How it works Sleep and recovery
Sleep, HRV, resting HR and energy
Every night, your watch measures your sleep and your heart. Stamio turns that into a sleep score, tonight's sleep need, your HRV and resting HR, then your energy and stress through the day.
What Stamio uses
- Your sleep stages (awake, light, deep, REM), as measured by your watch.
- Every heartbeat through the night, one by one, for HRV, plus your heart rate.
- Your respiratory rate, wrist temperature and blood oxygen, if your watch measures them.
- Your daytime heart rate and your workouts, for energy and stress.
How it's calculated
Sleep score
It starts from a perfect night and deducts points for sleeping less than you need, high overnight stress (heart rate and HRV), time awake, and too little deep or REM sleep. Sleep stages come straight from your watch, untouched. 90 and up: excellent; 80 to 89: good; 60 to 79: fair; below 60: poor.
Tonight's sleep need
It starts from your baseline need and adjusts for today's training load, last night's sleep, your HRV and your naps. Stamio then suggests a bedtime based on your usual wake-up time.
Your overnight HRV
Stamio collects every heartbeat of the night and computes the average difference between successive beats (RMSSD), the same measure sports watches use. Poorly measured beats are thrown out, and a naturally high HRV is never penalized.
Your HRV status
Your 7-night average is compared with your baseline, set from your previous 60 nights. Inside your range: Balanced. Outside it: Unbalanced. Well below it: Low.
Your resting HR
It's the level your heart rate dips below only 10% of the time overnight: steadier than a single reading. It's compared with your baseline over the last 30 days. The median of your last 14 nights anchors your heart rate zones and your load.
Energy and stress
Your stress (0 to 100) comes from your heart rate when you're still: the further above your normal resting rate, the more strain on your body. Your energy, a reserve from 5 to 100, recharges mostly while you sleep, a little while you rest, and drains with stress and workouts.
Your night at a glance
Resting HR, HRV, respiratory rate, wrist temperature and blood oxygen are compared with your own range over the last 30 nights. They don't feed any other calculation: they just tell you whether your night was normal for you.
When it changes
- Score, HRV and resting HR arrive when you wake up, once your watch has synced your night.
- Tonight's sleep need updates during the day, after a workout or a nap.
- Energy and stress follow your day; during a workout or a brisk walk, stress isn't measured (shown in gray).
- A nap recharges your energy like sleep does, only more slowly: often nothing for the first few dozen minutes.
What can throw it off
- A watch worn too loose at night, or no watch at all: no measured night means no score, no HRV, and no energy recharge.
- HRV values depend on the watch and the method: compare them with your own baseline, never with another device.
- A night of drinking, a cold coming on, deep fatigue: your resting HR goes up and your HRV drops. That's exactly what these numbers are there to show.
- Lying down awake during the day doesn't count as a nap.
What you can set
- Naps: the ones from your watch count automatically; the ones from other apps or estimated by Stamio need your confirmation.
- Your resting HR, if you'd rather enter it yourself (Settings › Heart rate and zones).
- The values pinned to the top of the home screen, and the previews on your watch.
How it was checked
Calibrated, then checked night after night against a high-end GPS watch worn at the same time: an average difference of 4.9 points on sleep score (89 nights), 4.8 ms on HRV (93 nights), 1.4 bpm on resting HR (105 nights) and 4.1 points on energy (38 days).
Just one runner so far: me. The beta will tell the rest.
Questions
Why doesn't my score match the Health app's?
Stamio uses the same sleep stages but scores the night its own way: duration against your need, how calm your heart was, and time awake. The two scores aren't measuring the same thing.
Should I turn on AFib History to get more HRV readings?
No. Stamio doesn't need it. Turning it on makes your watch measure HRV more often, but you lose irregular rhythm notifications. Your call.
How long until I get an HRV status?
About three weeks of nights. Until then, the screen shows "Calibrating" and your night-by-night HRV.
Further reading
- Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology (1996), "Heart rate variability: standards of measurement, physiological interpretation and clinical use", Circulation, 93(5), 1043-1065.
- Hirshkowitz M. et al. (2015), "National Sleep Foundation's sleep time duration recommendations: methodology and results summary", Sleep Health, 1(1), 40-43.
- Kim H.-G., Cheon E.-J., Bai D.-S., Lee Y. H., Koo B.-H. (2018), "Stress and heart rate variability: a meta-analysis and review of the literature", Psychiatry Investigation, 15(3), 235-245.
Estimates for wellness, not a medical device. If a value stays outside your range for several days, talk to a doctor.