As I understand it, HRV - Heart Rate Variability allegedly measures the spacing in beats. More variability means your body is chillin' and relaxed; less variability means something is physically stressing you, like sickness, lack of sleep, etc.

At the end of Aug, I was starting to feel under the weather so I cut back on training and spent some time resting. Eager to not lose momentum, I headed out on a 40 mile bike ride as soon as my HRV was almost back to normal and pushed it right back down again.

Lesson learned: err on the side of giving yourself too much time to recover. Hope you found it interesting!