Should You Chase an Exact Zone 2 Heart Rate?
Trying to find your Zone 2 heart rate? Explore what training zones can tell you and how to interpret the numbers on your watch.
A fixed percentage of maximum heart rate is a convenient target, but it may not identify the same physiological intensity for everyone. Research also does not establish Zone 2 as uniquely optimal for all fitness goals. Those are two different reasons to avoid treating one displayed number as a universal requirement.
Common markers did not line up uniformly
A 2025 laboratory study of 50 cyclists compared markers used to describe Zone 2 within a five-zone model. Thirty men and 20 women completed incremental ramp and step tests while researchers measured heart rate, power, blood lactate, ventilation, and fuel use.
The study found substantial variation among commonly used boundaries. The first ventilatory threshold and the intensity associated with maximal fat oxidation aligned relatively closely, whereas fixed percentages of maximum heart rate and lactate-based thresholds showed wide individual differences.
This was a study of measurement boundaries, not a training trial proving that a personalized zone produces better long-term results. The authors suggested individualized physiological measurements as a potentially more accurate way to align the target with metabolic responses. That does not mean everyone needs laboratory testing before low-intensity activity can be worthwhile.
A precise target is not automatically the best target
A 2025 narrative review examined claims that Zone 2 is the optimal intensity for mitochondrial and fat-oxidation adaptations in the general population. The authors argued that the evidence did not support that universal claim and pointed to evidence for higher-intensity exercise, particularly when training volume is limited.
The review is an interpretation of a wider literature, not proof that low-intensity training is useless or that everyone should replace it with hard sessions. It also does not identify an exact intensity that maximizes every health or performance outcome.
Keep the target attached to its purpose
When using a zone, identify how it was defined and what you intend the session to accomplish. A percentage estimate, a measured ventilatory threshold, and a label in a training system are not automatically equivalent.
These sources support using intensity targets with context: common markers vary between people, and precision does not by itself establish superiority. A more useful decision than chasing an exact number is understanding what that number represents and whether the evidence addresses your actual goal.