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Zone 2 and Heart Rate Training for Ultrarunners

Zone 2 is easy, conversational running, roughly 60 to 70 percent of your max heart rate, just below your first lactate threshold. For ultrarunning this is the zone you live in. About 80 percent of your training should sit here, because those easy aerobic miles are what build the mitochondria, capillaries, and fat-burning engine that a long race runs on. The catch is trails. Pace lies on every climb and your heart rate spikes and drifts all over the place, so the signal you actually trust is effort, with heart rate as a backup check. Below I will walk you through the zone models, three ways to find your zones, the MAF method, and how to keep your easy days actually easy.

What zone 2 is, and the zones around it

Zone 2 is the easy aerobic effort that sits just below your first lactate threshold (LT1), the point where blood lactate first creeps above its resting baseline. You can hold a full conversation, breathe through your nose, and keep going for hours. Here is where it sits in the common five-zone model. The percentages are of your max heart rate, and the ranges reflect the spread between the standard systems, so treat the edges as soft, not gospel.

⏵ The five-zone model

Where zone 2 lives, and what each zone is for

Zone	% max HR	How it feels	What it is for
Zone 1 · Recovery	50 to 60%	Very easy, almost a stroll	Shakeouts, warm-ups, true recovery jogs
Zone 2 · Easy / aerobicyou live here	60 to 70%	Conversational, nose-breathing, all day	The bulk of your miles and your long runs
Zone 3 · Steady / tempo-ish	70 to 80%	Comfortably hard, talk in short phrases	The "gray zone" to mostly avoid on easy days
Zone 4 · Threshold	80 to 90%	Hard, sustainable about an hour	Tempo and cruise intervals, one quality day
Zone 5 · VO2 / max	90 to 100%	Very hard, breathless, minutes only	Short hill and VO2 reps, used sparingly

Different systems (Coggan, Friel, the Norwegian model) draw the lines a little differently, but they all agree on the big thing. Most of your running should be in zone 1 to 2, and zone 3 is a gray zone you mostly want to stay out of on easy days. This is the engine room of base-building for ultrarunning.

Why train 80 percent easy

The most repeated finding in endurance science is also the one people ignore the most on the trail. The best athletes do most of their training easy. Here is why that works, and how to count it.

The 80/20 polarized model

Exercise physiologist Stephen Seiler tracked elite endurance athletes across rowing, cycling, running, and skiing, and he kept finding the same split. Roughly 80 percent of training at low intensity (easy zones 1 to 2) and only about 20 percent genuinely hard (threshold and above). This polarized split beats living in the moderate middle, which is too hard to recover from and too easy to actually drive real top-end adaptation. The gray zone gives you the worst of both worlds.

For ultrarunners the case is even stronger, because your race is run almost entirely at an aerobic effort. The training that carries over the most is high-volume easy running, with the hard work boiled down to one or two focused sessions a week. A lot of ultrarunners end up even more lopsided than 80/20, often 85 to 90 percent easy, just because their long runs are aerobic by nature.

How to count it (and the trap)

You can count 80/20 by time or by sessions. Here is a simple way to think about it. If you run six days a week, five are easy and one is genuinely hard. If you run more than that, the easy share goes up, not down. The hard day might be threshold cruise intervals, short hill reps, or a fast finish, kept to one or two a week with full easy days on either side.

The trap is letting your easy days creep up into zone 3. It feels productive in the moment, but it beats you up just enough that you cannot nail the hard day and cannot fully recover either, so you stall out. Easy should feel almost embarrassingly slow. The discipline to hold it back is what lets you stack the kind of weekly volume an ultra asks for. See our guide on how many miles per week to train for an ultra for how that volume scales, and how the easy share makes the mileage survivable.

How to find your heart rate zones

You do not need a lab, though one helps. Here are three ways to set your zone 2 ceiling, from the quickest setup to the most precise. Pick one, treat the result as a cap you stay under on easy days, and re-test it every few months as you get fitter. Your zones move when your fitness moves.

⏵ Three ways, roughest to most precise

Setting your zone 2 ceiling

Method	How	Zone 2 ceiling	Tradeoff
The 180 Formula (MAF)	Subtract your age from 180, then adjust for health and training history.	Your MAF number is your easy ceiling	Fastest to set up. A simplification, but a safe upper bound that errs slow.
Field test (LT1 / talk test)	The fastest pace you can still hold a full conversation at, confirmed with a 30 to 40 min steady effort.	Sits just below your first lactate threshold (LT1)	Free, repeatable, more individual than an age formula.
Lab lactate or metabolic test	Finger-prick blood lactate or a metabolic cart pins LT1 and LT2 exactly.	Set right at measured LT1, around 1.5 to 2.0 mmol/L	The gold standard. Worth it if you train seriously or zones feel off.

One warning on the popular "220 minus age" max-HR estimate. It can be off by 10 to 20 bpm for any one person, so zones built on it are a rough start at best. A talk test or a field effort is more honest, and a lab lactate test is the truth.

The MAF method (the 180 Formula)

MAF (Maximum Aerobic Function) is the simplest way to put a hard ceiling on your easy days. It is a blunt tool, but the bluntness is the whole point. It keeps you genuinely easy on the days your ego wants to push you faster.

⏵ 180 minus your age, then adjust

The 180 Formula, step by step

1Start with 180 minus your age. So a 45-year-old starts at 135 bpm.
2Subtract 10 if you are coming back from a major illness or overtraining. Subtract 5 if you are injured, often sick, or not improving.
3No change if you have trained consistently for about two years with no issues. Add 5 if you have trained 2+ years and you are making good progress.
4Run all of your aerobic base work at or below that number for a block of months, and keep that first mile slow to warm up.

Athletes like Mark Allen and Stu Mittleman built famous aerobic engines this way. The 180 Formula is a simplification, not measured physiology, and it can read too low for a few very fit athletes or too high for some beginners, so cross-check it against your talk test. The value is the discipline. It is a conservative cap that errs slow.

Effort vs heart rate vs pace on trails

Here is what most zone 2 guides miss. They were written for flat road, where heart rate tracks effort and pace actually means something. On steep, rough trail both of those signals break, and effort becomes the one you trust. Use this to decide what to watch, by terrain.

⏵ What to trust, by terrain

The right signal depends on the ground

Terrain	Trust this	Why
Flat road or smooth path	Heart rate or pace	Steady conditions, so HR tracks effort well and pace is meaningful.
Rolling trail	Effort, with HR as a check	Pace lies on every grade change; HR lags the terrain by a minute or two.
Steep climbs	Effort (and breathing)	HR can spike past zone 2 at an easy effort, pace is meaningless. Hike it easy.
Long efforts and heat	Effort, expect HR drift	Cardiac drift adds 10 to 20 bpm over 30 to 60 min at the SAME effort.

Here is the rule. Run by feel, let your heart rate float on the climbs (power-hike them easy instead of forcing a HR cap), and use heart rate after the run to confirm your easy days really were easy. To turn the climbs into an honest effort, our grade-adjusted pace calculator shows what your flat-ground equivalent pace really is, and our guide on pacing an ultra by effort carries the idea into race day.

Cardiac drift, and why long runs read high

If your heart rate climbs through a long run while your effort stays flat, you are not getting unfit mid-run. You are just seeing cardiac drift, and it is normal.

What it is and why it happens

Cardiac drift (or cardiovascular drift) is the slow rise in your heart rate during a steady effort even when your pace and effort do not change, usually 10 to 20 bpm over 30 to 60 minutes. As you heat up, your body sends more blood to the skin to cool you, your stroke volume (blood pumped per beat) drops, and your heart beats faster to keep the output steady. Dehydration accounts for roughly half of it, so it gets worse when you are underhydrated or out in the heat.

Here is what that means for zone training. A long run that felt easy at minute 20 can read a full zone too high at minute 70, even though nothing about your effort changed. So if you chase a fixed heart-rate cap you end up walking when you should be jogging, purely because of drift.

What to do about it

Anchor your long-run intensity to effort (and to pace on flat ground), not to a fixed heart-rate number. Stay ahead of your hydration, since fluid loss drives a lot of the drift. And put the drift to work for you. A heart-rate-to-pace decoupling test, where you run a steady aerobic effort and compare the first and second halves, is a clean way to track your aerobic base. As your engine gets better that decoupling shrinks, which is direct proof the easy work is paying off.

This is exactly why one watched number is a bad boss for trail and long-run training. Pairing effort with heart rate and pace, and knowing how to read the gap between them, beats staring at any single figure.

How easy running makes you faster

It feels backwards that running slow is what makes you fast. But easy running is the strongest trigger for the cellular changes that decide endurance. Hard sessions sharpen the top end. Easy volume builds the engine.

The adaptations easy miles drive

Steady low-intensity running is the main stimulus for mitochondrial biogenesis (more and bigger mitochondria, so every muscle cell makes more aerobic energy) and angiogenesis (new capillaries, so oxygen and fuel reach the muscle and waste clears faster). It also improves fat oxidation, so you spare your precious glycogen, and it sharpens lactate clearance. Add all that up and you run faster at the same heart rate and hold a given pace at a lower effort, which over an ultra is the whole game.

Because easy running is low-stress, you can do a ton of it without breaking down, and the aerobic gains stack up year over year. That is why a consistent long-term runner beats a newer runner at the same weekly mileage. They have banked more of these adaptations. The engine gets built one easy mile at a time.

⏵ Free calculators for your aerobic training

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⏵ Keep your easy days actually easy

Knowing the 80/20 rule is the easy part. Holding it is the hard part. Summit Line reads your actual training and builds a plan where the easy days stay easy and the hard days are hard, with grade-adjusted effort on the climbs, a real aerobic base block, and a long-run progression that respects cardiac drift. And it tells you when an "easy" run was actually a gray-zone grind, so you stop quietly sabotaging your base.

Build my aerobic plan free →See it on a real plan

Keep reading

This is the aerobic-base pillar. These guides put that easy engine to work.

Pointing the aerobic base at a goal? A climber-heavy course like the Cuyamaca 100K is exactly where effort-over-pace zone discipline pays off, because the vert will spike your heart rate no matter how easy you keep it.

Zone 2 and heart rate FAQ

What is zone 2 training?

Zone 2 is easy, conversational aerobic running, the effort that sits just below your first lactate threshold (LT1), the point where blood lactate first starts to rise above resting levels. In a five-zone model it usually lands around 60 to 70 percent of your maximum heart rate. The tell is that you can hold a full conversation and breathe through your nose, and you could keep going for hours. It feels almost too easy, and that is exactly the point. Zone 2 is the effort where your body burns mostly fat and builds the aerobic machinery (mitochondria, capillaries, lactate clearance) that carries you through an ultra. It is the zone you live in, not a slow version of a hard run.

Why train 80 percent easy (the 80/20 rule)?

Exercise physiologist Stephen Seiler studied world-class endurance athletes across a lot of sports and kept finding the same pattern. Roughly 80 percent of their training is done at low intensity (easy, zones 1 to 2) and only about 20 percent is genuinely hard (threshold and above). This "polarized" split beats spending most of your time in the moderate gray zone, which is hard enough to wear you out but not easy enough to recover from or hard enough to drive top-end adaptation. For ultrarunners the case is even stronger, because your race is run almost entirely at an aerobic effort, so the training that matters most is high-volume easy running, with the hard work kept to one or two focused sessions a week. You can count the 80/20 split by time or by sessions, but the message is the same. Most of your running should feel easy.

How do I find my heart rate zones?

There are three honest ways, from fastest to most precise. The quickest is the 180 Formula (the MAF method). Subtract your age from 180, then adjust for your health and training history, and use that number as your easy ceiling. More individual is a field test. Find the fastest pace at which you can still hold a full conversation (that is roughly LT1, the top of zone 2), and confirm it with a steady 30 to 40 minute effort. The gold standard is a lab lactate or metabolic test, which pins your LT1 and LT2 exactly with finger-prick blood samples. Whatever you use, treat the resulting zone 2 ceiling as a cap you stay under on easy days, and re-test it every few months, because your zones move as you get fitter. And be careful with the generic "220 minus age" max-HR estimate. It can be off by 10 to 20 bpm for any one person.

Should I use heart rate, pace, or effort on trails?

On trails, effort is the signal you trust, with heart rate as a check and pace mostly ignored. Pace is meaningless the second the trail tilts. You will run an 8-minute mile on the flat and a 20-minute mile on a steep climb at the exact same effort. Heart rate is more honest, but it lags the terrain by a minute or two and can spike well past your zone 2 number on a short steep climb even at an easy effort, so chasing a heart-rate cap uphill makes you walk when you should jog or stop when you should hike. Here is the rule. Run by feel (conversational, nose-breathing easy), let your heart rate float on the climbs, and use HR after the fact to confirm your easy days really were easy. On flat road, heart rate and pace are both fine.

How much of my training should be easy?

About 80 percent, following the polarized 80/20 model from Stephen Seiler. In practice most ultrarunners run even more of their volume easy, often 85 to 90 percent, because their hard days are few and their long runs are aerobic by nature. Here is a simple way to frame the week. If you run six days, five are easy (zone 1 to 2) and one is genuinely hard. If you run more than that, the easy share goes up, not down. The most common mistake is letting your easy days creep into the moderate gray zone, which leaves you too tired to nail the hard day and too beat up to recover. Easy should feel almost embarrassingly easy. The discipline to hold it back is what lets you stack the volume an ultra asks for.

What is the MAF method?

MAF stands for Maximum Aerobic Function, a low-heart-rate training approach developed by Dr. Phil Maffetone. You find your maximum aerobic heart rate with the 180 Formula. Subtract your age from 180, then adjust (subtract 10 if you are recovering from illness or overtraining, subtract 5 if you are injured or sick or not improving, add 5 if you have trained consistently for two or more years and are progressing). Then you run all of your aerobic base work at or below that number for a block of months, with no faster running. Athletes like Mark Allen and Stu Mittleman built famous aerobic engines this way. The 180 Formula is a simplification, not lab-measured physiology, and it can read too low for some very fit athletes or too high for some beginners, but it is a safe, conservative ceiling that keeps your easy days easy, which is exactly why it works so well for ultrarunners.

Does heart rate drift mess up zone training?

Yes, and you should expect it rather than fight it. Cardiac drift (also called cardiovascular drift) is the slow rise in your heart rate during a steady effort even when your pace and effort stay flat, usually 10 to 20 bpm over 30 to 60 minutes. It happens because as you heat up your body sends more blood to the skin to cool you, your stroke volume drops, and your heart beats faster to keep the output steady. Dehydration accounts for roughly half of it. Here is what that means in practice. A long run that felt perfectly easy at minute 20 can read a full zone too high at minute 70, even though nothing about your effort changed. The fix is to anchor your long-run intensity to effort (and pace on flat ground) instead of chasing a fixed heart-rate cap, stay on top of your hydration, and treat a stable decoupling between heart rate and pace as a sign your aerobic base is improving.

How does easy running make me faster?

Easy, zone 2 running is the single strongest stimulus for the aerobic adaptations that decide endurance performance. Steady low-intensity effort drives mitochondrial biogenesis (more and bigger mitochondria, so each muscle cell makes more aerobic energy), angiogenesis (new capillaries, so oxygen and fuel reach the muscle and waste clears faster), better fat oxidation (so you spare your precious glycogen), and improved lactate clearance. Add it up and you can run faster at the same heart rate and hold a given pace at a lower effort, which on a long course is the whole game. Because easy running is low-stress, you can do a ton of it without breaking down, and those aerobic gains stack up year over year, which is why consistent long-term runners beat newer runners at the same weekly mileage. Hard sessions sharpen the top end, but the easy volume builds the engine.

This guide is for general training and planning purposes and reflects expert-consensus ranges, not a substitute for personalized coaching or medical advice. Heart rate zones, the 180 Formula, and cardiac drift all vary a lot from runner to runner, so treat the numbers here as starting ranges and confirm them against your own field tests and how you feel. If you are new to running or have a heart or health condition, check with a clinician before starting hard or high-volume training.