Zone 2 Training, Explained: Why Easy Days Make You Faster

How do you find your actual zone 2?

Start with the talk test, because it works and it costs nothing. In zone 2 you can say a full sentence without gasping, though you would rather not hold a long conversation. If you could sing, you are too easy. If you are answering in three-word bursts, you have already slipped into zone 3. Nasal breathing staying comfortable is another decent rough marker.

Then be sceptical about formulas. The 220 minus age rule was never derived from a controlled experiment: Fox, Naughton and Haskell sketched it in 1971 by plotting rough data points from around ten earlier studies and drawing a line through them. Its error runs somewhere near 10 to 15 beats per minute in either direction, wide enough to place your zone 2 ceiling inside someone else’s zone 3. Even the better replacement, the Tanaka equation built from a meta-analysis of 351 studies and 18,712 people, still carries a standard deviation close to 10 bpm. Formulas describe populations. You are one person.

The zones worth training on come from your own numbers: a field test, a lab test, or bands built from your measured maximum and resting heart rate rather than your birthday. If you want the practical setup, we went through it in how to build custom heart rate zones.

This is also where FitWoody is useful. You can set your own heart rate and cycling FTP zones instead of inheriting generic ones, and each workout is analysed against your individual cardiac load, so you see what a session actually cost your body rather than just how long it lasted.

How much zone 2 training do you actually need?

If you train three to five times a week, the useful shape is simple: keep most sessions easy and one or two genuinely hard. That tends to land near an 80/20 split, but the exact percentage matters far less than whether your easy days are honestly easy. Getting the easy end right fixes most of the problem on its own.

Duration matters more than frequency here, since the adaptations track total accumulated time at intensity. That is why zone 2 sessions are usually prescribed at 45 to 90 minutes. If you only have 30, do 30. It still counts. What does not work is five 40-minute sessions that all sit in the murky middle.

Volume is also the thing most likely to break you if you add it too quickly, which is why watching how training load accumulates across weeks is more informative than judging any single workout.

Is zone 2 training overrated?

Partly, and it is worth saying plainly. A 2025 narrative review in Sports Medicine, titled ‘Much Ado About Zone 2’, concluded that the evidence for zone 2 being the optimal intensity for mitochondrial and fat oxidation adaptations is considerably weaker than the popular narrative claims. When low and high intensity are compared directly at matched volumes, higher intensities frequently produce equal or larger mitochondrial responses.

That does not make easy training pointless. It makes the marketing wrong. Zone 2 earns its place because it is sustainable, low-risk, and lets you accumulate hours without accumulating damage, not because it flips a metabolic switch nothing else can reach. The elite athletes cited as proof do enormous volumes of easy work, and they also do more absolute high intensity work in a month than most recreational athletes manage in a year. Both halves are doing the job.

What to change this week

One thing. Make your next steady run, ride or row honestly easy, at a pace where you could answer a question in a full sentence, and let it feel slower than your ego wants. Then notice how your hard session two days later goes. Give it two weeks before you judge it. And on the weeks when even easy feels like a lot, easy is still the right answer: showing up, in any form, counts.