This is from my weekly email newsletter but I republish it here for sharing and referencing. If you're not already a subscriber you can join below:
Got a wearable?
If you wear a device that tracks sleep and recovery like a Whoop strap, FitBit, or Oura ring, you're actually measuring a common underlying biomarker.
That marker is your heart rate variability or HRV. Modern wearables primarily use your HRV, in combination with your heart rate, to make predictions about your overall physical state.
You may have heard of HRV before but what is it actually? Why do all these technologies rely on it?
Heart rate variable is a measure of the variability in timing between the beats of your heart. Compared to your heart rate, measured in total beats per minute, heart rate variability is measured as the average difference in milliseconds between beats.
Throughout the day your HRV is going to change a lot because you're moving around so much. Therefore the most accurate measure of HRV is when you're deep asleep.
Wearable technologies use your HRV because it's a strong indicator of the balance between the two parts of your autonomic nervous system. If you recall, your autonomic nervous system functions automatically and consists of two subsystems:
When your HRV is low, meaning there isn't much variation in timing between beats, this generally indicates your sympathetic system is dominant. When your fight and flight system is dominant you are less able to rest and recover. A low HRV while at rest indicates you may be fatigued and need additional time devoted to recovery.
On the contrary, a higher HRV indicates a healthier balance between the sympathetic and parasympathetic nervous systems. A high HRV is a signal that your body is adaptable and capable of performing optimally.
Your wearables are smart enough to hide your HRV because the raw metric is almost meaningless. What's considered a "good" HRV depends a lot on individual factors like your age, genetics, and behaviors. More important is understanding what is "good for you". And this is why these wearables are so useful. They can compare your current data against your past data in the context of other information like your age and sleeping habits etc.
If you really wanted to measure your HRV directly you could use an EKG however out of context it's probably not a very helpful metric.
By understanding the underlying mechanism that drives these recovery scores it's easier to find strategies to improve them. Ultimately it comes down to making sure you're allowing your nervous system to calm itself. Activities like yoga, meditation, breath work, endurance exercise and most importantly ... good sleep, will all help relax your nerves and literally calm your organs.
That's all for this week!
Get some rest 🌙
Nick