When starting a fitness journey, you may hear chatter about heart rate zone training, and what zone you should stay in for particular goals. Many coaches and fitness enthusiasts promote age-predicted max heart rate equations – most commonly, using 220 minus age to determine an estimate of max heart rate.
But here’s an unpopular opinion in the fitness community: When it comes to exercise, I often trust how people feel over heart rate calculations. And that’s because age-predicted max heart rate equations can be pretty inaccurate.
Let’s dig in…
Disclaimer: This post was written by Chrissy Carroll, RRCA Running Coach, USAT Level I Short Course Triathlon Coach, and Certified Personal Trainer. It is for informational purposes only and should not be construed as training advice. Consult a doctor prior to starting any new exercise routine.
What is Age-Predicted Max Heart Rate?
As the name implies, age-predicted max heart rate is simply a type of calculation that attempts to estimate your maximum heart rate based only on your age.
The 220-age equation, the most popular equation, is known as the Fox equation. But there are actually several other equations as well…
- Gulati = 206–0.88*age
- Astrand = 216.6-0.84*age
- Nes = 211-0.64*age
- Fairbarn = 208-0.8*age (male) or 201-0.63*age (female)
- Gellish = 207–0.7*age
- Tanaka = 208 – 0.7*age
- Arena = 209.3–0.72*age
There are probably a few others floating around, but those are the main ones that have been used in exercise research, with the Fox equation being the most common.
The Problem: Equations are Not Always Accurate
Here’s the problem with any of these equations though: they can all be quite inaccurate.
In fact, a 2020 study looked at each of these and compared them to a participant’s actual max heart rate that was determined by a graded exercise test (the gold standard for determining this number). The study concluded “All equations used in this study show poor agreement between measured max heart rate and age-predicted max heart rate.”
Below is an image of the data that was published in this study. The left axis represents the difference between the actual heart rate on the test versus the age-predicted equation. In other words, if there was no difference, the dots should land on the zero line.
Do you see how much variation there is there? Most of these equations have at least 20 beat per minute variations in either direction.
In other words, if your age-predicted max was 170 bpm, it could in actuality be around 150 bpm or 190 bpm.
You’ll also notice the blue line on the graph, which points out proportional bias. A bigger slanted blue line means that the equation was more likely to under and overestimate max heart rate in people who happened to have lower and higher max heart rates, respectively. The Fox equation did have the lowest risk of proportional bias.
While equations, namely the Fox equation, can give good population level information – there is a LOT of variability from individual person to person with max heart rates. The equations are not always great for giving you an accurate estimate of your true max heart rate.
As a personal anecdote – I’m actually one of those outliers. My age-predicted max should be in the low 180’s, but in reality it’s up closer to 200 right now. This is a pretty big difference.
You might notice something similar yourself – maybe your watch tells you your max heart rate is 175, but you have noticed it go higher during interval training. Or maybe you’ve never come even close to that, even during tough intervals. Those are signs your true max could be higher or lower, respectively.
How Should You Figure Out Max Heart Rate?
So if age-predicted equations aren’t always accurate, what should you do?
For many beginners, I would not even worry about figuring out your exact max heart rate. As a coach and trainer, I think looking at how you feel can be equally – if not more – important.
For example, let’s say you’re scheduled to do an easy run. If you’re doing heart rate training, this might be a Zone 2 run, and you might have a specific heart rate number to stay below. But if you don’t know your actual max heart rate because you’re relying on an age calculation, this might not be effective. You might be working too hard or too easy, depending on if your max is lower than expected or higher than expected.
But if you flip that and go solely based on how you feel – then you’re likely going to choose the right intensity. If you feel comfortable, like you could run like this for miles and miles, and you can speak in full sentences….well then you’re probably at your easy pace!
You can also use subjective tools like RPE, where you’re rating difficulty on a scale of 1 to 10 – an easy run might fall around a 4.
If you do still want to use heart rate training (there can be value to this when done properly!), then most athletes would benefit from field tests to set heart rate ranges. Actual lab-supervised stress tests would be a more accurate method, but it’s understandable that not everyone has the ability to do these. Field tests are a good alternative though – these could include:
- Max heart rate field test, where you warm up then do several hill sprints – sprint up, jog down, repeat several times until your heart rate stops increasing at the top of the hill – this is a good estimate of max. (There are other ways to test this too, like repeated 400 meter sprints). *This is very strenuous and should not be attempted by beginners. Consult a physician before attempting.
- Lactate threshold field test, where you warm up and then run at a comfortably hard pace for 30 minutes straight (imagine the best pace you think you could sustain for an hour). You take your average heart rate from minutes 10 to 30.
Training zones can be set off either of these. Since a max heart rate field test is quite strenuous, it’s not recommended for beginners – a lactate threshold field test would be a better option. Even experienced athletes should recognize that a max heart rate field test can be stressful and potentially dangerous.
Word of Caution
If you notice your heart rate during easy exercise is higher than you’d expect, it’s always smart to check in with a doctor. There are other medical reasons for high heart rate, and it’s always good to get evaluated and make sure everything is A-OK. For some people, it may just be your genetic normal.
The Bottom Line
Age-predicted max heart rate might provide good population level data, but it is not always useful at the individual level. Subjective metrics like “conversational pace” or RPE ratings can be more useful for beginners looking for intensity guidance. If you are interested in heart rate training, field tests may provide more accurate data for you to work off of for setting training zones.
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