Body · lesson 3 of 10
Resting heart rate: your easiest trend line
What it reflects, what moves it, how wearables measure it, and when a heart alert means see someone.
7 min read · reviewed October 2026
Beats per minute, at rest
Resting heart rate (RHR) is how many times your heart beats per minute at complete rest. The conventional adult range is 60–100 bpm, and fit endurance athletes often sit in the 40s or 50s. Within the normal range, a lower RHR usually reflects a more efficient heart and higher aerobic fitness.
Measure it under the same conditions every time: on waking, before you get up, or the overnight value a wearable reports.
What moves your resting heart rate
Regular aerobic training is the main lever. Better sleep helps too.
Alcohol (especially late), a late heavy meal, dehydration, heat, short or poor sleep, psychological stress, and a hard training block.
An infection or fever coming on often raises RHR, sometimes before you feel ill.
Beta-blockers lower it. Stimulants, decongestants, some asthma inhalers, an overactive thyroid, anemia and pregnancy raise it. Don't read a medication change as a fitness change.
How your watch counts beats
Wrist and ring sensors shine light into your skin and detect the tiny surge in blood volume with each heartbeat. This is called photoplethysmography (PPG). At rest it's generally accurate. During movement it's less so.
How it works →
PPG picks up changes in how much light is absorbed. Motion creates signals that can be mistaken for a pulse; when running, a sensor can 'lock on' to your step rhythm instead of your heartbeat. A loose fit, cold hands, tattoos under the sensor, and fast changes in intensity (intervals, lifting) all add error. Chest straps read the heart's electrical signal, like an ECG, and remain the reference for heart rate during exercise.
What the studies show →
Validation studies consistently find optical wrist heart rate agrees well with ECG at rest and gets worse during activity, especially intense or irregular movement, with large differences between devices. Evidence on skin tone and optical heart rate is mixed. That's unlike blood-oxygen readings, where the bias on darker skin is well documented (see lesson 8). For overnight resting heart rate, measured while you're still, consumer wearables are good enough to track trends.
A meta-analysis pooled 46 studies and over 1.2 million people. For every 10 bpm higher resting heart rate, how much higher was all-cause mortality?
Somewhere between 0 and 50 %.
Reveal the answer →
~9% per 10 bpm
About 9% per 10 bpm (Zhang et al., CMAJ 2016). This is observational, so part of the link reflects fitness and underlying health. Still, in the Copenhagen Male Study of 2,798 healthy middle-aged men, those with RHR above 90 had about three times the mortality of men at 50 or below, even after accounting for measured fitness (Jensen et al., Heart 2013). The practical meaning: a sustained rise in your own baseline is worth noticing, and aerobic training is the main thing that brings RHR down.
Watch your baseline, not anyone else's
Learn your usual overnight range over a few weeks. If RHR sits clearly above that range for several days without an obvious reason (alcohol, travel, heat, a hard training week), treat it as a prompt to rest and pay attention. Illness, overreaching and stress are the usual causes.
In a 2019 study of 419,297 smartwatch wearers, 0.52% got an irregular-pulse notification. Among those who then wore an ECG patch, what share had atrial fibrillation confirmed?
- Almost all (~95%)
- About a third (34%)
- Almost none (~2%)
- Exactly half
Show the answer →
B.About a third (34%)
About 34% (Perez et al., New England Journal of Medicine 2019). Atrial fibrillation is often intermittent, and patches went on an average of 13 days after the alert, so some episodes were probably missed. When a new alert happened while the patch was on, the patch showed atrial fibrillation 84% of the time. The takeaway: an alert is a reason to get checked, not a diagnosis, and no alert doesn't rule anything out.
Every wrist and ring tracker on the Body shelf reports resting heart rate. If exercise heart rate matters to you, a chest strap is still the reference.