Updated September 26, 2022; text and figure added in Does HRV index autonomic tone?, and text added in Respiratory sinus arrhythmia.
Updated August 10, 2022; text added in “Measuring RSA” section.
Heart rate variability (HRV) is a fascinating metric. It’s been around for over a century in the clinical and research space, and has exploded in popularity both in research and household settings because it can be measured easily and noninvasively, providing a window into the complexities of physiological and psychological processes without perturbing the underlying systems. Athletes use it to optimize training and recovery, doctors use it to predict patient outcomes, and psychologists use it to measure a whole host of cognitive activities…yet still today, nobody seems to be able to agree on precisely what these measurements actually mean.
As I’ll explain below, HRV is not a single measurement but rather a biological phenomenon that can be quantified in a number of different ways, which one needs a fair bit of technical and mathematical expertise to correctly interpret. A thorough understanding of the physiology underlying HRV has lagged well behind enthusiasm for its potential, which has led to a number of very persistent misunderstandings and a glut of unhelpful or misleading research. Reading through recent reviews and editorials, you often get the sense that the experts in the field are sighing with exasperation at the fact that controversies that ought to have been laid to rest in the late 1990s are still alive and well today.[Read more…] about Heart Rate Variability 101: What It Is, How It’s Measured, and Controversies in the Literature