Key takeaways
Zone 2 is the top of the easy range below the first threshold, roughly 60 to 70% of max heart rate
Intervals at 90 to 95% of max heart rate raise VO2max more than the same time spent in zone 2
Best mix for VO2max: about 75 to 80% of training time easy plus one or two hard sessions a week
Zone 2 has become one of the most talked-about ideas in fitness. Some of the claims are well supported; some are overstated. Here is what zone 2 is, how to find it, and where it fits if your goal is a higher VO2max.
What zone 2 is
Most physiologists describe intensity with two thresholds:
- The first threshold (first lactate or ventilatory threshold): the point where blood lactate starts to rise above resting levels and breathing first deepens noticeably.
- The second threshold (often called lactate threshold or critical power): the highest intensity you can sustain for a long time, roughly your one-hour race effort.
In a three-zone model, zone 1 is everything below the first threshold. In the popular five-zone models used by watches, zone 2 is the top part of that easy range — as hard as you can go while staying below the first threshold. Names differ between systems, but the idea is the same: steady, comfortable, sustainable for hours.
How to find it
| Method | How | Accuracy |
|---|---|---|
| Talk test | You can speak in full sentences, but you'd rather not sing | Good, free, works every day |
| Heart rate | Roughly 60–70% of maximum heart rate | Rough; depends on knowing your true HRmax |
| Nasal breathing | You can breathe comfortably through your nose | Rough rule of thumb |
| Lab test | Lactate or gas-exchange test identifies the first threshold | Most accurate, costs money |
Heart-rate percentages are only a starting point. Age-based formulas such as 220 − age can be off by 10 beats or more for an individual, which shifts every zone. If your watch zones and the talk test disagree, trust the talk test. Heart rate also drifts upwards in heat and late in long sessions, so slow down to stay in the zone.
What zone 2 does
Easy aerobic training drives a set of adaptations that take months to build:
- More mitochondria and capillaries in the trained muscles, so they extract and use more oxygen.
- Better fat use at a given pace, sparing carbohydrate.
- Larger blood and plasma volume and, over time, a bigger stroke volume.
- Lower heart rate at the same pace — the classic sign of a growing aerobic base.
Crucially, it does this with little fatigue, so you can do a lot of it. That is why elite endurance athletes spend most of their training time at low intensity. See 80/20 training.
What zone 2 doesn't do
- It is not the strongest VO2max stimulus. For people with limited time, intervals at 90–95% of maximum heart rate raise VO2max more than the same time spent easy. See the Norwegian 4×4.
- It doesn't work on small doses. Two 30-minute easy sessions a week will help a beginner, but the benefits of easy training come from accumulated volume over many weeks.
- It isn't magic for fat loss. You burn a higher share of fat at low intensity, but total energy expenditure matters more for body weight. See VO2max and body weight.
For complete beginners, almost any regular activity — including zone 2 — raises VO2max, because the starting point is low. As fitness grows, easy work alone tends to plateau and harder sessions become necessary.
How it fits with intervals
The best-supported approach for VO2max combines both:
- Most sessions easy — zone 2 and below. Roughly 75–80% of your training time.
- One or two hard sessions a week — intervals near VO2max or threshold work.
- Few sessions in the grey zone between — too hard to recover from easily, too easy to be a strong stimulus.
Easy volume builds the engine that lets you complete and recover from hard intervals; intervals push the ceiling. A 12-week plan to improve VO2max shows how to put them together.
Safety: if you have a heart condition or have been inactive, get medical advice before adding hard intervals to your easy training.
Checking it works
Track your pace at a fixed easy heart rate over weeks: if it rises, your aerobic base is growing. Check your estimated VO2max with the VO2max calculator every 6–8 weeks and compare it with the VO2max chart. Remember that watch numbers are estimates — see how accurate is your watch's VO2max.
Frequently asked questions
Does zone 2 training increase VO2max?
It helps, especially for beginners, by building mitochondria, capillaries, blood volume and stroke volume over months. But it is not the strongest stimulus: intervals at 90 to 95% of max heart rate raise VO2max more in the same time.
How do I find my zone 2 heart rate?
Roughly 60 to 70% of your maximum heart rate, but formulas like 220 minus age can be off by 10 beats or more. The talk test is a good check: you can speak in full sentences but would rather not sing.
How much zone 2 training should I do?
Roughly 75 to 80% of your training time easy, in zone 2 and below, plus one or two hard sessions a week. The benefits come from accumulated volume over many weeks, not small doses.
Sources
- Seiler S. What is best practice for training intensity and duration distribution in endurance athletes? Int J Sports Physiol Perform, 2010.
- Stöggl T, Sperlich B. Polarized training has greater impact on key endurance variables than threshold, high intensity, or high volume training. Front Physiol, 2014.
- Holloszy JO, Coyle EF. Adaptations of skeletal muscle to endurance exercise and their metabolic consequences. J Appl Physiol, 1984.
- Persinger R, et al. Consistency of the talk test for exercise prescription. Med Sci Sports Exerc, 2004.
- Milanović Z, et al. Effectiveness of high-intensity interval training (HIT) and continuous endurance training for VO2max improvements: a systematic review and meta-analysis of controlled trials. Sports Med, 2015.