Four options, in ascending order of accuracy: an age formula (free, instant, ±10–12 bpm error), a field max-heart-rate test (personal but strenuous), the talk test (measures your actual threshold, needs no equipment), and lab testing (most precise, least accessible). For most runners the talk test is the best trade — it measures you without a lab.
Zone 2 is the training intensity below your first ventilatory threshold (VT1) — the point where breathing starts rising disproportionately to clear carbon dioxide. Below it you can sustain effort for a long time and hold a conversation. Above it, neither stays true for long.
Every method below is an attempt to locate that same boundary. They differ in whether they measure it or guess at it.
| Method | Accuracy | Cost / effort | Best for |
|---|---|---|---|
| Age formula 220 − age, or Tanaka |
Poor for individuals (±10–12 bpm) | Free, instant | A rough starting bracket |
| Field max HR test | Moderate | Free, very strenuous | Experienced athletes wanting a personal max |
| Talk test | Good — measures VT1 directly | Free, one easy-to-moderate run | Most runners |
| Lab test lactate or gas exchange |
Highest | Typically $100–300, needs a facility | Competitive athletes, or anyone wanting certainty |
Take 220 − age as maximum heart rate, then 60–70% of it. This is what your watch already did. It is instant and free, and its individual error is large enough that the resulting zone 2 can be badly wrong in either direction. Full detail on where the formula came from and how far off it is →
Use it as a starting bracket, not a prescription.
After a thorough warm-up, run several hard efforts — commonly 3 × 3 minutes uphill, progressively harder, going all out on the last — and take the highest heart rate observed. Then apply the same percentages.
This replaces the formula's guessed maximum with your own, which is a genuine improvement. Two caveats: it is genuinely strenuous and not appropriate for everyone, and the percentage step is still a population assumption. Your VT1 may not sit at 70% of your max just because it does for the average person.
Run at a steady effort and speak continuously for about thirty seconds. If speech is fluent you are below VT1; if it fragments you are above it. Note the heart rate at the last fluent effort.
This skips the maximum-heart-rate step entirely and measures the threshold itself. It needs no equipment, costs nothing, and can be done on any easy run. Its weakness is subjectivity — you are judging your own breathlessness, and people tend to be generous with themselves. How to run one properly →
A graded exercise test with blood lactate sampling or gas-exchange analysis identifies your thresholds directly. It is the most precise option available and the benchmark the others approximate.
The trade-offs are access and cost, plus the fact that thresholds drift — a lab number is a snapshot, and repeating it every few weeks is impractical for most people.
Thresholds move as fitness changes. A number measured during a consistent training block will drift over the following months, usually upward as aerobic fitness improves. Every three to four weeks is a reasonable cadence during consistent training.
A useful signal: if your heart rate at a familiar easy pace has noticeably changed, your threshold has probably moved with it.
It is worth saying that chasing an exact number can be its own trap. A 2025 review in Sports Medicine questioned whether zone 2 is uniquely effective for the adaptations it is often credited with, and coaches including Steve Magness have argued the popular version of zone 2 suffers from false precision — that "mostly easy, some moderate, a little hard" captures nearly all the benefit without the arithmetic.
That critique is fair, and it does not conflict with measuring your threshold. The argument for measurement is not that 138 bpm is meaningfully different from 140. It is that a formula can be wrong by twenty beats, which is the difference between running easy and walking — and that error is large enough to change what you actually do.
A note on training. This is general training information, not medical advice. Maximum-heart-rate field tests in particular are strenuous by design. If you are new to exercise, returning from illness or injury, or have a heart condition, talk to your doctor first.
RunEasy automates the talk test on Apple Watch. One guided ramp — warm-up, then stages of increasing effort with a spoken question near the end of each — locates where your speech starts breaking down and reports the corresponding heart-rate band and pace range, beside the formula's prediction. Afterwards, ordinary runs are coached silently from that band.