Zone 2 cardio: what it is, how to find it and what the science really says

Published on 26 September 2026

Zone 2 has become the headline recommendation of longevity podcasts. A 2025 review concluded that the evidence does not support it as the optimal intensity. What it is, what it is really good for and how to fit it in if you lift.

In recent years, zone 2 has gone from professional cycling jargon to the headline recommendation of longevity podcasts: easy, long, steady cardio to "train your mitochondria" and burn fat. It sounds reasonable, and part of it is. But in 2025 four researchers reviewed what really sits behind the promise, and their conclusion was far less enthusiastic than social media.

Here we separate what is proven from what has been overstated, and how easy cardio fits in if you also lift.

What zone 2 actually is

It is a low intensity, just below the first lactate threshold: the point beyond which blood lactate starts rising above its resting level. In practice it is a pace you can hold for a long time and at which you can speak in full sentences, even though you notice you are breathing harder.

The percentages of maximum heart rate that circulate online are approximations: the real threshold varies a lot from person to person. The talk test is imperfect, but for most people it is more reliable than a generic formula.

Where zone 2 got its reputation

There are two serious sources behind it, and they are worth reading carefully. The first is the study by San-Millán and Brooks (2018), which compared professional cyclists, moderately active people and patients with metabolic syndrome. The professionals oxidised far more fat and accumulated less lactate at the same intensity, and in every group lactate and fat oxidation moved in opposite directions. It is a useful way of measuring "metabolic flexibility", but it is a descriptive study: it shows that elite athletes are like this, not that zone 2 made them so.

The second is Stephen Seiler's (2010) review of how the best endurance athletes train: around 80% of their sessions are low intensity and the remaining 20% high intensity. Again, solid data on people who train 10 to 13 times a week, which does not transfer as is to someone with three hours a week.

The review that cooled the hype

In 2025, Storoschuk, Moran-MacDonald, Gibala and Gurd published a review in Sports Medicine with a telling title: "Much ado about zone 2". Their argument: the popular recommendation rests mainly on observations of elite athletes who pile up huge volumes, and it clashes with substantial evidence that higher intensities improve mitochondrial capacity and cardiometabolic health as much or more.

Their conclusion is that current evidence does not support zone 2 as the optimal intensity for improving mitochondrial capacity or fat oxidation and that, especially when training time is limited, it makes sense to prioritise higher intensities.

So is it useful? Yes, very

Not being magic does not make it useless. Continuous cardio clearly improves fitness: in the meta-analysis by Milanović and colleagues (2015), with 28 studies and 723 participants, endurance training increased maximal oxygen uptake (VO₂max) by about 4.9 ml/kg/min compared with no training, an effect the authors rated as possibly large.

And that fitness matters: in the study by Mandsager and colleagues (2018) of more than 122,000 patients who took an exercise test, mortality fell as cardiorespiratory fitness rose, with no upper limit of benefit: those with elite fitness had an 80% lower risk than those with the lowest fitness.

The best synthesis comes from combining intensities. In the trial by Stöggl and Sperlich (2014) with 48 trained endurance athletes, the polarised model —lots of easy volume plus some high intensity— improved peak VO₂ by 11.7% in 9 weeks, more than threshold training, high intensity alone or high volume alone.

How much cardio you need: the official benchmark

The World Health Organization guidelines (Bull and colleagues, 2020) are the best compass for most people: 150-300 minutes a week of moderate intensity, or 75-150 of vigorous intensity, or a combination, plus muscle-strengthening work. Zone 2 counts towards those moderate minutes; high-intensity intervals count twice as fast.

How to use zone 2 if you also lift

Two details make the difference. First, easy cardio interferes very little with strength gains, unlike high volumes at high intensity; we explain it in how to combine cardio and strength. Second, brisk walking falls in zone 2 for many people: Japanese walking and adding daily steps are easy ways to accumulate those minutes.

How to find your zone 2: four methods

The sensible approach is to combine two: the heart rate monitor as a guide and the talk test as a check. If your watch says zone 2 but you cannot speak in full sentences, trust the feeling.

Common zone 2 mistakes

• Doing all your cardio in zone 2 when time is short: if you only have an hour a week, the 2025 review suggests higher intensity pays off more.
• Going too hard "just in case": many people end up in zone 3, which is more tiring without being either easy or intense.
• Forgetting strength: the WHO recommends it for all ages, and zone 2 does not replace it.
• Expecting it to make you lose weight on its own: without a calorie deficit, no cardio zone burns fat on balance.

The "fat-burning zone" myth

It is true that in zone 2 a larger share of energy comes from fat. But losing fat depends on the balance of the whole day, not on the fuel of one session: the same reasoning that debunks fasted cardio. If your goal is fat loss, the calorie deficit rules; cardio of any intensity helps widen it.

If you want a plan that spreads strength and cardio across your real days, the Progrevia generator organises it for you.

Progrevia · Updated 26 September 2026 · How we write our guides

Informational content based on the available scientific evidence: it does not replace advice from a healthcare professional. If you have an injury or a medical condition, or are pregnant, check with one before changing your training or diet.