01
Everyday activity
A population reference for understanding activity, with your situation in view.
Observed association
7,000
steps a day
The benchmark large cohort studies point to. A benchmark, not a promise about you.
Observational findings do not establish a personal prescription or a guaranteed outcome.
Ding et al. (2025), Lancet Public Health, 57 studies
02
Sleep, beyond a score
Duration, continuity and stages describe different aspects of a night. Watch measurements retain their own limitations.
Observed association
7h
of sleep
Your nights are read against this benchmark, and against your own weeks.
This association does not mean that everyone should sleep exactly seven hours.
Yin et al. (2017), J Am Heart Assoc
Expert consensus
85%
sleep efficiency, at least
Time asleep over time spent in bed. With it, 20 minutes awake at most after falling asleep and at most one awakening longer than five minutes, two after 65: the continuity benchmarks, where the consensus is clear.
Ohayon et al. (2017), Sleep Health, National Sleep Foundation consensus panel, 277 studies
Laboratory observation
16 to 20%
deep sleep, in the laboratory
The same panel’s range for adults aged 26 to 64, with 21 to 30% REM. The consensus there is weak: the app shows it as a laboratory observation, never as a target.
Ohayon et al. (2017), Sleep Health
Device measurement
43 min
of deep sleep not seen by an Apple Watch Series 8 (one study)
Against polysomnography, over one night in the laboratory. On a Series 7, at home, another study finds no clear gap in deep sleep, but 74 minutes less light sleep and 30 minutes more REM. Hence the app’s rule: a watch share is not read literally against a laboratory range.
Robbins et al. (2024), Sensors, 35 adults; Alhejaili et al. (2026), Sleep Medicine, 19 Apple Watch wearers
Laboratory observation
90 min
per cycle on average, with wide gaps from one cycle to the next
The average length of a cycle in 205 healthy adults. In adults, no meta-analysis sets either the length or the number of cycles: the app counts them from the stages the watch estimates, to describe the night, not to score it.
Rosenblum et al. (2025), eLife, 205 adults
03
Heart rate and estimates
A formula, a resting measurement and your own trend answer different questions.
Population estimate
208 − 0.7 × age
your maximum heart rate
A formula derived from population data. It estimates maximal heart rate; it does not measure your individual maximum.
Tanaka et al. (2001), 351 studies, 18,712 subjects
Research base
46 studies
on resting heart rate
Your resting heart is read against that base, and against your own weeks, not against a round number.
Zhang et al. (2015), CMAJ, 1.2 million participants
04
Effort in strength training
An effort reference needs the exercise, technique and recovery around it.
Effort reference
0 to 3
reps in reserve
Repetitions in reserve describe the repetitions you estimate you could still complete with the chosen technique. Getting close to failure differs from reaching it on every set.
Adjust this reference to the exercise, experience and recovery. It is not one compulsory range for every set.
Robinson et al. (2024), Sports Medicine
05
Body size and its limits
Body mass index relates weight to height. It cannot describe your body composition on its own.
A reading example
23.4
Your body index
of body mass index
You are within the reference range. It's a population benchmark: it doesn't tell muscle from fat.
World Health Organization reference range for adults: 18.5 to 25.
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