With roughlyone in five American adults regularly wearing a smartwatch or a fitness tracker, people are becoming more and more familiar with their own heart rates — a simple measure defined by the number of heartbeats per minute. Whenmeasured at rest, heart rate can be an important health indicator (generally speaking, lower resting heart rates are associated with longer lives). And when measured during exercise, heart rate is becoming a widespread tool to plan and monitor physical activity.
Exercise programs like the one created by Orangetheory, a large chain of fitness studios, are heavily based on achieving certain heart rate zones by measuring heart rate during the workout. Their promise is that, if your heart beats fast enough, your body will continue to burn calories even after the end of the training session. Orangetheory’s heart rate–based interval training, they say, “burns more calories post-workout than traditional exercise.”
If you want to make the best out of your workout using the heart rate data on your wrist, you first need to get familiar with the concept of maximum heart rate — the fastest your heart manages to beat during an intense workout.
The ideal way to find your true maximum heart rate is an exercise stress test at the doctor’s office in which you run on a treadmill at an increasingly faster pace while your heart activity is being monitored. The test goes on until you just can’t go any faster or develop severe shortness of breath or even an abnormal heart rhythm — a sign that your heart has reached its full capacity.
Of course, most people don’t have immediate access to a stress test at the doctor’s office, and some might not even want to undergo such a strenuous test. In this case, you can rely on ready-made formulas to calculate your maximum heart rate. These formulas are based on an average of the maximum heart rate in the population and provide a rough estimate of your heart’s full capacity.
The most popular one, which has been in use for decades, is 220 minus your age. For a 30 year old, that would be 190 beats per minute. (You can find your maximum heart rate by age here.)
Over the last few years, many research teams have revisited this formula, coming up with more refined versions that better assess the heart rates of specific population groups. One of these teams was led by Thomas Allison, PhD, director of Sports Cardiology at the Mayo Clinic and professor of Sports Medicine at the Mayo Clinic School of Medicine. By analyzing data from thousands of stress tests, Allison’s teamrealized that women older than 40 can best estimate their maximum heart rate through the formula 200 minus 67% of their age.
For men of all ages, they found that the most adequate formula is 216 minus 93% of their age.
Still, the difference between the old and the newer formulas is not crucial, according to Allison. “For many ages, the differences are going to be only a couple of heartbeats,” he says.
Heart rate tracking can guide your way into losing weight or improving your performance when you exercise. That’s because heart rate is a good indicator of exercise intensity: The higher the intensity, the faster your heart beats.
According to Barbara Bushman, PhD, professor at the Department of Kinesiology at the Missouri State University and the editor of the American College of Sports Medicine’s Complete Guide to Fitness & Health, 55% of your maximum heart rate is considered a very light exercise. At about 60%, it is considered light, at 70%, moderate, and at 85%, vigorous.
The American Heart Association (AHA) considers 50–85% of your maximum heart rate to be the target heart rate zone to maximize the benefits of your workout and improve your performance in any chosen activity. And people trying to lose weight should aim at the zone’s upper limit, keeping their hearts beating at 70–85% of their maximum heart rate, according to the AHA.
Studies have also associated different heart rate zones with specific fitness outcomes. For example, there is a range in which people tend to burn more calories derived from fat (according to a 2009 study, that “fat-burning zone” lies within 59–76% of maximum heart rate). When the heart rate goes above that level, you continue to burn calories, but more carbohydrate-derived calories than fat-derived calories.
This phenomenon has been used to advocate that, in order to burn more fat, you should avoid racing your heart too much. But according to Allison, this line of thinking doesn’t make much sense. The harder people exercise (and the faster their heart races), they will burn more calories in total. Even if the percentage of fat burnt at a higher heart rate is lower than the percentage of carbohydrates, the absolute amount of fat burnt at the end will be greater.
In addition to that, studies have found that the more intense the workout gets, the longer it takes for the body to recover its normal levels of oxygen. That effect is known as the excessive post-exercise oxygen consumption (EPOC), also called the “afterburn effect.” When the body is in that state, it keeps burning calories even after the exercise session ends, which is the principle Orangetheory bases its workout program on.
There is no determined heart rate threshold that determines if you will get the afterburn effect. Butevidence suggests the higher the heart rate during exercise, the bigger the chances you will experience it.
The bottom line is: If you are focused on losing weight, research suggests to aim high in terms of heart rate, but avoid going over 85% of your maximum heart rate because of increased cardiovascular risks at that level.
Tracking your heart rate during exercise makes it easier to identify when your heart is speeding up to unsafe levels. When your heart starts beating at more than 85% of your maximum heart rate (for a 30 year old, that’s 167 beats per minute), the exercise risks increase disproportionately in comparison to the benefits in the general population, according to Barry A. Franklin, PhD, director of preventive cardiology & cardiac rehabilitation at Beaumont Health.
He says there is no reason to get close to your maximum heart rate during exercise. “You should stay below any intensity that leads to abnormal signs such as chest pain or unusual shortness of breath.”
Franklin and a team of researchers recently published ascientific statement warning about the dangers of high-intensity exercise for people who aren’t used to it, including an increased risk of sudden cardiac arrest, atrial fibrillation (a heart rhythm disorder) and heart attack. One of the document’s recommendations is to let your heart rate rise gradually by warming up and increasing the activity intensity slowly.
For people who already have cardiovascular issues, heart rate tracking can be especially important, as they may be advised not to exceed certain heart rate levels while exercising, according to Franklin. This may vary from patient to patient, so a personalized professional assessment is required.
If you’re not specifically focused on losing weight or improving your performance at a given activity, you don’t need to worry so much about tracking your heart rate while exercising. “The Surgeon General’s latestdocument on achieving good cardiovascular health is couched in terms of how many minutes of exercise you should do per week, not in the heart rate you achieve,” notes Allison.
And in case you don’t own (or want) a fitness tracker, heart rate is not the only indicator of exercise intensity. Your ability to talk or sing while exercising can be a measure of intensity.
As arule of thumb, if a person can talk but not sing while doing physical activity, the exercise intensity is moderate. If they cannot say more than a few words without pausing for a breath, that’s a vigorous intensity activity and could mean that you’ve reached 85% of your maximum heart rate.
Bushman also notes that people should be careful not to get so focused on their heart rate numbers that they lose the ability to recognize when their body tells them to slow down.
“There are days when it may be great to push intensity to improve overall fitness or in pursuit of performance goals, while other days having some recovery at a lower intensity is needed.”