HRV (Heart Rate Variability) is often used as a readiness metric. Our heats have small irregularities between beats known as interbeat intervals or RR. The more irregular the more stress we can handle. A low HRV value suggests that we need to take time off and recover. It is common for athletes to measure their HRV each morning for two minutes upon waking up. This is to make sure their system is ready for the upcoming workout. There are multiple ways to measure HRV such as using a chest strap or taking finger based readings. We will review three different options to measure HRV and discuss how to improve the score through breath timing.
 By slowing down our breathing we can increase our HRV score and quickly get ourselves into flow state. Taking a long slow deep inhale through the nose of up to 5 – 7 seconds followed by a slow exhale of the same time will boost HRV. We can dial in the exact breath frequency by using biofeedback. In this case we are seeing our HRV values as we breath. Flow state is typically and peak HRV are typically reached when breathing every 10 – 12 seconds.
Pulse Sensor Amped + Arduino
The Pulse Sensor Amped provides all the code necessary to get visual biofeedback of your HRV from the finger sensor. There is are step by step instructions for getting started and all the code necessary is provided on their site. 
Here is a brief summary of what is required to get going below:
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requires Arduino and Processing Apps be installed
- hookup: Arduino board, connect sensor: A0, 5v, GND
- Arduino App : install library “PulseSensor Playground”
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modify this variable in example code PulseSensor_BPM
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compile and upload code to Arduino
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cp PulseSensor_Heart-Rate-Variability folder to ~/Documents/Processing
- launch Processing App
- open sketch
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cover the sensor LED with your finger and breath with the expanding / contracting circle
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keys 1, 2, 3, 4, etc. will adjust breathing rate
Oura Ring
The Oura Ring provides a HRV chart and an average value for the previous nights sleep after syncing with the app phone app. Getting continuous HRV data all night without having to consciously remember to do a morning test upon waking makes this device a clear win for the lazy biohacker. A relatively new feature for the Oura App is a meditation activity called “Moment” which can also record HRV. As long as the meditation is over 5 minutes in duration the Oura App will generate a HRV chart to accompany the activity. Finally, the Oura ring does a good job of detecting rest periods through the day. It will provide an average resting heart rate and average HRV during a rest period without any need to trigger the app. This is particularly great as it means naps are normally recorded and can provide some a snap shot of your HRV value when you are most calm during the work day.
Garmin Watch, Chest Strap (HRM-Dual), Monitor+HRV App
Most of the Garmin watches support an app called Monitor+HRV. It requires a chest strap be worn and will not use the watches built-in heart rate sensor. This watch app has given me the most reliable HRV numbers and is incredibly convenient to use as no phone is required to gather the data and it can be viewed on the watch during acquisition. The Garmin Connect App will scrape the data from the watch upon next sync and provides visual graphs.
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