henry copeland:

Heart rate variability: Get to know what it brings to the fitness party

Bottom line, it's an exciting time that more wearables are being able to tap into heart rate variability whether it's for improving fitness or just being able to know when you're feeling a bit stressed. This is really just the start of the relationship between the two, so don't be surprised if more HRV tracking devices are on their way over in the not too distant future.
- www.wareable.com