Training
Zone 2 running: the art of going slow on purpose
Zone 2 running is easy, conversational running just below your first threshold, where breathing and blood lactate first start to rise. It lets you run often and recover, and staying there mostly means running slower than feels natural.
What is zone 2 running?
Zone 2 running is the top of the easy range, just under your first threshold: the point where blood lactate first rises above resting levels (LT1) and breathing first quickens out of proportion to effort (VT1). Below it, you can talk in full sentences and keep going for a long time.
Zone systems differ. In the three-zone research model, zone 1 is everything below the first threshold and zone 2 sits between the thresholds; the five-zone systems most watches use put "zone 2" near the top of research zone 1. The watch version, easy and conversational, is what runners almost always mean.
The hype owes a lot to research on metabolic flexibility, the ability to switch between burning fat and carbohydrate. San-Millán and Brooks (2018) found professional endurance athletes oxidized more fat, with lower blood lactate, than moderately active people and people with metabolic syndrome as power output rose. That describes trained physiology; it does not prove one intensity builds it best.
How do I find my zone 2 heart rate without a lab test?
Without a lab, the most reliable field marker is your breathing and speech: comfortable full sentences mean you are almost certainly below your first threshold, and when speech first becomes difficult, you are close to it. Heart-rate formulas are a rough starting point, not an answer.
The talk test has decent support. In Persinger and colleagues (2004), 16 young, healthy volunteers read aloud at each stage of treadmill and cycle tests. Where speech first became difficult, intensity sat almost exactly at the ventilatory threshold; once speech was uncomfortable, it was consistently above, and the last comfortable stage sat just under it.
Fixed percentages of maximum heart rate are weaker. A 2020 review by Jamnick and colleagues concluded that prescribing intensity from a fixed percentage of maximal anchors "has little merit" for producing distinct physiological responses, and pointed to thresholds such as LT1 and VT1 instead. In 50 cyclists, Meixner and colleagues (2025) found VT1 and the point of maximal fat oxidation lined up well, while fixed heart-rate percentages and blood-lactate values varied widely against them from person to person.
| Marker | What it reflects | What you need | Main caveat |
|---|---|---|---|
| Ventilatory threshold (VT1) | First rise in breathing relative to oxygen use | A lab with gas analysis | One day, one test; it moves as you get fitter |
| Lactate threshold (LT1) | First rise in blood lactate above baseline | Finger-prick lactate meter and a step test | Method choices change the answer |
| Talk test | Speech becoming difficult near VT | Nothing | Subjective; harder to judge on hills and in wind |
| Fixed % of max heart rate | A population average | A max heart rate, measured or estimated | Agrees poorly with individual thresholds |
Why does my heart rate go up when my pace stays the same?
That is cardiovascular drift: during prolonged steady exercise, heart rate climbs while stroke volume (blood pumped per beat) falls, even at a constant speed, and heat and fluid loss make it larger. A pace that read as zone 2 in the first twenty minutes can read well above it an hour later.
Coyle and González-Alonso (2001) describe stroke volume declining progressively after 10 to 20 minutes and argue the rising heart rate mainly drives it, rather than blood moving to the skin. Dehydration adds to it: in Montain and Coyle (1992), fluid loss was linearly related to the rise in core temperature and heart rate and the fall in stroke volume.
So which number do you hold? On an easy day, the effort: let the pace fall. Chasing the morning's pace through a hot afternoon turns an easy run into a steady one, and your watch's pace is not a promise you made to anyone. A climb raises heart rate within a minute, so slow down, shorten your step, or walk.
- Easy, running above the Easy range
You're creeping up. Ease off, this is meant to be easy.
- Easy, heart rate climbing at the same pace late in a run
Your heart rate's climbing at the same pace. That's heat or fatigue. Ease off slightly.
- Easy, heart rate above its range, so the pace target comes down
Same effort, slower pace today. That's the right trade.
- Back inside the range
That's it. Right where we want you.
Is zone 2 training the best way to build aerobic fitness?
Not uniquely. A 2025 narrative review concluded that current evidence does not support zone 2 as the optimal intensity for improving mitochondrial capacity, and that harder work matters most when total training time is low. Zone 2 earns its place another way: it lets you accumulate the most running for the least cost.
In the words of Storoschuk and colleagues (2025), evidence "does not support Zone 2 training as the optimal intensity for improving mitochondrial or fatty acid oxidative capacity," and "prioritizing higher exercise intensities (> Zone 2) is critical to maximize cardiometabolic health benefits, particularly in the context of lower training volumes."
Easy running still matters: elite endurance athletes do most of their training at low intensity. In Seiler and Kjerland (2006), nationally competitive junior cross-country skiers logged about three quarters of their sessions below the first threshold, however intensity was measured. Over nine weeks in 48 well-trained athletes, Stöggl and Sperlich (2014) found the polarized group, mostly easy with some hard, improved VO2peak (peak oxygen uptake in a test) the most: 11.7%.
| Measured by | Below first threshold | Between thresholds | Above second threshold |
|---|---|---|---|
| Heart rate | 75% | 8% | 17% |
| Session RPE | 76% | 6% | 18% |
| Blood lactate (60 sessions) | 71% | 7% | 22% |
The sensible reading: zone 2 is the base that lets you run often and recover, and a little hard running on top does work easy running alone does not. Three short runs a week? Make one harder. Six days? Keep most of them easy.
Is it OK to walk during a zone 2 run?
Yes. If your slowest jog takes you above your first threshold, walking is the zone 2 session, which is common for newer runners, on steep ground and on hot days. An honest easy pace often feels uncomfortably slow at first; that is information, not a verdict. Run-walk is legitimate easy time, the breaks shrink as fitness grows, and what counts is the effort, not whether every minute looks like running.
Do I need a chest strap for zone 2 training?
No, but it helps. For steady running, a well-fitted wrist sensor is usually close to a chest strap. The strap earns its keep when heart rate changes quickly, in the cold, with a poor wrist fit, or whenever you steer by a narrow range.
Against an ECG, Gillinov and colleagues (2017) found a chest strap almost perfectly aligned (rc 0.996, an agreement score where 1 is perfect), with Apple Watch the closest of the wrist devices (rc 0.92). More in Apple Watch heart rate vs a chest strap.
What does a zone 2 training plan look like?
A simple six-week block holds the effort and lets the time grow. It suits a healthy runner who already runs a few times a week, and is a suggestion, not a prescription or a promise of results: shorten it, slow it or add walking as needed.
Weeks 1–2: learn the effort
Three or four easy runs of 30 to 40 minutes. Talk-test every run, and walk any climb that takes your breath.
Weeks 3–4: extend one run
Keep the short runs. Grow one run by about ten minutes a week, at the same effort.
Weeks 5–6: hold, then check
Hold the longer run. Near the end, repeat a familiar route on a similar day and compare pace at the same heart rate.
Any week: add a little hard work
Time allowing, one short harder session a week complements the easy running. Keep it away from the long run.
Progress is the same heart rate buying a slightly quicker pace over weeks, in similar conditions. Single runs are noisy; trends are not.
How does Gears keep easy runs easy?
In Gears, easy running is Easy (Gear 1): a pace range placed from your own running and refined by every run with heart rate, and meant to allow full sentences. More on personalized running zones and the zone 2 running app.
- Pace leads, heart rate guards. You steer by pace; when your heart says an easy stretch is too much, the coach eases it. Heart rate can only ever make a gear easier.
- Drift is named, not punished. When heart rate climbs at the same pace, the coach says so and asks you to ease off.
- Walking is a gear. Run-walk runs and walk breaks are built in; plans for new runners start with walking.
- Indoors, heart rate leads. On iPhone alone, it comes from a Bluetooth chest strap or a Garmin's Broadcast Heart Rate.
Questions
Is zone 2 the same as the fat-burning zone?
Partly. Fat supplies a large share of energy at easy intensities, and trained athletes burn more of it at a given output. But a 2025 review found no evidence that zone 2 is uniquely best for fat-burning capacity, and total energy use matters more than one run's fuel mix.
How do I calculate my zone 2 heart rate?
Use the talk test rather than a formula: the top of zone 2 sits close to where full sentences first become difficult. Fixed percentages of maximum heart rate agree poorly with individual thresholds.
Why is my zone 2 pace so slow?
Because your first threshold is lower than your habits: most runners drift into steady running on easy days. Hold the effort for a few weeks and judge progress by pace at the same heart rate, not by single runs.
How much of my running should be zone 2?
Most of it, for most runners: elite endurance athletes do roughly three quarters or more of their sessions at low intensity. If your weekly running time is short, keep one harder session too.
References
- Seiler KS, Kjerland GØ (2006). Quantifying training intensity distribution in elite endurance athletes: is there evidence for an "optimal" distribution? Scand J Med Sci Sports 16(1):49–56.
- Stöggl T, Sperlich B (2014). Polarized training has greater impact on key endurance variables than threshold, high intensity, or high volume training. Front Physiol 5:33.
- Storoschuk KL, Moran-MacDonald A, Gibala MJ, Gurd BJ (2025). Much Ado About Zone 2: A Narrative Review Assessing the Efficacy of Zone 2 Training for Improving Mitochondrial Capacity and Cardiorespiratory Fitness in the General Population. Sports Med 55(7):1611–1624.
- Meixner B, Filipas L, Holmberg HC, Sperlich B (2025). Zone 2 Intensity: A Critical Comparison of Individual Variability in Different Submaximal Exercise Intensity Boundaries. Transl Sports Med 2025:2008291.
- Jamnick NA, Pettitt RW, Granata C, Pyne DB, Bishop DJ (2020). An Examination and Critique of Current Methods to Determine Exercise Intensity. Sports Med 50(10):1729–1756.
- Persinger R, Foster C, Gibson M, Fater DC, Porcari JP (2004). Consistency of the talk test for exercise prescription. Med Sci Sports Exerc 36(9):1632–1636.
- Coyle EF, González-Alonso J (2001). Cardiovascular drift during prolonged exercise: new perspectives. Exerc Sport Sci Rev 29(2):88–92.
- Montain SJ, Coyle EF (1992). Influence of graded dehydration on hyperthermia and cardiovascular drift during exercise. J Appl Physiol 73(4):1340–1350.
- San-Millán I, Brooks GA (2018). Assessment of Metabolic Flexibility by Means of Measuring Blood Lactate, Fat, and Carbohydrate Oxidation Responses to Exercise in Professional Endurance Athletes and Less-Fit Individuals. Sports Med 48(2):467–479.
- Gillinov S, Etiwy M, Wang R, et al. (2017). Variable Accuracy of Wearable Heart Rate Monitors during Aerobic Exercise. Med Sci Sports Exerc 49(8):1697–1703.
Last updated . Training guidance, not medical advice: read our health and safety note.