Zone 2 training: what it is and how much you need

At a glance

What is Zone 2 training?

Zone 2 is the second of five training zones in many coaching systems (some use seven), and it means easy, steady aerobic work. It is the pace of a long run you could chat through or a ride you could keep up all afternoon. You finish feeling you could have gone on.

Physiologically, it sits below your first lactate threshold (LT1), the point where blood lactate first starts to rise above its baseline level during easy exercise. Below it, your body can supply energy aerobically at a steady state for a long time. Above it, effort becomes harder to sustain and needs more recovery.

The name causes confusion. Research papers usually use a three-zone model, where everything below the first threshold is called Zone 1. So the "Zone 1" in a study and the "Zone 2" in your watch app often describe the same easy effort. When you read advice about Zone 2, check whose zones it means.

What heart rate is Zone 2?

It depends on the method, and the methods disagree by a lot.

Age-based formulas are the most common and the least reliable.

• The best-known starting point is estimating maximum heart rate as 220 minus your age, then taking 60 to 70% of it as Zone 2. Garmin, for example, defines Zone 2 as 60 to 70% of maximum heart rate.
• The 220-minus-age formula was never derived from original research, and for any one person it can easily be out by 10 beats per minute or more.
• A later formula from Tanaka and colleagues (208 minus 0.7 × age) is more accurate across a population, especially for older athletes, but still carries an error of around 10 beats per minute for an individual.

Heart rate reserve (the Karvonen method) uses the gap between your resting and maximum heart rate. Zone 2 is often taken as 60 to 70% of that reserve, added to your resting rate. It personalises the bottom of the range, but it still depends on a maximum you have probably estimated.

The MAF method, from Phil Maffetone, sets a ceiling of 180 minus your age, adjusted up or down for health and training history. It gives a maximum to stay under, not a range.

Threshold-based zones are the most reliable. You do a field test in each sport to find your threshold, then set Zone 2 as a percentage of it. Two athletes of the same age can have very different thresholds, and this method captures that where age-based maths can't. If you have had a lactate test, you can go further and set the top of Zone 2 at your own LT1.

This is the approach LOAD takes. See Training zones for the field tests and Lactate thresholds for LT1.

Find your Zone 2

Enter any threshold you know: your FTP on the bike, your threshold pace on the run, your CSS in the pool, or your threshold heart rate. We'll show your Zone 2 range for that sport.

These ranges come from your threshold, not your age, because thresholds vary far more between people than age formulas allow. If you don't know your threshold yet, see Training zones for simple field tests you can do this week.

Use the range as a guide, not a rule. On long sessions your heart rate will drift up even at a steady pace, so set the session by power or pace and treat heart rate as a ceiling. If a Zone 2 session feels hard, your threshold may have changed, or you may just be tired, and both are worth knowing.

Want all five zones for every sport? Use the training zones calculator.

These are LOAD's Endurance zone (Z2) in each sport, each running up to where the next zone starts: 55–76% of FTP on the bike; 1.14–1.29× threshold pace, 78–88% of run threshold power or 85–90% of run threshold heart rate on the run; 1.09–1.15× CSS pace in the pool; 81–90% of threshold heart rate on the bike. Run pace and heart-rate zones are based on Joe Friel's.

How do you train in Zone 2 when running?

Expect it to feel slow. Running is where Zone 2 frustrates people most. Many athletes reach a higher heart rate running than cycling at the same perceived effort, and many runners find their Zone 2 pace is noticeably slower than their usual easy pace. That's normal, and it tends to improve as your aerobic fitness develops.

Use walk breaks without guilt. If your heart rate climbs above Zone 2 on a gentle jog or a hill, walk for a minute, let it settle, and carry on. Coaches commonly suggest a short walk every few minutes for runners who can't yet stay in range. A 2016 study of non-elite marathon runners found a run-walk strategy finished in similar times to running throughout, with less muscle pain and fatigue.

Watch for heart-rate drift. On a long run or ride at a steady pace, heart rate gradually creeps up over one to two hours, by as much as 10% if you don't drink, and more in heat. This is cardiovascular drift. If you hold your heart rate perfectly steady late in a long session, you are actually slowing down. A practical rule: set the session by pace or power, and use heart rate as a ceiling you respect rather than a number you chase.

Choose flat routes or the treadmill while you learn the feel. Hills and wind make it hard to stay in range.

What are the benefits of Zone 2?

• It builds your aerobic engine. Long, easy training develops the heart, blood vessels and muscle adaptations that let you go further and faster before tiring.
• It lets you train more. Easy sessions cost little recovery, so you can stack more weekly hours than you could at higher intensity.
• It protects the hard days. Keeping easy days easy leaves you fresh enough to do your interval and threshold sessions properly.
• It teaches pacing. Long-course triathlon is raced mostly at steady, controlled effort. Many hours at that kind of effort build the patience to hold back early.

You will also hear stronger claims: that Zone 2 is uniquely good for your mitochondria, for "metabolic health" or for clearing lactate. Some of these come from respected scientists, but they are not settled. See Should you trust the Zone 2 hype? below.

How much Zone 2 does a triathlete need?

For most triathletes, most of the week. Stephen Seiler's research on elite endurance athletes found they do roughly 75 to 80% of their sessions at low intensity, with most of the rest at high intensity and relatively little in between. A six-month study of Ironman triathletes found around 70% of their training in the lowest intensity zone. In a study of nine Ironman athletes over a season, those who did more low-intensity training tended to race faster, and those who spent a larger share of their training in the moderate zone between the two thresholds tended to race slower. That is a correlation in a small group, not proof, but it points the same way.

How it differs by sport

• Bike: the easiest place to build Zone 2 volume. It's low impact, so long rides cost less recovery than long runs. The weekly long ride is usually a triathlete's biggest Zone 2 session.
• Run: Zone 2 matters most here, because running carries the highest injury risk and easy running is where most athletes go too hard. Keep the long run easy.
• Swim: wrist heart rate is often unreliable in water, so go by pace against your CSS (Critical Swim Speed) or by feel. In LOAD, swim Zone 2 is 9 to 15% slower than CSS pace: at a CSS of 1:34 per 100 m, that's about 1:42 to 1:48.

How it fits your week

• In a polarised week, around 80% of sessions are easy and most of the rest are hard, with little in between.
• In a pyramidal week, most training is still easy, but there is more moderate work such as tempo and sweet spot.

Both put Zone 2 at the base. A 2025 analysis of 13 studies found no clear winner between the two overall. For VO2max, competitive athletes responded better to polarised training and recreational athletes to pyramidal. See Polarised, pyramidal and threshold training.

If you train about 6 hours a week, Zone 2 should still be most of it, but not all of it. The elite 80/20 split comes from athletes training ten or more sessions a week; at low volume, one or two quality sessions a week matter more. A 2025 review argued that when total training time is low, higher intensities may give more benefit per hour. For a 6-hour week, that could mean two key sessions (intervals or threshold) and the rest easy.

My own split

Here's my own split, measured by heart rate across swim, bike and run. In the season that finished in Almere, 82% of my training time was in Zones 1 and 2, up from 77% the year before, and my time in Zone 3 fell from 12% to 10%.

Should you trust the Zone 2 hype?

Trust the core idea. Be sceptical of the bigger claims.

What the evidence supports

• Elite endurance athletes really do train mostly at low intensity. That pattern is well documented across sports.
• Easy days done easy make hard days better, and many amateurs go too hard on easy days.
• Fitter athletes burn more fat and produce less lactate at a given effort. In a 2018 study, Iñigo San Millán and George Brooks found professional cyclists oxidised far more fat and had lower lactate than moderately active or less-fit men at similar workloads.

Where it's overstated

• "Zone 2 is the best way to build mitochondria." San Millán argues that Zone 2 specifically trains mitochondrial function and lactate clearance. His 2018 paper with Brooks compared athletes of different fitness; it did not test Zone 2 training, and it didn't measure mitochondria directly. A 2025 review by Storoschuk, Gibala and colleagues concluded that current evidence doesn't support Zone 2 as the optimal intensity for building mitochondria or fitness in the general population, and that higher intensities may do as much or more, especially when training time is limited.
• "It's the fat-burning zone." At low intensity, a bigger share of your energy comes from fat. But the actual rate of fat burning peaks higher, at moderate effort. In one study of moderately trained cyclists it was close to its peak between about 55 and 72% of VO2max, and it peaks at lower intensities in less-trained people. Neither fact makes low intensity the best intensity overall. Fuel use during a session is not the same as long-term adaptation.
• "Zone 2" isn't one thing. A watch app's 60 to 70% of maximum heart rate, a coach's 85 to 89% of threshold heart rate, Andrew Coggan's 56 to 75% of FTP, and a lab's "below 2 mmol/L lactate" can all be called Zone 2, and they don't land in the same place. Two people arguing about Zone 2 are often describing different efforts.
• Elite numbers don't scale down neatly. The 80/20 split is partly a product of very high training volume. At five or six hours a week, the same proportions leave little room for the work that raises your ceiling.

Who it suits least

• People training three or four hours a week mainly to get fitter. They will usually get more from some harder sessions.
• Athletes who make every session Zone 2 and drop the race-specific work they need.
• Anyone treating a heart-rate number from an age formula as precise. If it feels wrong, it probably is.

The honest summary

Zone 2 is the foundation of endurance training, not a magic intensity. It earns its place by letting you train more and train hard days well, not because the zone itself is special.

Related

• Training zones calculatorAll five training zones for swim, bike and run from your FTP, threshold pace, CSS or threshold heart rate, using the same zones as LOAD.
• Training zonesHow FTP, threshold pace, CSS and heart rate become zones, LOAD's five-zone model, and where zones mislead.
• Lactate thresholdsWhat LT1 and LT2 are, how a lactate test sets your zones, lactate-guided training, and why turn points never stay fixed.
• Polarised, pyramidal and thresholdHow the main intensity-distribution models differ, what the research actually shows, and how triathletes should use them.

Sources

1. Seiler KS, Kjerland GØ. Quantifying training intensity distribution in elite endurance athletes: is there evidence for an "optimal" distribution? Scandinavian Journal of Medicine & Science in Sports. 2006;16(1):49–56.
2. 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.
3. Esteve-Lanao J, Foster C, Seiler S, Lucia A. Impact of training intensity distribution on performance in endurance athletes. Journal of Strength and Conditioning Research. 2007;21(3):943–949.
4. San-Millán I, Brooks GA. 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 Medicine. 2018;48(2):467–479.
5. San Millán I. Zone 2 training. TrainingPeaks. His own definition of Zone 2 and the claims made for it.
6. Storoschuk KL, Moran-MacDonald A, Gibala MJ, Gurd BJ. 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 Medicine. 2025;55(7):1611–1624.
7. Achten J, Gleeson M, Jeukendrup AE. Determination of the exercise intensity that elicits maximal fat oxidation. Medicine & Science in Sports & Exercise. 2002;34(1):92–97.
8. Achten J, Jeukendrup AE. Optimizing fat oxidation through exercise and diet. Nutrition. 2004;20(7–8):716–727.
9. Robergs RA, Landwehr R. The surprising history of the "HRmax = 220 − age" equation. Journal of Exercise Physiology Online. 2002;5(2):1–10.
10. Tanaka H, Monahan KD, Seals DR. Age-predicted maximal heart rate revisited. Journal of the American College of Cardiology. 2001;37(1):153–156.
11. Garmin. Heart rate zones (Forerunner owner's manual).
12. Maffetone P. The MAF 180 Formula.
13. Friel J. Joe Friel's quick guide to setting zones. TrainingPeaks. The basis of the run pace and heart-rate ranges used here.
14. Allen H, Coggan AR, McGregor S. Training and Racing with a Power Meter, 3rd edition. VeloPress, 2019.
15. Hamilton MT, González-Alonso J, Montain SJ, Coyle EF. Fluid replacement and glucose infusion during exercise prevent cardiovascular drift. Journal of Applied Physiology. 1991;71(3):871–877.
16. Coyle EF, González-Alonso J. Cardiovascular drift during prolonged exercise: new perspectives. Exercise and Sport Sciences Reviews. 2001;29(2):88–92.
17. Hottenrott K, Ludyga S, Schulze S, Gronwald T, Jäger FS. Does a run/walk strategy decrease cardiac stress during a marathon in non-elite runners? Journal of Science and Medicine in Sport. 2016;19(1):64–68.
18. Runner's World. How to run slower on your Zone 2 days (coach Janet Hamilton).
19. Neal CM, Hunter AM, Galloway SDR. A 6-month analysis of training-intensity distribution and physiological adaptation in Ironman triathletes. Journal of Sports Sciences. 2011;29(14):1515–1523.
20. Muñoz I, Cejuela R, Seiler S, Larumbe E, Esteve-Lanao J. Training-intensity distribution during an Ironman season: relationship with competition performance. International Journal of Sports Physiology and Performance. 2014;9(2):332–339.
21. Rosenblat MA, Watt JA, et al. Which training intensity distribution intervention will produce the greatest improvements in maximal oxygen uptake and time-trial performance in endurance athletes? A systematic review and network meta-analysis of individual participant data. Sports Medicine. 2025;55:655–673.
22. Stöggl TL, Sperlich B. The training intensity distribution among well-trained and elite endurance athletes. Frontiers in Physiology. 2015;6:295.