Resting heart rate and HRV: what your watch is telling you

Resting heart rate and HRV can flag poor recovery, illness or a heavy night out. Learn to read the trend against your own baseline, not one number.

Most watches now report resting heart rate and heart rate variability (HRV) every morning. Used well, they give you an early hint that recovery is off. Used badly, they become a source of worry over numbers that move for all sorts of reasons. This guide covers what they are, what changes them and how to read them sensibly.

What they measure

Resting heart rate is how many times your heart beats per minute when you are fully at rest. For adults it is usually between 60 and 100 beats per minute, and below 60 can be normal in people who are very fit ^[1].

HRV is the variation in time between one heartbeat and the next ^[2]. A healthy heart is not a metronome: the gaps between beats constantly shift as your body adjusts ^[2]. Most watches report a measure called RMSSD, which mainly reflects the activity of the vagus nerve, the "rest and digest" side of your nervous system ^[2]. Broadly, a higher HRV compared with your usual means your body is in a more relaxed, recovered state.

What changes them

Both numbers react to almost everything going on in your life:

• Training load. HRV responds to how much hard work you do. In elite athletes, its pattern over weeks reflected whether they were adapting well or sliding towards overreaching, and the balance of hard and easy training affected it ^[3].
• Illness. Infections and fever raise heart rate ^[1]. Data from tens of thousands of Fitbit users showed that resting heart rate tends to rise when people get an infection, along with changes in sleep and activity ^[5].
• Alcohol. In a study of more than 4,000 Finnish employees, alcohol lowered HRV and impaired overnight recovery in a dose-dependent way ^[4]. Even small amounts had a measurable effect, and larger amounts had a bigger one ^[4].
• Sleep, stress and other factors. Anxiety, stress, dehydration, heat, smoking and some medicines all affect heart rate ^[1]. HRV also falls with age and rises with aerobic fitness ^[2].

Because so many things move these numbers, a change tells you something is different, not what it is. You have to bring the context.

Why your own baseline matters more than one reading

HRV in particular varies a lot between people. Age and sex both shift typical values ^[2], so comparing your number with a friend's, or with a chart online, tells you very little. What matters is how today compares with your normal.

Day-to-day noise is large too. In research on elite endurance athletes, single-day HRV readings had almost no relationship with performance, while weekly averages tracked it closely ^[3]. That work recommended averaging readings across at least 3 days a week rather than reacting to one morning ^[3].

Practical rules that follow from this:

1. Measure the same way each time, ideally overnight or first thing on waking.
2. Look at a rolling 7-day average, not today's figure alone.
3. Pay attention when the trend moves for several days in a row, especially with other signs: poor sleep, sore throat, heavy legs, low mood or lifts going backwards.
4. One low reading after a late night or a hard session is expected. It is not a reason to cancel training.

How accurate are wrist wearables?

Accuracy depends on the device and on measuring at rest. A 2021 study compared several consumer devices and apps with an ECG (the clinical standard) ^[6]. Resting heart rate was acceptably accurate across devices, while HRV accuracy ranged from excellent for some products to very poor for others ^[6]. The authors called for continued independent testing because manufacturers' claims vary ^[6].

Two takeaways. First, your watch is most trustworthy for overnight or resting readings, where movement is minimal. Second, stick with one device. Switching watches can shift your numbers simply because the hardware and algorithms differ, which breaks your baseline.

Should you train by HRV?

HRV-guided training means adjusting each day's hard or easy session based on your HRV. A 2021 meta-analysis, mostly of endurance athletes, compared it with fixed pre-planned training ^[7]. HRV-guided training was better at improving HRV itself, and fewer people responded poorly ^[7]. For fitness and performance, any advantage was small and not statistically clear ^[7].

For lifters, the honest summary is that HRV is a useful flag, not a programme. Use a sustained dip to ask questions: are you sleeping, eating enough, ill, or piling on too much hard work? If the answer is yes, a lighter day or an earlier deload is sensible. If you feel fine and are lifting well, one low number does not need to override your plan. For more on sleep's role, see sleep and recovery, and for when numbers stay low for weeks, see overtraining.

When to see a doctor

These numbers are not a diagnosis. The British Heart Foundation advises seeing a GP if your resting heart rate is consistently above 100 or below 60 beats per minute (unless you are very fit and it is normally low), if your heartbeat feels irregular, or if you have dizziness, fainting or breathlessness ^[1]. Chest pain is a reason to seek urgent help, whatever your watch says.

Tracking it in ETS

ETS reads resting heart rate and HRV from your watch through Health Connect and shows them against your own recent trend, so a single odd morning stands out less than a run of them. Both feed into the daily readiness score alongside sleep, and the weekly report puts them next to your training so you can spot patterns over time.

Sources

1. British Heart Foundation. Your heart rate. BHF. bhf.org.uk
2. Shaffer F, Ginsberg JP. An overview of heart rate variability metrics and norms. Frontiers in Public Health, 2017. Frontiers
3. Plews D. The practical application of heart rate variability: monitoring training adaptation in world class athletes. PhD thesis, Auckland University of Technology, 2014. AUT repository
4. Pietilä J, et al. Acute effect of alcohol intake on cardiovascular autonomic regulation during the first hours of sleep in a large real-world sample of Finnish employees: observational study. JMIR Mental Health, 2018. JMIR
5. Radin J, Wineinger N, Topol E, Steinhubl S. Harnessing wearable device data to improve state-level real-time surveillance of influenza-like illness in the USA: a population-based study. The Lancet Digital Health, 2020. Scripps Research summary
6. Stone JD, et al. Assessing the accuracy of popular commercial technologies that measure resting heart rate and heart rate variability. Frontiers in Sports and Active Living, 2021. Frontiers
7. Manresa-Rocamora A, et al. Heart rate variability-guided training for enhancing cardiac-vagal modulation, aerobic fitness, and endurance performance: a methodological systematic review with meta-analysis. International Journal of Environmental Research and Public Health, 2021. MDPI (PDF)

More on recovery

Last reviewed 7 October 2026. General information, not medical advice. Found a mistake? Email [email protected].