Zone 2 Isn’t Magic. It’s a Volume Tool — and You’re Probably Doing the Wrong Zone.

The internet says Zone 2 is the secret to endurance. A 2025 review from a mitochondrial researcher went looking for the evidence — and found something more useful. Here’s what it actually means for how you train.

You’ve heard it everywhere — podcasts, social media, your training-buddy who just bought a lactate meter. Zone 2 has become the most talked-about intensity in endurance sport. And there’s real truth buried in the hype: easy aerobic training is the foundation of everything we do.

But the way the claim gets repeated online is doing a lot of athletes a disservice. It’s built on a misread of where the science comes from — and, for most people, it’s not even describing the zone they think it is. Let’s clear both of those up.

What the Research Actually Says

In July 2025, a team led by mitochondrial physiologist Kristi Storoschuk published a narrative review in Sports Medicine with a pointed title: “Much Ado About Zone 2.” The authors set out to find the evidence that Zone 2 is the optimal intensity for improving mitochondrial capacity and cardiorespiratory fitness.

What they found surprised a lot of people. The current evidence does not support Zone 2 as the best intensity for driving mitochondrial or fat-oxidation adaptations. In fact, when training time is limited, the data point toward higher intensities — above Zone 2 — being the more powerful stimulus for those adaptations.

So where did the Zone 2 obsession come from? From watching elite endurance athletes. Pros really do spend enormous amounts of time training easy — but that’s observational data. They can absorb 15–25 hours a week, and the easy volume is what lets them stack that much work without breaking. The mistake is copying the ratio without the volume, and assuming the easy work itself is the magic ingredient.

This is exactly what the polarized-training research has shown for years. Stephen Seiler’s work found that elite athletes across cycling, running, rowing, and skiing cluster around roughly 80% easy / 20% hard, with very little time in the mushy middle. And it’s not just description: Stöggl and Sperlich’s 2014 controlled trial found polarized training produced larger gains in VO₂max and time-to-exhaustion than threshold-heavy or pure-volume programs. Easy volume and hard intensity aren’t rivals. They’re partners — and you need both.

The Part Nobody Tells You: Your “Zone 2” Probably Isn’t Zone 2

Here’s the confusion that trips up almost everyone. “Zone 2” is not a universal number — it depends entirely on whose zone model you’re using. The popular Zone 2 everyone talks about means truly easy, conversational, below your first lactate turn — the pace where you can hold a full conversation for hours.

At Angela Naeth Coaching, that effort has a name, and it isn’t Zone 2. It’s our Zone 1.

What the internet calls…	In the ANC system it’s…	How it should feel
“Zone 2” (easy aerobic base)	ANC Zone 1 — Aerobic Endurance	Full sentences, easily. Where most of your training should live.
“Tempo” / “Zone 3”	ANC Zone 2 — Endurance Tempo	3–5 word phrases. 70.3 race feel after a solid base.
“Threshold”	ANC Zone 3 — Threshold	Single words only. Hard but controlled. 30–60 min max.

This matters more than it looks. We build our zones from Critical Power (CP) and Critical Speed (CS) — your actual, tested physiological thresholds — not from a generic percentage of max heart rate. So when an ANC athlete hears “go ride Z1,” they’re getting a precise, individual target, not a vague guess at where the internet’s “Zone 2” might fall for them. The athletes drifting too hard on their “easy” days are almost always the ones using a borrowed zone number that was never theirs to begin with.

What This Means for Your Training

None of this means easy training is a waste — the opposite. It means easy training has a job, and that job is volume and durability, not chasing a mitochondrial jackpot. Here’s how to put it to work:

The ANC Bottom Line

Zone 2 didn’t get debunked — it got put in its place. Easy aerobic training is the bedrock of endurance, but it’s the bedrock because it lets you build volume and durability while your hard sessions supply the sharp end of the adaptation. The magic was never the zone. It was the distribution.

That’s exactly how we’ve always coached at ANC: a big base of true Zone 1, precise CP/CS-anchored intensity when it counts, and zones that are actually yours instead of a number you inherited from a podcast. Do that, and you don’t have to pick a side in the Zone 2 debate. You just train the whole athlete.

Want the polarized picture completed? Read the companion piece on why staying power — not peak fitness — decides races: Durability vs. Intensity →