Millions of us rely on smartwatches to track our health, from our steps and sleep to our heart rate. A growing feature is stress monitoring, which promises to give us a heads-up when life is getting on top of us. But a new academic study suggests these devices might not be as insightful as we think. In fact, when it comes to stress, your smartwatch may have no idea what it's doing.
The Study: A Mismatch Between Body and Mind
Researchers conducted a study, published in the *Journal of Psychopathology and Clinical Science*, to compare the stress levels recorded by Garmin smartwatches with the self-reported feelings of the participants. The results were stark: the correlation between the smartwatch's stress scores and what people actually felt was "basically zero."
"This is no surprise to us given that the watch measures heart rate and heart rate doesn't have that much to do with the emotion you're experiencing," said Eiko Fried, an author of the study. "It also goes up for sexual arousal or joyful experiences.”
The study found that for a quarter of participants, their smartwatch indicated they were stressed when they felt fine, or vice-versa. The devices simply couldn't differentiate between the physiological signs of negative stress and positive excitement. The relationship with physical fatigue, what Garmin calls "Body Battery," was slightly stronger but still weak overall.
Why Stress Is So Hard to Track
The core of the problem lies in what these watches actually measure. They primarily use optical sensors to track Heart Rate Variability (HRV) and electrodermal activity (changes in sweat). While these can be indicators of your body's autonomic nervous system response, they are not exclusive to stress. Your heart rate can spike for many reasons:
- Positive emotions: Joy, excitement, love.
- Physical exertion: A brisk walk, climbing stairs.
- Environmental factors: A hot room, a sudden loud noise.
Current consumer-grade sensors are not sophisticated enough to distinguish the nuanced context behind these physiological changes. They see a spike in heart rate and a change in sweat and label it "stress," regardless of the emotional cause.
The Bottom Line: Consumer vs. Medical Device
It's crucial to remember that smartwatches are consumer wellness gadgets, not certified medical devices. While they are becoming increasingly advanced, their data should be seen as an estimate or a guide, not a diagnosis. "Be careful and don't live by your smartwatch," warns Fried.
What About Sleep and Fatigue?
It's not all bad news. The study did find a much stronger correlation when it came to sleep. The researchers noted that if a participant reported a good night's sleep after a bad one, their Garmin watch accurately predicted an increase in sleep duration of around two hours. This suggests that for more clearly defined physiological states like sleep, the sensors are far more reliable.
The Future of Wearable Mental Health
While current stress-tracking technology is unreliable, the research is part of a larger goal: to create an early warning system for mental health conditions like depression. Researchers are hopeful that by analyzing long-term patterns in activity levels, sleep, and other metrics, wearables could one day help people seek preventative treatment before a major depressive episode begins.
For now, however, it's best to take your watch's stress score with a grain of salt. If you're feeling overwhelmed, listen to your mind and body—not just the data on your wrist.