How (not) to use heart rate

Driving, Data & Fitness.
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Over the Imola race weekend, I noticed that some of the Formula 2 drivers were broadcasting their heart rates. Then I read that the FIA thinks it has to be careful with the data, which is absurd. A heart rate graph with a BPM reading means nothing.

Over the last 25 years, I’ve looked at thousands of hours of heart rate data as an endurance athlete and a coach. I thought that I’d detail when heart rate is informative and when it’s not.

Think of it like RPM for an engine. If an engine is running at 6,000 RPM, is it working hard? Impossible to tell, right? For a Corvette? Sure. For an F1 car? No. It depends on the redline of the engine.

Heart rate is like engine speed, and we’re all driving different cars.

Whenever you hear a comment like, “His heart rate was X!” you can smile and ignore it. Heart rate data is only meaningful when the readings are relevant to the individual through specific testing with the proper equipment. Otherwise, it’s just cocktail party chatter.

Here’s the checklist for meaningful heart rate data:

  1. Ignore formulas. Formulas like “220 minus your age” (for maximum heart rate) don’t work. Generic formulas describe populations, but rarely individuals. I’ve worked with athletes with maximum heart rates from 160 to 212. (The 212 was 45 years old.)
  2. Don’t trust estimates. Unless a person has spent thousands of hours comparing their perceived exertion to a proper reading, estimates are just guesses. And even with lots of experience, estimates are still questionable.
  3. Record electrical activity with a chest strap. Wrist-based, optical monitors attempt to read blood flow below the skin, not electrical activity of the heart. They’re an indirect measurement and horribly imprecise. Over long sampling periods—measured in hours—the average might be close, but their precision isn’t good enough to capture short-term variation. This is especially true when the device is being jostled around like running downhill or in high-vibration environments like karting.
  4. Find a personally relevant benchmark. There are three to choose from:
    1. Aerobic threshold (most important, but hardest to measure)
    2. Maximum heart rate (little use outside of cocktail parties)
    3. Anaerobic threshold (most practical to measure)
  5. When karting, discount for heat. For every 1˚C (1.8˚F) that body temperature increases, heart rate can increase 7-10 beats. At low intensities, 10 beats is not a big deal, but near anaerobic threshold, it is. So heart rate while karting on hot summer days will bias the reading upward.
  6. Compare readings to your benchmark as a percentage. This is the only way that heart rate readings can be compared to other people. “Joe’s at 160!” doesn’t mean anything. But “Joe’s at 102% of anaerobic threshold!” does. (Formula below.)

Or, if the above is too much hassle, you can go by feel, save money by not buying trendy gadgets, and ignore all the chatter.

How to find your anaerobic threshold

There is a huge amount of variation in our own thresholds. I’ve worked with athletes with anaerobic thresholds ranging from 150 to 195. And just like RPM, higher BPM values do not reflect higher performance, just unique physiology.

The most practical way to find your anaerobic threshold is Joe Friel’s 30-minute test. Again, you need to use a chest strap and a proper monitor. The effort should be self-propelled—no treadmills—and using a movement pattern that is well-trained. Runners should not use cycling and vice versa. If neither running or cycling is familiar, then try walking uphill. (For most people, a gradual hill of 1,000 vertical feet—or a 10-storey building—will be more than enough.)

How to find how hard you’re working

In a 20-minute race, if Joe has an average heart rate of 132 and John has an average of 157, who’s working harder? With just the BPM readings, it’s impossible to tell.

But if Joe and John had chest straps and knew their anaerobic thresholds (from above), they could measure the intensity of any workout with this formula:

[average of the workout] / [anaerobic threshold] x 100 = [percentage of anaerobic threshold]

(Most training watches have percentage of anaerobic threshold built in. Trendy gadgets rarely do…)

Joe John
20-minute average (BPM) 132 157
Anaerobic threshold (BPM) 154 193
Percentage of AnT (%) 85.7 81.3

Joe, at 132 BPM, is working at 85.7% of his anaerobic threshold while John, 25 beats higher, is working at 81.3%. Although John’s heart rate is higher, his stress level is lower. But Joe, even with his lower heart rate, is working harder.

And heart rates in F1?

If the FIA ever starts broadcasting each driver’s percentage of anaerobic threshold, that would be very interesting indeed. But it would make for bad TV. I suspect the readings will be lower than the broadcasters want.

And the last thing TV needs is precision and relevance. So BPM-only readings will do nicely. The general public is none the wiser, the FIA doesn’t have to worry about “being careful,” and the teams don’t have to worry about creating any competitive disadvantages.

P.S. In 2018, I tested a Whoop against a proper heart rate monitor. I returned the Whoop for a refund.

P.P.S. If anyone goes through this process and records some karting sessions (with a chest strap), I would love to see the data.

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What’s your thoughts on elevated heart rate from adhd meds? Straterra, for example, causes elevated resting rate. I found it alarming to see resting rates 90-100ish. It seems to me that if you run at elevated revs like that, there’s a cost?

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90-100 is high from a training perspective, but it could be normal for that medication and others. That’s best answered by a doctor.

For most people, heart rates during exercise will be above that even for base training. For example, if someone had a very low maxHR of 150, a good base training range would be the low 120s.

So there may not be a negative impact on performance. But again, I would confirm that with a doctor.

It’s worth noting that sedentary doctors seem to view the absence of decay and disease as health. In my experience, doctors that are also competitive masters athletes are the most sympathetic to performance concerns. (Young athlete doctors and ex-athlete doctors often underestimate active masters athletes.)

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I have some data from… going to say 2012 ish with a peak heart rate of 196… Scared the $hit out of me. But had I not logged it, I would have been none the wiser.

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What was it measured with? If it was 2012, that was probably before optical monitors, I think? Did you measure with chest strap? Do you remember which monitor? Polar? Garmin?

Barring any health conditions, I wouldn’t worry about the high reading from an exertion point of view. I’ve seen athletes average low-190s for two hours and low-180s for six.

As another example, one of my athletes went to get a cardiac stress test done by a sports cardiologist that works with masters athletes. He finished the test without stopping—normally people quit or are stopped—and his final HRs were in the low-200s. The sports cardiologist didn’t bat an eye, but two other cardiologists were observing for professional development purposes. They were wide-eyed and surprised the athlete was fine.

But again! All of that is barring any health conditions.

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Was watching some KZ footage and the guys HR was pegged at about 190-200 from moment flag dropped till he crashed.

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It was a Garmin chest monitor. I still have the watch from it somewhere. Body temp was definitely elevated

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Love this discussion and the level of detail. I use a Garmin Swim 2 for hr, and for my daily watch, so not the best solution but I still try to log my karting hr data when I can.

Here’s one from a KZ race at NCMP last Sunday, Stars layout. Ambient temp was 86*F and fairly humid. I’m out of shape even by my “normal” standards, but wasn’t falling out of the saddle by any means. I start the watch manually before heading to the grid, so you can see where that ticks up and then I think there’s a dip during the out lap and start sequence then bazinga (race). Also forgot to shut it off until late ish, so I think the end is around that 22 minute mark.

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For comparison purposes, I will dig up my garmin and wear it for the next endurance race.

I would be very surprised if rentals create much heart rate increase. I am gonna guess it’s like a medium jog.

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Interesting timing, as i was thinking of putting my heart rate monitor on my son for this weekends race, just out of sheer curiosity.

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If I read between the lines you are basically saying that wrist wearables such as an iwatch aren’t worth the cost if I was buying specifically for heart rate?

This is an interesting subject. As a 54 year old karter and a 2-3 times a week mountain biker I believe that biking has helped my stamina in karting. I’ve never really checked my rate other than realizing when I climb while biking my heart is beating fast. So what happens when you reach your anaerobic threshold?

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Cool! Do you have the .fit file by chance? And do you mind sending it to me? (It looks like you can attach files with direct messages.)

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Yeah, my guess is that the track time was that raised plateau in the first half?

Was this recorded with a chest strap? I haven’t used a Swim 2, but it looks very similar to Garmin’s other watches that can connect with straps.

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Because rentals are slower?

My son and I just started, and we haven’t raced yet, so I’m not familiar with the demands. And we have 206s which I assume are less demanding than shifter karts?

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It depends what your goals are. Optical heart rate monitors will give you a decent average over long samples (like daily average.) But for measuring heart rate over a 20-minute stint in a high-vibration environment, I would be skeptical about what they report.

Mountain biking is pretty intense, so I’m sure your heart rates are high and it has helped your fitness. But interestingly enough, to build a really high level of fitness, the most important work is the low intensities supplemented with a little higher intensity here and there.

Nothing happens per se, it’s just the highest intensity that most people can maintain for 30 minutes on their own. (In an endurance race, people can often push for longer.) It’s a reliable enough test that it becomes a good benchmark for all other intensities.

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By my approximation, yellow is outlap, orange is race start, and red is race finish. This was recorded via the wrist unit, so just the optical sensor. I’ll have to get a chest strap at some point, as it should be compatible with the watch.

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Wow, highly unlikely I do, but I’ll do a search. Are there any other extensions I can look for?

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Interesting. Why do you think there was that big drop off at the end?

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Garmin primarily uses .fit, but .gpx might be another one.

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I had lost touch with the top 2 by that point, so I think I backed off my pace about 0.5”/lap, as I also had about an 8 second gap to P4. I was also trying to watch the leaders to see if they battled since I was out on an island with no one to race lol