The human heart beats at a non-constant rate; heart rate variability (HRV) is a statistical measurement of heart rate irregularity. Originally used as a predictor of survival after acute medical emergencies, the application of HRV has rapidly expanded, and it has now one of the most studied areas of physiological response to exercise. HRV has been shown in numerous studies to positively correlate with athletic performance and training adaptation, and to negatively correlate with risk of overtraining and injuries. This document provides coaches with an overview of HRV with a focus on its utility as an athlete training tool.
