3 heart rate range and acquiring a method of measuring it during your efforts, like a heart rate monitor or fitness tracker.

Then, ease into it: “Beginners should start slowly, whereas people who have worked out in zones for a while can start varying and trying to test what works best for them,”Dr.  Charlotte says.

The amount of time you spend in Zone 3 differs by person and by goal. For example, if you’re training for a race that will take you at least 90 minutes, you’ll spend more time in Zone 3 to physically and mentally prepare than if your race would take less time, she says.

If you’ve only been doing Zone 2 training until now, Zone 3 will feel pretty challenging, so you might start with a few short intervals of Zone 3 efforts, she says. “These can be increased in duration when it starts to feel easier.”

And like with any fitness routine, you may find you plateau if you only train in Zone 3, or any other zone for that matter, Dr. Charlotte adds, “meaning the pace doesn't improve anymore and you might feel depleted despite training at a similar intensity than normal.”

To mix things up again, try alternating one longer Zone 2 only workout, an endurance workout based on Zone 2 but with Zone 3 intervals, and one or two HIIT workouts where you go to higher Zones (4 or 5) followed by recoveries in Zone 2 or Zone 1, she says. This gives the body diverse intensities and helps boost metabolic adaptations. 

Types of Cardio Exercises You Can Do to Reach Zone 3

Lots of types of cardio workouts can get you into Zone 3 because they allow you to ramp up your effort as needed. Check in with your heart rate monitor or fitness tracker during any of the following activities—all of which are available on the Peloton App!—and you’ll likely see you’re squarely in Zone 3 (or be able to make adjustments to get there):

The Takeaway

Zone 3 cardio refers to training at 70 to 80 percent of your maximum heart rate, or about a 5 to 6 out of 10 on a scale of perceived exertion. It should feel challenging but doable, and over time, it can improve your endurance and help your body store and use energy more efficiently. You can reach Zone 3 doing any number of cardio exercises that you enjoy. If you’re new to exercise, start with a few short bursts of Zone 3 training. If you’re more experienced, you can spend more time in this zone—especially if you’re training for a longer race or effort. That said, “there is no ideal amount of Zone 3 effort, and it will change in an individual's training program,” Dr. Charlotte says.