Heart Rate Reserve: What It Is and How to Use It

Heart rate reserve (HRR) is a calculation you can use to find your target heart rate (THR).

It’s simply the difference between your maximal heart rate (MHR) and your resting heart rate (RHR). In other words:

Your MHR is the highest rate at which your heart can pump, and your RHR is the number of heartbeats per minute during inactivity — such as when you’re relaxing on the couch.

Summary

Heart rate reserve is the difference between your maximal heart rate and resting heart rate.

To calculate your THR, it can be helpful to know your HRR.

Your THR is useful for determining your optimal training capacity for a certain activity.

In other words, your THR will change depending on the desired outcome of the exercise. Generally, cardio exercise is divided into two types (1):

• Moderate-intensity exercise. This is an intensity you can sustain for a relatively long time with moderate effort. Your heart rate is elevated, but you can continue exercising for more than a few minutes.
• Vigorous-intensity exercise. This intensity involves a high amount of effort in a short period of time, usually a few minutes at most.

For instance, if your goal is to run on the treadmill for 45 minutes, you’ll want to make sure your heart rate is at a sustainable pace to allow you to keep going without needing a break.

Similarly, if you’re looking to do a quick 15-minute high intensity interval training (HIIT) workout, you’ll want to make sure your heart rate is high enough to reap the desired benefits.

The Physical Activity Guidelines for Americans recommend getting 150–300 minutes of moderate-intensity activity, 75–150 minutes of vigorous activity, or a combination of both every week (1).

Summary

You can use your HRR to calculate your TRR for exercising at different intensities.

To calculate your HRR, you first need to know your MHR and RHR.

Step 1: Calculate your maximal heart rate (MHR)

You may be familiar with the old way to calculate your MHR based on your age — specifically, by subtracting your age from 220.

However, this calculation was never meant for the general population, and numerous studies have shown that it’s flawed (2, 3).

Importantly, it tends to overestimate MHR in young adults and underestimate it in older adults. For example, a 20-year-old may never reach 200 beats per minute (bpm), while a 65-year-old may reach 155 bpm with no issue (2, 3).

Further, individual differences such as age, genetics, fitness level, body size, and altitude may affect your MHR. Therefore, experts discourage using this method to calculate your MHR (2, 3).

Because it can be difficult to identify someone’s true MHR, modified formulas have been developed. The Gellish formula is one of the more accurate options (2, 3, 4):

MHR = 207 – (0.7 x age)

For example, a person who is 45 years old would have an MHR of 175.5 based on the calculation above.

Step 2: Calculate your resting heart rate (RHR)

Calculating your RHR is a much easier task.

Take two fingers and place them on the radial artery on your wrist or the carotid artery on your neck while at rest. Set a timer for 30 seconds and count how many times your heart beats.

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Then, multiply this number by 2 to calculate the number of times your heart beats per minute:

RHR = heartbeats per 30 seconds x 2

For example, if you counted 36 heartbeats in 30 seconds, your RHR would be 72 bpm, calculated as 36 x 2.

If you wear a smartwatch, it may automatically calculate your RHR.

Step 3: Calculate your heart rate reserve (HRR)

Once you’ve calculated your MHR and RHR, simply find the difference between the two:

HRR = MHR – RHR

For example, a 45-year-old person with an MHR of 177 and an RHR of 80 would have an HRR of 97, calculated as 177 – 80 = 97.

Step 4: Calculate your target heart rate (THR)

Your THR is the ideal range in which your heart should be beating during a given workout, depending on the desired intensity.

You can calculate this using the Karvonen formula:

THR = (HRR x % intensity) + RHR

For example, moderate-intensity cardio exercise is estimated to be 40–59% of your HRR, while vigorous-intensity cardio exercise is 60–89% of your HRR (1).

A person with an HRR of 97 and RHR of 80 would have a THR of:

• Moderate intensity: 119–137 bpm, calculated as (97 x 0.4 or 0.59) + 80
• Vigorous intensity: 138–166 bpm, calculated as (97 x 0.6 or 0.89) + 80

Summary

To calculate your HRR, you’ll need to determine your MHR and RHR. Then, find the difference between the two. You can use this to calculate your THR for exercise.

An increase in cardio fitness can increase your HRR.

First, it can help lower your RHR, which means your heart gets stronger and does not have to work as hard to pump out blood (5).

Second, it may help increase your MHR, which means you can exercise at a higher intensity for longer. However, this is largely determined by your age, genetics, and other factors such as diet, smoking, or medications, so it is harder to change (6).

By increasing your MHR and lowering your RHR, you’ll have a larger HRR. Ultimately, this could mean you’ll be able to reach a higher THR.

To achieve these results, focus on improving your cardio fitness through a combination of moderate-intensity and vigorous-intensity exercise.

If you’re new to exercise, be sure to start off slowly and incorporate mostly moderate-intensity exercise a few times per week (1).

For some people, moderate-intensity exercise may be a 5–10-minute walk. For others, it may be an hourlong bike ride. Generally, start with your current fitness level and work toward making gradual improvements (1).

As you improve your fitness, you can gradually add vigorous-intensity exercise a few days per week. However, consult a healthcare professional first if you have any underlying medical conditions, such as heart disease (1).

You’ll be able to tell your cardio fitness is improving by looking at changes in your RHR and noticing how much longer you can sustain exercise.

Summary

You can improve your HRR by increasing your cardio fitness. It’s best to do a combination of moderate- and vigorous-intensity exercise each week.

If you don’t want to calculate your HRR, there are other ways to determine whether you’re working at a moderate or vigorous intensity.

One of the easiest tests you can use is the talk test. If you can carry out a conversation and speak comfortably, you’re likely exercising at a moderate intensity. If you have trouble speaking for long or can’t speak at all, you’re likely at a vigorous intensity (1).

Another useful measure of exercise intensity is the rate of perceived exertion (RPE) scale, which has been used as a quick tool to measure the level of intensity (1, 7).

Two forms of this scale exist. The first is the Borg scale, which ranges from 6–20. The second is the modified RPE scale, which is based on the original Borg scale but ranges from 1–10. The latter is generally easy for the average person to understand (1, 7, 8).

Modified RPE scale:

• 0–2: limited effort; not out of breath — e.g., sitting in a chair, watching TV, walking to the kitchen
• 3–4: moderate effort; breathing slightly heavier but can do this activity for a long time — e.g., going for a long walk, doing household chores
• 5–6: high effort; breathing heavier and can carry on a short conversation — e.g., light jog, brisk walking
• 7–8: very high effort; breathing may be uncomfortable, and you cannot sustain the exercise long — e.g., fast-paced running, cycling, playing singles tennis
• 9–10: extremely high effort; breathing fast, unable to talk, and may feel like you can’t go much longer — e.g., all-out sprinting, some HIIT exercises

Generally, a rating of 5–6 is considered moderate-intensity exercise, while a rating of 7–8 is considered vigorous. In some cases, you may reach 9 or 10, but you won’t be able to sustain it long (1).

Though it has its limitations, RPE can be a simple, quick tool to determine which intensity level you’re at and whether you need to adjust your exercise (9).

Summary

The talk test and the RPE scale are two convenient alternatives to determine the intensity level of your workout without having to do any calculations or heart rate measurements.

Your heart rate reserve is simply the difference between your maximal and resting heart rate.

It can be useful to know your HRR when determining the intensity of your workouts to see whether you’re reaching the desired intensity. However, it requires a bit of math to find out.

Other options are the talk test and the rate of perceived exertion scale, which are more subjective to the individual and easy to use.

If you’re looking to improve your cardio fitness, make sure to get in a combination of moderate- and vigorous-intensity exercise every week.