Zone 2 is a way of classifying a relatively low intensity of aerobic exercise. In practice, it usually represents a comfortable, sustainable effort where the runner can hold a conversation with relative ease. But there's no single heart rate or pace value that corresponds to zone 2 for every person.
So "zone 2" shouldn't be understood as simply a number on your watch.
What are training zones?
Zones are a way of organizing different levels of intensity.
A common system splits effort into five zones, from lowest to highest intensity:
| Zone | General intensity | Feel |
|---|---|---|
| Z1 | Very low | Very comfortable |
| Z2 | Low | Comfortable, conversation possible |
| Z3 | Moderate | Sustainable, but requires focus |
| Z4 | High | Strong and hard to sustain |
| Z5 | Very high | Maximal or near-maximal effort |
These zones are a training tool. They're not fixed properties of the body.
Why are there different ways to calculate zones?
Because intensity can be estimated from different indicators. The most common are:
- heart rate;
- pace;
- power, when available;
- perceived exertion.
These indicators aren't equivalent. A runner can be at a given pace with a different heart rate on a hot day, on a hill, after poor sleep, under stress, or when fatigued.
So looking at just one metric can give an incomplete picture.
How do I know if I'm in zone 2?
One of the simplest ways is to use perceived effort. At a light intensity, you should be able to run comfortably and hold a conversation without needing to pause for breath.
Heart rate can complement that assessment, but it needs to be interpreted in context. Pace can help too, but shouldn't be treated as a constant — your zone 2 pace on a hot day may not match a cooler day.
Can I use a formula to calculate my zone 2?
You can use formulas as a starting point.
For example, some approaches estimate maximum heart rate from age and then calculate percentage-based zones. Others use resting heart rate and heart rate reserve (the Karvonen method).
The problem is treating the result as an exact measurement. Population-based formulas produce estimates — they don't necessarily replace an individual assessment.
That's why a zone calculator can be useful as an initial estimate, but the runner should interpret that result alongside perceived effort and training data.
Is zone 2 always a specific percentage of heart rate?
No. That's one of the most common misconceptions about zone 2 online.
You might see recommendations like "zone 2 is 60–70% of max heart rate" or "zone 2 is 70–80%." Those ranges can differ across systems because there's no single convention for defining zones — different models can use different physiological reference points.
So before comparing numbers, it's worth knowing which zone model is being used.
Which is the better indicator: pace or heart rate?
Neither is always better. Each answers a different question.
- Pace: how fast you're running.
- Heart rate: how your cardiovascular system is responding to the effort.
- Perceived effort: how that effort actually feels to you.
What is zone 2 training for?
Low-intensity training lets you accumulate exercise time with less strain than very intense sessions. That's why easy running tends to make up a significant part of many endurance programs.
But that doesn't mean every workout should happen in zone 2. Training plans can also include different intensities depending on the goal.
What about the famous 80/20 training?
So-called polarized training has gotten a lot of attention for putting most training volume at low intensity, with a smaller share at high intensity.
A 2024 meta-analysis found an advantage for polarized training in improving VO₂peak compared with other distributions, especially in shorter interventions and in highly trained athletes. For other performance outcomes, the models performed similarly.
So 80/20 is an intensity-distribution strategy, not a universal law of running. A more recent review also found benefits across different intensity-distribution models, with differences more apparent in high-level athletes than in lower-level ones.
What depends on the runner
Your zones depend on individual characteristics and the method used to estimate them. That's why two people running at the same pace can be at different physiological intensities.
And the same person can respond differently to the same pace depending on temperature, terrain, fatigue, sleep, hydration, recovery, or stress.
What the evidence says
There's no single zone system that's universally correct for every runner. Zones are models for organizing intensity.
The best approach depends on the goal, the data available, and the quality of the information used to estimate each zone.
How Rai uses zones
Rai's calculators estimate your maximum heart rate from your age (and sex, when provided) and calculate zones as percentages of that estimate. When you provide your resting heart rate, the calculation switches to heart rate reserve — the Karvonen method — for a more personalized estimate.
Rai can combine this information about the runner to guide training intensity, instead of treating a single number as absolute truth. The goal is to turn zones and other metrics into practical instructions: run easy, hold this effort, push here, recover before the next repetition.
Zones are a tool to guide training — not the goal of training.
Use Rai's calculators
Want to estimate your zones? Rai offers free tools to help:
Use the results as estimates and interpret them alongside your training context.
Read also:
- Running Training Types: Practical Science to Evolve Safely
- How to Improve Your Running Pace
- Rai's Methodology
References
Comparison of polarized versus other types of endurance training intensity distribution on athletes' endurance performance: systematic review with meta-analysis (Oliveira, Boppre & Fonseca, 2024, Sports Medicine)
The effect of polarized training intensity distribution on maximal oxygen uptake and work economy among endurance athletes: a systematic review (2024, PMC)