When I started training for this 5K, my goal was simple: run the whole race without walking. To do that, I thought I needed to push myself in every run. Most of my training ended up in Zone 4 heart rate — hard but not all-out — and I convinced myself that was the best path forward. But as I’ve learned, Zone 2 running for endurance training may actually be the key to reaching my bigger goals.
I was walking to my usual starting point for a run, moving quickly up a small hill. Nothing special, just part of my warmup walk. I glanced at my watch — my heart rate was 109 bpm. Based on the chart I’d been using, that was Zone 2. That meant I wasn’t even “running” yet, and I was supposedly training in the endurance zone.
That felt… off.
The next day, on my off day, I decided to test it out using the Apple Fitness app. I switched to the fitness face that shows heart rate zones in real time. Starting my “Zone 2 run,” I hit 106 bpm (what I thought was Zone 2)… and my watch still said Zone 1. I pushed harder, hit 126 bpm (what I thought was Zone 3)… and the watch still said Zone 1.
What was going on?
When I got home, I dug into Apple’s zone setup and realized something important: Apple calculates zones differently than the simple formula I’d been using. And honestly, after some research, Apple’s approach makes more sense.
Two Ways to Calculate Heart Rate Zones
1. The Classic Formula (220 − age)
This is the one you’ll see everywhere. You subtract your age from 220 to estimate your max heart rate (MHR), then assign zones based on percentages of that number.
I’m 44, so:
- Max HR = 220 − 44 = 176 bpm
Zones using this method:
- Zone 1 (50–60%) → 88–106 bpm
- Zone 2 (60–70%) → 106–123 bpm
- Zone 3 (70–80%) → 123–141 bpm
- Zone 4 (80–90%) → 141–158 bpm
- Zone 5 (90–100%) → 158–176 bpm
This is the chart I was using when I thought 106 meant Zone 2 — which is why that brisk walk at 109 bpm felt like “training.”
2. Apple’s Method (Resting HR + Max HR)
Apple uses a more personalized calculation based on both resting heart rate and max heart rate. My resting HR is 57 bpm and my max HR is 177 bpm. Using those, Apple gives me:
- Zone 1: <128 bpm
- Zone 2: 129–140 bpm
- Zone 3: 141–152 bpm
- Zone 4: 153–164 bpm
- Zone 5: 165+ bpm
Compared to the simple formula, Apple’s version shifts the zones upward — which means what I thought was Zone 3 was actually still Zone 1.
If you want to calculate your HR zones you can do so on RunBundle, just make sure you select the Heart Rate Reserve method.
Why Zone 2 Matters So Much
Here’s the part I had been missing: endurance running isn’t built on hammering every run in Zone 4. The best distance runners follow the 80/20 rule (sometimes called “polarized training”):
- ~80% of training in Zone 2 (easy effort, building aerobic base).
- ~20% of training in Zones 3–5 (harder workouts, speed, intervals).
That means most runs should feel “too easy” — conversational pace, sometimes frustratingly slow. Zone 2 is where your body builds capillaries, mitochondria, and efficiency. It’s the foundation that makes long distances possible.
The harder zones (3–5) are still important, but they’re like seasoning — small amounts on top of a steady diet of easy miles.
What Each Zone Feels Like & Is Good For
- Zone 1 (Very Easy / Recovery): Gentle effort, full conversation. Good for warmups, cooldowns, and recovery.
- Zone 2 (Endurance): Easy effort, sustainable, conversation still possible. Builds aerobic base and endurance. This is where most distance training should happen.
- Zone 3 (Moderate / Tempo): Comfortably hard. Improves aerobic capacity and steady-state fitness.
- Zone 4 (Threshold): Hard effort, speaking in single words. Improves lactate threshold, makes race pace feel easier.
- Zone 5 (VO₂ Max): All-out. Short sprints, hills. Builds max speed and power.
My New Training Plan
Now that I’ve seen the difference, I’m shifting to Apple’s method. It’s more accurate for me because it accounts for both my resting HR and max HR, not just age.
- On my speed interval days (like tomorrow), I’ll do my .6 mile warmup in Zone 2 and try to bring my cooldown back to Zone 2 as well, even though that will be tougher.
- I’ll continue my normal Zone 3/4 training runs on Wednesday, Friday, and Sunday.
- On Monday and Thursday, I’ll add extra Zone 2 runs to boost my aerobic percentage without burning myself out.
The goal isn’t to hit Zone 2 all the time — it’s to balance my week so I’m not just hammering Zone 4.
Why This Matters for Me (and Maybe You)
For weeks, I thought Zone 2 meant walking. But with Apple’s calculation, Zone 2 is actually running at a pace that feels natural and sustainable. That’s a huge mindset shift.
Zone 2 isn’t glamorous, but it’s the foundation. By slowing down now — using the right version of my zones — I’ll build the endurance that makes running longer and faster possible.
Catch up on all my other post here.
