Raw sleep metrics
Apple Health provides sleep stages (core / deep / REM / awake), time in bed, sleeping wrist temperature and respiratory rate, but **no sleep score** — Vita's sleep score is computed from those raw stages.
Core / deep / REM / awakemin
Field: sleep_core
- What it measures
- Apple assigns each sleep sample to one of four classes. “Core” roughly corresponds to light sleep (N1+N2) in traditional staging, deep to N3, and REM to rapid eye movement.
- What Vita does with it
- The sleep score (deep share 25%, REM share 15%) and recovery's sleep term.
- Easily misread
- 🚨 **Total sleep must be the SUM of the asleep stages.** Apple Health also has an “unspecified asleep” field which happens to equal the whole night on devices that do not report stages, but is only a fragment on devices that do — reading it alone substantially understates sleep. We got this wrong once.
Time in bedmin
Field: sleep_in_bed
- What it measures
- The whole span from getting into bed to getting up, INCLUDING time awake before falling asleep and during the night. It is always at least as long as total sleep, and the gap between the two is time in bed but not asleep.
- What Vita does with it
- Sleep efficiency (asleep ÷ in bed), 10% of the sleep score.
Sleeping wrist temperature°C
Field: apple_sleeping_wrist_temperature
- What it measures
- On Apple Watch Series 8 and later, the wrist temperature during sleep expressed as a DEVIATION from your own baseline — not an absolute body temperature.
- What Vita does with it
- Recovery (5%, and in both directions — any deviation costs).
- Easily misread
- Needs several consecutive nights to establish a baseline; infection, alcohol, the menstrual cycle and room temperature all move it. **Not a thermometer.**
Respiratory ratebr/min
Field: respiratory_rate
- What it measures
- Breaths per minute estimated during sleep — the steadiest of the nightly vitals.
- What Vita does with it
- Recovery (10%, both directions), stress (15%), and a sustained rise of about 2 br/min triggers a nightly alert.
- Easily misread
- Because it is stable, a sustained rise often flags infection, overreaching or alcohol earlier than other metrics — but it is an observation, not a diagnosis.
Limitations
- Consumer sleep staging still differs meaningfully from polysomnography, deep and REM especially. So stages carry only 40% of the sleep score and duration — the most reliable part — carries 50%.
- Users who also wear a WHOOP get WHOOP's own sleep performance score rather than Vita's algorithm — an overlapping metric trusts the more specialised band.
References
Apple. HealthKit — HKQuantityTypeIdentifier reference. Apple Developer Documentation, accessed 2026.
What it supports：The official definition, unit and aggregation style of each metric — the source for how every field on this page is described.
What it supports：Normative sleep duration and stage proportions by age.
de Zambotti M, Cellini N, Goldstone A, Colrain IM, Baker FC. Wearable Sleep Technology in Clinical and Research Settings. Medicine & Science in Sports & Exercise. 2019;51(7):1538-57.
What it supports：Accuracy and limits of consumer wearable sleep staging.
Related metrics
Every metric on this page is a reference index for observing your own trends. It is not medical advice and cannot replace a professional diagnosis. If you have health concerns, consult a qualified clinician.
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