An acute stress score turns the beat-to-beat intervals in one Apple Watch ECG into a 0 to 100 snapshot. A higher score means the short recording contains less heart rate variability and reads as more physiological strain.
Body Insights reads the latest Apple Watch ECG stored in Apple Health. It calculates RMSSD and other short-term HRV values from the recording, then shows them beside the Stress Score. This is one ECG snapshot, separate from the all-day Stress Balance result.
What does the ECG Stress Snapshot show?
The ECG Stress Snapshot shows the 0 to 100 Stress Score first. The supporting rows let you inspect the HRV values calculated from the same recording.
Stress Score
A number from 0 to 100Higher means the ECG contains less short-term variability and reads as more physiological stress.
HRV (RMSSD)
MillisecondsThe change between neighboring heartbeat intervals. Lower RMSSD usually pushes the Stress Score higher.
SDNN
MillisecondsThe overall spread of the valid heartbeat intervals in the recording.
SD1
A numberAnother view of short-term variation from the same intervals.
pNN50
A percentageHow often neighboring intervals differ by more than 50 milliseconds.
Read the Stress Score and the supporting rows together. The score gives you the quick summary. RMSSD, SDNN, SD1, and pNN50 show what sits underneath it.
Example: one ECG snapshot
An example result can show:
- Stress Score
- 77
- RMSSD
- 35 ms
- SDNN
- 19 ms
- SD1
- 25
- pNN50
- 0%
The higher Stress Score comes from lower short-term variability across that ECG. It describes that recording only. For a cleaner comparison, take the second ECG under similar conditions. Keep your activity, posture, and caffeine intake consistent.
How does the latest ECG become a score?
Body Insights follows five steps without exposing the proprietary score weights.
- Apple Watch records the electrical signal during an ECG, and Apple Health stores the available recording.
- Body Insights reads the latest ECG and isolates the heartbeat peaks in the voltage signal.
- The app converts the time between those peaks into RR intervals and removes intervals outside a plausible range.
- The remaining intervals produce RMSSD, SDNN, SD1, and pNN50.
- Those HRV values build the 0 to 100 Stress Score. Less short-term variation moves the score higher.
The ECG score uses fixed short-term HRV normalization. Personal-history comparisons belong to Waking Recovery and Stress Balance.
Why can two ECG readings differ?
Breathing, posture, and movement can change a short RMSSD result. Recent exercise, illness, caffeine, and recording quality can do the same. Two ECGs taken under different conditions are not a clean comparison.
Take the ECG while seated and settled. If you compare two snapshots, keep your posture, time of day, and recent activity as similar as practical. When a score surprises you, check the recording conditions and repeat after you have settled.
Which stress result is available now?
Stress Balance is the stress result available in the public Body Insights app. It reads valid waking HRV from Apple Health and shows Low, Medium, and High periods with one daily label.
The ECG Stress Snapshot is currently disabled in App Store and TestFlight builds. The calculation remains in the product source for development, but the public app does not show the Analyze Latest ECG card. Use Stress Balance for the daily stress pattern available now.
See your daily Stress Balance
Body Insights turns waking HRV from Apple Health into a daily label and a clear breakdown you can use for pacing.
Check my Stress Balance