Daily readiness: what HRV, resting heart rate and sleep tell you
Form and fitness say what you have done. Daily readiness says how your body is coping today. Four signals help, each compared with your own values.
Why comparing with yourself counts
HRV and resting heart rate are highly individual. An HRV of 45 ms can be normal for one person and a warning for another. That is why population values are of little use. What carries meaning is the deviation from your own normal range.
Why a single day says little
HRV varies a lot from day to day. One short night or a late meal is enough. What carries meaning is the trend. That is why ZonePit does not compare today's value but the average of the last 7 days with your normal range of the last 60 days. This is also what the HRV guide of the Australian Institute of Sport recommends.
The four signals
- HRV (heart rate variability): the 7-day average needs at least three measurements. It is compared with your normal range: your 60-day mean plus or minus half a standard deviation. Below that band is a negative signal, above it a positive one, inside it a neutral one.
- Resting heart rate: the same, only the other way round. Above the band is negative, below it positive.
- Sleep: the basis is last night's sleep score (0 to 100). Less than 6 hours of sleep or a sleep score of 40 or lower always counts as negative. A sleep score at least 20 % below your average of the last 28 nights is negative too, at least 20 % above it is positive. Until there are 10 nights of history, a sleep score of 81 or more counts as positive.
- Wellbeing: your own rating on a scale of 1 to 5. Up to 2 is negative, 4 and above positive.
Calibration and changing devices
HRV and resting heart rate need at least 14 days of history. Until then the signal drops out instead of being guessed. After about two months the normal range is fully established. If you switch to a different watch or ring, only measurements from the new device count and calibration starts again. Different devices measure differently, and mixed values would show false deviations.
Good to know: Apple Health stores HRV as SDNN. Many other apps and studies use rMSSD. The numbers are therefore not directly comparable, but the trend against yourself is.
How level and number emerge
Two or more negative signals mean limited readiness. No negative and at least one positive signal mean good readiness. Anything in between is normal.
The number from 0 to 100 starts at 50. Each signal moves it up or down by up to 25 points, depending on how clearly it deviates. ZonePit also shows how reliable the assessment is: high with three or more signals, medium with two, low with one. If a signal is missing, for example because you do not wear your watch at night, it simply drops out. Nothing is estimated.
What to do with it
- A single bad signal is normal. One short night or a glass of wine in the evening is enough.
- Several negative signals over several days, plus high fatigue, are a good reason to move a hard session or train easy.
- Heat, illness, stress and alcohol change HRV and resting heart rate strongly. The numbers do not say why.
In ZonePit
ZonePit reads HRV, resting heart rate and sleep from Apple Health and rates them by these rules against your own normal range. Below your readiness you see every signal with its value and its band. Daily readiness never changes your plan by itself. At most it creates a suggestion that you confirm.
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Sources
- Australian Institute of Sport: Heart Rate Variability: Best Practice Guide (7-day average, 60-day normal range, smallest worthwhile change 0.5 SD).
- 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 43(9).
- Marco Altini: work on interpreting heart rate variability in training (comparison with your own normal range).
- Task Force of the ESC and NASPE (1996): Heart rate variability: standards of measurement.
ZonePit is a training and wellness app, not a medical device.