There are several different ways to calculate target heart rate zones. The easiest is to subtract your age from 220 and use that number as your maximum heart rate. From there, you can calculate each target zone based on the percentages established for each method. This method is a good start as our maximum heart rate decreases with age. It is determined by genetics and cannot be changed. However, if your genes vary from typical, these measurements will be incorrect. The worst thing about this method is it doesn’t account for fitness.

I recently took VO2 Maximal test at an academic Physiology Lab. The test incrementally pushed me harder and harder on a treadmill until my maximum heart rate was recorded. That last minute was pretty hard, I had to push through my body telling me to slow down for almost 2 minutes. Once my heart rate reached 180, I had to keep it there long enough to confirm it wouldn’t go any higher. The test dispelled a common myth about heart rate, one that I believed up until that moment. For some reason, I assumed “maximum” heart rate meant that my body couldn’t handle heart rates beyond it, and would die. I thought of my heart like a car, that would shake, rattle, and eventually crash if it went at speeds beyond what it could handle. Turns out that’s not true at all. All “maximum heart rate” means is that your heart will not beat any faster. That’s it. That’s the maximum. At that point, other processes take control and work to slow us down. Our bodies do a superb job of keeping us intact, better than any piece of mechanics or electronics I’ve used. My blood lactate levels and ventilatory were also tested.

I spent some time looking at my maximum heart rate (which is perfectly typical, by the way) to try to understand what makes my personalized zones so personal. Note that the college uses a “4 zone” system and Garmin uses 5. The images above are from Garmin, so I had to add a “zone zero” in the zone 1 place, which is fine because zone 1 is essentially a warm-up zone for Garmin, too. My calculated fat-burning zone is 121-141. This is the zone trainers suggest endurance athletes spend most of their time training in. Garmin’s default would have me at 108-126. I would essentially make no basic endurance gains if I used Garmin’s calculations. This is a shocking difference. My resting heart rate gets closest with 130-142.

Resting heart rate calculation is spot on for the low end of the endurance zone (zone 3) at 142. But the calculation using my lactate threshold got the top end closest at 157 versus 164. Still, Garmin’s default is way worse at 126-144. The lactate threshold zone (zone 4) has some differences based on definition. Nearly all zone methods I’ve seen top this zone out at your lactate threshold. However, the college tops it out at a few beats above your lactate threshold. My lactate threshold is high for my cohort, meaning I am an endurance athlete. A sprinter would have a very different lactate threshold. Interestingly, this is estimated pretty well from my resting heart rate at 167. Even the default method, using only my age and gender for source data, got pretty close at 162. I guess the “default” person is better adapted for endurance than sprints. All charts show my max heart rate at 180 as max heart rate is static and I have no genetic anomalies changing that.

The big take home lesson here is that heart-rate-based training appears to be useless without more data beyond your age. I am very glad I took this test, even though I’m not “training” for anything in particular.