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HRV rest or move: should you work out when your HRV is low?

Compare today's heart rate variability with your own recent baseline and get a rest, gentle or go suggestion, with every threshold explained.

Runs entirely in your browser. Nothing you enter is sent anywhere.

Compare a device only with itself

Devices measure HRV differently. Some report RMSSD, others SDNN, and they record at different times and for different lengths. Use readings from the same device, taken the same way, ideally first thing in the morning.

This morning's reading from your watch, ring or chest strap.

ms
How would you like to give your baseline?
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How do you feel today?Optional. How you feel counts too.

This tool gives general wellness information, not medical advice. If something feels wrong, talk to your doctor or midwife.

Quick take: Enter today's HRV and either your 7-day average or your recent readings. The tool compares today with your own baseline: within your normal day-to-day range means go, somewhat below means keep it gentle, and clearly below means rest. How you feel can soften the suggestion. Only compare readings from the same device.

How it works

Eggsports Editorial

Why compare HRV with your own baseline?

Quick take: Heart rate variability is the small, constant change in time between heartbeats. Values differ widely with age, sex, fitness, the measure used and the length of the recording, so published norms tell you little about your own morning. Comparing today with your recent readings shows whether your body is in its usual state.

Even at rest, the gaps between healthy heartbeats keep changing. RMSSD, one of the most common HRV measures, is the main time-domain index of the vagally mediated, rest-and-digest influence on the heart.[1] When it falls below your usual range, your body may still be recovering, from training or from the rest of life. In one study, work stress kept a runner's HRV below his usual range for weeks.[2] Higher is not automatically better either: in elite athletes, both rises and falls in HRV have been linked with poor adaptation to training.[5]

How are the rest, gentle and go thresholds set?

Quick take: With three or more recent readings, normal variation reaches half a standard deviation below your average. Between that and one standard deviation below, the suggestion is gentle; further down, it is rest. With only an average, the tool uses fixed steps instead: up to 10% below is normal, 10 to 20% below is gentle, and more is rest.

The half-standard-deviation band is the "smallest worthwhile change" used in HRV-guided training research. In one study, recreational runners did their moderate and hard sessions only while their HRV stayed within that band, and trained easily or rested otherwise. Their 3,000 m running performance improved, while the group on a fixed plan did not improve significantly.[2] An earlier study prescribed easy training or rest when HRV fell below the average minus one standard deviation.[3] In well-trained cyclists, HRV-guided training also improved peak power and time-trial performance, although the difference from traditional planning was not statistically significant.[4]

Today compared with your baselineWith 3 or more readingsWith an average onlySuggestion
Within your normal range, or aboveAt or above average minus 0.5 SDDown to 10% belowGo
Below your usual rangeBetween 0.5 and 1 SD below10% to 20% belowGentle
Clearly below your usual rangeMore than 1 SD belowMore than 20% belowRest

The fixed 10% and 20% steps are a deliberately cautious Eggsports rule of thumb for when the spread of your readings is unknown, not a figure from a study. If your readings barely vary, the normal band never gets narrower than 5% of your average, so a tiny dip does not set off a rest day.

The science: How this compares with the studies
The running study compared a rolling weekly average of morning HRV with a baseline built over four weeks, and the earlier study used a ten-day reference. This tool makes a simpler comparison of a single morning with up to seven recent readings, so treat its suggestion as a nudge. How you feel adjusts it: feeling flat caps the day at gentle, feeling unwell means rest, and feeling good lifts a rest suggestion to gentle. A review of 56 studies found that simple self-reports of wellbeing tracked training load more sensitively than many objective measures.[7]

Why do different devices give different HRV numbers?

Quick take: Because they measure different things in different ways. Some devices report RMSSD and others SDNN, and they record for different lengths of time, at night or in the morning. These values are not interchangeable, so only compare a device with itself, measured the same way each day.

SDNN is the standard deviation of the intervals between normal heartbeats, while RMSSD is built from the differences between successive beats. Short recordings and 24-hour recordings give values that cannot substitute for each other, and comparing a measure such as SDNN across recordings of different lengths is inappropriate.[1] If you change watch, ring or chest strap, build a new baseline before trusting the comparison.

Can my menstrual cycle change my HRV?

Quick take: Yes. A meta-analysis of 37 studies found that vagally mediated HRV tends to fall from the first half of the menstrual cycle to the second, with the clearest drop in the days before a period. A lower reading at that time may reflect your cycle rather than poor recovery.

The largest decreases appeared between the menstrual or mid-to-late follicular phase and the premenstrual phase.[6] If your HRV dips before your period while you feel fine, a gentle day is a reasonable choice, and so is carrying on. The cycle phase calculator can show where you are in your cycle, and the energy calculator turns your sleep and mood into a movement suggestion without any device at all.

Frequently asked questions

What is a good HRV number?

There is no single good number. HRV depends on age, fitness, genetics, the device and the measure it reports, so a number that is low for one person can be perfectly normal for another. What matters for day-to-day decisions is how today compares with your own usual range.

When is the best time to measure HRV?

Measure at the same time and in the same way every day, ideally just after waking and before you get up. Many wearables do this automatically overnight. Consistency matters more than the exact time.

My HRV looks fine, but I feel awful. What should I do?

Trust how you feel. Choose "Unwell or run down" and the tool suggests rest, whatever the number says. HRV is one signal among many, and your own sense of your body counts too.

Does the tool save my readings?

No. Everything is calculated in your browser, and nothing you enter is sent to a server, stored or added to the page address. Refreshing the page clears your numbers.

Sources

  1. Shaffer F, Ginsberg JP (2017). An overview of heart rate variability metrics and norms. Frontiers in Public Health. doi:10.3389/fpubh.2017.00258
  2. Vesterinen V, Nummela A, Heikura I, Laine T, Hynynen E, Botella J, Häkkinen K (2016). Individual endurance training prescription with heart rate variability. Medicine & Science in Sports & Exercise. doi:10.1249/MSS.0000000000000910
  3. Kiviniemi AM, Hautala AJ, Kinnunen H, Tulppo MP (2007). Endurance training guided individually by daily heart rate variability measurements. European Journal of Applied Physiology. doi:10.1007/s00421-007-0552-2
  4. Javaloyes A, Sarabia JM, Lamberts RP, Moya-Ramon M (2019). Training prescription guided by heart-rate variability in cycling. International Journal of Sports Physiology and Performance. doi:10.1123/ijspp.2018-0122
  5. Plews DJ, Laursen PB, Stanley J, Kilding AE, Buchheit M (2013). Training adaptation and heart rate variability in elite endurance athletes: opening the door to effective monitoring. Sports Medicine. doi:10.1007/s40279-013-0071-8
  6. Schmalenberger KM, Eisenlohr-Moul TA, Würth L, Schneider E, Thayer JF, Ditzen B, Jarczok MN (2019). A systematic review and meta-analysis of within-person changes in cardiac vagal activity across the menstrual cycle: implications for female health and future studies. Journal of Clinical Medicine. doi:10.3390/jcm8111946
  7. Saw AE, Main LC, Gastin PB (2016). Monitoring the athlete training response: subjective self-reported measures trump commonly used objective measures: a systematic review. British Journal of Sports Medicine. doi:10.1136/bjsports-2015-094758

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