Tech billionaires in pursuit of conquering aging have triggered a global wave of rising awareness of fitness – both physical and mental. Growth in wearable technology like smartwatches and trackers which offer real time monitoring of key health indicators such as heart rate, insulin levels, sleep quality, oxygen levels, etc are helping with feedback and motivation. Among the measured parameters, heart rate variability or HRV is emerging as the most useful indicator of overall health. What exactly is HRV and why is it such an important indicator of health?
“HRV measures not how quickly the heart beats, but how regularly spaced those beats are. With heart rate a lower score is usually better, other things being equal, since it suggests a high level of cardiovascular fitness. When it comes to HRV, though, a higher number—that is, a more irregular pattern—is generally what you want.
HRV arises from the way the body regulates the heart. Left to its own devices, the heart will chug along at 100 beats per minute or so. That default rate is nudged up or down by the opposing halves of the autonomic nervous system (ANS), which acts unconsciously to control things like body temperature, breathing and digestion.
One half is the sympathetic nervous system, often known as the “fight-or-flight” system. This revs up the heart in response to things like exercise or fear or excitement. Its control is mostly exerted through hormones in the blood and neurotransmitters in the brain. That makes it a blunt instrument, and as the heart rate rises, so the time between beats becomes steadier.
The other half of the ANS is the parasympathetic, or “rest-and-digest” system. This slows the heart down when it is time to relax. It communicates with electrical signals sent via the vagus nerve. That allows precise control from moment to moment, which makes the time between heartbeats more variable. (Your heart rate speeds up slightly when you breathe in, for instance, and slows down as you breathe out.)
All else being equal, stress on the body boosts the sympathetic nervous system, decreasing HRV. All sorts of stress count, whether psychological or physical. A hard workout will cause HRV to fall for hours (or sometimes days) as your system recovers. So will lack of sleep, a cold, a failing marriage or worries about money.
At a population level, higher HRV is a sign of an ANS that is in good nick, and a body that can adapt itself to the stresses of life. It is associated with a lower risk of heart attacks, and a higher chance of survival if you do have one. (It was in cardiology wards that HRV first proved its usefulness.) It is also associated with slower progression of dementia, less inflammation, a lower chance of suffering depression, and more.”
Essentially, a metric that shows our ability to deal with stress makes sense as an indicator of overall health.
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