Heart Rate Variability(HRV)-is the physiological phenomenon of variation in the time interval between heartbeats. It is measured by variation in the beat-to-beat interval.
HRV monitoring is a very useful tool in keeping track of your stress levels and how well you are recovering from your workouts. It is very easy to test every day and is not time consuming thanks to apps on your phone. It's a cheap and easy way to monitor your nervous system and is something I use myself and for my clients.
HRV is a unique way to assess the effects of stress on your body. It basically measures the pattern of your heart beat. For example if your pulse is 60 beats per minute(BPM) your heart would assumably beat once every second,but the variability is more like 1.1 then 1.05 then .95. So it averages 60 BPM. HRV is exclusive to heart rate(HR). You can have a high resting HR and still have a healthy HRV and vise versa. HRV testing logs the average and gives you a number from 0-100. A high number is a sign of a healthy nervous system. HRV is controlled by the autonomic nervous system(ANS),which has two branches;
Sympathetic Nervous System-Also known as the fight or flight response.
Parasympathetic Nervous System-Also known as the rest and digest response.
LF(Low Frequency) is the measure of the Sympathetic branch.
HF(High Frequency) is the measure of the Parasympathetic branch.
So these two systems are basically in a tug of war. Sympathetic system is speeding heart rate up and the parasympathetic is slowing it down. The key is having a balanced nervous system and quality training in combination with quality rest and recovery are keys to this. Of coarse a good relaxed state of mind can also do wonders for your HRV.
I think the best product out right now is made by SweetWater Health. I have used others in past like ithlete,but this app is much more comprehensive and tests LF and HF along with a lot of other measurements. As of right now it's only available in the iTunes store on the iOS platform. They say an Android version is on the way. If your not an iOS user I would try ithlete since it's available on both platforms. Sweetbeatslife is the name of the app. You can click on the link to see compatible heart rate monitors and they even have there own HealthPatch that does it all plus takes a few other measurement like skin temperature.
The process takes 5 minutes of your time every morning upon awaking. I use this for myself and my clients daily to keep track of recovery and make a quality plan for training on that day. It has been an invaluable tool in finding the balance between hard training and quality recovery. When you get this right you keep cortisol levels low and stress levels balanced. The cost is very low for the feedback you get and if you have a compatible HR monitor it will just cost you $9.99 for the app as of now. This is one of the only self quantifications I use daily and I highly recommend it!