A Zone By Any Other Name Would Be Complete

I recently had an e-mail exchange with an athlete regarding training intensity zones. He wanted to know how he could merge the industry standard Zone 1 definition of 50-65% of maximum heart rate into the 80/20 Endurance zones. This was news to me, because after more than thirty years participating in endurance sports this was the first time I’d seen this particular definition of Zone 1. I was further surprised after using the discredited age-based calculation of maximum heart rate (220 minus age) in combination with this definition because a 50-year-old would have an upper Zone 1 of 110bpm, or the intensity equivalent of light gardening.

It’s not the first time I’ve been asked about how 80/20 Endurance intensity zones can be combined with other training systems. What was surprising was the athlete’s insistence that 50-65% of maximum heart rate was the industry standard Zone 1.

There is no “industry standard” definition of a training intensity zone (hereafter referred to as simply “zone.”) To illustrate this, look at the available zone methods within TrainingPeaks. There are at least 16 proven and credible options to choose from, all with completely different breadth and depth in their methods. TrainingPeaks even excludes popular zone methods offered by their direct competitors such as Garmin, Zwift, Stryd, and many more. I’d estimate the top eighty percent of all endurance training plan providers represent no less than forty different zone methods to choose from. And those forty methods have some serious variety. We have everything from the two-zone MAF method to the fifteen-zone Borg RPE. Further, each competing zone method might use lactate threshold, maximum heart rate, ventilatory threshold, critical velocity, threshold speed, functional threshold, resting heart rate, rate of perceived excursion or a mix of one or more as the “anchor” of the zone system.

How did we arrive at this modern-day intensity Tower of Babel? The more important question is: does it matter? (spoiler! no)

A zone is a unit of measure such as temperature, length, area, mass or volume. And just like other units of measure, zones evolved independently from necessity. About the same time Alexander the Great was using cubits to build warships, the Maurya Empire of South Asia was using a different measurement called the aṅgula. Which measurement system was better at building a boat? It didn’t matter if all the Greek craftsmen and all the Maurya craftsmen used the same system. I’m not bothered by the ever-evolving number of methods to measure exercise intensity because I and our 80/20 Endurance athletes stick to a common unit of measure.

Even when it’s evident that it’s normal (and even healthy) for multiple zone systems to exist, I still get queried as to why our Pace, Power and Heart Rate zones use different percentages. 80/20 Endurance Heart Rate Zone 1 starts at 72% of LTHR, but Power Zone 1 starts at 50% of FTP. Should they both be the same? To answer this, I’ll use temperature as an example. The following table represents the respective boiling points of water at sea level as measured by Kelvin, Celsius, or Fahrenheit, with the corresponding percentage of boiling point found at room temperature.

Kelvin Celsius Fahrenheit
Boiling Point 373 100 212
Room Temperature 294 21 70
Room Temperature as a % of Boiling Point 79% 21% 33%

Imagine that “boiling point” represents a threshold intensity (lactate, power, pace…), and “room temperature” represents Zone 1. This table provides two helpful examples. First, it re-confirms that we can use completely different units to measure the exact same intensity (does water boil at 373 Kelvin, 100 Celsius, or 212 Fahrenheit? The answer is “yes”). Second, as we go up and down the scale of a particular unit of measure, the change won’t be fixed relative to other units of measure. Just as Kelvin, Celsius, and Fahrenheit will have different proportional “room temperature” levels compared to boiling point, so will the zones for Heart Rate, Pace and Power relative to lactate threshold, threshold pace, and threshold power.

At the risk of repeating myself, no unit of temperature is “better” than another. It’s all a matter of context. If you’re an astrophysicist, it’s convenient to use Kelvin instead of Celsius. If you’re Alexander the Great, you use cubits over aṅgula. If you’re a general contractor in Cleveland, you’ll use feet instead of meters. Likewise, we don’t claim that the 80/20 Endurance zones are better than our competitors. We do claim that our zones are the most effective option when you adopt an 80/20 intensity balance.

And that’s really the bottom line. When you choose the 80/20 Endurance system, you put aside all other zone systems. Our electronic training plans make this easy because the 80/20 workouts sync’d to your device will replace any device-specific zones for that session. You can completely ignore any other zone unit of measure. Trying to mix and match zone systems is a recipe for disappointment, and even disaster. It’s like saying, “I just moved to Norway, I love it here, but I really, really, want the highway signs to be in miles instead kilometers. How can I have my new environment conform to my preference?” You can’t. Move back to Cleveland.

As the fictional character Juliet said, “A rose by any other name would smell as sweet.” Whether you choose the 80/20 Endurance zone system or another competent system, you’re likely to be just as successful: if you commit to following only one system at a time. There is no “industry standard” or “best” zone method. It’s fine to use 50-65% of maximum heart rate for Zone 1 or using cubits to build boats, but even Alexander the Great recognized the risks of mixing allegiances when he said, “Heaven cannot brook two suns, nor earth two masters.”