What each metric tells you
HRV (heart rate variability)
HRV is a proxy for autonomic nervous system balance. Higher values, compared against your own baseline, generally line up with better recovery. Lower values can reflect physical load, illness, sleep debt, alcohol, stress, or just statistical noise. The number on its own is not very useful, the direction across two weeks is.
VitalBrief uses overnight HRV only. A reading taken while you are awake measures stress, not recovery, so a stress check or a breathing session never enters a recovery baseline. Where your watch records the raw beat-to-beat series, the app computes RMSSD from it on your device; otherwise it uses the overnight values Apple Health already stores. It never mixes the two in the same history.
Resting heart rate (RHR)
RHR is the most stable of the three. A consistent upward shift over a few days, alongside lower HRV, is one of the more reliable signs that recovery is not keeping up with load. A drift downward over months can reflect aerobic conditioning, but it is slow.
Sleep
What matters most week to week is duration and consistency. Sleep stages are interesting but noisy on the Apple Watch. The report leans on duration, regularity, and how the rest of the metrics responded. In the daily reading, sleep is used differently again: only to flag a night that was clearly too short, never to hand out credit for a long one.
Why trends, not single days
Take any one of these metrics and one bad day. There are too many explanations to choose from. Take seven days, with the same direction repeating, and the picture sharpens.
VitalBrief compares every night against your own rolling 60 days. Sixty is a deliberate number: long enough that a single odd night cannot move the reference, short enough that the reference follows your fitness, your season and your training phase instead of ranking you against a version of yourself from last winter. Reports get a much longer history separately, because narrative context and a recovery baseline are not the same question.
How VitalBrief contextualizes them
The Wellness Score combines two pieces:
- Recovery: daily HRV and RHR values converted to percentiles against your baseline, then aggregated across the week.
- Training: calorie volume relative to your baseline, plus a population reference based on body mass.
The two are combined into a 5 to 100 score with eight labels (peak week, strong week, moderate week, light week, overload week, rest week, strain week, recovery week). Confidence is part of the result: a high score built on too few nights is downgraded automatically rather than presented as a good week.
The narrative report uses the score and its commentary as constraints, so the AI cannot say "great recovery week" when the score says otherwise.
Cold start. With less than about two weeks of usable nights, neither the score nor the daily reading runs. The card says it is still building your pattern, and shows how far along it is, until there is enough history to compare against.
