How to know what you really need: Heart rate variability


Heart Rate Variability (HRV) is a relatively new metric in health – it is simple to track and gives you powerful information about how stress affects your physiology.

A stressful situation triggers two processes within the body.

  1. First, stress from any source activates our fight or flight system, the sympathetic nervous system (SNS). It boosts heart rate, produces stress hormones, and puts us on high alert.
  2. When the stressful situation passes, our rest and digest system, the parasympathetic nervous system (PNS), takes over to relax us and return our body to homeostasis.

Did you know that the time between each of our heartbeats is a little different with every beat? Whether our heart rate is fast or slow, the precise time between beats varies. Even more interesting, the amount of difference in beat timing seems to be related to the activity of our SNS and PNS.

When we are rested and relaxed, we have more PNS activity. In this state, our heart rates display lots of variability in the timing of beats. Picture a dance party: dancers move quickly, then slowly, then faster again, and so on. When we’re rested, our heartbeat dances like nobody’s watching.

Running Female With Mobile Phone Connected To A Smart WatchIf we are stressed out or not yet recovered from our last workout, we’ll be more SNS dominant. Our heart rates will be less varied and more consistent – more like the metronome from piano lessons, or a ticking clock.

If stress is high, variability in the heart rate decreases. If stress is low, variability in the heart rate increases.

Why does this matter to us? Because now we can track it. Using a simple heart rate monitor and app, we can track and examine our own heart rate data. Since stress from all sources contributes to SNS activity, we can use this data to gauge our exercise readiness. If our HRV is low, it means we are stressed out and need a workout that will help us recover.

We can (and should!) exercise daily. Monitoring heart rate variability helps us decide how to exercise – when to go for the HIIT class, and when to choose a low-intensity workout to promote recovery.

Start Tracking

To get started tracking your own Heart Rate Variability (and a gazillion other metrics), see this tech guide at Quantified Self.

For a more in-depth look at tracking HR Variability in the action, see this article. Author Ernesto Ramirez takes a fascinating look at his HRV data from a high-stress