Endurance
The most common reaction to being told your Zone 2 pace is that it must be wrong, because it is far too slow to be doing anything. That reaction is the reason most people never get the benefit.
Zone 2 is easy aerobic work at roughly 60–70% of maximum heart rate, just below the first lactate threshold — the intensity where you can hold a full conversation. It builds mitochondrial density, capillary networks and the heart’s stroke volume, which is the base everything faster is built on.
| Method | How | Reliability |
|---|---|---|
| Talk test | Full sentences without gasping | Surprisingly good; free |
| Percentage of max HR | 60–70% of estimated max | Rough; max HR estimates vary widely |
| Percentage of HR reserve | 60–70% of (max − resting) + resting | Better than plain max HR |
| Nose breathing | Can breathe through your nose only | Crude but effective |
| Lactate testing | Blood lactate around 2 mmol/L | The reference standard; needs a lab |
The talk test is genuinely the most practical. If you can speak a full sentence comfortably but would rather not recite a paragraph, you are close enough.
Because it is easy — that is the mechanism, not a compromise. At this intensity you are working almost entirely aerobically, clearing lactate as fast as you produce it, and the adaptations being driven are structural: more mitochondria, denser capillary beds, a heart that moves more blood per beat.
Those adaptations respond to duration, not to suffering. An hour easy does more for them than twenty minutes hard, which is why the volume has to be easy enough to sustain.
Elite endurance athletes across sports train roughly 80% of their volume at low intensity and 20% hard, and meta-analyses of polarised versus threshold-heavy distributions favour the polarised approach. The counter-intuitive part is that the professionals go easier on their easy days than most amateurs do.
The failure mode this prevents has a name in running circles: the grey zone. Every run at a moderately hard effort, too taxing to recover from and not hard enough to drive high-intensity adaptations, producing chronic fatigue and a plateau.
| Situation | Zone 2 per week |
|---|---|
| General health | 150–180 min, in any form |
| Recreational runner | 3–4 sessions, 2.5–4 hours total |
| Hybrid athlete | 2–3 sessions, 2–3 hours |
| Endurance competitor | 80% of a much larger volume |
Sessions want to be at least 45 minutes to be worth doing, and an hour is better. The adaptation is duration-driven, so three 20-minute efforts are not equivalent to one hour.
Low-intensity aerobic exercise at roughly 60 to 70 percent of maximum heart rate, sitting just below the first lactate threshold. At this intensity lactate is cleared as fast as it is produced and you can hold a full conversation.
The talk test is the most practical method: you should be able to speak full sentences without gasping. Heart rate methods work too, using 60 to 70 percent of maximum heart rate, or better, of heart rate reserve.
For general health, around 150 to 180 minutes a week. For a recreational runner, three to four sessions totalling two and a half to four hours. Sessions should be at least 45 minutes, since the adaptations are driven by duration.
Because the adaptations it drives — mitochondrial density, capillary growth and cardiac stroke volume — respond to duration rather than to intensity. Running easy runs too hard is the most common endurance training mistake and produces fatigue without high-intensity benefits.
The only way to know whether your easy runs are actually easy is to look at them afterwards. NutriMacro records runs by GPS with pace, splits and heart rate, so the 80/20 split stops being an intention and becomes a number.
NutriMacro is a nutrition and training tracker for iPhone and Android. It logs food by barcode, photo or search, counts food in slices and units rather than grams, and keeps strength training, GPS activities, sleep and recovery in the same daily view. It runs in the language of your phone across 108 countries.
General training guidance for healthy adults. If you have an injury, a health condition or are new to training, get coaching before adding load or volume.
Read next: Zone 2 vs HIIT Improving your 5K time What is hybrid training?
