How to Dial-In Your Personalized Heart Rate Zones

Never has so much been given to so many. Smart watches, smart phones, and smart apps produce reams of valuable intelligence. People have so much more data than ever before at their fingertips to use—if they are smart enough to understand it and agile enough, mentally and physically, to apply it.

This is especially true with heart rate data, which can now be read by myriad devices: straps, watches, earbuds, even rings. But what do those accumulated beats per minute really tell you and how should you react? Whole books have been written on the subject—like the one we wrote: Heart Rate Training—but at a minimum, as soon as you strap on a new heart rate monitor, you need to understand some things about individual variability.

Irrational Numbers

In general, the reported numbers you see on a heart rate monitor (HRM) will be reliable, at least from a mechanical perspective, once you have followed the instructions for wearing and using your HRM. But too many people who have spent money on monitors stop using them and bury them in the back of their sock drawer.

Why? Because they are frustrated by irrational numbers that make them, for example, jog way too slow or run way too fast. After doing the math to determine their target heart rates for their exercise program, or following the pre-programmed zones, users often find that the numbers don’t seem to make sense.

The Myth of a Universal Max

What’s the story? Let’s start with the math involved with determining target heart rates (THR). Most heart rate targets or zones are based on the generic guideline that you can predict your maximum heart rate by subtracting your age from 220. Trust us when we say that is a myth. The fact is, just like so many human characteristics such as height, eye color, and intelligence, individual maximum heart rates (MHR) are naturally spread across the standard distribution of a bell-shaped curve.

With MHR, there is a wide range from one end of the curve to the other even for people of the same age. On each of the plus and minus sides of the mean is a standard distribution of roughly 12 bpm. This distribution explains that only those at the mean can reliably predict MHR by using the age-adjusted formulas. Depending on where you fall on the curve, your MHR may surprisingly be as much as 36 bpm higher or lower what the formula predicts. Whatever number of beats your very own MHR is, any error is then obviously reflected in your workout’s target heart rates.

You might be asking, “How come the myth of 220-age is so widespread?” It’s easy; it’s based on the fact that the average MHR of a brand-new baby, who has a heart the size of a walnut, is 220 bpm. And we know that as a person grows, the heart also grows.

At adulthood, the heart is about the size of the person’s fist. Naturally, it has more capacity for holding blood in its chambers. This means that more blood is pumped with each stroke (greater stroke volume), and hence, fewer beats are required at any given level of effort. By age 20, growth of the heart brings the average MHR down to about 200 (± 5 bpm).

From here on the aging process causes a further decline at the convenient rate of about one beat per year. This explains the logic of the formula 220 minus age equals predicted MHR. But it is based on the average baby, and assumes the same starting point for everyone at birth.

The bottom line: You probably need a better way to determine your own maximal heart rate—which has nothing to do with your fitness, but varies genetically, and has been unique since birth. The gold standard for finding your maximal heart rate is a treadmill stress test in a lab, where, after hooking you up to monitors, they gradually increase the speed and incline until you call uncle. Before you sign up for a graded, treadmill stress test, however, consider the following bit of reverse logic.

The Common Sense Effort Test

If you want to avoid the cost, time, pain, torture and agony of pushing yourself to a high risk, all-out, lung-searing maximal test, you can use Coach Benson’s low-rent, low-risk minimal stress test. It simply relies on the common sense of this truth: If the effort is easy and the pace is slow, your HR should be low. If not, your heart could be capable of beating faster or slower than average.

Begin your self test with the assumption that you have an average-size heart. Use the 220 minus your age formula to predict your MHR. Next calculate a target heart rate for the test by using the standard for the least amount of work and effort required for a conditioning response: 60% of MHR.

If you want to try the minimal test but have not been exercising, just try walking briskly. If you are in shape, start by jogging. In any case, if your HR accelerates quickly to your THR of 60%, forcing to you to slow down, get suspicious. If your brisk walk turns into a crawl, or your jog turns into a walk, you probably have a significantly higher than average MHR. If so, repeat the test, adding 12 beats to your target HR. If you’re still being forced into a pace that doesn’t feel like even the first level of easy exercise, keep repeating this no-sweat test until you feel that common sense rules.

On the other hand, you might find that you can’t walk fast enough and have to jog or even break into a run to elevate your HR to 60%. If your heart rate while jogging was so low that you had to break into a run to hit your target, be suspicious. If you feel like it will take a full speed sprint for a couple hundred yards just to hit 60%, stop immediately. Adjust your target down in 12 beat increments (up to as much as 36 bpm) until you feel that the test is more accurate than the age-adjusted prediction. Remember, we promised just a low-rent, low-risk minimal stress test, not an exhausting, smoke-coming-out-of-your lungs, maximal test.

Case Study

As an example, here is the older of your authors’ sample calculation: 220 bpm − 78 years old = 142 bpm x 60% = 85 bpm. This very low level of effort will normally result for him, a very, very slow jog that is an embarrassing picture of a tight, weak, mincing stride. In fact, he often hits 85 bpm during just an ambitious walk. It feels too slow to even be considered exercise.

So what might his real MHR be? He has also noticed that recent modest (but far from maximal) efforts have raised his HR to the mid 140s. He suspects a true MHR between 155 to 160 bpm, almost exactly one of those standard deviations. This would be an age-adjusted max that duplicates what real laboratory testing revealed about 50 years ago.

photo: 101 Degrees West

Perceived Effort Across Heart Rate Zones

The chart below has more extensive clues as further checkpoints to see if the ease or difficulty of a run matches up with your THR’s.

Coach Benson’s Workouts and Perceived Effort Chart

 Patiently work on calculating your own personal THR’s. If you are a frustrated early adaptor who gave up on the numbers, open up the sock drawer, unbury your monitor and try this no-sweat approach. Your heart beats have to be as exceptionally smart as your watches and apps.

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Excerpted and adapted from Heart Rate Training, 2^nd Edition, December 2019, Human Kinetics.