It sounds contradictory. You want to get faster as a runner, so you would expect to have to train harder too. But the majority of your training (about 80%) is done at a relaxed pace. Deliberately relaxed. Zone 2.
This is not a popular message. Zone 2 pace does not feel like "real training." It is slow. You pass people walking their dogs. Your heart rate stays low. And yet these are precisely the training sessions that build your aerobic engine and determine how hard you can train in the rest of your week.
What is zone 2?
On a heart rate basis: roughly 60-75% of your maximum heart rate via the Karvonen method (with resting heart rate). You can read more about the exact calculation in our guide to training at heart rate.
Many runners sit at their "quiet" workouts actually in zone 3: the comfortable middle pace that is too fast for real zone 2 benefits and too slow for the adaptations of zones 4-5. That gray area is the most wasted training there is.
Why is zone 2 so effective?
More mitochondria
Mitochondrions are the power plants in your muscle cells. More mitochondria means more ability to convert oxygen into energy. Zone 2 is the most effective stimulus to produce new mitochondria.
Better capillary density
Your body builds more blood vessels to the muscles, which improves oxygen supply.
More efficient fat burning
Your body learns to use fats as fuel more efficiently. This saves glycogen, which you can use later in a race or training.
Stronger heart
A larger stroke volume: the heart pumps more blood per beat. Your resting heart rate drops. Your aerobic system becomes fundamentally stronger.
The result of all this? You run faster with the same heart rate. And that basis is the basis of everything.
"Zone 2 is the most valuable zone for endurance runners, but also the most underestimated. Precisely because it is so inconspicuous, most runners skip it."
Iñigo San Millán, sports physiologist University of Colorado
How slow is zone 2 actually?
This is a sobering discovery for many runners: for most people, zone 2 is actually slower than they think.
For reference: Eliud Kipchoge does his easy endurance runs at roughly 5:00-5:20/km. For him that is zone 2. Runners who normally run 6:00/km when they are "calm" are often in zone 3. Really quiet for them is 6:30-7:00/km or even quieter.
That feels uncomfortable. The ego wants faster. But it works. After four to eight weeks of real zone 2 training you will see the first results: the same pace with a lower heart rate.
The 80/20 rule
Sports physiologist Stephen Seiler examined the training habits of elite endurance athletes and discovered a consistent pattern: about 80% of training takes place at low intensity (zone 1-2), and only 20% at high intensity (zone 4-5).
Zone 3 (the middle pace that dominates most recreational runners) hardly plays a role in the training schedule of elites. Not because it's useless, but because it's a compromise that misses the best of both worlds: too tiring to do much of, but not intensive enough for strong adaptations.
The practical implication: if you train three times a week, two of those workouts are zone 2 runs. The third is quality training. It's that simple.
Zone 2 vs. zone 3: the difference in practice
| Zone 2 | Zone 3 | |
|---|---|---|
| Feeling | Comfortable, easy to talk | Slightly strenuous |
| Heart rate (global) | 60-75% HRR | 75-85% HRR |
| Conversation | Complete sentences | Short sentences |
| Recovery | 1 day or less | 1-2 days |
| Training effect | Aerobic base, mitochondria | Moderate aerobic improvement |
The crux: zone 3 is not "bad", but it is not efficient if you do a lot of zone 3. Replace some of your zone 3 training with real zone 2 running and see what happens to your performance after six weeks.
How long should a zone 2 workout last?
An indicative weekly structure:
| Training day | Type | Duration |
|---|---|---|
| Tuesday | Zone 2 | 45 minutes |
| Thursday | Quality training | 50-60 minutes |
| Saturday | Long zone 2 | 75-90 minutes |
Zone 2 and HYROX
Are you training for a HYROX? Then zone 2 is the absolute basis. The eight kilometers you run with a HYROX is largely compromised running (= walking after an exhausting workout). The stronger your aerobic engine, the better your body recovers between stations and the better you can maintain the running kilometers.
Frequently asked questions
Can I also do zone 2 by bike or in the swimming pool?
Zone 2 takes too long for me. What if I only have 30-40 minutes?
I'm bored with zone 2 tempo. What do I do about it?
Related pages: Training zones · Training at heart rate · Training on power · Interval training
Bart Vandenbussche is passionate about sport and never shies away from a sporting challenge. He has run several marathons (including sub-3h), is an Iron+Ultra Viking, and currently has the Hyrox bug.
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