If you own a fitness tracker, you’ve likely come across the term HRV (heart rate variability). You may have even seen people proudly posting their HRV numbers on Instagram. But what can the ...

That tension becomes especially clear with heart rate zone training, a popular five-tier system that endurance athletes use to measure effort and fine-tune performance. The well-known formula is ...

Heart rate variability (HRV) typically increases with parasympathetic activation (rest-and-digest response) and decreases with sympathetic activation (fight-or-flight response). The autonomic nervous ...