Tabela de Variabilidade da Frequência Cardíaca por Idade e Gênero

Heart rate variability is the variation in time between consecutive heartbeats, and it reflects the balance between the sympathetic and parasympathetic branches of the autonomic nervous system. It has become a headline metric on consumer wearables, usually presented alongside a population chart. That comparison is the least useful thing you can do with it: between-person variation is enormous, and a value that is low for one person is unremarkable for another.

A fórmula

RMSSD = square root of the mean of the squared differences between successive RR intervals
SDNN = standard deviation of all normal RR intervals

• RR interval = time between consecutive heartbeats, in milliseconds
• RMSSD reflects short-term, parasympathetic (vagal) activity and is what most wearables report
• SDNN reflects overall variability and needs a longer recording, conventionally 24 hours, to be interpreted properly

Metric definitions follow the standards used across the HRV literature. Normative ranges below are from published systematic reviews of short-term recordings.

Typical values by age

The figures below give an orientation for short-term RMSSD in healthy adults. They are wide because the underlying distributions are wide: published normative reviews report standard deviations of a similar magnitude to the means themselves, so overlapping between age groups is the rule.

• HRV declines with age in essentially everyone, reflecting reduced vagal tone and increased arterial stiffness.
• The overlap between adjacent age bands is so large that an individual value tells you very little about whether that person is unusual.

Why your own baseline is the only useful comparison

Between-person differences in HRV are driven by genetics, resting heart rate, body position, breathing rate and measurement method, and they dwarf the day-to-day changes people are trying to detect. Two equally healthy 35-year-olds can differ threefold. Comparing your number to a chart therefore answers a question you do not have.

The question you do have is whether today differs from your own recent average, and that is answerable. Establishing a baseline over two to four weeks of consistent morning measurement, then watching for deviations beyond your normal range, is what makes the metric informative. A drop of a meaningful magnitude below your own baseline, sustained over several days, is associated with accumulated training load, poor sleep, alcohol, illness onset and psychological stress.

• Measure at the same time each morning, in the same position, before getting up and before caffeine. Position alone changes HRV substantially.
• A single low morning is noise. Multi-day trends are the signal.
• Alcohol suppresses HRV markedly for one to two nights and is often the clearest single-input effect people observe.

What HRV is and is not evidence of

Reduced HRV is well established as a marker of poorer outcomes at population level, including after myocardial infarction and in heart failure, and it tracks with fitness, age and cardiovascular risk. That is a genuine and long-standing research finding.

What it does not do is diagnose anything in an individual, and it is not a readiness score in any validated sense despite being marketed as one. The proprietary readiness and recovery scores wearables derive from HRV combine it with other inputs through undisclosed algorithms that have not been independently validated against training outcomes. Treat the underlying trend as informative and the score built on top of it as a product feature.

Limitações

• Between-person variation is very large, so population charts cannot tell you whether your value is good. Only your own baseline can.
• Measurement conditions dominate the result. Body position, breathing rate, time of day, recent caffeine and recording length each change HRV enough to swamp real physiological differences.
• Devices are not interchangeable. Chest straps, optical wrist sensors and rings use different sampling and different artefact correction, so values do not transfer between them.
• Any arrhythmia, particularly atrial fibrillation, invalidates standard HRV metrics, which assume normal sinus beats.
• RMSSD from a short morning reading and SDNN from a 24-hour recording are not comparable, and mixing them is a common error.
• HRV is not a diagnostic test. A low value is not a diagnosis and a high one is not a clean bill of health.

Perguntas frequentes

What is a good HRV for my age?

The question is less useful than it seems. Published ranges are wide and overlap heavily between age bands, so an individual value cannot be judged against a chart. What matters is whether today differs from your own baseline measured the same way.

Why does my HRV differ so much from someone else my age?

Because genetics, resting heart rate, breathing pattern, body position and device all affect it, and those differences are much larger than the day-to-day changes people track. Two equally healthy people of the same age can differ threefold.

How do I measure HRV consistently?

Same time each morning, same position, before getting up and before caffeine, using the same device. Position and breathing rate alone change HRV enough to make inconsistent measurement useless.

What lowers HRV?

Alcohol, which suppresses it markedly for one to two nights, poor or short sleep, accumulated training load, illness onset, psychological stress, and dehydration. A sustained drop below your own baseline across several days is more meaningful than any single reading.

Are wearable readiness scores based on HRV reliable?

The underlying HRV trend is informative; the readiness score built on it is a proprietary composite that has not been independently validated against training outcomes. Treat the trend as data and the score as a product feature.

Referências

1. Shaffer F, Ginsberg JP. An Overview of Heart Rate Variability Metrics and Norms. Frontiers in Public Health, 2017.
2. Nunan D, Sandercock GRH, Brodie DA. A quantitative systematic review of normal values for short-term heart rate variability in healthy adults. Pacing and Clinical Electrophysiology, 2010.
3. MedlinePlus. Arrhythmia.
4. US Department of Health and Human Services. Physical Activity Guidelines for Americans, 2nd edition.