TL;DR: Heart rate training zones are useful, but the neat five-color chart on your watch makes human physiology look considerably more precise than it actually is. Your real training zones are better thought of as intensity ranges separated by physiological thresholds, and those thresholds vary from person to person.

• Heart rate zones help organize easy, moderate, threshold, and high-intensity training.

• The common five-zone system is useful, but it isn't a universal physiological law.

• Zone 2 should generally sit below your first lactate or ventilatory threshold.

• Fixed percentages of maximum heart rate can misclassify training intensity in some athletes.

• A measured or well-estimated lactate threshold can produce more individualized training zones than a generic age-based maximum-heart-rate equation.

• Most endurance training should generally feel easy, with harder sessions added deliberately rather than accidentally.

• Heart rate is affected by heat, dehydration, fatigue, caffeine, altitude, stress, and other factors.

• Pace, power, heart rate, perceived exertion, and the talk test are best used together.

• HRV can provide useful recovery information, but it shouldn't dictate your training based on a single morning measurement.

• Your zones can change as fitness improves.

Want to understand the numbers instead of just staring at your watch? Use our Guide to Understanding HRV and Training Zones to better understand heart rate, HRV, training intensity, and recovery.

Heart rate zones look wonderfully precise.

Zone 1: 112–128 bpm.

Zone 2: 129–145 bpm.

Zone 3: 146–161 bpm.

Apparently at 145 bpm you're building your aerobic system, and one heartbeat later you've entered an entirely different physiological universe.

That's not really how it works.

Heart rate zones are useful.

Very useful, actually.

But they're a model we use to simplify something considerably more complicated: the gradual physiological changes that occur as exercise intensity increases.

Understanding that difference can make heart rate training considerably more useful.

What Are Heart Rate Training Zones?

Heart rate training zones divide exercise intensity into different ranges based on heart rate.

A typical five-zone model might look something like this:

Zone 1: Very easy / recovery

Zone 2: Easy aerobic endurance

Zone 3: Moderate / tempo

Zone 4: Threshold

Zone 5: High intensity / VO₂ max

Each zone represents a different level of exercise intensity.

As intensity increases:

Heart rate rises.

Breathing increases.

Carbohydrate use generally increases.

Lactate production increases.

Fatigue accumulates more rapidly.

The amount of time you can sustain the effort decreases.

The zones give us an easy way to describe those changes.

But there's a problem.

Not Everyone Uses the Same Heart Rate Zones

Open three training apps and you may get three different definitions of Zone 2.

One might define it as:

60–70% of maximum heart rate.

Another:

70–80%.

Another might calculate it using heart-rate reserve.

A coach might define it from lactate threshold.

An exercise physiologist may use ventilatory threshold.

And your watch has somehow decided it knows everything after you wore it while mowing the lawn twice.

This is why conversations about training zones become confusing.

The word zone doesn't always mean the same thing.

The Five-Zone Model vs. the Three-Zone Model

Scientists studying endurance training frequently use a simpler three-zone model based around physiological thresholds.

Zone 1: Below the First Threshold

This is relatively easy aerobic exercise.

Lactate remains low.

Breathing is controlled.

You can speak comfortably.

This corresponds broadly with what many athletes call easy training or Zone 2 in a five-zone system.

Yes, Zone 1 in one system can roughly correspond to Zone 2 in another.

Welcome to endurance sports.

Zone 2: Between the First and Second Threshold

Exercise is harder.

Breathing becomes more pronounced.

Lactate rises but can remain relatively stable.

This covers intensities often described as steady, tempo, or moderate-to-hard training.

Zone 3: Above the Second Threshold

Now you're working hard.

Lactate accumulates rapidly.

Breathing is heavy.

The effort can only be sustained for a limited amount of time.

This includes hard intervals and VO₂-max-type training.

These three physiological intensity domains are separated by boundaries commonly estimated using lactate thresholds, ventilatory thresholds, or related measures.

So What Exactly Is Zone 2?

This may be the most argued-about training intensity on the internet.

Zone 2 has become incredibly popular.

Depending on who you follow, it apparently improves:

Mitochondria.

Fat oxidation.

Aerobic fitness.

Metabolic health.

Longevity.

Your taxes.

Probably your marriage.

The underlying concept is legitimate.

The terminology is where things get messy.

A 2025 expert consensus involving sport scientists and professional coaches concluded that Zone 2 training is preferably performed immediately below the first lactate or ventilatory threshold.

That's a much better definition than saying:

"Zone 2 is exactly 65–75% of your maximum heart rate."

Because individual physiology doesn't always cooperate with percentages.

Why Maximum Heart Rate Percentages Can Be Wrong

One of the easiest ways to calculate training zones is using a percentage of maximum heart rate.

For example:

Maximum HR = 180 bpm

Zone 2 = 60–70%

That gives:

108–126 bpm.

Easy.

The problem is that two athletes with the same maximum heart rate can have very different physiological thresholds.

Recent research comparing different Zone 2 markers found substantial individual variability between fixed percentages of maximum heart rate and physiological measures such as the first ventilatory threshold.

So percentages are useful estimates.

They're not personalized physiological measurements.

What About 220 Minus Your Age?

You've probably seen this formula:

220 − age = maximum heart rate

If you're 50:

220 − 50 = 170 bpm.

Simple.

Also fairly crude.

Maximum heart rate varies considerably between individuals.

Two healthy 50-year-olds could have meaningfully different true maximum heart rates.

If the number you're using for maximum heart rate is wrong, every training zone calculated from that number is also shifted.

That doesn't make age-based formulas useless.

They provide estimates.

Just don't confuse an estimate with a measurement.

Better Ways to Determine Your Training Zones

There are several options, ranging from simple to laboratory testing.

Method 1: Rating of Perceived Exertion

You already have a surprisingly useful intensity-monitoring tool.

Your brain.

A simple 1–10 effort scale might look like:

2–3: Very easy

3–4: Easy aerobic

5–6: Moderate

7–8: Hard / threshold

9–10: Very hard

RPE isn't perfect.

But neither is heart rate.

Using both together gives you more information than either one alone.

Method 2: The Talk Test

The talk test is remarkably practical.

During easy aerobic exercise, you should generally be able to speak in complete sentences.

As you approach your first ventilatory threshold, talking becomes more difficult.

Above it, conversation becomes increasingly broken.

This makes the talk test particularly useful when you don't have laboratory measurements.

Even clinical exercise-intensity guidance recognizes subjective methods such as RPE and the talk test as useful alternatives when direct physiological testing isn't available.

No chest strap required.

Method 3: Heart Rate Reserve

Heart-rate reserve accounts for both resting and maximum heart rate.

The formula is:

HRR = Maximum HR − Resting HR

Then:

Target HR = (HRR × intensity %) + Resting HR

Example:

Maximum HR = 180

Resting HR = 50

HRR = 130

At 70%:

130 × 0.70 = 91

91 + 50 = 141 bpm

Heart-rate reserve can provide a more individualized estimate than simply using a percentage of maximum heart rate.

But you're still working with estimates unless maximum heart rate has actually been measured.

Method 4: Lactate Threshold

Now we're getting more useful for serious endurance athletes.

Your lactate thresholds represent meaningful physiological boundaries.

The first threshold, commonly called LT1, occurs when blood lactate begins rising above baseline.

The second threshold, often called LT2, occurs at a substantially higher intensity where lactate accumulation accelerates and sustainable duration becomes much shorter.

These thresholds help separate exercise into meaningful intensity domains.

If you know your lactate threshold heart rate, you can build training zones around your actual physiology rather than an age-based formula.

We have a Lactate Threshold Calculator specifically for this purpose.

Method 5: Ventilatory Threshold Testing

A laboratory cardiopulmonary exercise test can measure breathing and gas exchange as intensity increases.

This allows identification of:

VT1: First ventilatory threshold

VT2: Second ventilatory threshold

These correspond reasonably well with important metabolic transitions.

For athletes who want highly individualized zones, physiological threshold testing is considerably more informative than asking your smartwatch to guess.

What Should Zone 1 Feel Like?

Very easy.

Think:

Recovery jog.

Easy cycling.

Walking.

Warm-up.

Cool-down.

You should be able to speak easily.

Breathing is relaxed.

RPE might be around 2–3 out of 10.

This intensity is useful for recovery and adding movement with very little training stress.

It should almost feel suspiciously easy.

That's okay.

What Should Zone 2 Feel Like?

Easy but purposeful.

Breathing is deeper than at rest, but controlled.

You can still speak in sentences.

You could maintain the effort for a long time.

RPE might be around 3–4 out of 10.

In physiological terms, the upper end should generally remain around or slightly below the first lactate or ventilatory threshold.

Zone 2 shouldn't feel like a race.

If you're checking your watch every 15 seconds while fighting for your life to stay under 149 bpm, you're probably missing the point.

What Happens Physiologically During Zone 2 Training?

Low-intensity endurance training produces several important adaptations.

Over time, consistent aerobic training can improve:

Mitochondrial density and function.

Capillary development.

Fat oxidation.

Stroke volume.

Aerobic enzyme activity.

Ability to sustain exercise.

These adaptations form the aerobic foundation that endurance performance is built on.

And because Zone 2 produces relatively low fatigue compared with harder training, you can accumulate a lot of it.

That's important.

Why Not Just Train Harder?

Because training stress has a cost.

Hard training creates a strong stimulus.

It also creates more fatigue.

If every run becomes moderately hard, you accumulate substantial fatigue without necessarily getting the specific benefits of either truly easy training or properly hard training.

This is where a lot of recreational endurance athletes get stuck.

Easy days aren't easy.

Hard days aren't really hard.

Everything becomes:

"Kind of uncomfortable."

That's a training zone too.

It's called I don't know what today's workout is supposed to accomplish.

What Is Zone 3?

In a common five-zone system, Zone 3 is moderate.

It's faster than easy aerobic training but below threshold.

You can maintain it for quite a while, but you're definitely working.

RPE might be around:

5–6 out of 10.

This intensity isn't useless.

Far from it.

Steady-state and tempo training can be valuable.

The problem is accidentally turning every easy workout into Zone 3.

Use moderate training intentionally.

What Is Zone 4?

Zone 4 usually corresponds roughly with threshold training.

This is comfortably uncomfortable.

Actually, let's stop pretending.

It's uncomfortable.

You're working around an intensity you might sustain for somewhere around 30–60 minutes depending on fitness, sport, and how the zone is defined.

Breathing is heavy.

Conversation is difficult.

RPE might be around:

7–8 out of 10.

Threshold workouts might include:

3 × 10 minutes.

4 × 8 minutes.

2 × 20 minutes.

20–30 minutes continuous.

These sessions can improve your ability to sustain a high percentage of your aerobic capacity.

What Is Zone 5?

Hard.

This is where we're working at intensities associated with VO₂ max and severe exercise.

RPE:

9–10 out of 10.

Intervals might include:

5 × 3 minutes.

4 × 4 minutes.

6 × 2 minutes.

Short hill repeats.

Longer recovery is usually necessary.

You can't accumulate huge amounts of Zone 5 training.

That's partly why it works.

How Much Training Should Be Easy?

A lot.

Research examining successful endurance athletes consistently shows that large portions of training are performed at relatively low intensity.

That doesn't mean every athlete needs exactly:

80% easy

20% hard

The famous 80/20 concept is a useful approximation, not a universal commandment.

Training distribution depends on:

Sport.

Experience.

Training volume.

Competition schedule.

Goals.

Current phase of training.

But if you're an endurance athlete and almost every workout feels hard, that's usually worth examining.

Heart Rate Drift: Why Your HR Rises During Easy Runs

You've probably experienced this.

You start running at:

9:00/mile

140 bpm.

Forty-five minutes later:

9:00/mile

152 bpm.

Same pace.

Higher heart rate.

This is commonly called cardiovascular drift.

It can be influenced by:

Heat.

Dehydration.

Rising core temperature.

Fatigue.

Exercise duration.

That's why heart rate isn't an absolute command.

If it's hot, your heart rate may rise at the same pace.

Slow down if maintaining a specific physiological intensity is the goal.

Heat Can Completely Change Your Heart Rate

This is especially important for runners.

Your cardiovascular system isn't only delivering oxygen to working muscles.

In hot conditions, it also has to send blood toward the skin to dissipate heat.

Heart rate rises.

Pace often slows.

This is why trying to force your normal cool-weather pace while staying in the same heart-rate zone can become impossible.

Don't fight physiology.

Adjust the pace.

Caffeine Can Affect Heart Rate Too

Caffeine can alter cardiovascular responses and perceived effort.

So can:

Poor sleep.

Stress.

Dehydration.

Illness.

Altitude.

Medications.

Recent training.

This is another reason not to let one number control your entire workout.

Heart rate provides information.

Interpret it in context.

What Is Heart Rate Variability?

Heart rate variability, or HRV, measures variation in the time interval between heartbeats.

If your heart rate is 60 bpm, your heart doesn't literally beat exactly once every second.

The intervals vary.

That variability is influenced heavily by the autonomic nervous system.

HRV has therefore become popular as a tool for monitoring recovery and training readiness.

Many watches and wearable devices now give you an HRV score every morning.

Useful?

Potentially.

Magic?

No.

What Does a High HRV Mean?

Generally, higher HRV relative to your own normal baseline is associated with greater parasympathetic influence and can indicate good recovery status.

But comparisons between people aren't particularly useful.

Your HRV might normally be:

35 ms.

Someone else's might be:

90 ms.

That doesn't automatically mean they're three times more recovered than you.

HRV is highly individual.

Your trend matters more than somebody else's number.

What Does a Low HRV Mean?

A drop in HRV can occur with:

Hard training.

Poor sleep.

Psychological stress.

Alcohol.

Illness.

Travel.

Dehydration.

Heat stress.

A single low reading doesn't automatically mean you should cancel your workout.

Look for trends.

Combine HRV with:

Resting heart rate.

Sleep.

Muscle soreness.

Mood.

Training performance.

How you actually feel.

Data should improve decision-making.

It shouldn't replace it.

Can HRV Determine Your Training Zones?

Interestingly, HRV has also been studied as a method for identifying physiological thresholds during incremental exercise.

Systematic reviews have found that HRV-derived thresholds can show reasonable agreement with lactate and ventilatory thresholds at the group level. However, individual limits of agreement can be fairly wide, and the research has methodological limitations.

So HRV-derived thresholds are interesting.

They're not yet something I'd use blindly to replace established threshold testing for every athlete.

Heart Rate vs. Pace: Which Should You Follow?

Both.

Let's say your easy run normally looks like:

9:00/mile

140 bpm.

Today it's 90°F.

At 9:00 pace you're running:

155 bpm.

What should you do?

If the goal is easy aerobic training, slow down.

Now imagine the opposite.

You're extremely fit and rested.

At 140 bpm you're suddenly running 8:30 pace.

Great.

Don't slow down because your training plan says 9:00.

Heart rate tells you about internal load.

Pace tells you about external performance.

Together they tell a much better story.

Heart Rate vs. Power

Cyclists have another useful metric:

Power.

Power measures the actual mechanical work you're producing.

Heart rate measures your physiological response to that work.

Suppose you're normally riding:

200 watts at 140 bpm.

Today:

200 watts requires 153 bpm.

Something changed.

Maybe it's heat.

Fatigue.

Dehydration.

Illness.

Poor recovery.

That's useful information.

Power plus heart rate is more informative than either alone.

Why Your Watch Zones Might Be Wrong

Your watch doesn't know your physiology unless you've given it good data.

If it calculates zones from:

220 − age

or another estimated maximum-heart-rate equation, the zones may be off.

If you've actually measured:

Maximum heart rate.

Resting heart rate.

Lactate threshold heart rate.

Then your zones become considerably more useful.

Before obsessing over your watch's zones, check how they're calculated.

You might discover you've spent six months training according to a number your watch invented during setup.

How Often Should You Recalculate Your Zones?

Maximum heart rate doesn't change dramatically with training.

Thresholds can.

As fitness improves, you may be able to produce more pace or power at the same heart rate.

Your threshold heart rate may also shift somewhat.

I'd reassess zones periodically, particularly after:

A major training block.

A long layoff.

Large fitness improvements.

Major changes in training.

You don't need to test every week.

Training should produce adaptations.

Give it enough time to do that.

A Simple Weekly Training-Zone Example

For a recreational endurance athlete training five days per week:

Monday: Rest or Zone 1 recovery

Tuesday: Threshold intervals

Wednesday: Zone 2 easy endurance

Thursday: Zone 2 easy endurance

Friday: Rest

Saturday: Long Zone 2 session

Sunday: Easy endurance with strides or short higher-intensity work

That's only an example.

The exact structure depends on your sport and goals.

The important part is that easy training stays easy and hard training has a reason for being hard.

The Biggest Heart Rate Training Mistakes

Treating Zone Boundaries Like Walls

Physiology doesn't completely change because your heart rate increased one beat per minute.

Zones are ranges.

Using 220 Minus Age as Absolute Truth

It's an estimate.

Treat it like one.

Running Easy Days Too Hard

Probably the most common mistake.

Slow down.

Ignoring Perceived Effort

Your body provides information too.

Listen occasionally.

Chasing Zone 2 Every Second

Heart rate fluctuates.

A hill temporarily pushing you two beats above Zone 2 hasn't destroyed your mitochondrial adaptations.

You'll survive.

Letting Your Watch Dictate Every Workout

Wearables are tools.

You're still the athlete.

Comparing Heart Rate With Other Athletes

Your training partner runs at 145 bpm.

You run at 132.

Who cares?

Heart rate is individual.

How to Know Whether Your Training Zones Are Working

Don't judge them only by whether you successfully kept your heart rate inside a colored box.

Look at performance.

Over time, you may notice:

Faster pace at the same heart rate.

Higher cycling power at the same heart rate.

Lower heart rate at the same pace.

Improved threshold pace.

Improved VO₂ max.

Faster recovery.

Ability to handle more training.

Those are meaningful adaptations.

The purpose of training zones isn't to become good at staying inside training zones.

It's to become fitter.

Want to Understand Your HRV and Training Zones?

Heart rate data becomes much more useful once you understand what the numbers actually mean.

Our Guide to Understanding HRV and Training Zones explains how to interpret heart rate, HRV, training intensity, recovery, and training zones so you can make better decisions instead of simply accepting whatever your watch tells you.

Get the Guide to Understanding HRV and Training Zones →

You can also use our Lactate Threshold Calculator to estimate your threshold and build more individualized training zones.

And if you want to estimate your aerobic capacity, try our VO₂ Max Calculator.

You can browse all of our free training programs and workout plans for running, strength, endurance, hybrid training, nutrition, and more.

Your watch collects the data.

You should still understand it.

Frequently Asked Questions About Heart Rate Training Zones

What are the five heart rate training zones?

A common five-zone model includes Zone 1 for recovery, Zone 2 for aerobic endurance, Zone 3 for moderate or tempo work, Zone 4 for threshold training, and Zone 5 for high-intensity or VO₂-max work. Exact boundaries vary depending on the method used.

What should Zone 2 heart rate be?

There isn't one universal percentage. Current expert consensus favors defining Zone 2 physiologically as exercise immediately below the first lactate or ventilatory threshold rather than relying entirely on a fixed percentage of maximum heart rate.

Is Zone 2 60–70% of maximum heart rate?

It can be used as a rough estimate, but individual variability is substantial. Research comparing Zone 2 markers has shown fixed percentages of maximum heart rate don't always align well with individual physiological thresholds.

How do I calculate my maximum heart rate?

Age-based equations can provide estimates, but measured maximum heart rate from an appropriate maximal exercise test is more individualized. Maximum heart rate varies substantially between people of the same age.

Is 220 minus age accurate?

It's useful as a rough population estimate but can be meaningfully inaccurate for an individual athlete. Don't assume it represents your actual maximum heart rate.

What is lactate threshold heart rate?

Lactate threshold heart rate is the heart rate associated with a physiological transition where blood lactate begins accumulating more rapidly. It can be used to establish more individualized training zones.

Should most running be in Zone 2?

Most endurance athletes benefit from performing a large percentage of their total training at relatively low intensity. The exact percentage depends on the athlete, sport, training volume, goals, and training phase.

Is Zone 3 bad?

No. Moderate and tempo training can be extremely useful. The problem is unintentionally performing every workout at moderate intensity instead of using different intensities for specific purposes.

Why is my heart rate higher when it's hot?

Heat increases cardiovascular demand because blood flow is needed for both working muscles and heat dissipation through the skin. Heart rate can therefore increase even when pace or power remains unchanged.

Should I slow down if my heart rate is too high?

If the goal of the workout is maintaining an easy aerobic intensity, slowing down is appropriate when heart rate and perceived effort indicate you're working too hard.

Is HRV useful for training?

HRV can provide useful information about autonomic nervous system status and recovery, particularly when viewed as a trend relative to your own baseline. It shouldn't be interpreted from a single measurement in isolation.

Should I skip training when my HRV is low?

Not automatically. Consider HRV alongside sleep, resting heart rate, soreness, illness symptoms, mood, and training performance before adjusting your workout.

About the Author

Matt Mosman, MS, CISSN, CSCS

Matt Mosman is the founder and Chief Science Officer of Simply Good Supplements. He holds a master's degree and is a Certified Sports Nutritionist through the International Society of Sports Nutrition (CISSN) and a Certified Strength and Conditioning Specialist (CSCS).

He's also an endurance athlete who spends plenty of time looking at heart-rate data.

Heart rate zones are useful.

But your watch isn't your coach, your physiologist, or your central nervous system.

Use the data.

Understand what it means.

Then combine it with how you're actually performing and feeling.

That's considerably more useful than blindly chasing a colored bar on your watch.

References

1. Kaufmann S, Gronwald T, Herold F, Hoos O. Heart Rate Variability-Derived Thresholds for Exercise Intensity Prescription in Endurance Sports: A Systematic Review of Interrelations and Agreement with Different Ventilatory and Blood Lactate Thresholds. Sports Medicine Open. 2023;9:59.

2. Tanner V, Millet GP, Bourdillon N. Agreement Between Heart Rate Variability-Derived vs. Ventilatory and Lactate Thresholds: A Systematic Review with Meta-Analyses. Sports Medicine Open. 2024;10:109.

3. What Is "Zone 2 Training"?: Experts' Viewpoint on Definition, Training Methods, and Expected Adaptations. International Journal of Sports Physiology and Performance. 2025. The expert panel favored performing Zone 2 immediately below the first lactate or ventilatory threshold.

4. Zone 2 Intensity: A Critical Comparison of Individual Variability in Different Submaximal Exercise Intensity Boundaries. 2025. The study found substantial individual variation between commonly used Zone 2 markers and cautioned against relying solely on fixed percentages of maximum heart rate.

5. Seiler S. What Is Best Practice for Training Intensity and Duration Distribution in Endurance Athletes? International Journal of Sports Physiology and Performance. 2010;5(3):276–291.

6. Jamnick NA, Pettitt RW, Granata C, Pyne DB, Bishop DJ. An Examination and Critique of Current Methods to Determine Exercise Intensity. Sports Medicine. 2020;50:1729–1756.