How do I read the heart rate on my smartwatch? What is a normal resting heart rate?
This answer is a draft. It stays unpublished until legal review and source verification are complete.
Smartwatches and fitness trackers are everywhere in Japan too, and many people now check their "resting heart rate", "heart rate variability" and "sleep score" every morning. A number on a screen is hard to ignore. But many people worry without knowing what is normal and what is a reason to see a doctor. Here are the guide figures, and the limits of the devices.
Heart rate guide figures
| Item | Guide | Notes |
|---|---|---|
| Resting heart rate (adults) | 60–100 beats/min is the normal range. 50–70 is the measured range for many healthy adults | People who exercise regularly are often fine in the 40s–50s ("athlete's heart") |
| Caution at the low end | See a doctor if below 50 with dizziness, breathlessness or fainting | Without symptoms, watchful waiting is usually fine |
| Caution at the high end | Consistently above 100 at rest (tachycardia). Thyroid problems, anaemia, dehydration, fever, caffeine or medicines may be behind it | See a doctor if it lasts several days |
| "Gap from your usual" | 10 or more beats above your normal for several days: an indicator of a cold starting, lack of sleep, alcohol, dehydration or stress | The most practical use of a wearable |
| Heart rate variability (HRV) | Fluctuation in the interval between beats. Higher means recovery and relaxation; lower tends to mean fatigue or stress | Varies hugely between people; comparing with others is meaningless. Watch your own trend |
| During exercise | Maximum heart rate ≈ 220 − age. Moderate intensity is 60–70% of that, high intensity 70–85% | At 40: maximum 180, moderate 108–126 |
| During sleep | Normally 10–20% lower than at rest | If it stays high: alcohol, fever or possible sleep apnoea |
- Accuracy of wearables: many validations find heart rate at rest and when walking is close to medical-device accuracy (errors of a few beats). Errors increase with intense exercise or sports with big arm movements (tennis, weight training), a cold wrist, and tattoos or darker skin tones. Wear it one finger-width above the wrist bone, neither too tight nor too loose.
- Irregular-rhythm alerts: the atrial fibrillation (AF) notification feature on the Apple Watch and others is approved as a medical device in Japan too; if alerts keep coming, see a cardiology clinic. But one alert is not a diagnosis. The ECG function records 30 seconds, and showing it at your appointment helps.
- Sleep score, stress score: each maker's own index, with no medical definition; use them only for day-to-day comparison. Some people chase the score until they cannot sleep (orthosomnia) — if it bothers you too much, take the device off at night.
- How to use your records: at an appointment, show "the trend of your resting heart rate" and "the heart rate at the time your symptoms appeared" — it gives the doctor something to work with. Use a screenshot or the app's sharing function.
- Symptoms to act on (whatever the device says): palpitations with chest pain, cold sweat or breathlessness, fainting, a feeling of skipped beats that goes on for a long time. Chest pain with cold sweat means an ambulance (call 119).
[Verify] The normal range for resting heart rate and the formula for estimating maximum heart rate are general cardiology guide figures. Check the statements on wearable accuracy against each device's validation papers and approval information.
Misunderstanding 1｜A resting heart rate in the 50s means a weak heart
In people who exercise regularly it is normal, and if anything a sign of good cardiorespiratory fitness. Without symptoms (dizziness, breathlessness, fainting) there is no cause for concern.
Misunderstanding 2｜Wearable numbers are accurate, so they can be used directly for diagnosis
Accuracy at rest is high, but errors appear during exercise and with irregular rhythms. The right use is to show them to a doctor as reference data.
Misunderstanding 3｜Low HRV means illness
HRV varies enormously between people; comparing with others or with an "average" is meaningless. It is an index for spotting fatigue and recovery in your own trend.
Misunderstanding 4｜One irregular-rhythm alert means something terrible has happened
A single alert can be a measurement error. If they repeat, or come with symptoms, get an ECG at a cardiology clinic.
Misunderstanding 5｜Checking every number every day makes you healthier
The more you chase the numbers, the more anxious some people get, and sleep can suffer. A weekly look at the trend, plus a record when you have symptoms, is enough.
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Sources
- Japanese Circulation Society, "Guidance on the diagnosis of arrhythmia and wearable devices" [不整脈の診断とウェアラブルデバイスに関する指針]
https://www.j-circ.or.jp/
- Ministry of Health, Labour and Welfare (MHLW) e-Health Net, "Heart rate and exercise intensity" [心拍数と運動強度]
https://www.e-healthnet.mhlw.go.jp/information/exercise/
- Japanese Heart Rhythm Society, "Atrial fibrillation: information for the public" [心房細動と一般向け情報]
https://new.jhrs.or.jp/
⚠️ Editorial note: the source URLs above were identified by search. Our working environment cannot reach go.jp domains, so the contents have not been checked against the text. Verify every source before publication and record who checked it and when.
About this article
What we share here are ideas and everyday practices passed down among people living in Japan, together with general information drawn from public sources. They are not official recommendations, and they are not professional instruction. Practices vary between households and regions.
This is general information. Results vary from person to person and depend on your own conditions and surroundings.
Please decide for yourself, using your own judgement, whether any of this suits your situation. We cannot accept responsibility for any damage, loss or injury arising from following this article.
This article is not meant to diagnose or manage any specific medical condition. If you are worried about your health, see a doctor rather than relying on your own judgement.
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