Google Research

The Role of HRV in Readiness

  • Cathy Speed
  • Robert Keith Harle


Heart rate variability (HRV) is defined as the variation in the time intervals between adjacent heartbeats. It allows humans to adapt to physiological, environmental and psychological challenges and it is a powerful biomarker. The advent and continued development of technologies (both hardware and software) that measure HRV has led to it being used by a spectrum of individuals, from elite athletes to the general population and those with a range of diseases. HRV is unequivocally a useful measure in many of these situations, but the literature is full of contradictory studies and conclusions. This white paper reviews the science as it pertains to the use of HRV to estimate a user's readiness for exercise.

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