If you’re someone who uses your heart rate as a way of making the most of your workout, we have bad news: that number you’re relying on—that is, your maximum heart rate—is probably not accurate.
This number serves as the basis for all those heart rate zones and percentages that are supposed to tell you how hard you’re working, and you may even own some sort of gadget to help you keep track of it. Many people, and many devices, use a formula (usually 220 minus your age) to determine it, but as it turns out, there are problems with that formula, and even with the alternative equations that have been proposed to replace it. Here’s what you need to know.
Why use this method?
Before we go any further, what’s the appeal of this training method? According to a March 2019 article in Runner’s World, the idea is to train your aerobic system without over-stressing your skeletal and muscular systems. As Erin Carr, certified personal trainer and cofounder of Union Running in Massachusetts told the magazine:
[It] is a different way to be successful at running. It doesn’t have to be ‘no pain, no gain,’ or going as hard as you possibly can, and it allows for continued improvements over time.
Another part of the appeal, according to Joel French, Ph.D., Senior Director of Science, Fitness, and Wellness for Orangetheory Fitness (interviewed for the same Runner’s World article), is that it’s accessible and affordable, thanks to the new wave of health-tech devices. Now, we’ll take a look at where that max heart rate number is coming from, whether it’s accurate and how to find your actual maximum heart rate.
If you go higher than your max
It’s a myth that you shouldn’t exceed your maximum heart rate; that’s just an assumption people make because it’s called a “maximum.” In truth, that number is supposed to be your maximum possible heart rate—but there are problems with that idea too. As a cardiologist told the New York Times:
More than 40 percent of patients, he said, can get their heart rates to more than 100 percent of their predicted maximum. “That tells you that that wasn’t their maximum heart rate,” Dr. Lauer said.
That article tells the tale of an Olympic rower who blew his max out of the water in the first 90 seconds of a test. I also have a higher-than-usual max, which means my attempt to use a heart rate monitor failed miserably: it sounded an alert whenever I hit my “max,” and there was no way to adjust that number above 199. (My age at the time predicted a max of 192.) The dang thing was beeping through my whole workout.
By the way, if you know your max is very different from the formula, that would be important information to give your doctor if you ever need to take a stress test, since they base the test’s stopping criteria on a percentage of what they believe is your max heart rate.
More accurate formulas
You don’t have to turn every workout into a math lesson, but there are a few formulas that are more accurate, at least for some people.
If you’re not in your 20s: 207 minus 70 percent of your age worked better in tests of folks over 30, and of 10 and 16 year old boys.
If you’re female, and over 35: try 206 minus 88 percent of your age.
We previously reported on a formula that says 211 minus 64 percent of your age works well for older healthy adults, and for women.
A major caveat: Even if you pick the best formula for you (and I know, it’s not necessarily clear which one that is), the number you get will have a pretty big margin of error: it could be 10-20 beats off.
With that level of uncertainty, are formulas worthwhile? For a doctor calibrating a stress test, they’re better than nothing. For athletes, they’re probably not reliable enough to dictate your workouts.
Runner’s World, usually fond of obsessing over numbers, actually took down their target heart rate calculator in 2013 because, they write, “it has recently been proven an inaccurate measurement of the rate your heart should beat during aerobic exercise.”
If you want to be really accurate (and don’t mind working hard)
There’s a simple way to find out your actual max heart rate: Exercise really hard, and see how high the meter goes. Here are the protocols that will crank your heart up to its true maximum.
Standard disclaimer goes here: if you have a health condition where all-out exercise might be dangerous (or if you’re not sure), get a doctor’s OK before trying any of this.
Run as fast as you can stand for three minutes. Rest for three minutes, then repeat the hard run again, and note the highest reading from that second trial.
Another simple running test: Run a mile at tempo pace (hard, but not killer), then a fifth lap that’s faster, and a sixth that’s as fast as you can go, accelerating as much as you can toward the end. The highest number you see is your max.
Some runners also swear by 5k races. If you race that distance (about 3 miles) with every ounce of effort you’ve got, your highest reading toward the end of the race should be your max.
You’ll get the most accurate (highest) results if you come to the workout fresh (so don’t plan the test for the day after a hard workout), and make sure to do a long warmup that, even if it starts out easy, gets you working at moderate intensity as a ramp-up to the test.
Your max heart rate for running may be different from your max heart rate for other sports, like cycling and, most notoriously, swimming. Your heart has to work harder to pump blood around when you’re upright versus horizontal. If you determine your max heart rate with a running test, then use that to guide pool workouts, you’ll be chasing numbers you can’t actually achieve in the pool.
If you’re not up for those tests, you may wonder: does it really matter if I know my max heart rate? The truth is, you don’t have to train by heart rate, and if you have a training program that assumes you do, you can still translate its zones and percentages into descriptions of effort that you’ll know by feel.
Heart rate numbers are only as good as the training they guide you to do, so whether you should use heart rate percentages to run your workouts depends on whether those mathematically-guided workouts are helping you get faster, stronger and healthier. If you work best without numbers, that’s fine; if you do use numbers, make sure they’re accurate.
This story was originally published on 2/4/15 and was updated on 9/13/19 to provide more thorough and current information.