Zone 2 running: what it is and what the research says

Zone 2 means easy running just below your first threshold, but sources draw its edges differently. A panel of experts says its expected adaptations may also come from slightly harder or easier running.

By RunFast · Updated 27 October 2026 · 10 min read

What is zone 2 cardio for a runner? It is easy running at an intensity just below the first lactate or ventilatory threshold: that is how a 2025 panel of 14 applied sport scientists and professional coaches defined zone 2 training.¹ The panel said it can be done as continuous, variable or interval-type sessions, and that the adaptations they expect from it might also come from slightly higher or lower intensities.¹

So what is zone 2 running in heart-rate terms? It depends on whose scale you read. The five-zone scale, the most used in a survey of 778 endurance practitioners, splits the low-intensity zone in two, zones 1 and 2, while in the research’s three-zone model zone 2 is the band between the two thresholds.^{2, 3} Studies also set the heart-rate or speed limits of low intensity in different ways.^{4, 5, 6}

In practice, check it with the talk test first: in healthy adults and patients with cardiovascular disease, comfortable speech is likely possible below the ventilatory or lactate threshold, and not above it.⁷ Use heart rate as a rough guide, since fixed percentages of maximum heart rate showed wide individual differences in a lab study of 50 cyclists.⁴ And when you read about 80/20 running, remember that its zone 2 is the research’s middle band, a harder effort than the five-zone zone 2.^{3, 2}

What zone 2 means

The expert definition

The 2025 viewpoint summarises the views of a panel of 14 applied sport scientists and professional coaches, so it is expert opinion rather than a trial.¹ They agreed that zone 2 training should preferably be performed at intensities immediately below the first lactate or ventilatory threshold.¹ Sessions can be continuous, variable or interval-type, so zone 2 describes an intensity rather than one kind of run.¹ A 2025 narrative review noted that popular media define zone 2 as low-intensity exercise below the lactate threshold.⁸

Three zones or five

Running zones come in more than one scale. In the three-zone model used in intensity-distribution research, zone 1 is below the first ventilatory or lactate threshold, zone 3 is above the second, and zone 2 lies between them.³ The five-zone scale described in a 2025 survey paper splits that low-intensity zone 1 into zones 1 and 2, and its zone 3 aligns with zone 2 of the three-zone scale.² In that survey of 778 endurance practitioners, a five-zone scale was the most frequently used, at 47%.²

So the experts’ zone 2, just below the first threshold, sits inside the research’s zone 1, while the zone 2 of polarised-training studies is the harder band between the two thresholds.^{1, 3} The guide to what the research says about 80/20 running uses that three-zone meaning, and how to run a tempo run covers the harder end. When you see heart rate zones for running, check which scale they use before you compare numbers.

Why the heart-rate numbers disagree

Ask what a zone 2 heart rate is and the answer depends on the source. In the 2025 survey, practitioners’ lower limits for zones 2 and 3 differed between regions, and zones 1 to 3 differed between sports, particularly between running and cycling.² The three studies below drew their boundaries in three different ways.

Zone 2 markers also varied from person to person. In the 50 cyclists, the coefficients of variation, a measure of spread, ranged from 6% to 29% across different zone 2 markers, and fixed percentages of HRmax and blood lactate thresholds showed wide individual differences.⁴

In a 2025 treadmill study of men and women of low, medium and high training status, the ventilatory thresholds occurred at a higher %HRmax the higher the training status.⁹ Its authors concluded that a fixed percentage of maximum might not be effective to match intensity across people of different training status.⁹ So a zone 2 heart rate taken from a percentage of your maximum is an estimate, not a measurement of your threshold.^{4, 9}

How to tell if you are in zone 2

The talk test

The simplest way to check you are running in zone 2 is to talk. A 2014 review found that comfortable speech is likely possible when exercise intensity is below the ventilatory or lactate threshold, and not likely possible when it exceeds it.⁷ A 2022 review found the talk test appears to be a valid measure of the ventilatory threshold, and noted that it doesn’t require an exercise test first.¹⁰ Neither review was about runners: the first covered healthy adults and patients with cardiovascular disease.^{7, 10}

On a run, say a few full sentences out loud, or talk with a partner. If speaking stays comfortable, you are likely below the threshold.⁷ If it doesn’t, slow down until it does.

Heart rate, with care

Heart rate can help, within limits. Objective methods of setting intensity need anchor measurements from a maximal or submaximal graded exercise test.¹⁰ Without one, a fixed percentage of maximum is a rough guide, given the wide individual differences in the cyclists and the shift with training status on the treadmill.^{4, 9}

If you run with a heart-rate monitor, warm up before you read it, and when the number and the talk test disagree, go by the talk test. On hills and on hot days, run by the talk test rather than holding a number.

What the research says zone 2 does

What experts expect

The 2025 panel expected a broad range of central and peripheral adaptations from zone 2 training.¹ These are expectations rather than findings, and the panel said they might not be unique to zone 2: sessions at slightly higher and lower intensities could also induce them.¹

Low-intensity training and fitness

A 2026 meta-analysis pooled 50 studies, with 824 people in the training groups, of low-intensity endurance training lasting at least 3 weeks in healthy adults aged 18 to 65.⁵ Against control groups, low-intensity training had a large effect on relative VO2max (maximal oxygen uptake, a measure of aerobic fitness, scaled to body mass), with an effect size of 0.94.⁵ Within that low-intensity range, higher exercise intensity was associated with greater VO2max gains.⁵ That compares training with a control group, not with other intensities, in adults who weren’t necessarily runners, and it defined low intensity more broadly than the experts’ zone 2.^{5, 1}

How much of your running

Endurance athletes tend to do most of their training at low intensity, with a smaller portion at moderate and high intensity.¹¹ In training logs from the 16 weeks before 151,813 marathons, the fastest runners featured large training volumes, achieved mainly by doing more running in zone 1, the study’s lowest zone.⁶ That is an association in what runners chose to do, not a test of zone 2.⁶ The 80/20 running guide covers the trials on splitting easy and hard running, and the marathon training plan guide shows how a plan places easy runs around harder sessions.

Where the evidence is thin or mixed

The popular recommendations for zone 2 training largely stem from observational data of elite endurance athletes, a 2025 narrative review found.⁸ Reviewing the evidence in the general population, it concluded that current evidence does not support zone 2 as the optimal intensity for improving mitochondrial or fatty acid oxidative capacity.⁸ It is a narrative review rather than a systematic one, so read it as one group’s assessment.⁸ We found no trial in runners that compares zone 2 with other easy intensities: what zone 2 does rests on expert opinion, reviews in the general population and studies of training distribution.

On how to split training across intensities, the reviews are mixed. A 2025 network meta-analysis of individual participant data, from 13 studies of 348 trained endurance athletes, found no statistically significant differences between polarised training and any other distribution.¹¹ A 2026 Bayesian network meta-analysis of randomised trials in endurance athletes found that no other distribution showed a definite advantage over polarised training.¹² In the 2025 analysis, which included 150 recreational and 198 competitive athletes, recreational athletes may have improved VO2max more with pyramidal training and competitive athletes with polarised, a subgroup result its authors hedged.¹¹ In the meta-analysis of low-intensity training, responses varied notably between studies.⁵

So the evidence doesn’t single out zone 2 as the best intensity: a review found it not shown to be optimal for mitochondrial or fatty acid oxidative capacity, and the experts expect similar adaptations from slightly harder or easier sessions.^{8, 1} In practice, keep your easy runs conversational and don’t chase an exact heart rate.

Common questions

What is zone 2 cardio?

For a runner, it is easy running just below the first lactate or ventilatory threshold, as an expert panel defined it.¹ A five-zone scale splits the research’s low-intensity zone 1 in two, and zone 2 is the upper part; in the research’s three-zone model, zone 2 is the harder band between the two thresholds.^{2, 3}

What is a zone 2 heart rate?

There is no single number. A lab study of 50 cyclists notes that zone 2 in a five-zone model typically corresponds to about 72–82% of HRmax, but in the same cyclists, fixed percentages of HRmax showed wide individual differences.⁴ The ventilatory thresholds also occurred at a higher %HRmax in people with higher training status.⁹ So if you are asking what your own zone 2 heart rate is, a percentage of your maximum gives only an estimate: check it with the talk test.

How do I find my zone 2 pace?

Find it by effort rather than by formula: run at a pace where comfortable speech stays possible, which is likely below the ventilatory or lactate threshold.⁷ The talk test needs no exercise test beforehand.¹⁰ Note the pace you run when it feels conversational, and keep checking it by the talk test rather than holding that pace whatever the effort.

Is zone 2 the same as an easy run?

The experts define zone 2 by intensity, just below the first threshold, not by a pace or a type of run, and they said its expected adaptations might also come from slightly harder or easier sessions.¹ So an easy run doesn’t need to land exactly in zone 2: if speaking stays comfortable, you are likely below the threshold.⁷

Is zone 2 better than harder running?

The evidence is mixed. Two network meta-analyses in endurance athletes found no distribution clearly ahead of polarised training, a 2025 review concluded that zone 2 is not shown to be the optimal intensity for mitochondrial or fatty acid oxidative capacity, and the experts expect its adaptations might also come from slightly higher or lower intensities.^{11, 12, 8, 1}

This guide is general information, not medical advice. If you have an injury, a health condition or are pregnant, ask a doctor or physiotherapist before changing how you train or eat.

Related guides

• 80/20 running: what the research says80/20 running means keeping most training easy. A 2024 meta-analysis found a small VO2peak advantage for polarised training, but small studies in recreational runners found no significant difference in performance.
• What is a tempo run, and does it work?A tempo run is a sustained run at about threshold pace. Older reviews favoured polarised or pyramidal training over threshold training, and the 2025 and 2026 network meta-analyses found no significant or definite difference.
• How a marathon training plan is builtA marathon training plan combines rising weekly distance, a long run, easy and hard running, lighter weeks and a taper. The research backs some of these parts and says little about how to combine them.

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