Endurance Athlete Training Zones: What is Zone X and Zone Y?

Athletes often bring their own definitions of training zones with them, whether from devices, coaches, or articles they’ve read online. One version I’ve encountered more than once claims that Zone 1 should fall between 50–65% of maximum heart rate.

Plug that into the old 220-minus-age formula, and you get some surprisingly low numbers. For a 50-year-old, that’s an upper limit of just 110 bpm—barely a brisk walk.

And yet, I’ve had this type of question many times: “Can I combine 80/20 zones with [insert other system]?” What stands out isn’t just the question—it’s the assumption that one specific version of Zone 1 is the standard.

 

Here’s the truth:

There. Is. No. Industry. Standard.

 

The Training Zones System: Tower of Babel

Let’s take a look at TrainingPeaks. There are 16+ training zones built in—and that doesn’t even include zones from Garmin, Zwift, Stryd, Polar, or a dozen other platforms! From two-zone approaches like MAF to 15-zone RPE scales, every method has its own rules, thresholds, and language.

Why so many? Because a training zone is a unit of measurement, like temperature, distance, or weight. And just like how different cultures historically measured with cubits, aṅgula, feet, or meters, different training philosophies evolved their own scales to measure intensity.

None of these training zones are inherently wrong. But trying to mix them is like measuring the same room using both cubits and meters. It’ll get messy fast.

 

So What Makes the 80/20 Training Zones System Different?

The 80/20 Endurance training zones system is anchored in the proven principle that you should do about 80% of your training at low intensity and 20% at moderate to high intensity. The exact training zones help you stay in those lanes. You can figure out your own 80/20 Endurance training zones with our 80/20 Endurance Zone Calculator.

 

Here’s where it gets interesting: to make this easy (and to stop the slow drift toward “always kinda hard” training), we built in guardrails, specifically:

• Zone X: The danger zone. Not easy enough for true low-intensity training, not hard enough to build fitness. It’s the gray zone where many athletes accidentally live.

• Zone Y: Intense, but not maximal. Above threshold, but not all-out. It’s where deliberate, focused, hard efforts live—just not every day.

These zones aren’t “extras”—they’re critical to keeping your training polarized and purposeful.

 

But Why Don’t All Training Zones Use the Same Percentages?

Some athletes get tripped up comparing our training zones across different intensity types: “Why does 80/20 Heart Rate Zone 1 start at 72% of LTHR, but Power Zone 1 starts at 50% of FTP?”

Let’s break it down with a temperature analogy:

Same water. Different scales. The key? Pick one and stick with it.

 

Choose Your Training Zones System—and Commit

At 80/20 Endurance, we’re not claiming our training zones system is better than others. We’re saying it’s built to support the 80/20 training principle, and it works best when used on its own, not mashed together with other systems.

If you follow an 80/20 training plan, your structured workouts will automatically override any default device training zones. You don’t need to compare or combine—you just follow the workout as it’s given. No translation required.

Trying to train with multiple training zones at once is like moving to Norway and insisting the road signs be in miles. You can’t bend the environment to your preference. You just have to commit—or move back to Cleveland.

 

Final Thought on Training Zones: A Zone by Any Other Name…

A rose is still a rose, and a Zone 1 is still “easy”—if you understand the context. You can use any credible system and still become a faster, healthier athlete. Just don’t mix systems. That’s where things fall apart.

Whether you choose the 80/20 Endurance principle and our training zones or another approach, success comes from consistency, clarity, and commitment.

But if you’re ready to train smarter with the 80/20 system, just remember:
Respect the zones. Avoid Zone X. Embrace the process.

 

Want to Train Using the 80/20 System?

Join Team 80/20 to get access to our complete library of Training Plans and Workouts – all structured to the 80/20 Endurance Training Zones.

This post builds on our earlier article: A Zone By Any Other Name Would Be Complete.