Heart-rate zones are ranges for describing effort. Their boundaries depend on the method: maximum heart rate, heart-rate reserve or measured thresholds. I start with your available data, check the result against how the run feels, and revise it when better measurements arrive. An age equation is only an estimate.
Why do two watches show different zones?
A percentage of maximum heart rate is different from the same percentage of heart-rate reserve. A three-zone model also differs from a five-zone model. Check the calculation method and the input values before moving a boundary.
How does heart-rate reserve work?
Reserve = maximum HR minus resting HR. A boundary = resting HR plus the chosen fraction of reserve. With resting HR 55 and maximum HR 185, 70% of reserve gives 146 bpm. This is a calculation example, not a measured aerobic threshold.
What if I do not know my maximum?
An age equation can provide a starting estimate. It cannot identify your individual maximum or replace threshold testing. A watch peak may be an artefact or may fall below your true maximum. I check the recording and the context before using it.
What should an easy zone feel like?
Use breathing and the talk test alongside the number. Comfortable full sentences suggest an easy effort. Heat, hills, fatigue and sensor error can change the reading. If the number and your body disagree, slow down and check the cause.
Same runner, different 70% boundaries
Using the same example, 70% of maximum HR is 0.70 × 185 = 129.5 bpm, about 130. The reserve calculation gives 55 + 0.70 × (185 - 55) = 146 bpm. Neither number, by itself, identifies your measured threshold or proves that a zone labelled 2 is easy.
Before changing the settings on your watch
Check these inputs together. Keep the same method when comparing your watch, training log and calculator.
- Method: % of maximum, % of reserve or a threshold-based model. The percentages are not interchangeable.
- Inputs: distinguish an age estimate, a recorded peak and a measured test result. Do not label an estimate as a measurement.
- Zone model: check the boundaries and the number of zones, not only the zone name.
