How To Find Your Heart Rate Zones

For most people, cardio has a weird ambiguity to it. Once the idea of actually getting cardiovascular exercise sinks in, the questions start. How hard do I exercise? How much fat will I burn? Should I just try to burn a lot of calories? What does “doing cardio” actually mean?

The purpose of cardio: Create energy fuel cells that run on fat.

Simply put, cardiovascular exercise is continuous movements that get the blood flowing through the lungs and delivering oxygen to the tissues int he body. Basically it’s a workout for the heart and lungs. But there are some cool benefits that aren’t always talked about. 

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Mitochondria are like fuel cells in the body. They take fat and oxygen and turn it into energy. When we have a lot of them, we feel amazing and are more likely to be healthy and lean. Mitochondria are built by the body as a reaction to lower intensity aerobic workouts. During aerobic workouts, the body is producing energy using mitochondria, which takes a little while since there are several steps it has to take. I could go into the Krebs cycle here, but honestly it’s stab-me-in-the-eyes boring and hard to remember. There’s no quiz at the end of this post anyway. The word aerobic basically means “with oxygen,” and it’s important to know that not all cardiovascular workouts use the combination of fat and oxygen to make energy. 

The other way the body produces energy is by pulling it from blood sugar, and if needs more quick energy, it can even break down muscle (and sometimes bone) to create it. This is known as anaerobic exercise, which (you guessed it) means “without oxygen.” During high-intensity exercise, the body doesn’t have time to combine fat and oxygen to make energy, so it pulls from the anaerobic energy system. It should be noted that most peoples’ bodies can only store about 1,100 calories of energy in the blood and liver (our glucose reservoir), and after we burn through a portion of that, the blood sugar will drop and signal the body to make more blood sugar. This is where the body basically starts to eat itself, and breaks down muscle into blood sugar for quick energy.

Anaerobic workouts are good for making the heart stronger and increasing something called VO2 max, which is a measurement of how much work the body can do at a high intensity. High VO2 has been correlated with longevity and decreased risk of all-cause mortality. Higher intensity work is extremely good at increasing VO2 max, so it is important to get a mixture of high, medium and low intensity cardiovascular exercise.

So we need a way to measure how much work you’re doing when you do cardio. That’s where heart rate zone training comes in handy. Let’s do a brief overview of the zones, what they feel like and what they are good for.

Understanding Heart Rate Zones

Zone 1 - Easy pace. On a 1-10 (10 is hardest) scale it feels like your working between 1 and 4. Zone 1 is good for recovery, either recovery workouts or recovery between segments of more intense work within a workout. The body burns the most fat here, but also the fewest calories.

Zone 2 - Moderate pace. Should be a little more challenging, but if you were talking to someone you would be saying full sentences and not out of breath. 4 to 6 out of 10. Zone 2 is good for building mitochondria, which increases the aerobic base. This is a primarily fat-burning zone. About 80% of cardiovascular exercise should be done in Zones 1 & 2.

Zone 3 - Faster pace.  You're pushing yourself a little more. If you were talking to someone, the sentences become a little shorter and you're a little out of breath. 7 out of 10. Zone 3 builds exercise tolerance and helps us develop endurance. The body uses a bit more stored sugar as it starts to approach the anaerobic threshold (AT). About 12% of Cardiovascular exercise should be done in Zone 3.

Zone 4 - Difficult pace. Out of breath. 1-2 word sentences. 8-9 out of 10. Zone 4 helps us develop speed and strengthens the heart and further improves our ability to push ourselves. The body is above its AT and is now burning sugar as a primary fuel source. There is a benefit, because the body will burn additional fat in the hours after exercise is stopped. For most people, 8% of cardiovascular exercise time should be spent in zones 4 & 5.

Zone 5 - You might feel like you're dying. Can't speak because you have to breathe instead. 10 out of 10. Zone 5 helps us develop power and push our maximum output a little bit further. Here, the body is burning tons of calories, but zero of them are coming from fat.

Finding Your Heart Rate Zones

There are a few ways of finding heart rate zones. They vary in complexity and accuracy, but they can all be helpful.

Age and Activity Estimate

Subtract your age from the number 220 to find your estimated maximum heart rate (HR). Then calculate your zones based on these equations. 

Zone 1 - 40-65% of max HR 

Zone 2 - 65-80% of max HR

Zone 3 - 80-90% of max HR

Zone 4 - 90-99% of max HR

Zone 5 - max HR and higher (because it’s an estimate, people’s HR sometimes get higher than their “max”)

RPE Method

This is based exclusively on how your feel. It can be tricky to get used to at first, but is the most intuitive method for busy people or those who get too bogged down by crunching numbers.

Zone 1 - Feels easy.

Zone 2 - Feels easy-ish to moderate.

Zone 3 - Feels like hard work, but you can breathe easy and could still talk to your cardio buddy if you had to.

Zone 4 - Very hard work, breathing is getting more difficult, can’t manage to say more than a few words if.

Zone 5 - Feels impossible. Gulping air and waiting for the sweet kiss of death.

Metabolic Testing

This is usually done by a trained professional in a lab, but during the COVID-19 pandemic, respiratory testing in a lab setting is not something I would recommend. Pandemics aside, it can be a great option and gives the most data driven results.

Max Heart Rate Test

Outside of metabolic testing in a lab, this is where you get the most accuracy. But be advised that doing the test is a tough workout all on its own! Start out by warming up for 5 minutes or longer. After the warm up, do a tempo run for a mile or so. Start measuring at regular 1-2 minute increments (pick one and stick to it), or 400 meter increments if you are running on a track or outdoors. Use a heart rate monitor to check for intensity (heart rate) and pace (if pace is a feature) during your test. Increase your speed (or incline if walking on a treadmill) every segment. Eventually, your body will be ready to quit. Record all the data from your final segment, heart rate, speed/pace, incline, and anything else that seems relevant. Enter your data in our downloadable tool to find your zones and workloads and you are ready to go!

Want to learn more about your heart rate zones and how heart rate zone training can work for you?