By JuanPa, creator of TrainingForever · Reviewed by JuanPa · Updated 19/10/2026 · With the experience of Marc Bañuls, coach with more than 15 years of experience.
Short answer: HRV (variability of heart rate) is the time variation between one beat and the next, and reflects mainly vagal activity. The RMSSD (or its logarithm, lnRMSSD) is used for training, measured every morning in the same conditions and read as an average of 7 days in front of the athlete's own baseline.
Quick summary
- What is it: the variation between beats; at rest it reflects mainly vagal activity (Task Force, 1996; Shaffer and Ginsberg, 2017).
- What metric to use: RMSSD or lnRMSSD, measured at awakening, always the same. 60 s are enough at rest (Esco and Flatt, 2014).
- How much to measure: minimum 3 valid days per week (Plews et al., 2014).
- How to read it: average 7 days versus baseline and normal band; 7 day CV adds information (Plews et al., 2012).
- What science says: guiding intensity with HRV gives results equal or somewhat better than a fixed plan, with a small effect on VO2max (Granero-Gallegos et al., 2020).
- Golden Rule: HRV reports; the coach decides, along with sleep, sensations and burden.
What is HRV (heart rate variability)?
The variability of heart rate (HRV) is the variation, in milliseconds, of the time between a beat and the next (R-R interval). A healthy heart does not beat like a metronome: even at 60 beats per minute, intervals last 980 ms and another 1,030 ms. This variation is normal and useful (Shaffer and Ginsberg, 2017).
At rest, short-term HRV primarily reflects the influence of the parasympathetic nervous system (vagal) on the heart (Task Force, 1996). This is why it is used as an indirect indicator of how an athlete is tolerating the training load, sleep, and overall stress.
HRV is not heart rate: two athletes with 50 resting pulsations may have very different HRV. Nor is it a form note: it is a sign to be read in its context.
What HRV metrics are used in sport: RMSSD, lnRMSSD and CV?
There are dozens of HRV indices (temporal, frequency and non-linear domains). For the daily monitoring of athletes one has been imposed for its simplicity and reliability in short records: the RMSSD (Buchheit, 2014; Plews et al., 2013).
- RMSSD · Variation beat to beat · Square root of the mean square differences between consecutive R-R intervals. In milliseconds.
- lnRMSSD · RMSSD on logarithmic scale · Natural logarithm of RMSSD. It makes the changes more comparable day by day; it is the one used in most training studies.
- 7-day CV · How stable the HRV is · Last week lnRMSSD variation coefficient. Indicates whether the HRV ‘dance’ much or little overnight.
The formula, no mystery
RMSSD = √( mean of (RR₍ᵢ₊₁₎ − RRᵢ)² )
lnRMSSD = ln(RMSSD)
Average 7 d = average of the last 7 values of lnRMSSD
CV 7 d (%) = standard deviation of these 7 values ÷ their mean × 100
Example of calculation (unustrative, five beats):
| R-R interval (ms) | Difference from previous (ms) | Difference squared |
|---|---|---|
| 800 | — | — |
| 820 | +20 | 400 |
| 790 | −30 | 900 |
| 810 | +20 | 400 |
| 805 | −5 | 25 |
| Average squares | 431,25 | |
| RMSSD is equal to √431,25 | ≈ 20.8 ms | |
| lnRMSSD = ln(20,8) | ≈ 3,03 |
In practice, the app or band makes this calculation with all the beats of the record. What interests you as a coach is what value you use (RMSSD or lnRMSSD) and that is always the same.
What is a normal HRV by age?
There is no universal "good" figure. The HRV depends on age, sex, genetics, posture, time of day and method of measurement, and the reference values of 24-hour, 5-minute and ultra-short records are not interchangeable (Shaffer and Ginsberg, 2017). A review of normal values found great dispersion between people and between studies (Nunan et al., 2010).
As a population reference, these are the values of RMSSD in 1,906 healthy adults (not athletes), measured in 5 minute lying records:
| Age | RMSSD women (ms, mean ± SD) | Men's RMSSD (ms, mean ± SD) |
|---|---|---|
| 25–34 years | 42,9 ± 22,8 | 39,7 ± 19,9 |
| 35–44 years | 35,4 ± 18,5 | 32,0 ± 16,5 |
| 45–54 years | 26,3 ± 13,6 | 23,0 ± 10,9 |
| 55–64 years | 21,4 ± 11,9 | 19,9 ± 11,1 |
| 65–74 years | 19,1 ± 11,8 | 19,1 ± 10,7 |
Two useful readings: the HRV drops with age, and the standard deviation is almost half the mean, that is, two healthy people of the same age can have very different values. That is why the table serves to understand, not to judge an athlete: always compare it with yourself.
How is the HRV measured correctly every morning?
Morning measurement at rest is the most used in HRV-guided training studies (Kiviniemi 2007; Vesterinen 2016; Javaloyes 2019). Here are the steps to make the data comparable overnight:
- Choose a method and don't change it. Chest band or app validated with the mobile camera, always the same. If the athlete wears a watch that measures at night, decide whether to use that data or the morning measurement, but do not mix both.
- He measures when he wakes up. Before you get up at all, from coffee, from looking at your phone or from training. If you need to go to the bathroom, go back to the same position.
- Same posture and same duration. Lying or sitting, always the same. At least 60 seconds of registration after one minute of stabilization (Esco and Flatt, 2014); 5 minutes is the classic standard (Task Force, 1996).
- Breathe normally. Without forcing your breath or speaking during the search.
- Write down the context. Sleep, sensations, stress, alcohol, travel or symptoms of illness. Without context, the number cannot be interpreted.
- Register at least 3 valid days per week. Better daily; with less than 3 the weekly average loses reliability (Plews et al., 2014).
- Build the baseline. You need several weeks of data under normal training conditions before drawing conclusions; studies used, for example, 10 days (Kiviniemi 2007) or 4 weeks (Javaloyes 2019).
Band, cell phone or watch? At rest, a chest band and the mobile camera (photopletismography) gave an RMSSD very similar to the electrocardiogram (Plews et al., 2017), and a validated app with ultra-short records also showed good agreement (Flatt and Esco, 2013). Clocks measuring at night use another time of the day and often another algorithm: they may be useful, but their numbers are not compared to mornings or other devices.
If your athlete uses a Garmin watch, the data you will see every morning is the state of HRV; here we explain what is Garmin HRV status and how to read it (balanced, unbalanced or low).
"The first thing I ask is not an expensive band, but a constancy: always measure the same, when I wake up. A data taken in any way confuses me more than it helps me."
— Marc Bañuls, coach with more than 15 years experience
How is the HRV interpreted: 7 day average, baseline and CV?
The value of a loose day is noisy: a bad dream, a coffee or a discussion move it. Therefore studies with endurance athletes work with trends: the 7-day moving average of the lnRMSSD and its coefficient of variation (CV) (Plews et al., 2012; Plews et al., 2013).
How to build the reading, step by step:
- Baseline: mean (and standard deviation) of lnRMSSD of several weeks of normal training.
- Normal band: a range around that mean. Kiviniemi et al. (2007) used as a threshold the average of 10 days minus a standard deviation; Vesterinen et al. (2016) used an individual band of "relevant minimum change". Many coaches set it at ±0.5 standard deviations: it is a practical convention, not a law.
- Average of 7 days: compares last week's average to the band.
- 7-day CV: See if HRV becomes much more stable or much more irregular than usual.
- Context: contrasts with sleep, sensations, week load and performance.
Interpreting individual changes requires taking into account the measurement error, the relevant minimum change and the training context (phase, load, intensity distribution), and combining the HRV with the training diary, questionnaires and simple tests (Buchheit, 2014).
| Status | Guidance reading | What the coach would look at |
|---|---|---|
| Average 7 d within the band, stable CV | Normal load tolerance | Keep plan; keep recording |
| Descent of a day after a hard session | Expected acute response | Nothing special if recovered within 24–48 h |
| Average 7 d below the band several days | Possible accumulated fatigue, stress or incipient disease | Ask for sleep, stress and symptoms; assess softening intensity |
| Average 7 d above the band after a discharge | Good recovery (fresh) | Confirm with sensations before reloading |
| CV that falls or shoots from the usual | Change in signal stability | Look at the trend of several weeks, not act for a single fact |
| HRV rising while performance falls (highly trained athletes) | Possible vagal "saturation": High HRV is not always a good sign | Contrast with heart rate at rest, performance and sensations (Plews et al., 2013) |
In the case of two elite triathletes followed 77 days, in which it ended with non-functional overtraining the average of 7 days of the lnRMSSD and its CV were falling towards the competition, while they remained stable in the other (Plews et al., 2012). It is a case study: it illustrates a signal to be watched, not a rule.
| Do this. | Avoid this. |
|---|---|
| Look at the 7-day trend, not today's value. | Cancel a session for a single low value |
| Always measure the same and with the same device | Compare the HRV of two athletes |
| Contrast with sleep, sensations and burden | Mix night and morning measurements |
| Recalculates baseline after major changes (altitude, disease, new season) | Use population tables as targets |
Does HRV-guided training work?
In HRV-guided training, morning measurement helps decide the type of session of the day: if the HRV is in your band, the expected intense session is done; if it is clearly low, it is changed to a smooth session or rest. Here's what the main studies say:
| Study | Participants and duration | How the HRV was used | Main outcome |
|---|---|---|---|
| Kiviniemi et al., 2007 | 26 moderately trained men, 4 weeks of race | If the HRV fell below the average of 10 days − 1 SD (or dropped 2 days in a row): soft session or rest | The maximum speed improved more in the group guided by HRV; the VO2pico only improved significantly in that group, although no difference between groups in that change |
| Kiviniemi et al., 2010 | 21 men and 32 moderately active women, 8 weeks | Vigorous session only if HRV did not go down (or only if it went up) | In men, more improvement of the maximum load; in women, the same improvement with fewer vigorous sessions |
| Vesterinen et al., 2016 | 40 recreational runners, 8 intensive weeks | Moderate or intense session only if the HRV was in the individual band | Less intense sessions (13.2 versus 17.7); 3,000 m improved only in the HRV group; difference between small groups |
| Javaloyes et al., 2019 | 17 well-trained cyclists, 8 weeks | Daily prescription according to HRV versus traditional periodization | Improvements in peak and counterclockpower of 40 min in the HRV group; no significant differences between groups |
| Granero-Gallegos et al., 2020 (meta-analysis) | Randomized trials in endurance athletes | HRV-Guided Training | Small but positive effect on VO2max, higher at amateur level and in women |
Honest reading: guiding intensity with HRV is not magic. The results are the same or somewhat better than a fixed plan, often with fewer intense sessions. Its great practical value is to help put the hard sessions on the days when the athlete best tolerates them, always at the discretion of the coach.
"When the trend and what the athlete tells me go in the same direction, I act. When they contradict each other, I ask before I touch the plan."
— Marc Bañuls, coach with more than 15 years experience
What limitations does HRV have?
- A lot of individual variation: normal values depend on age, sex and genetics (Voss et al., 2015; Nunan et al., 2010). It only makes sense to compare every athlete to himself.
- Sensitive to everything: sleep, alcohol, caffeine, stress, heat, altitude, disease, or menstrual cycle can move it. Without context, it gets misinterpreted.
- In highly trained athletes, both increases and decreases of the HRV have been associated with maladaptation, and "saturation" may appear (Plews et al., 2013).
- Depends on the protocol: changing device, posture or time of day breaks the series.
- It doesn't measure everything: heart rate does not report all aspects of fatigue or performance; it should be combined with the training diary, questionnaires and simple tests (Buchheit, 2014).
- It's not a medical diagnosis: persistent abnormal values or symptoms (dizziness, palpitations, chest pain) are the reason for medical consultation, not plan adjustment.
How does the HRV fit into coach planning?
The HRV is one more piece of tracking, along with the training load (CTL, ATL and TSB), the RPE of each session and what the athlete counts. A practical scheme:
- Plan the block as always (for example, with your intensities for VAM or for heart rate zones).
- Defines in advance What will you do if the average of 7 days comes out of the band: soften the intense session, move it one day or keep it if everything else is okay.
- Check every week the trend along with the load and sensations.
- You decide. The HRV tells you where to look; the athlete tells you what's going on.
«The HRV does not decide for you. It helps me to ask better questions: if I go down for several days in a row and the athlete tells me that I sleep badly, I adjust. If you go down one day after a hard session, it's normal."
— Marc Bañuls, coach with more than 15 years experience
In TrainingForever: You plan the sessions of your athletes and they sync with Garmin Connect (Strava can be connected optionally; the sessions are also exported to Coros and Polar), and you see what has been done versus what is planned. The interpretation of the HRV and the decision to adjust a session are always from the coach.
With the current version of TrainingForever you have all the features free up to 5 athletes; then, 0.99 € per active athlete per month, with a maximum of 49 €/month, and for your athletes it is always free. HRV reports; coach decides.
To go
- The HRV is your sign of how the athlete is tolerating the load; it is not a form note.
- He always measures the same, waking up, at least 3 days a week, and looks at the average of 7 days in front of his band.
- A low data opens a conversation; several low days with bad sleep or bad sensations justify adjusting. It's up to coach.
Frequently Asked Questions
What is HRV and what does it measure?
The HRV is the variation, in milliseconds, between consecutive beats. At rest it reflects above all the activity of the parasympathetic nervous system (vagal). A higher HRV than your baseline usually indicates good load tolerance, but it is not a "smaphor": you have to read it with the trend, context and what the athlete counts.
What is a normal HRV?
There is no universal normal value: it depends on age, sex, genetics, posture and device. In 1,906 healthy adults, the average RMSSD dropped from about 40 ms (25–34 years) to about 19 ms (65–74 years), with a lot of dispersion (Voss et al., 2015). That's why every athlete compares with himself, not with tables.
When is it best to measure HRV?
In the morning, when waking, after urination if necessary and before coffee, mobile or exercise, always in the same posture and with the same device. A 60-second record of lnRMSSD is well consistent with the 5 minute rest standard (Esco and Flatt, 2014). The important thing is to always repeat the same conditions.
How many days a week do you have to measure?
The ideal is daily, but a triathlete study concluded that at least 3 valid measurements per week are needed to make the weekly average of lnRMSSD reliable (Plews et al., 2014). With less data, the average 7 days becomes too sensitive to a single rare day.
A low HRV means the athlete shouldn't train?
Not necessarily. A descent of one day after a hard session is expected. What deserves attention is an average of 7 days below the normal band for several days, especially if it matches bad sleep, more fatigue or worse performance. Even then, the HRV opens the conversation: the coach decides whether to adjust.
Does HRV-guided training serve?
Several essays found results equal or somewhat better than a fixed plan, often with fewer intense sessions (Kiviniemi 2007; Vesterinen 2016; Javaloyes 2019). A meta-analysis found a small but positive effect on VO2max (Granero-Gallegos et al., 2020). It's a useful tool, not a guarantee.
Can the HRV be measured with the mobile phone or clock?
A chest band and mobile photopletismography gave resting RMSSD values very similar to the electrocardiogram (Plews et al., 2017). Watches measuring at night use another time and another method: do not mix night and morning measurements or compare figures between devices.
Sources
- Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. Heart rate variability: standards of measurement, physical interpretation and clinical use. Circulation. 1996;93(5):1043-65. PubMed 8598068
- Shaffer F, Ginsberg JP. An Overview of Heart Rate Variability Metrics and Norms. Front Public Health. 2017;5:258. doi:10.3389/fpubh.2017.00258 · PubMed 29034226
- Plews DJ, Laursen PB, Stanley J, Kilding AE, Buchheit M. Training adaptation and heart rate variability in elite duration athletes: opening the door to effective monitoring. Sports Med. 2013;43(9):773-81. doi:10.1007/s40279-013-0071-8 · PubMed 23852425
- Plews DJ, Laursen PB, Kilding AE, Buchheit M. Heart rate variability in elite triathletes, is variation in variability the key to effective training? A case comparison. Eur J Appl Physiol. 2012;112(11):3729-41. doi:10.1007/s00421-012-2354-4 · PubMed 22367011
- Plews DJ, Laursen PB, Le Meur Y, Hausswirth C, Kilding AE, Buchheit M. Monitoring training with heart rate-variability: how much compliance is needed for valid assessment? Int J Sports Physiol Perform. 2014;9(5):783-90. doi:10.1123/ijspp.2013-0455 · PubMed 24334285
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- Javaloyes A, Sarabia JM, Lamberts RP, Moya-Ramon M. Training Prescription Guided by Heart-Rate Variability in Cycling. Int J Sports Physiol Perform. 2019;14(1):23-32. doi:10.1123/ijspp.2018-0122 · PubMed 29809080
- Granero-Gallegos A, González-Quílez A, Plews D, Carrasco-Poyatos M. HRV-Based Training for Improving VO2max in Endurance Athletes. A Systematic Review with Meta-Analysis. Int J Environ Res Public Health. 2020;17(21):7999. doi:10.3390/ijerph17217999 · PubMed 33143175
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- Flatt AA, Esco MR. Validity of the ittleTM Smart Phone Application for Determining Ultra-Short-Term Heart Rate Variability. J Hum Kinet. 2013;39:85-92. doi:10.2478/hukin-2013-0071 · PubMed 24511344
- Voss A, Schroeder R, Heitmann A, Peters A, Perz S. Short-term heart rate variability — influence of gender and age in health subjects. PLoS One. 2015;10(3):e0118308. doi:10.1371/journal.pone.0118308 · PubMed 25822720 (values in Tables 5 and 7 tested in PMC4378923)
- Nunan D, Sandercock GR, Brodie DA. A quantitative systematic review of normal values for short-term heart rate variability in healthy adults. Pacing Clin Electrophysiol. 2010;33(11):1407-17. doi:10.1111/j.1540-8159.2010.02841.x · PubMed 20663071
All references have been verified in PubMed (E-utilities) on 19/10/2026; the figures cited come from the abstracts, except the Voss table, taken from the full text in PMC.
