New fitness trackers claim they can go beyond counting people’s steps and measuring how long they sleep — now, these devices can tell people when they’re stressed out.

The goal is to help people identify the things that trigger their stress, so they can avoid them if possible.

Most of the devices that offer such stress detection measure the change in the interval between heartbeats — a measure known as heart rate variability. For instance, the Tinké by Zensorium, which costs $119, plugs into a phone and measures heart rate variability from the thumb. HeartMath’s Inner Balance sensor, which costs $129, uses an earlobe clip and a plug-in phone sensor to measure heart rate variability.

But although heart rate variability has been used for decades to measure stress, fitness trackers may lack the capacity for dataprocessing that makes accurate measurements possible. And without additional information and context, there’s no way to know whether a dip in variability is caused by stress or positive excitement, experts say.

Managing stress

People don’t always recognize the physiological signs of stress, and their memories of past stressful events can be colored by their current mood, said Daniel McDuff, a researcher at Affectiva, a Cambridge, Massachusetts-based company that analyzes emotion from facial expressions.

But noticing stress can help people cultivate a more mindful attitude toward their bodies, which could have practical benefits, said Frederic Shaffer, the head of the Center for Applied Psychophysiology at Truman State University in Kirksville, Missouri. Reducing stress can improve people’s health, he said.

For instance, if people could identify that certain people, places or activities stress them out — and, for instance, cause a rise in blood pressure — they could change their habits, Shaffer said.

Heart rate variability

Heart rate variability is one of the most robust, noninvasive measures of stress response, McDuff said.

Researchers first linked heart rate variability to stress in the 1960s, when doctors realized that tests of babies who were in distress before birth revealed a more regular spacing between their heartbeats, compared with those not in distress. Subsequent studies have tied changes in heart rate variability to a host of diseases, from heart disease to diabetes to post-traumatic stress disorder (PTSD).

Full Article