A research team from the University of Waterloo in Canada researched the ECG sensor of the Apple Watch in-depth and discovered that their data can be used to make a precise tool that predicts stress levels.
Apple Watch does not currently provide a Stress score, unlike competitors like Samsung, Fitbit, and Garmin who have been providing this feature for some time.
Fitbit and Garmin Stress Score Methodology
Fitbit Smartwatches use heart rate variability (HRV), EDA sensors, and skin temperature tracking to measure how stressed you are and give you a score based on that data.
Unlike other companies, Garmin watches use a simplified HRV model to determine the user’s stress levels. By gathering heart rate data, it can measure the interval between each beat. The less variability there is in these beats, the more stress one is under, whereas a higher variability implies lower levels of stress.
These wearables will inform the user when they detect a decline in variability and propose breathing exercises to counter the stress signals.
Using Apple Watch ECG to Forecast Stress Levels
According to a recent study, it is possible to use the ECG sensor data of Apple Watches to determine someone’s stress score.
Apple Watch’s single-lead ECG
Apple Watch’s single-lead ECG sensor has been proven to be very reliable by many studies. A clinical trial including 600 participants revealed that the ECG sensor had 99.6% specificity in determining sinus rhythm and 98.3% sensitivity for atrial fibrillation, which is highly accurate.
This is the first research to use Apple Watch ECG data to predict stress, with results published this week in Frontiers Digital Health.
For two weeks, participants in the research project were given an iPhone 7 running iOS 15.0 and an Apple Watch Series 6 with the Apple Watch ECG app installed (WatchOS 8.3).
Over the course of the day, participants were instructed to collect data 6 times at approximately 3-hour intervals. They were also asked to complete a stress questionnaire using an iPhone app built by the researchers beforehand.
ECG data were obtained from HealthKit, turned into a CSV file, then brought into Kubios to calculate HRV.
Machine Learning Algorithms
Machine learning algorithms were deployed with Apple watch ECG data in order to investigate the effects of age on stress prediction models, as well as the influence of gender, profession, and socioeconomic status.
The study found that models taking in “stress” data had a greater level of accuracy, but the models with “no stress” data performed better with a recall rate typically above 60%. For such short electrocardiography readings compared to the standard times and for measurements taken in real life, these results yielded highly encouraging outcomes.
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Heart AC and DC
The heart acceleration (AC) and deceleration capacity (DC) were important HRV factors included in the model, along with variables such as SDNN and other frequency domain parameters.
The researchers hypothesize that with the Apple Watch collecting sleep and physical activity data when it is combined with ECG data and other stress variables, the models can become more accurate in predicting outcomes.
According to the researchers, having a wearable device that can measure stress in real-time would help people recognize when their mental health is deteriorating and take action. Additionally, such devices could also collect data at scale, informing public health policies and initiatives.
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Why Apple Has Not Added Stress Monitoring?
Given that Apple Watch’s data on heart rate and other activities could be utilized in stress monitoring, it is unclear why they have not done so yet. It could be possible that they might eventually offer a more comprehensive feature by utilizing additional sensors such as EDA.
Another option may be that the company is waiting to reveal this with their next AirPods, which would theoretically read EEG signals and show a more in-depth mental health monitoring platform. Earlier in the year, we observed studies where earbuds were tailored to access EEG data from users successfully.
We won’t know what Apple has in store in terms of products and features until the future reveals it.
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