You’ll see it all over Instagram and TikTok, with brands even naming themselves after it. But do you really need to run everything in zone 2 to make progress? Let’s break it down.
What is Zone 2 training, really?
Zone 2 usually refers to easy runs at a low heart rate, often described as “conversational pace”, meaning that you should be able to talk while running. The problem is that different systems define Zone 2 differently - following a 5-zone-model.
Depending on who you ask, Zone 2 could be:
the first lactate threshold (LT1), where lactate starts to accumulate
the mythical “2 mmol” blood lactate level
the ventilatory threshold (that talking pace)
FatMax, where fat oxidation peaks
a percentage of maximum heart rate
or even an RPE score
Each of these gives you a slightly different number. At Trenara, we consider Zone 2 to end at LT1, which can be measured reliably in a lab test and compared over time.
Is Zone 2 really “easy”?
Not necessarily. Many amateurs see Zone 2 as slow, but for well-trained athletes it can be a serious effort. Remember: although intensity is relative, as your fitness improves, the absolute speed and strain of Zone 2 also go up.
Pro cyclist Tadej Pogačar once mentioned in a podcast that after a Zone 2 endurance ride, he wouldn’t schedule a hard session the next day. That tells you something.
On the other hand, for someone running a 4h30 marathon, Zone 2 feels “slow.” But because it feels slow, many runners actually overshoot it – and end up training too fast.
Zone 2 and fat burning: the facts
Zone 2 is often called the “fat-burning zone.” That’s partly true: in Zone 2, your body uses a higher percentage of fat as fuel compared to carbs. But at higher intensities, you also burn fat. And in absolute terms, often more.
Duration also matters. You can accumulate much more time in Zone 2 than in Zone 4, so the total fat burned might be higher simply because you can sustain it longer.
The big takeaway: fat loss comes from overall energy balance, not from running in one specific zone.
Is Zone 2 the best way to build your aerobic base?
This is where the hype comes in. Zone 2 is useful, but not automatically the best way.
Per minute of training: sessions around LT1 or LT2 (thresholds) provide a stronger aerobic stimulus. The bigger the stressor, the bigger the adaptation.
Over the long term: Zone 2 lets you build more volume with less mechanical strain. And it’s that total training volume that makes you stronger as a runner.
In short: higher zones are more efficient, but Zone 2 is more sustainable.
Can running slow make you faster?
Yes, indirectly. I've said it before and I'm going to stand by it. Training at lower intensity allows you to also train at higher intensity when it matters. Think of your threshold or interval sessions around LT2. Without a foundation of lower-intensity work, you wouldn’t be able to handle those quality workouts. The scientific proof might not be in the mitochondria, but that's just one part of the equation: running slow will make you mechanical more loadable.
Is Zone 2 for everyone?
No. Especially not for beginners, even though they’re often the ones targeted by social media posts, because they are new.
If you’re just starting out, your physiology is still developing and “zones” don’t mean much yet. Energy metabolism isn’t an on/off switch between fat and carbs; it’s a continuum. For beginners, that continuum is narrow. Consistency matters more than obsessing over heart-rate zones.
What about the 80/20 rule?
The “80/20” principle – 80% easy, 20% hard – became famous because it describes how elites train (approximately). But remember, it’s the Pareto principle, not a law of sports science.
If you run fewer hours per week, your ratio might look more like 60/40 or 70/30. The point is not the exact number, but the balance between easy and hard.
Conclusion: Balance is key
Zone 2 isn’t a miracle cure, but it is a valuable building block. It helps you safely add mileage, strengthen your aerobic system, and reduce injury risk. Certainly in running you can't just focus on physiology alone, mechanical load is an important factor as well. Just keep in mind that the physiological most efficient training isn’t always the most sustainable.
Zone 2 deserves its place in your plan – but it should never be your only type of training. The best runners combine plenty of Zone 2 mileage with smart doses of intensity. That’s exactly how we structure training in Trenara: a strong base plus well-timed quality.
That’s how you build a complete, resilient runner.
