After two years of lockdowns, home-working, home-schooling, restrictions, and now a war in Ukraine, it’s no surprise we’re stressed about stress. According to data from Google Trends, searches for “stress trackers” have increased by 80 per cent since January 2020, with sales up by around 20 per cent over the same period.
We might tend to think of stress as a psychological or emotional condition, but there is a physical dimension to it too. When we’re stressed our bodies go into fight-or-flight mode. This worked for our cavemen ancestors who were stressed about hunting and predators. Less so for the modern human whose stresses are more ongoing: working long hours, looking after family members, keeping up appearances.
When in this stress-induced state the body deprioritises other functions: the stomach is less efficient at breaking down food and absorbing nutrients, you’ll retain more fat, you’re less able to focus. Prolonged stress can even lead to a reduction in grey matter in the hippocampus, harming memory recall among other things.
“We know that stress increases your heart rate, your blood pressure, your breathing rate,” says Dr Sundip Patel, consultant cardiologist at London Bridge Hospital. “It’s associated with an increased surge in various chemicals which can have an adverse impact on various parts of the body including the arteries, the brain, the heart, the kidneys, everywhere really.”
For a lot of us, stress is so endemic to our lives that we’ve become less good at recognising it and preventing it. This is where stress tracking comes in. Almost all modern activity trackers and smart watches have some kind of stress-tracking facilities built in. But how do you actually measure something as individual and specific as stress? The most common way is looking at heart rate variability (HRV).
“Our heart rate has slight variations in everyday life,” explains Patel. “When we’re asleep, our heart rate is nice and slow and when we’re out and about, our heart rate increases because the heart needs to work harder to get us moving. If we’re under stress, be it physical or emotional, then the release of hormones and chemicals in the body will make the heart rate run a little higher than normal; it will probably remain a little higher than normal throughout the 24-hour period. It isn’t by very much – you wouldn’t normally be able to notice it – but you can detect it with technology.”
This isn’t the same as the number of times our hearts beat every minute, but rather the interval between heartbeats, which can vary by a couple of milliseconds. When a person is stressed, there are fewer of the ups and downs in heart rate that you’d normally see as a person alternates between rest and activity, so by measuring the variability in heart rate, or lack thereof, the more people can get a sense of what is and isn’t normal for them. If your heart rate is constant it’s an indication that it’s always at that heightened level caused by stress because you’re not getting as much of a slowdown from rest.
The downside to HRV tracking is that optical monitors, found on most wrist-mounted devices, aren’t usually as precise as chest-worn devices. Your smart watch can monitor beat to beat intervals to an accuracy of about 10 milliseconds, while a chest-mounted tracker can do so at 1-3 milliseconds. Additionally, movement can throw off these sensors, which work best when you’re sitting still. Not ideal if the thing causing you stress is a particularly busy and active day. Still, “For general public usability, these are adequate measures,” says neuroscientist Anne-Sophie Fluri, head of mindfulness at Mindlabs.
Thankfully, in most cases, stress can be mitigated relatively easily. “When you’re stressed, you’re in this see-saw between that fight-or-flight response and the parasympathetic nervous system, which calms you down,” says Fluri. “Something as simple as breathing slowly activates your parasympathetic nervous system and the physical processes which help you recover. Taking deep breaths and focusing on the exhale, going for a walk, meditating or exercise can also work.”
Perhaps it’s interesting to note that when a Garmin device detects stress, it swiftly activates a guided breathing exercise as a stress-buster. So who knows; perhaps the future of tracking stress is preventing it automatically…
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Garmin Venu 2