Zone 2 is having a moment, and deservedly so. The problem is that most of the advice being handed out quietly assumes you already have the fitness to follow it.
BLUF: If you are early in your fitness journey, you will struggle to hold your heart rate inside Zone 2. That is not a discipline problem, it is a fitness problem, and chasing the number will make it worse. Run to effort instead: 3 to 4 out of 10, at a pace where you can hold a full conversation.
The number that stops people before they start
Here are my own numbers, because they make the point better than a hypothetical. My maximum heart rate sits up in the 190s. That puts the top of my Zone 2 at around 152 beats per minute.
For me, 152 is genuinely easy. Legs turning over, breathing relaxed, the sort of effort I could hold for a couple of hours and finish feeling like I had barely been out.
Now hand that same 152 to someone who has not run consistently for a few years. They set off at what feels like a gentle jog. Four minutes in, the watch reads 161. They slow down. It reads 158. They slow down again, shuffling now, faintly embarrassed. It reads 156. Eventually they are walking, and the number still has not come down to where the internet told them it needed to be.
They come home having done a session that felt like nothing, achieved nothing they can point to, and confirmed a suspicion they already had, which is that they are not built for this. That is a rotten outcome from a session that should have been one of the easiest wins in the sport.
Why an unfit body runs hot
None of this means anything is wrong with them. It means the engine is not efficient yet, and heart rate is a very direct readout of efficiency.
Your heart is a pump. Every beat moves a certain volume of blood, and your muscles need a certain amount of oxygen to do the work you are asking of them. In a trained athlete, each beat moves more blood, the network of capillaries feeding the muscle is denser, there are more mitochondria to use the oxygen once it arrives, and the whole system is better at burning fat for fuel at low intensity.
In an untrained body, every one of those is smaller or less developed. The demand is the same, so the only lever available is beats per minute. The heart simply beats more often to deliver the same oxygen. Your heart rate is high at an easy effort because your body is doing the same job less efficiently, and that is exactly what it should be doing while it is still adapting.
So a high heart rate on an easy run is not a sign you are getting it wrong. It is a sign you are at the beginning. Which, incidentally, makes you the person who stands to gain the most from easy aerobic work, not the person who should be excluded from it.
Why chasing the number backfires
When the number and the body disagree, one of two things happens, and both are bad.
The first is that you obey the number. You slow down until the watch is happy, which for a lot of beginners means walking. There is nothing wrong with walking, and run-walk is a legitimate way to build. But walking because a device told you to, on a run you were enjoying, is demoralising in a way that ends training blocks. People do not quit because the training is too hard. They quit because it stops feeling like it is going anywhere.
The second is that you ignore the number and push on regardless, and because you now feel behind, you run a bit harder than you would have. That lands you in the grey zone: too hard to be genuinely easy, too easy to be genuinely hard. It drains your recovery without sharpening anything, which is the single most common way to train consistently and still not improve.
What to use instead
Two things, both of which work from day one and neither of which needs a device.
Rate of perceived exertion, at 3 to 4 out of 10. That is an effort you are aware of but not troubled by. You should finish feeling you could comfortably have kept going. If you finish an easy run feeling worse than when you started, it was not easy. Our RPE guide converts that felt effort into real numbers for every discipline once you want them.
The talk test. This is the one I would use above everything else, because it does not drift and it cannot be gamed. At a genuinely easy effort you can speak in full, complete sentences. Not three words between gulps of air. A proper conversation, the kind where you could tell someone about your week without them noticing you were running.
One more thing worth doing: set easy runs by time rather than distance. Thirty minutes easy, not three miles easy. The moment there is a distance to finish, there is a reason to run faster to get it over with, and the discipline goes out of the window. The only way to do a timed easy run badly is to run it too hard.
What changes, and how you will know
Here is the part that makes all of this worth it. Hold that easy effort consistently for a few weeks and something quietly excellent happens: at the same effort, your heart rate comes down and your pace comes up.
You do not force this and you cannot rush it. You allow it, by staying honest with the effort and letting the pace come to you. The same conversational jog that had you at 161 in week one has you at 150 a couple of months later, and you are covering more ground while you do it. That gap is the adaptation, made visible.
Which is also the answer to the question everyone asks, the one that goes "if I keep running this slowly, won't I stay slow?" No. The opposite. Your easy pace gets quicker at the very same easy effort, because the engine underneath it got bigger.
When to bring heart rate back in
Once your easy effort settles into a repeatable band, the number becomes genuinely useful, and you can work out your own zones with our heart rate zone calculator. At that point heart rate confirms what your effort is already telling you, which is the right way round.
Even then, let the data guide rather than govern. Heart rate wobbles with poor sleep, caffeine, dehydration, stress, heat and the very beginning of an illness. If it reads high one morning and you cannot bring it down without walking, do not force the pace down to satisfy the watch. The talk test does not lie, and it does not care that you had a bad night.
The bottom line
Zone 2 is not a heart rate number. It is an intensity, and the number is only ever one way of describing it. For a trained athlete it is a good description. For someone in their first months of running it is a poor one, and treating it as the definition turns the most beneficial training you can do into a source of failure.
Run at 3 to 4 out of 10. Hold a conversation. Go by time. Let the number catch up with you, because it will.
If you want the full picture on what this training does and why it works, we covered that in Zone 2: why training slower makes you faster. And if you are not sure what any given run in your week is actually for, that is worth reading too.