Heart rate variability (HRV) is the variation in the time between two consecutive heartbeats over a specific period. Doctors may use HRV as an indicator for certain aspects of a person’s health, ...

Micro-fluctuations in the time between heartbeats are proving a helpful indicator of mental health, stress levels and exercise capacity. They could even provide insight into how well you are ageing.

These days, it may seem like there’s a million different data points that you’re supposed to keep track of—hello, steps, sleep, and recovery scores!—and it’s difficult to know which ones are worth ...