Heart Rate Variability — What, Why & How?

Justin Lawler
Biohackers Collective
7 min readAug 11, 2016


Heart Rate Variability is probably the cheapest, easiest and most useful metric to track health and fitness levels. Anyone considering lifestyle changes — whether running a marathon or simply trying to loose weight — will gain from tracking their HRV daily.

Its been hailed as the one key biometric anyone can measure easily that gives the best all-round indicator of health and stress on the body.

It’s being used by athletes to optimise their training and prevent overtraining.

The Palo Alto institute has given a prize of 500,000 USD to anyone who can consistently & easily restore Heart Rate Variability of an aging reference mammal to that of a young adult.

It can be used by anyone right now to manage & reduce stress and improve health.

We can hack Heart Rate Variability (HRV) right now. There are tools & techniques we can use to improve HRV over the long term to improve our own health & vitality.

What is Heart Rate Variability?

Heart Rate Variability comes about from the interaction of the sympathetic nervous system (fight or flight), and the parasympathetic nervous system (rest & digest).

We need variability in our heart rates to allow us to quickly switch from rested to alert states (low HRV could be one cause of dizzyness when standing up).

Measuring Heart Rate Variability is simply the variability in the time between the heart beats (R-R interval) over a measurement period.

As we’re breathing in & out, the heart will beat slightly faster & slower — see below graph taken from a good day on the EliteHRV app. Heart rate is low & theres a clean sign-wave signal with fairly large variance in the heart rate.

What Impacts Heart Rate Variability?

In general as we age, our HRV lowers, but there are many other factors can increase or decrease HRV in both the short & longer term.

Decreases HRV over Short Term

  • Stress
  • Poor sleep — quantity & quality
  • Diet
  • Food intolerances
  • Alcohol
  • Sickness
  • Exercise
  • Hot therapy
  • Medication — antihistamine, antidepressants & others

Decreases HRV over Long Term

  • Age
  • Chronic disease or inflammation
  • Chronic stressors or burnout
  • Chronic lack of sleep
  • Lack of fitness
  • Overtraining
  • Unhealthy environment

Increases HRV over Short Term

  • Improved diet
  • Improved sleep — quantity & quality
  • Breathing exercises
  • Hot and cold therapy — saunas and cold showers
  • Intermittent fasting
  • Supplements — Omega3 & many others
  • Getting into ‘flow’ state
  • Lowered stress — meditation, taking vacations

Increases HRV over Long Term

  • Aerobic fitness
  • Managed stressors
  • Hot therapy
  • Ketogenic diet
  • Reduced alcohol intake
  • No overtraining

Note — many factors that decrease the HRV in the short term also increase average HRV over the long term.

What Does Poor Heart Rate Variability Look Like?

Poor HRV scores will differ depending on the stressors — physical or emotional.

Emotional Stress

Below was the morning after a very stressful day. Heart rate up, and the signal is very noisy.

Physical Stress

Below was taken after very poor sleep, alcohol and a heavy workout the day before. Variability in the signal is much less, although there is little noise.

Measuring HRV

Most HRV apps or devices will give a HRV ‘score’ at the end of the measurement. Different apps sometimes use different algorithms to calculate the score, but most are using something called RMSSD (Root Mean Square Successive Difference).

Good ranges of HRV values depend on age, fitness, etc, we’re more interested in what causes dips & getting a gradual upwards trend in our scores.

Heart Rate Variability is dependant on the conditions of when your measuring. All of the below will impact:

  • Time of day
  • Drinking liquids just before
  • Having just passed water
  • Standing or lying
  • Deliberate breathing exercises
  • Hardware issues, including connection of sensors to the body

The best way I’ve found to take HRV readings are:

  • First thing in the morning
  • Before checking social media/emails
  • Just after emptying bladder
  • Lying back down in bed & waiting 2–3 minutes for the heart rate to settle back down
  • Take a 2.5 minute ‘morning readiness’ test
  • Normal breathing — don’t try to pace or slow down the breathing

Alternatively there are a few devices that take HRV measurements while sleeping, giving the most consistent testing conditions.

  • Emfit — advanced sleep & HRV tracker.
  • Beddit — a dedicated sleep tracker that has HRV values when exporting to Excel.

Hacking my HRV

Over the last 12 months I’ve been working on below to improve my HRV scores:

  • Diet — reducing carbs and processed foods. Intermittent fasting
  • Alcohol — Reducing quantity
  • Sleep — More time. Improved conditions, including blackout blinds
  • Acupuncture — anecdotally I’ve seen HRV increase for a day or two after
  • Exercise — bootcamps and training for an obstacle race
  • Managed stressors — acting & improv classes
  • Cold Therapy — Cold showers & sea swims. Work in progress

So any positive results so far? Average has definitely gone up as long as life doesn’t get in the way. However, over the last year there have been a number of occasions when results went down:

  • Ketogenic diet for 4 weeks — HRV going down & then up
  • Long vacation in Italy — high-carb & red wine diet
  • Christmas — again, alcohol & food
  • Death of close friend

By far the biggest benefits has been from a greater understanding of my body & motivating me to improve my diet & overall wellness. This reflects in other tests, such as blood biomarkers and improved IBS symptoms.

I’m much more aware of how my body is behaving, if its under stress, what foods impact be badly.

Tracking HRV when starting out new diets, intermittent fasting or reducing alcohol for me has been incredibly helpful. Helpful for both understanding how my body is reacting to its environment and motivation to keep on improving overall health.

Tracking Apps & Devices


  • EliteHRV — Android & iPhone. Needs an external chest strap.
  • ithlete — Android & iPhone. Works with external chest strap or ithlete’s own finger sensor.
  • Sweet Water Health — iPhone & Android, although Android support not great. Needs an external chest strap
  • HRV4Training — iPhone only. Can use the iPhone camera to measure HRV, so no need for external chest strap.


  • EMFit — Sleep & HRV monitor.
  • Heartmath emWave — HRV monitor that has tools to improve HRV & reduce stress levels through paced breathings.
  • Whoop — 247 HRV measuring in wrist strap. Not out until end of 2016 however.
  • FirstBeat — 247 HRV measuring chest monitor. Requires a ‘FirstBeat Lifestyle Assessment’ coach to work with you on using & analysing results.
  • OmegaWave — High-ended device targeted towards athletes
  • Beddit — Sleep monitor, but HRV data accessible through data exports on the website.


Sympathetic Nervous System — or the flight or flight system. This is the nervous system that triggers adrenal glands & other systems that get the body ready to handle stressful situations.

Parasympathetic Nervous System — or rest & digest system. This nervous system is responsible for activities while the body is at rest. So eating, sexual arousal, salivation, lacrimation (tears), urination, digestion and defecation.

RMSSD — or root mean square successive difference. Generally apps will normalise this value by getting the log & multiplying by 20.

Further Reading/Research

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Justin Lawler
Biohackers Collective

Self-Quantifier, tech-lover and biohacker. Organiser of Dublin Quantified Self. Developer. More at http://justinlawler.net