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The basic appeal of heart rate-based training is that it offers a scientific approach to optimize your workouts. Whether you’re putting in miles before a marathon, prepping for a big game, or simply looking to improve your overall fitness by logging time on your treadmill or your favorite cardio machine, it allows you to “train your cardiovascular system to accept the demands that you're about to put on it,” says Kyle Krupa, doctor of physical therapy and strength and conditioning coach at Kru Lab.

With the help of a heart rate monitor or trusted fitness tracker, heart rate training uses your pulse to estimate your exercise intensity: The harder your blood is pumping, the harder you're working. You’ve may have heard of the benefits of zone two training on your favorite fitness podcast—that's just the tip of the iceberg.

How to Calculate Your Heart Rate Zones

There are many systems to train according to heart rate, but the most popular divides your heart rate into five “zones.”

The most precise delineation of these zones relies on blood testing in a lab during exercise to determine your lactate threshold, the point at which lactate rapidly begins to build up in your blood. More common are methods that estimate your lactate threshold based on your maximum heart rate. You can get a very rough estimate of your max heart rate by subtracting your age from 220, but wearing a heart rate monitor during an all-our effort is more accurate. (Think something like 30 minutes as hard as possible on an exercise bike, a 500m time trial on the rowing machine, or simply racing a 5k.)

Heart rate straps, which go around your chest, are the most precise method, says Jason Sawyer, PhD, exercise and movement science program director at Bryant University. Wrist wearables also work, but they use your radial pulse, which is farther from your heart and won’t be as accurate as a strap.

Once you have your max heart rate, you can use percentages of that number to set your zones. The American College of Sports Medicine outlines the five zones like so:

Zone One (Very Light): Less than 57% of HR max

A pace that you could sustain all day. It should feel like one or two on a scale of 10. Many use this for active recovery.

Zone Two (Light): 57 to 63% of HR max

A pleasant pace that you could hold for a long time. You can maintain a conversation, but may feel out of breath between sentences. This zone works to build your aerobic base.

Zone Three (Moderate): 64 to 76 percent of HR max

This is a moderate intensity pace where holding a conversation feels difficult.

Zone Four (Vigorous): 77 to 95% of HR max

This is your threshold pace, right before you cross over into anaerobic work. It should feel uncomfortable, and you will need to push yourself mentally and physically to maintain this pace. Working in this zone is an effective way to improve your VO2 max.

Zone Five (Near Maximal): 96% and above

This is where you enter an anaerobic state. You should only be able to sustain this effort for 30 seconds to a minute.How to Train Using Heart Rate Zones

For more casual athletes just looking to get enough exercise during the week, Sawyer recommends asking yourself how much time you have during the week to dedicate to exercise. The higher the intensity, the less time you need to reap the benefits. If you are limited on time, he recommends doing zone four high-intensity interval training for 74 to 150 minutes, in line with ACSM guidelines. "If you have a bit more time or don’t like high intensity exercise, then I would recommend zone two for anywhere from 150 to 300 minutes per week,” he says. Sprints on a running treadmill would also work your heart into a higher zone, while half an hour a day on a rower or elliptical would satisfy that zone two.

But if you’re looking to train more intentionally, you can get a bit more in depth. Using specific heart rate zones at specific times can be “the special sauce for some of these high level workouts,” says Knox Robinson, a running coach and trainer at iFit. According to all experts we spoke to, the most effective training plans include workouts in both low-intensity zones and high-intensity zones—and not too much in the middle. “We need to stress our bodies to improve,” says Katelyn Tocci, a running coach and managing editor of Marathon Handbook. “If you're gonna run an hour a day every day at a moderate intensity, you're gonna have an aerobic base but you're not going to push your body. So the ideal situation is to have some easy days and some really hard days.”

Krupa recommends you tailor your heart rate training to the needs of your activity, as different zones have different energy demands. “You can’t only train zone two if 90 percent of your sport is done in zone four or five,” he adds. For example, if you want to be able to throw punches during your last round of sparring at your boxing gym, you need to work close to your lactate threshold (zone four to five) for longer intervals.

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Alternatively, if you’re training for a marathon or ultramarathon, Tocci recommends spending 80 percent of your running time at a lower intensity, like zone one or two. This seems counterintuitive to a lot of people—they don’t want training to feel that easy. But “you need a lot of low intensity training to support your hardest efforts,” says Robinson. “With low intensity, you're cultivating more red blood cells and increasing the oxygen carrying capacity of your blood. So I really, really stress everyone to learn how to jog at the lowest level.”

Tocci says that many trainers are now using rate of perceived exertion (RPE)—or how hard an exercise feels—in addition to heart rate to improve accuracy because variables like weather, altitude, caffeine intake, stress levels, hydration, and individual fitness level can impact your heart rate. (If you prefer to go device-free while lifting dumbbells and exercise based solely on perceived effort, the same principles apply.)

Overall, heart rate is one tool in your entire training repertoire—and if it prevents you from enjoying your workouts, you don’t need to use it. But if you struggle to either tone down the intensity or push your upper limits, you may want to strap on a heart rate monitor and learn a bit more about yourself.

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Hannah Singleton is a freelance journalist who writes about fitness, health, wellness, and the environment. Her work has been featured in publications such as the New York Times, Wall Street Journal, GQ, Vox, Wired, National Geographic, Forbes, and Fast Company. She earned a master's degree in environmental studies from Prescott... Read moreRelated Stories for GQRunningWorking OutHealth