Zone 2 Training: What It Is and How to Find Yours

Zone 2 is steady, sustainable exercise just below the point where your breathing starts to climb faster than your effort. In practice, it is roughly the hardest pace you can hold while still talking comfortably in full sentences. It has become one of the most talked-about ideas in fitness, but the research behind it is less settled than the popularity suggests, and a fixed heart rate formula is not a reliable way to find it.

What exactly is Zone 2?

There is no single agreed definition, which is the first thing worth knowing. A 2025 expert commentary in the International Journal of Sports Physiology and Performance opens by noting that there is no clear consensus among coaches, athletes and scientists on what Zone 2 means.

The 14 sport scientists and coaches on that panel agreed that Zone 2 should ideally sit immediately below the first lactate or ventilatory threshold. That threshold is the point where lactate in the blood first starts to rise above resting levels and breathing begins to quicken out of step with effort. Below it, exercise feels steady and sustainable. Above it, it starts to feel like work.

Different training systems also number their zones differently, so "Zone 2" on one app or watch will not always mean the same thing on another.

Why is a heart rate formula a poor guide to Zone 2?

Because the threshold sits at a different percentage of maximum heart rate from one person to the next. A 2025 study of 50 cyclists tested each rider in the lab and compared common ways of setting Zone 2. Markers based on breathing and fat use lined up well with each other, but fixed percentages of maximum heart rate showed wide individual differences. The authors concluded that fixed percentages are practical but may not reflect what is actually happening in the body.

That problem compounds if your maximum heart rate is itself an estimate from your age, which typically carries an error of around 11 beats per minute. Two layers of estimation leave a lot of room for error.

How do you find your Zone 2 without a lab?

Use your breathing. A 2022 systematic review of the talk test found that the last point at which people could still speak comfortably matched their first ventilatory threshold measured in the lab. Most of those studies were small and involved people with heart disease, so it is an approximation, but it is aimed at exactly the threshold Zone 2 sits under.

• You can speak in full, comfortable sentences: you are at or below Zone 2.
• Talking takes a little effort but you can still manage whole sentences: you are likely near the top of Zone 2.
• You are breaking sentences to breathe: you have moved above it.

Our guide to the talk test explains how to run it properly. If you use a heart rate monitor, note the number you see when you are just at the top of comfortable speech on a cool, rested day. That personal number is a better Zone 2 marker than any formula.

Our target heart rate calculator deliberately does not label a Zone 2, for the reasons above. Its moderate zone is a reasonable starting range, and the talk test fine-tunes it from there.

Is Zone 2 the best kind of exercise?

Not on the current evidence. A 2025 narrative review in Sports Medicine examined the claim that Zone 2 is the optimal intensity for improving the body's capacity to use oxygen and fat. The authors found that the idea rests largely on observational data from elite endurance athletes, who train for many hours a week at low intensity, and that current evidence does not support Zone 2 as the optimal intensity for those outcomes in the general population.

They argue that prioritising harder efforts above Zone 2 is important for cardiometabolic health, particularly for people with limited time to exercise. The expert panel made a related point from the other direction: the adaptations people hope to get from Zone 2 may not be unique to it, and slightly harder or easier sessions could produce them too.

So how should you use Zone 2?

As one useful part of a week, not the whole of it. Steady Zone 2 sessions are comfortable and easy to recover from, which makes them a good base for anyone building up. If you have plenty of time, a large volume of easy work is a sound foundation, and it is how elite endurance athletes do much of their training. If you only have a few hours a week, the review above suggests including some harder efforts rather than keeping every session easy.

Our guide to how much exercise you actually need sets out the weekly targets for moderate and vigorous activity, and both kinds count. If your Zone 2 heart rate reads unusually high on a given day, our article on why heart rate is higher on some days explains the usual reasons.