A study shows that the ECG function of the Apple Watch, together with other measurements, can predict whether someone is stressed. As a simple method it appears to work well, but there is room for improvement. 
Stress research on Apple Watch
The study involved taking six ECG measurements per day, while HRV measurements were also included. It also turned out that the measurements were more accurate if sleep, activity and heart rate measurement were also taken into account. There were already rumors in 2020 that the Apple Watch Series 6 would be equipped with functions to track your mental health, especially in relation to panic and other feelings of anxiety. Apple has not yet added such a function, while other wearable makers such as Polar, Fitbit and Garmin do monitor your stress.
Little attention to stress measurement on Apple Watch
Internally, Apple will have already done research into measuring stress, but such functions are not yet widely available on the Apple Watch. The only thing you can use is the Mindfulness app, which allows you to do breathing exercises. You will not receive a measurement of your stress level. The Apple Watch also measures your heart rate variability (HRV), but the measurements are somewhat hidden in the Health app. You will only see them if you explicitly search for them.
The study to see if the Apple Watch can also detect stress was carried out by Frontiers in Digital Health and the University of Waterloo (Ontario, Canada). 33 participants took part, of which 73% were women and 27% were men. Their ages varied between 18 and 65+. These participants were given an iPhone 7 with iOS 15 and an Apple Watch Series 6 to take measurements for two weeks. They had to collect data 6 times a day, with intervals of about three hours. Before taking the ECG measurement, they had to complete a stress questionnaire on the iPhone. According to the researchers, this is the first time that the ECG function of the Apple Watch has been used to predict the stress level of individuals. The results are in line with advanced stress prediction methods, albeit on the low side. You could therefore use the Apple Watch as a simple, but limited stress detector.
What can you do right now?
Still, it would be better to take a wearable that already contains more functions to monitor stress, such as with Garmin sports watches. These watches analyze heart rate variations while you are inactive to determine overall stress levels. Training, physical activity, sleep, nutrition and general stress also affect this. However, if you have an Apple Watch on your wrist, you can check your HRV for yourself with our tip on heart rate variability. With apps like Stress Monitor for Watch you can also get a better view of your stress level.
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Measure heart rate variability with the Apple Watch and apps
You can measure heart rate variability (HRV) with the Apple Watch. How does that work, what can you deduce from it and how can you measure it with the Apple Watch itself and with all kinds of apps?