Heart rate zones explained: what each zone does and how to use them

Heart rate zones are the most over-explained, under-used idea in endurance training. Your watch shows them in five pretty colors. Most people glance at them, then run every session in the same slightly-too-hard middle, and wonder why they plateau.

Here's heart rate zones explained without the marketing: what the five zones are, how to find your target heart rate zones, what each one is for, and how to use them in a week that also has lifting in it. Whether you set them by hand or let one of the apps for runners who lift do it, the logic is the same.

What are heart rate zones?

A heart rate zone is a range of beats per minute that corresponds, roughly, to an effort level. Easy running sits low. All-out intervals sit high. The zones carve that range into bands so a plan can say "run this in zone 2" instead of "run this, you know, easy-ish".

Most watches and most coaches use a five-zone model built on percentages of your maximum heart rate. It's convenient, it's everywhere, and it's what you'll get if you punch your numbers into a heart rate zone calculator. The one zone everybody argues about is zone 2, the low-intensity aerobic training that builds the engine without wrecking you.

Two things to know before the table:

• ›Zones are a map, not the territory. The underlying physiology has two real turning points: a first threshold where blood lactate starts rising above baseline, and a second where it can no longer be cleared as fast as it's produced. Faude, Kindermann and Meyer (2009) describe exactly this two-breakpoint framework. Five zones is a practical way of slicing the space around those two points.
• ›Percent-of-max zones are approximations. A 2020 review of intensity-prescription methods concluded that a fixed percentage of maximal anchors like max heart rate "has little merit" for putting different people in the same physiological state (Jamnick et al., 2020). Translation: 70% of max is easy for one person and grey-zone for another. Use the numbers, but check them against how the run feels.

The five heart rate zones explained

This is the model exrsz uses across every post on this blog, so the numbers match wherever you read about them. The percentage bands are the common convention you'll find from watch makers like Polar; the RPE column is coaching practice, on a 1–10 scale.

Roughly, zones 1–2 sit below the first threshold, zone 3 lives between the two, and zone 4 straddles the second. That's why the boundaries are blurry and why your zone 4 can feel like zone 3 one day and zone 5 the next.

If you'd rather skip the strap entirely, the RPE column does most of the same job. Effort-based training is free, works on a treadmill, a trail, or under a barbell, and doesn't lag 30 seconds behind your actual effort like heart rate does.

Why zones matter: hard days hard, easy days easy

The point of zones isn't data. It's discipline. The classic failure in amateur training is "medium everything": every run in zone 3, every week, forever. Too hard to recover from properly, too easy to drive big adaptations.

Successful endurance athletes don't train like that. Across descriptive studies of well-trained endurance athletes, Seiler (2010) found the typical pattern was about 80% of sessions at low intensity and about 20% dominated by high-intensity work. In a nine-week trial in well-trained athletes, a polarized mix (lots of easy, some very hard, little in the middle) improved key endurance markers more than threshold-heavy, high-volume or interval-only training (Stöggl and Sperlich, 2014). Those were trained athletes, not beginners, so treat it as direction rather than a law. But the direction is clear: keep easy days genuinely easy.

For hybrid athletes this matters twice. Easy zone 2 runs are the sessions you can put next to a heavy lifting day without either one suffering. Hard zone 4–5 runs are the ones you have to place carefully, which is the whole game of running and lifting in the same week. Over a season, the balance between zones shifts too: more easy volume in a base phase, more zone 4–5 in a build. That's just macrocycles and mesocycles applied to intensity. Hyrox is the extreme case: a long, sustained hard effort that leans on a big aerobic base, which is why preparing for Hyrox involves a lot more boring easy running than people expect.

How to find your target heart rate zones

There are three ways to set zones, from laziest to best.

1. Estimate max heart rate from your age

The old rule of thumb is 220 minus your age. It's simple and it's everywhere. Tanaka, Monahan and Seals (2001) pooled data from 351 studies and then tested it in a lab, and proposed 208 − 0.7 × age instead, noting that 220 − age underestimates max heart rate in older adults.

Both are population averages. Your real max can sit well above or below either. If your "zone 2" feels like a tempo run, the formula is probably wrong for you, not your lungs.

2. Use heart rate reserve

The heart rate reserve method, which traces back to Karvonen and colleagues (1957), factors in your resting heart rate:

Target HR = resting HR + (max HR − resting HR) × intensity %

It accounts for the fact that two people with the same max can have very different resting heart rates. Two warnings: the same percentage gives a higher number with this method than with percent-of-max, so don't mix the two systems, and it still depends on a max heart rate you probably estimated. Different, not magic.

3. Anchor to your threshold

The best option is to anchor zones to a physiological marker: a lab test with blood lactate or gas analysis, or a hard field test that estimates your lactate threshold. Threshold-based zones move with your fitness, which age formulas never will.

Whichever method you use, heart rate on the day still varies with heat, sleep, caffeine, stress and illness. If your easy pace suddenly produces zone 3 numbers, that's information. Trends in HRV and resting heart rate can help explain it, but the simplest response is the same: slow down, and if something feels genuinely off, see a professional.

What each zone does

Zone 1: recovery

Very easy. Warm-ups, cool-downs, walk breaks, the day after a race. It feels like you're barely training, and that's the point. It moves blood and loosens legs without adding much fatigue.

Zone 2: your aerobic base

This is where most of your running should live, and it's the foundation of your aerobic base. Fitness at this end shows up as handling easy work with less strain: in one lab comparison, professional endurance athletes oxidized more fat and accumulated less blood lactate at the same submaximal intensities than moderately active people (San-Millán and Brooks, 2018). Zone 2 is easy enough to recover from quickly and to do a lot of, which is exactly why it works.

The catch is that real zone 2 is slower than most people's ego wants. Zone 2 running often means slowing down a lot, and sometimes walking hills. Two questions come up constantly. The first is the eternal search query, is zone 2 fat burning: fat oxidation does peak at moderate intensities (around 74% of max heart rate in Achten, Gleeson and Jeukendrup's 2002 cyclists), but the fuel mix during one session isn't the same thing as body fat over months. The second is is zone 2 training a waste of time if you only train three hours a week. Our take: it matters less when total volume is low, and more as volume grows.

Zone 3: the grey zone

Steady, moderately hard, the pace you drift into when you run without a plan. It's not useless. Marathon effort sits around here for many runners, and it builds real fitness. The problem is doing it by accident on days that should be easy. Zone 3 training has a place; it just shouldn't be every run.

Zone 4: threshold

Hard but controlled. This is where tempo and threshold work lives, sessions that push your lactate threshold up so you can hold faster paces for longer. In a well-known 2007 trial, Helgerud and colleagues used 85% of max heart rate as their "lactate threshold" intensity, which sits squarely in this zone. Structured or playful, fartlek training is one of the friendliest ways to start doing work here.

Zone 5: max

Very hard to all-out. Intervals of a few minutes, hill repeats, the last stretch of a race. This is the zone that most directly targets VO2 max: in the same Helgerud trial, 4 × 4-minute intervals at 90–95% of max heart rate improved VO2 max more than the same total work done at threshold or at 70% of max. It's also the most expensive zone to recover from, which is why zone 5 training is used sparingly, usually once a week at most for recreational runners.

Heart rate also lags in short efforts. In a 30-second rep you'll often finish before your heart rate catches up, so short intervals are better judged by pace or effort than by zone.

Other zone systems you'll run into

Five zones on percent of max is the most common model, not the only one.

• ›Three-zone models used in research split intensity at the two thresholds: below the first, between them, above the second (Seiler and Kjerland, 2006). Map them onto our table as zones 1–2, zone 3, and zones 4–5.
• ›Threshold-based systems (like coach Joe Friel's, based on lactate threshold heart rate) number their zones differently. A "zone 2" in one system isn't always a zone 2 in another, so check which model a plan is using before you obey it.
• ›Single-number methods like the MAF method skip zones and give you one ceiling heart rate for all easy running. Simple, but still a formula.

Common mistakes with heart rate zones

• ›Trusting the default. Most watches start you on an age formula. If you never changed it, your zones are a guess. That's especially true for older athletes, which is why running heart rate zones by age is a rougher tool than the colors suggest.
• ›Chasing the number on hard days. On intervals, heart rate is late and noisy. Run the prescribed pace or effort and let heart rate be the receipt.
• ›Ignoring drift. On long or hot runs, heart rate climbs at the same pace. That's normal physiology, not lost fitness. It's also why there's no single answer to what heart rate should you run a marathon at.
• ›Using zones as a ceiling for lifting. Heart rate during a heavy set says little about how hard the set was. For the barbell, use reps in reserve instead.
• ›Medium everything. If every run ends up in zone 3, you've built a plan with no easy days and no hard days. Fix that first; it's worth more than any formula.

How exrsz uses heart rate zones

exrsz builds a periodized plan from your goal, schedule, level and equipment, and every run in it comes with an intensity target that matches the zones above. It balances easy and hard running against your lifting in one plan, adapts each week to how you actually trained, and reshuffles missed sessions so the hard days stay hard and the easy days stay easy.

FAQ

What are heart rate zones?

Heart rate zones are ranges of beats per minute that roughly match effort levels, usually five of them, from very easy recovery (zone 1) to all-out (zone 5). They let a plan prescribe intensity in a way you can check during the run.

How do I calculate my target heart rate zones?

Estimate your max heart rate (220 − age, or Tanaka's 208 − 0.7 × age), then take percentages: zone 2 is 60–70% of max, zone 4 is 80–90%. A threshold test gives more accurate zones than any age formula.

Which heart rate zone is best for building an aerobic base?

Zone 2, at roughly 60–70% of max heart rate. It's easy enough to do a lot of and recover from quickly, which is how an aerobic base gets built.

Are age-based heart rate zones accurate?

They're population averages, so they can be off by a lot for an individual. Use them as a starting point and adjust if your easy runs feel hard or your hard runs feel easy.

How much time should I spend in each heart rate zone?

A common approach, based on how well-trained endurance athletes train, is roughly 80% of sessions easy (zones 1–2) and about 20% hard (zones 4–5), with little deliberate time in zone 3.