What Your 'Heart Rate Variability' Says About Your Health
by Rachel Fairbank from Lifehacker on (#5NHMP)
One feature a number of fitness trackers offer is a metric called heart rate variability," or HRV, which is the interval of time between each heartbeat. But given that we tend to think of our hearts beating at a steady and predictable pace, the fact that the interval between each beat varies can be a hard concept to...