What zone 2 means, and why people argue about it
Zone 2 sounds like one thing. It is a number on somebody's scale, and the scales do not agree.
On the five-zone scale Seiler and Tønnessen published, a simplified version of the one the Norwegian Olympic Federation uses, zone 2 is 75 to 85% of maximum heart rate, with blood lactate of 1.5 to 2.5 mmol/L: the steady end of aerobic work. Much of the research on training intensity uses three zones instead, split at two breathing thresholds. Zone 1 is below the first, zone 2 sits between them, and zone 3 is above the second. By the authors' own reading, zone 3 of the five-zone scale lines up with zone 2 of the three.
So two people can both be right. A coach who tells you to do most of your work in zone 2 is using something like the five-zone version: steady and controlled. A paper that says good athletes spend little time in zone 2 means the band between the thresholds, the comfortably hard pace that feels productive. This page uses plain words instead: easy, moderate and hard.
The other argument is about the race. A HYROX is hard from the first run to the last wall ball, so a slow run can look like wasted time. The research says otherwise.
What the research on intensity shows
Seiler's 2010 review gathered studies of nationally and internationally competitive endurance athletes training 10 to 13 times a week. They converge on about 80% of sessions at low intensity, below about 2 mmol/L of blood lactate, and about 20% built around hard work such as intervals.
That is what good athletes do. Three trials tested what happens when you change it.
| Study | Who | Easy / moderate / hard, % | What happened |
|---|---|---|---|
| Esteve-Lanao and colleagues, 2007 | 12 sub-elite runners, 5 months | About 80 / 12 / 8, against 67 / 25 / 8 | The mostly easy group took 157 seconds off a simulated 10.4 km cross-country race, the other group 122 seconds. The difference was significant. |
| Muñoz and colleagues, 2014 | 30 recreational runners, 10 weeks | About 77 / 3 / 20, against 46 / 35 / 19 | Both groups got faster over 10 km, by 5.0% against 3.6%. The 41-second gap was not significant across all 30 runners; among the runners who kept closest to each plan, it was. |
| Stöggl and Sperlich, 2014 | 48 well-trained runners, cyclists, triathletes and cross-country skiers (41 finished), 9 weeks | 68 / 6 / 26 (polarized), against 46 / 54 / 0 (threshold), 83 / 16 / 1 (high volume) and 43 / 0 / 57 (intervals) | The polarized group gained most on most measures, including 11.7% on VO2 peak. The threshold group, and the high-volume group with the most easy work and almost no hard work, showed no further gains in endurance performance. |
Competitive endurance athletes keep about 80% of their sessions easy (Seiler 2010), and in Seiler and Kjerland's 11 well-trained junior skiers only 6 to 8% of endurance sessions fell in the moderate band. When Muñoz and colleagues split 30 recreational runners into two groups and gave one more moderate time in place of easy time, that group improved no more than the mostly easy group, and on average a little less. Swapping easy time for moderate time bought nothing in either running trial.
These trials are small, short and run in runners and other endurance athletes, not HYROX racers. A 2026 network meta-analysis of randomized trials found no intensity model with a definite advantage over polarized training for VO2 max or time trials. Its ranking, though not definite, leaned towards threshold training for VO2 max and interval training for time trials. Treat 80/20 as a starting point from published practice, not a law.
Finding easy without a lab
You do not need a lactate test. You need three checks, and the first needs nothing but your voice.
The talk test
Foster and colleagues tested it in healthy young adults: the last stage at which they could speak comfortably tracked the first breathing threshold, moving with it when blood donation lowered the threshold and training raised it. Jeanes and colleagues then had 14 well-trained adults, training 5 to 7 hours a week, run 40 minutes at three intensities from the test: one stage below the last comfortable stage, the last comfortable stage, and the stage above it. At the last comfortable stage most could still talk comfortably. At the stage above, where speech was possible but not comfortable, none could, and heart rate and effort were too high for steady training.
- Settle into the pace for a few minutes first. Above the threshold, it took more than two minutes on average for talking to stop being comfortable in Foster's study.
- Say three or four sentences out loud, something you know by heart.
- Comfortable, full sentences: you are easy.
- Possible, but not comfortable: you are into moderate. Slow down, and walk the hills if you have to.
- Not possible: that is hard work, and it belongs in a hard session.
In Foster's study, mistakes leaned towards passing the test when the effort was already above the threshold. If the answer is probably, slow down.
How hard it felt
Rating how hard each session felt can sort your week almost as well as a heart-rate strap. Seiler and Kjerland followed 11 junior cross-country skiers for 32 days: sorted by heart rate, their endurance sessions split 75 / 8 / 17 across easy, moderate and hard; sorted by the athletes' own ratings, 76 / 6 / 18. An easy day should end feeling easy, not just start that way. If the honest word at the end of an easy run is hard, it was not an easy run.
Heart rate, as a ceiling
Percentages of maximum need a maximum that is your own, and Seiler and Tønnessen note that their five zones are not based on clearly defined physiological markers. A simpler route: run the talk test on a flat stretch, note your heart rate where talking stops being comfortable, and treat that as the top of easy. On a hill or a hot day, keep the effort and let the pace go.
How much easy work, and where it goes
Start from 80/20 and count it honestly. Seiler's 80% is of sessions, in athletes training 10 to 13 times a week; Esteve-Lanao and Muñoz counted minutes. In a week of four or five sessions, count minutes. The warm-up and cool-down of a hard session are easy minutes, and a long run is easy from start to finish.
- The split counts endurance work. The studies above split endurance training, and the two that logged strength sessions left them out. Station circuits and simulations are hard work and sit in the hard share.
- Easy and long runs are the bulk. The kinds of run, with examples, are in Running for HYROX.
- What an easy session looks like. A 30 to 45 minute run at talk-test pace, 20 to 30 minutes on the rower or SkiErg at a low stroke rate, or a long run built towards 60 to 90 minutes.
- The hard share is threshold runs and intervals. What each one trains is in threshold runs and intervals.
- Easy days go after hard ones. The easy day after a hard session is what lets the next hard session be hard. How to order the week is in days a week.
- Your other sports count. A match or a hard class is hard work and takes some of the hard share. More in hybrid training.
- Hold easy on good days. The easy share leaks when an easy run creeps up to comfortably hard because you feel fresh. That is the moderate band the trials above moved time into.
Easy work beyond running: rower, SkiErg and bike
Easy does not have to mean running. The rower, SkiErg and bike add aerobic minutes without adding running, which helps when your legs or your week cannot take another run. The rower and SkiErg are race stations too, so easy minutes on them double as technique practice. More in the ergs guide.
Two limits. Fitness is partly specific to the movement: reviewing cycling and running in triathletes, Millet and colleagues concluded that VO2 max is specific to the exercise and muscles adapt to the task they train, and judged that more training probably transfers from running to cycling than the other way. A machine supports your easy runs; it does not replace them. And heart rate differs between cycling and running at the same effort, so a running heart-rate ceiling does not carry over.
The talk test travels better. A review by Reed and Pipe found it consistent across walking, jogging, cycling, an elliptical trainer and a stair stepper. Rowing and the SkiErg were not among them, so on those it is a guide rather than a tested measure. Hold it to the same standard: full sentences, comfortably. On the rower, keep the stroke rate low and the pressure light.
Why train easy for a race this hard
In a study of 11 recreational athletes racing a simulated HYROX, the typical athlete's heart rate averaged 170.9 beats a minute across the whole race. You cannot train at that effort most days and recover from it. Easy days carry the volume, and they leave you fresh enough to make the hard sessions count. What the race asks of you is in how hard HYROX is, and the whole build is in Training for HYROX.
Keeping score of your easy days
The simplest check that your easy days are easy is to rate every session when it ends.
Open a session and tap Mark done. One slider asks how hard it felt, from one to ten, with a word beside it that moves from VERY EASY through MODERATE and HARD to MAX EFFORT. It starts at seven, so after an easy session you drag it down.
Under ANYTHING FOR YOUR COACH, add what the number cannot say: the heat, a bad night's sleep, a run that drifted. The finished session keeps your effort in a gold ring under STATS. More in Mark a workout done, or undo it.