Heart-Rate Zones: Useful Guide or False Precision?
EFWA KNOWLEDGE HUB · EXERCISE PHYSIOLOGY
By Dr Mert Eray Onen, Founder & Academic Director, EFWA · ORCID 0000-0001-8510-7293
Estimated reading time: 6 minutes
Direct answer: heart-rate zones are useful for organising aerobic training, but the coloured bands on a watch are estimates—not universal physiological borders. Two people at the same percentage of predicted maximum heart rate can be working in different intensity domains. A better coaching approach combines heart rate with breathing and speech, perceived exertion, external workload and the client’s response over time.
The attraction of a five-zone display is obvious: a complex physiological response becomes a simple number and colour. The risk is false precision. If the maximum value is estimated, the resting value changes, the sensor is inaccurate or the person’s thresholds sit in an unusual place, a mathematically tidy zone can misrepresent the actual metabolic demand.
What a heart-rate zone represents
Heart rate rises as exercise demand increases because cardiac output must support active tissues. Training systems then divide a heart-rate range into bands, commonly using a percentage of maximum heart rate or heart-rate reserve. Heart-rate reserve accounts for resting heart rate as well as maximum heart rate, but both approaches still depend on the quality of their anchor values.
A watch may estimate maximum heart rate from age, use the highest value it has recorded, or accept a value entered by the user. These are not equivalent. Even a directly measured maximum is task-specific to some extent: cycling, running and rowing can produce different responses, and environmental heat, hydration, fatigue, stress, caffeine and medication can change heart rate at a given pace or power.
Established evidence: fixed percentages of maximum values do not map neatly onto the moderate, heavy and severe exercise-intensity domains for every individual. Reviews by Jamnick et al. (2020) and controlled laboratory work by Iannetta et al. (2020) show substantial between-person variation in where lactate and ventilatory thresholds occur relative to percentage-based anchors.
Zones are not the same as physiological thresholds
Physiologists often describe two important transitions. Around the first ventilatory or lactate threshold, breathing begins to increase disproportionately to oxygen uptake and prolonged conversation becomes less comfortable. Around the second threshold or maximal metabolic steady-state boundary, sustainable steady exercise gives way to a domain in which disturbance continues to accumulate until the work must be reduced or stopped.
These boundaries help explain why a small increase in pace can sometimes feel disproportionately harder. They are also why a universal “zone 2 is exactly 60–70%” rule is too crude. In a study of 100 women and men, the first threshold occurred across a wide range of percentages of maximum heart rate, and the upper boundary varied widely too (Iannetta et al., 2020). Anselmi et al. (2021) similarly found that range-based classifications could misclassify intensity, particularly in cardiac patients.
Emerging evidence: individualised, domain-based prescription may produce a more consistent stimulus across people than fixed-percentage zones. A six-week randomised trial in healthy young adults found different adaptations across individually defined moderate, heavy, severe and extreme domains (Inglis et al., 2024). This improves physiological understanding, but it does not prove that every recreational client needs laboratory testing.
The EFWA five-signal method
This EFWA educational framework treats heart rate as one signal within a coaching decision, not as an unquestionable command.
1. Anchor
Identify where the zone came from. Was maximum heart rate measured in an appropriate test, observed during relevant training, or predicted from age? Is resting heart rate current? Label estimates as estimates rather than reporting them to the nearest beat as if they were exact.
2. Internal response
Ask how the work feels and observe breathing. The Talk Test and rating of perceived exertion can provide practical information without a laboratory. A 2022 review concluded that speech and perceived exertion can help locate intensity-domain transitions, although both require familiarisation and honest reporting (Bok et al., 2022).
3. External work
Record what produced the response: treadmill speed and gradient, cycling power, rowing pace or a repeatable route. Heart rate alone cannot show whether fitness is improving. A client who holds the same submaximal heart rate at a higher repeatable workload may be adapting, provided conditions are comparable.
4. Drift
During prolonged steady work, heart rate may gradually rise despite unchanged pace or power. Heat, fluid loss and fatigue can contribute. Do not automatically chase the original heart rate by repeatedly lowering output without considering the session goal and conditions; equally, do not ignore an unexpectedly large change.
5. Context and symptoms
Sleep, illness, altitude, heat, emotional stress and some medicines alter the heart-rate response. Chest pain, fainting, unusual breathlessness, palpitations with symptoms or a marked unexplained change require stopping and appropriate medical assessment—not a new zone calculation.
A worked example: when the watch and the client disagree
A recreational runner is prescribed a 35-minute easy session. Their watch labels the middle of the run “zone 3”, yet they can speak in full sentences, report a low-to-moderate effort and maintain relaxed mechanics. The day is warm and the heart rate has drifted upward by several beats while pace remains constant.
The trainer first checks the source of the watch zones and discovers they are based on an age-predicted maximum. Rather than declaring the session a failure, the trainer records pace, heart rate, Talk Test and perceived exertion. Across several comparable sessions, these observations create a client-specific picture. If precision becomes important for competition preparation, a suitable field test or laboratory assessment can be considered within professional scope.
The reverse disagreement matters too. If a client’s heart rate appears low while speech is broken, effort is unexpectedly high and symptoms are present, the number should not overrule the person. Sensor error, medication or a health issue may be involved.
When simple zones are useful
Estimated zones can be a reasonable starting scaffold for a healthy adult beginning general aerobic training, especially when paired with the Talk Test and effort ratings. They are less defensible when a programme demands tight control near a threshold, when the person takes heart-rate-altering medication, when environmental conditions are extreme, or when symptoms or known disease require clinical exercise guidance.
Expert interpretation: the required precision should match the decision. General activity does not need laboratory-level classification. High-performance programming, research and some clinical settings may benefit substantially from measured thresholds and sport-specific testing.
Evidence limitations
Threshold terminology and detection methods vary, and no single measure is perfectly objective. Laboratory studies often use cycling or treadmill protocols under controlled conditions, so translation to mixed-mode classes and field environments is imperfect. Wearable accuracy differs by device, activity and motion. Acute physiological agreement also does not guarantee superior long-term adherence or adaptation.
The practical EFWA position
Use zones to organise training, not to replace coaching. Record the source of the anchor, triangulate heart rate with speech, perceived effort and external work, and review trends under comparable conditions. The most useful zone system is not the one with the most colours; it is the one that helps the professional deliver the intended stimulus while responding to the person in front of them.
Explore more evidence-informed resources in the EFWA Knowledge Hub, meet EFWA’s educators on the Academic Team page, or compare professional learning pathways on the Personal Trainer Courses hub. For a related programming principle, read Progressive Overload: What Should Personal Trainers Actually Progress?
References
- Anselmi, F., Cavigli, L., Pagliaro, A., Valente, S., Valentini, F., Cameli, M., Focardi, M., Mochi, N., Dendale, P., Hansen, D., Bonifazi, M., Halle, M., & D’Ascenzi, F. (2021). The importance of ventilatory thresholds to define aerobic exercise intensity in cardiac patients and healthy subjects. Scandinavian Journal of Medicine & Science in Sports, 31(9), 1796–1808. https://doi.org/10.1111/sms.14007
- Bok, D., Rakovac, M., & Foster, C. (2022). An examination and critique of subjective methods to determine exercise intensity: The Talk Test, Feeling Scale, and Rating of Perceived Exertion. Sports Medicine, 52(9), 2085–2109. https://doi.org/10.1007/s40279-022-01690-3
- Iannetta, D., Inglis, E. C., Mattu, A. T., Fontana, F. Y., Pogliaghi, S., Keir, D. A., & Murias, J. M. (2020). A critical evaluation of current methods for exercise prescription in women and men. Medicine & Science in Sports & Exercise, 52(2), 466–473. https://doi.org/10.1249/MSS.0000000000002147
- Inglis, E. C., Iannetta, D., Rasica, L., Mackie, M. Z., Keir, D. A., MacInnis, M. J., & Murias, J. M. (2024). Heavy-, severe-, and extreme-, but not moderate-intensity exercise increase VO₂max and thresholds after 6 weeks of training. Medicine & Science in Sports & Exercise, 56(7), 1307–1316. https://doi.org/10.1249/MSS.0000000000003406
- Jamnick, N. A., Pettitt, R. W., Granata, C., Pyne, D. B., & Bishop, D. J. (2020). An examination and critique of current methods to determine exercise intensity. Sports Medicine, 50(10), 1729–1756. https://doi.org/10.1007/s40279-020-01322-8
This article is an educational overview for fitness and movement professionals and does not replace individual medical or clinical exercise advice.
Author disclosure: Dr Onen is EFWA’s Founder and Academic Director. EFWA provides professional education in this subject area.
