For a health coach, a client’s heart rate variability (HRV) is most useful as a way into a conversation about sleep, stress and recovery. Look at the 7-day average against the client’s own baseline Baseline Your own usual HRV level and range, built from weeks of readings taken the same way. Comparing a reading with your baseline says more than comparing it with other people. More about Baseline , ask what changed in their week, and leave diagnosis to clinicians.
Many clients already wear a ring, watch or strap that shows an HRV number every morning, and they bring it to sessions, sometimes pleased and sometimes worried. This post covers how to read that number with them, how big the usual effects are, how to keep tracking from turning into a source of stress, and where your role ends.
Start with the client’s own baseline
HRV differs a lot from person to person. Two healthy people of the same age can have very different numbers, and a lower one is not worse for that person. Different devices also measure in different ways. So the only fair comparison is the client against their own history, measured the same way on the same device.
A baseline has two parts: the client’s usual value, and how far they normally move above and below it. Building one takes a few weeks of steady readings. The lesson on building your HRV baseline walks through it, and you can send clients there before you start looking at their data together.
Why single mornings mislead
HRV jumps around from one day to the next. A review of heart rate monitoring in athletes put the typical day-to-day error of resting RMSSD RMSSD Root mean square of successive differences: an HRV metric built from how much each heartbeat interval differs from the next, in milliseconds. It mainly reflects vagal activity. More about RMSSD at about 12%, and the smallest change worth noticing at about 3%. In athletes in training, with the load changing from day to day, daily swings of 10 to 20% were common (Buchheit, 2014). A 10% drop on one morning can be ordinary noise.
Weekly averages are more dependable. In a study of 10 runners over a 9-week training block, the change in HRV averaged over one week tracked the change in their 10 km running performance closely. Values from a single isolated day did not (Plews and colleagues, 2013). This study measured athletes, but the reason it works applies to anyone: averaging cancels out much of the daily noise.
Go deeper How to work out a 7-day average
Add the last seven daily readings and divide by seven; the next day, drop the oldest reading and add the newest. Many apps already show a weekly average or a trend line. If they do, use that rather than doing the sums by hand, and make sure the client always looks at the same view.
Two clients, two conversations
Maria messages you before breakfast. Her HRV is 20% below her usual number and she wants to cancel her workout and her plans. Her 7-day average has barely moved, so you might say: “One low morning is common. What happened yesterday? Did you sleep late, have a drink, or start feeling a cold? Let’s see where the weekly average is on Friday.”
James is in a deadline week. His 7-day average has drifted down for ten days, and his resting heart rate Resting heart rate How many times your heart beats per minute while you are fully at rest. For adults it is usually 60 to 100 beats per minute, and lower in well-trained athletes. More about Resting heart rate has crept up. He says he is sleeping six hours a night and working late into the evening. Here the trend is real, and it gives you a concrete, non-judgemental way to talk about workload and sleep: “Your numbers have been lower since the project started. How are you sleeping? What could you protect this week?” You coach the habits, and the number serves as feedback.
For more on day-to-day swings, the answer on why HRV changes so much is a good one to share with clients.
How big are the usual effects?
Knowing the typical size of common effects helps you and your client keep a low reading in proportion. The largest set of real-life figures comes from a study of morning readings taken with a smartphone app, using the phone camera or an external sensor such as a chest strap (Altini and Plews, 2021). Users tagged stressors after each reading, and the researchers analysed 9 million measurements from 28,175 people, collected over up to five years. Within each person, morning RMSSD changed like this:
| What the user reported | Change in morning HRV |
|---|---|
| Hard training the day before | about 3% lower, a 4.6% gap from the day after an easy session or rest |
| High alcohol intake the day before | about 12% lower |
| Being sick | about 10% lower than when not sick |
| Luteal phase of the menstrual cycle | about 3% lower than in the follicular phase |
Heart rate rose by about 6% after heavy drinking and during sickness. The authors give a typical error of about 12% for HRV, and only the drinking and sickness effects come close to that size. They describe HRV as a sensitive but not specific marker of stress: it moves with many things, and the number alone cannot tell you which one.
Alcohol has the clearest dose effect. A study of 4,098 Finnish employees compared each person’s nights with and without alcohol, using heart recordings from the first three hours of sleep (Pietilä and colleagues, 2018). A measure of recovery during sleep, worked out from HRV, fell by about 9, 24 and 39 percentage points after low, moderate and high intake. Low meant up to 0.25 g of alcohol per kg of body weight, and high meant more than 0.75 g/kg. Being physically active did not protect people from the effect. See alcohol and HRV for the details.
Slow breathing is the habit clients ask about most. A 2022 review pooled 223 studies and found that HRV linked to the vagus nerve Vagus nerve The main nerve of the parasympathetic nervous system, running from the brainstem to the heart, lungs and gut. Its fast signals to the heart drive most beat-to-beat HRV. More about Vagus nerve rose during slow breathing, straight after a single session, and after programmes lasting several sessions (Laborde and colleagues, 2022). The lesson on HRV, stress and breathing explains how it works. A rise during the exercise does not mean a client’s overnight number will climb, so set expectations gently.
Keep tracking from becoming a stressor
Some people become anxious about their tracker data. In 2017, sleep researchers described three patients who sought treatment for sleep problems they had concluded from their sleep tracker, and who were chasing ideal sleep. They called it orthosomnia (Baron and colleagues, 2017). That report was about sleep trackers, but a similar pattern can show up with HRV: a client checks the number first thing, feels bad when it is low, and sleeps worse because they are worried about the number.
Signs to watch for:
- The client changes plans based on a single morning.
- They feel worse about a low number than about how they actually slept.
- They check the app many times a day, or test again to get a better reading.
If you see this, suggest they look only at the weekly view, or take a break from the number for a week or two while keeping their usual routine. Ask how they feel and how they slept before you look at any of the data together. A client who feels rested after a low reading is giving you useful information as well. The answer on feeling tired with a good HRV covers the other side of the same mismatch.
Know where your role ends
Health coaches support habits and behaviour change; they do not diagnose or treat. HRV fits inside that role as long as you treat it as feedback on lifestyle and recovery and never as a reading of someone’s health.
Some practical rules:
- Use careful words. Say “your HRV has been lower than usual this week,” and avoid phrases like “your nervous system is damaged” or “this shows you are ill.”
- Do not set HRV targets. Set goals for habits, such as bedtime, drinks per week or a short daily walk.
- Ask before you look. A client’s heart data is personal health information. Only review it with their consent, and keep it as private as your session notes.
- Do not tell clients to change medication because of their HRV. Some medicines affect it (see do medications affect HRV?), and only the prescriber can weigh that.
When to refer to a clinician
Suggest the client sees a doctor, and step back from coaching on this issue, if they report:
- palpitations, a racing or irregular heartbeat;
- fainting, near-fainting or dizziness;
- chest pain or pressure;
- shortness of breath that is new or out of proportion to effort;
- a large change in HRV or resting heart rate that lasts for weeks with no clear cause, especially with fatigue, weight loss or fever.
Chest pain, fainting or severe breathlessness needs urgent medical help, so the client should call their local emergency number rather than wait for an appointment.
For the other signs, you can say: “This is beyond what I can read from a wearable. It’s worth showing your doctor.” The lesson on HRV limits, myths and red flags lists these signs for clients, and the medical disclaimer explains what this site can and cannot do.
Where to go next on hrv.expert
- The free HRV course, for you or a client who wants the basics in short lessons
- Building your HRV baseline, to set up a fair comparison
- What affects HRV, the evidence on sleep, alcohol, stress, illness and more
- HRV and stress, on what HRV can and cannot show about stress
- Is my HRV normal?, to put a number next to reference data
- HRV for fitness instructors and trainers, if you also plan clients’ training