Recent fitness trackers assert that they can do more than just tally steps and monitor sleep duration — these devices can now indicate when a person is experiencing stress.
The objective is to assist individuals in recognizing their stress triggers so they can avoid those situations whenever feasible.
Most trackers featuring stress detection assess the variability in time intervals between heartbeats — known as heart rate variability. For example, the Tinké by Zensorium, priced at $119, connects to a phone and gauging heart rate variability using the thumb. Similarly, HeartMath’s Inner Balance sensor, retailing for $129, employs an earlobe clip and plugs into a phone for measuring heart rate variability.
However, despite heart rate variability being utilized for many years as a stress measurement tool, fitness trackers might not possess the necessary data processing capabilities to ensure precise readings. Additionally, without further information and context, it’s impossible to determine if a reduction in variability stems from stress or positive excitement, experts caution.
Managing stress effectively is crucial.
Often, individuals may not recognize their body’s physiological responses to stress, and their recollection of previous stressful experiences can be influenced by their current emotional state, according to Daniel McDuff, a researcher at Affectiva, based in Cambridge, Massachusetts, who studies emotions through facial expressions.
Recognizing stress can encourage a more mindful approach towards one’s physical state, which can offer tangible advantages, stated Frederic Shaffer, who leads the Center for Applied Psychophysiology at Truman State University in Kirksville, Missouri. He emphasized that alleviating stress could enhance individual health.
For example, if people could pinpoint specific individuals, locations, or activities that induce stress and raise blood pressure, they could alter their behaviors or routines, Shaffer pointed out.
Heart rate variability is a highly reliable and noninvasive indicator of stress response, McDuff explained.
The connection between heart rate variability and stress was first established in the 1960s, when doctors noted that tests carried out on distressed babies before birth showed a more consistent interval between heartbeats compared to those who weren’t distressed. Follow-up research has linked fluctuations in heart rate variability to numerous ailments, including heart disease, diabetes, and post-traumatic stress disorder (PTSD).
While many people assume the heart beats in a consistent manner, this is not accurate. In truth, healthy young adults experience a natural variation in the time between heartbeats, whereby the heart’s rhythm within a single breathing cycle (comprising one inhalation and one exhalation) can fluctuate by 10 to 15 beats per minute, Shaffer mentioned.
“A healthy heart does not act like a metronome,” Shaffer explained to Live Science.
When a person finds themselves in a distressing or frightening situation, the autonomic nervous system activates the fight-or-flight response, resulting in decreased variability in heart rate intervals. For instance, a heart under stress may only show a variation of two beats for every breath cycle, as noted by Shaffer.
The challenge of utilizing heart rate variability to assess stress lies in the fact that both distressing and exciting situations can elicit this nervous-system reaction, according to McDuff’s comments to Live Science.
For a fitness tracker to accurately determine stress levels, it would also need to monitor the context surrounding the individual’s situation, McDuff stated. These devices must gather data about what a person is engaged in at any given moment, he asserted.
Moreover, there are instances when sensors tracking heart rate may fail to register a heartbeat or may inaccurately generate one.
“Movement can introduce significant noise or erroneous data into the information being gathered,” Shaffer told Live Science.
In controlled environments, researchers utilize computer algorithms to filter the data and differentiate the signal from any noise. However, most fitness trackers likely lack the advanced computing abilities to conduct this level of complex analysis, according to Shaffer. He also highlighted the absence of agreement on the duration for which heart rate should be monitored to accurately assess heart rate variability.
“Since these trackers are relatively new, and there’s no consumer laboratory validating them against clinical-grade equipment, we currently have no way to assess their accuracy,” Shaffer commented. (The Tinké and Inner Balance claim that their data has been validated, and although Shaffer, not affiliated with HeartMath, confirmed that he has used the Inner Balance and found it to be precise.)
These “stress sensors” are still in the initial development phase, but as more advanced sensors are introduced to the market, and with advancements in computing power and user testing, it’s anticipated that future versions will improve, Shaffer remarked. The trackers might be enjoyable for those in good health who seek a basic indication of stress or for individuals who want to quantify every aspect of their bodily metrics.
However, currently, users should be aware that the accuracy of these devices hasn’t been independently verified.
“So essentially, it’s a case of buyer beware,” Shaffer concluded.
How smartwatches assess stress levels
Smartwatches evaluate stress by tracking heart rate variability. Essentially, they record the intervals between heartbeats. The nervous system controls heart rate variability. A heart rate that varies more signifies lower stress, while a more consistent heart rate indicates higher stress levels.
The assessment of stress is merely an approximation. For example, if you’re stationary but your heart rate is elevated, your smartwatch might still register a high stress level. The device may misinterpret excitement as stress.
Jorge Barraza, the co-founder of Immersion Neuroscience and a consumer psychology professor at the University of California, shares with Stylist that while smartwatches are beneficial for introspection, it’s important to note that the data provided is meant to be broadly indicative rather than exceptionally precise.
After participating in my watch’s guided breathing session, I didn’t achieve complete tranquility, but I became aware that my jaw was tense. I kneaded it with my fingers and moved on with my day. While driving home, I contemplated the situation.
Did supervising the test cause me stress? If so, what was the reason? How could I better manage my well-being at work to lessen my stress? The watch not only encouraged me to be more active, but it also enhanced my awareness of my stress levels and, more generally, my mental health.
With a smartwatch, individuals like me can begin to recognize specific times and places that are challenging. “Adults juggle so many responsibilities, and tracking mental health becomes difficult,” explains Barraza.
On multiple occasions in recent months, my watch has prompted me to breathe. Hurrying to make it to work: breathe. Disputing with my landlord: breathe. My watch has proven to be an effective tool in notifying me of my stress and assisting me in addressing it right away.
I often misplace my phone and wallet, but my watch is continuously on. Because of this consistent presence, I can identify when I’m stressed and know how to respond (at least for the next five minutes). Naturally, it has its limitations: the watch can’t guide me on whether I should change jobs or relocate. It also can’t indicate when I’m genuinely feeling good. However, I am learning to recognize stress as a state, and the watch serves as an excellent aid for that.