Full Strides
Stress
A 0 to 100 estimate of physiological stress through the day, from heart rate and HRV against your own baseline. Higher means more stress.
What it reads
Stress reads two things your Apple Watch already records: heart rate variability (HRV) and heart rate. Both are compared to your own 60-day baseline, the same baseline Recovery uses. There is no universal stressed HRV, only your HRV against your trend.
Weights
HRV, 60%. Suppressed HRV is the dominant stress signal.
Heart rate, 40%. Elevation above your resting rate.
Effort is not stress
A run raises heart rate and lowers HRV, which looks exactly like stress to a formula. Full Strides marks the minutes during workouts and sustained walking as Active, in grey, so the hour after a ride reads as effort rather than as a spike. The day's bar and legend both show it.
Zones
0 to 40, Calm. No color. Ordinary awake readings sit here, and an ordinary afternoon should not look like an alarm.
41 to 60, Mild.
61 to 80, Moderate.
81 and up, High.
Before the baseline exists
A new watch has no trend to compare against. Until enough days accumulate, the stress card says Building Baseline instead of showing a number that would mean nothing yet.
Live and daily are different
The live score through the day uses awake heart rate. The daily history uses each day's HRV and resting heart rate. The history legend names that difference, because the two are not interchangeable.
What it is not
Stress is a wellness estimate, not a medical measurement. HRV is moved by sleep, hydration, caffeine, alcohol, illness, and many other things. Full Strides is not a medical device.