Oct 2, 2020 | By Carlton Moeller | Illustration by Xixi Qin

Heart rate variability (HRV) is a very important biometric for gauging the general adaptability of our bodies. HRV is measured by taking the variance (generally in milliseconds) between each of our heart beats. A healthy HRV for adults is right above 100 milliseconds.

You can see your variance for yourself. Take your pulse and breathe in very slowly. Try to take a ten second inhale, then a ten second exhale. Your pulse might change based on whether you are breathing in or out.

The higher your heart rate variability in general, the more capable your body is at taking on stress. This is why HRV is often used to gauge athletic recovery. If an athlete displays a low HRV during their sleep, it is an indicator that they have not recovered from their day of exercise.

Beyond just a measurement of recovery, HRV is basically a measurement of your nervous system’s ability to adapt. If your heart rate is stuck beating like a metronome at either a high rate or a low rate, it may mean that your central nervous system is stuck in your sympathetic or parasympathetic nervous system, respectively.

For instance, some people decide to track their HRV while undertaking a new diet. A gradual decline in HRV over the first couple days of a new diet may be a sign that it is not right for you. Additionally, meditation and conscious breathing have been shown to increase HRV.

Heart rate variability trackers are popular among athletes for obvious reasons. Many have found that cold exposure before bed greatly increases recovery. This may be because cold exposure increases HRV. However, biohackers tout the benefits of cold exposure before sleep in a more diffuse way. They say that our bodies need to have a lower body temperature before we fall asleep (roughly two degrees lower than during daytime), and cold exposure before bed would accomplish this. Moreover, this body temperature decrease is based on our 24-hour circadian rhythms, meaning that lower body temps promote the “night-time” half of the circadian rhythm, which may promote deeper, more restful sleep.

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