Zone 2 cardio: what it is, and what the evidence shows

By the Voltra team · Updated 30 September 2026

What Zone 2 means

There is no single agreed definition [1]. In the five-zone scales common in endurance sport, Zone 2 is the second-lowest zone [6]. In 2025 a panel of 14 sport scientists and coaches agreed it should sit immediately below the first lactate or ventilatory threshold, done continuously or in intervals [1]. That threshold is the lower of the two turning points a lab test finds in blood lactate or breathing as effort rises [7].

Research papers often mean something else. In the three-zone model most studies use, Zone 1 is below the first threshold, Zone 3 is above the second, and Zone 2 is the band in between [7], which is harder than the popular Zone 2. Polarised training, for example, keeps that research Zone 2 under 10% of training [7].

Without a lab, the talk test is the practical check: talking is usually comfortable below the first threshold and not above it, whether you walk, jog, cycle or use a stair stepper [2]. Saudi Arabia's health ministry and Qatar's national guidelines both describe moderate activity as being able to talk but not sing [8] [9]. Dubai's 2026 guideline splits it finer: "Moderate-intensity: Can talk in phrases or short sentences", while talking in full sentences counts as light [10].

Why the heart-rate numbers disagree

How Voltra and other sources describe Zone 2 or moderate effort:

Voltra's figures are from its Zone 2 primer; the others are as cited.

Lab tests show why a fixed percentage is rough. In 100 adults, the first lactate threshold came anywhere from 60% to 90% of their measured max heart rate [3]. In 50 experienced amateur cyclists, the first ventilatory threshold averaged about 81% of measured max and the point of fastest fat burning about 72%, and fixed percentages of max heart rate showed wide differences between riders [6]. So, depending on the person, 60–70% of max can sit well below the first threshold or right at it [3]. If you can still talk comfortably, you are probably below it [2].

How good is 220 minus your age?

It's a rough estimate. A 2001 analysis pooling 351 studies with 18,712 people put max heart rate at about 208 − 0.7 × age, and concluded that 220 minus age underestimates it in older adults [12]. In 3,320 healthy adults in Norway's HUNT study, the best-fitting formula was 211 − 0.64 × age, yet people typically sat about 11 beats a minute above or below it (standard error 10.8), and the older formulas underestimated measured max in people over 30 [4].

Beats a minute, calculated from the two formulas [12]. An 11-beat error in your max moves a 60–70% range by about 7 beats (calculated).

What the trials show

Most trials don't use the name Zone 2. They compare steady, moderate-intensity training with intervals.

• Fitness. In 28 controlled studies of healthy 18- to 45-year-olds, steady endurance training and intervals both raised VO₂max, the usual measure of cardiorespiratory fitness, by a large amount; intervals added about 1.2 ml/kg/min more [13]. A 2026 Cochrane review in sedentary adults found a similar slight edge for intervals (37 trials), with low certainty [5].
• Heart and metabolic health. The same review found little to no difference between intervals and steady moderate training for waist size, blood pressure or triglycerides, with low to moderate certainty. None of the trials reported on deaths or side effects, and all the interval programmes were supervised [5].
• Fat loss. In 13 trials in overweight or obese adults aged 18 to 45, both cut body fat and waist size by similar amounts, and intervals took about 40% less time [14].
• Fat burning during exercise. The rate at which you burn fat does peak at moderate effort: in 300 healthy adults on a treadmill it peaked at about 62% of max heart rate on average [15]. But improving it doesn't take easy training: in non-athletes, intervals raised fat burning during exercise slightly more than steady moderate training did [16].
• Polarised training (mostly easy sessions plus some hard ones, with little in between). In athletes it gave a small extra gain in peak VO₂ over other patterns, but only in programmes under 12 weeks and in highly trained athletes, with no advantage in time trials [7]. Pooling individual data from 348 endurance athletes found no overall difference; competitive athletes may gain more from it than recreational ones [17].

What's claimed but not shown

Arabic coverage in 2026 describes Zone 2 as 60–70% of max heart rate, a way to burn fat without hard effort, and a way to build more mitochondria, the energy-producing parts of cells [18]. A 2025 review notes that popular media has cast Zone 2 as the best intensity for mitochondria and fat burning, and that the idea rests largely on observations of elite endurance athletes who do a lot of it [19]. A 2018 study cited for this rationale [6] compared professional endurance athletes, moderately active people and people with metabolic syndrome at a single point in time; it didn't test a training programme [20].

The wider evidence doesn't single out Zone 2. Across 353 studies, mitochondrial content rose by similar amounts after steady low- to moderate-intensity training (about 23%), high-intensity training (27%) and sprint intervals (27%), and per hour of exercise the harder formats did it faster [21]. The 2025 review concluded that current evidence doesn't support Zone 2 as the best intensity for mitochondria or fat burning, and that going harder matters for health benefits, especially when training time is limited [19]. One of its authors holds equity in a company whose services relate to exercise [19].

That doesn't make easy cardio pointless. The expert panel expects broad benefits from Zone 2, while noting that slightly harder or easier sessions may bring the same [1], and steady training raised VO₂max by a large amount in the trials above [13].

How much a week

The WHO's recommendation: "Adults should do at least 150–300 minutes of moderate-intensity aerobic physical activity; or at least 75–150 minutes of vigorous-intensity aerobic physical activity; or an equivalent combination of moderate- and vigorous-intensity activity throughout the week, for substantial health benefits." [11] It rates moderate against your own capacity: "On a scale relative to an individual’s personal capacity, moderate-intensity physical activity is usually a 5 or 6 on a scale of 0–10." [11] Saudi Arabia's Public Health Authority and the Dubai Health Authority give the same minutes [22] [10]. Kuwait's 2023 food-based dietary guidelines give the same global advice, at least 150 minutes of moderate or 75 minutes of vigorous activity a week, count brisk walking as moderate, and advise anyone with a medical problem to check with a physician before starting a new exercise programme [23]. None of these guidelines sets separate Zone 2 minutes; our weekly exercise guide covers strength training, heat and Ramadan.

In Voltra

In the Train tab, the Cardio page has a Zone 2 quick action that logs a Zone 2 session, and a Zone 2 primer. The primer's rule of thumb is a conversational pace at about 60–70% of your max heart rate, estimated as 220 minus your age, times 0.6 to 0.7; 30–60 minutes, 2–3 times a week; and low-impact options such as an incline treadmill walk, a stationary bike, a rowing machine, pool laps or a stair stepper. That comes to 60–180 minutes a week (calculated). Voltra uses 60–70% of max heart rate as a starting point; lab definitions put Zone 2 just below your first lactate or ventilatory threshold, which ranged from 60% to 90% of max in the study above [1] [3].

Frequently asked

Sources

1. Sitko S, Artetxe X, Bonnevie-Svendsen M, et al. (2025). What Is "Zone 2 Training"?: Experts' Viewpoint on Definition, Training Methods, and Expected Adaptations. Int J Sports Physiol Perform 20(11):1614–1617. Abstract. Expert commentary, 14 panellists.
2. Reed JL, Pipe AL (2014). The talk test: a useful tool for prescribing and monitoring exercise intensity. Curr Opin Cardiol 29(5):475–80. Abstract. Narrative review.
3. Iannetta D, Inglis EC, Mattu AT, et al. (2020). A Critical Evaluation of Current Methods for Exercise Prescription in Women and Men. Med Sci Sports Exerc 52(2):466–473. Abstract. 100 adults; thresholds and max heart rate measured.
4. Nes BM, Janszky I, Wisløff U, Støylen A, Karlsen T (2013). Age-predicted maximal heart rate in healthy subjects: The HUNT fitness study. Scand J Med Sci Sports 23(6):697–704. Abstract. 3,320 adults.
5. Strauss JA, Kirwan R, Ranasinghe C, et al. (2026). High-intensity interval training for reducing cardiometabolic syndrome in healthy but sedentary populations. Cochrane Database Syst Rev CD013617. Abstract. Funded in part by the UK's NIHR and FCDO.
6. 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. 50 experienced amateur cyclists; Table 2.
7. Silva Oliveira P, Boppre G, Fonseca H (2024). Comparison of Polarized Versus Other Types of Endurance Training Intensity Distribution on Athletes' Endurance Performance: A Systematic Review with Meta-analysis. Sports Med 54(8):2071–2095. Introduction and abstract. Athletes only.
8. وزارة الصحة، المملكة العربية السعودية (٢٠٢٠). دليل النشاط البدني للممارس الصحي. In Arabic. Pages 14–15, read from the page images.
9. Aspetar, State of Qatar (2021). Qatar National Physical Activity Guidelines, 2nd edition. Printed page 48.
10. Dubai Health Authority (2026). Physical Activity Guidelines (DHA/DG/PHP/GU01). Section 6.2.1 and the adult recommendations.
11. World Health Organization (2020). WHO guidelines on physical activity and sedentary behaviour. Glossary, page vii; adults, page 2.
12. Tanaka H, Monahan KD, Seals DR (2001). Age-predicted maximal heart rate revisited. J Am Coll Cardiol 37(1):153–6. Abstract. 351 studies, plus a lab study of 514 people.
13. Milanović Z, Sporiš G, Weston M (2015). Effectiveness of High-Intensity Interval Training (HIT) and Continuous Endurance Training for VO2max Improvements: A Systematic Review and Meta-Analysis of Controlled Trials. Sports Med 45(10):1469–81. Abstract. 28 studies, 723 adults aged 18–45.
14. Wewege M, van den Berg R, Ward RE, Keech A (2017). The effects of high-intensity interval training vs. moderate-intensity continuous training on body composition in overweight and obese adults: a systematic review and meta-analysis. Obes Rev 18(6):635–646. Abstract. 13 trials.
15. Venables MC, Achten J, Jeukendrup AE (2005). Determinants of fat oxidation during exercise in healthy men and women: a cross-sectional study. J Appl Physiol 98(1):160–7. Abstract. 300 adults, one treadmill test each.
16. Atakan MM, Guzel Y, Shrestha N, et al. (2022). Effects of high-intensity interval training (HIIT) and sprint interval training (SIT) on fat oxidation during exercise: a systematic review and meta-analysis. Br J Sports Med 56:988–996. Abstract. 18 studies in non-athletes.
17. Rosenblat MA, Watt JA, Arnold JI, et al. (2025). Which Training Intensity Distribution Intervention will Produce the Greatest Improvements in Maximal Oxygen Uptake and Time-Trial Performance in Endurance Athletes? Sports Med 55(3):655–673. Abstract. Individual data from 348 athletes.
18. د. عمرو ياسر، مجلة الرجل (٢٠٢٦). تمارين Zone 2.. حسّن لياقتك بأقل جهد. In Arabic. A magazine article, cited only for what is claimed.
19. 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. Abstract and conflict-of-interest statement. Narrative review.
20. 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. Abstract. A one-time comparison, no training.
21. Mølmen KS, Almquist NW, Skattebo Ø (2025). Effects of Exercise Training on Mitochondrial and Capillary Growth in Human Skeletal Muscle: A Systematic Review and Meta-Regression. Sports Med 55(1):115–144. Abstract. 353 studies.
22. هيئة الصحة العامة (وقاية)، المملكة العربية السعودية. إرشادات الحركة على مدار 24 ساعة للمملكة العربية السعودية: تكامل النشاط البدني والسلوك الخامل ومدة النوم. In Arabic. Pages 8 and 24.
23. Public Authority for Food and Nutrition, Kuwait (2023). Kuwait Food-Based Dietary Guidelines (KFBDG). Message 9, printed page 38.

Sources checked on 30 September 2026.

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