Sleep & HRV

There is a clear reason why Feelmo's Regulation Score is born mainly from heart data during sleep. This page explains the relationship between sleep and HRV, with sources.

Sleep is not uniform

A night of sleep cycles through light sleep, deep sleep (slow-wave sleep, N3), and REM. Autonomic activity shifts with these stages, and deep non-REM sleep shows parasympathetic dominance (Trinder et al., 2001).

WakeREMN1N2N3Parasympathetic / HRVBedtimeWake

Figure: top = sleep stages across a night (hypnogram), bottom = an illustration of parasympathetic activity / HRV. HRV rises in deep sleep (N3) and approaches waking levels in REM.

HRV during sleep relates to sleep stages, sleep quality, and sleep-disordered breathing, as organized in reviews (Stein & Pu, 2012; Tobaldini et al., 2013).

Why measure at night

Daytime HRV fluctuates with many factors — exercise, food, posture, caffeine, conversation. During sleep these disturbances are fewest, so each day can be compared under the same conditions. That is why Feelmo centers the Regulation Score on overnight data.

  • In REM, autonomic activity approaches waking levels; in deep non-REM it settles — and this difference reflects recovery (Trinder et al., 2001; Tobaldini et al., 2013)
  • Disturbed nights tend to show in HRV too, so the score can be a gentle clue to "sleep quality" (Stein & Pu, 2012)

At night, just wear it and sleep

That is why Feelmo is simple to use. Wear your Apple Watch at night and sleep. In the morning, that night's regulation arrives quietly.

But note

Feelmo does not diagnose sleep; if you suspect sleep apnea or similar, please consult a medical institution. The figure is illustrative, not actual measurements.

How Feelmo handles it

Feelmo translates the fluctuation of the heartbeat during sleep into the Regulation Score. How metrics are integrated is the core of Lumo Core and is not disclosed, as a trade secret. Related: Understanding HRV · Behavior & AI Coach.

References

  1. Trinder J, Kleiman J, Carrington M, et al. Autonomic activity during human sleep as a function of time and sleep stage. Journal of Sleep Research. 2001;10(4):253–264.
  2. Stein PK, Pu Y. Heart rate variability, sleep and sleep disorders. Sleep Medicine Reviews. 2012;16(1):47–66.
  3. Tobaldini E, Nobili L, Strada S, Casali KR, Braghiroli A, Montano N. Heart rate variability in normal and pathological sleep. Frontiers in Physiology. 2013;4:294.

About these references

The works above provide general scientific background on sleep and HRV; they do not prove the effect of the Feelmo app itself. Nothing on this page is a basis for medical decisions.

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