What is Heart Rate Variability? (HRV)

HRV is NOT Heart Rate. Check out the quick video below to understand why:

Heart Rate Variability (HRV) is an accurate, non-invasive measure of the Autonomic Nervous System (ANS) – which responds to everything: how you exercise, recover, eat, sleep and perceive stress.

Unlike basic heart rate (HR) that counts the number of heartbeats per minute, HRV looks much closer at the exact changes in time between successive heartbeats (also called inter-beat intervals, RR intervals, NN intervals, etc).

What is Heart Rate Variability (HRV) | RR intervals

By trending short HRV readings on a daily basis, our adaptive algorithms learn what your “normal” Autonomic Nervous System patterns look like, help you gain insights into your nervous system, stress and recovery activity, and then automatically guide you in improving those patterns over time.

Real World Application of Heart Rate Variability

Today, people use HRV to:

  • Improve resilience and adaptability
  • Reduce stress
  • Optimize training and recovery
  • Personalize nutrition and sleep
  • Improve mental health – mood, depression, anxiety
  • Improve mental performance and cognition
  • Identify risk of disease, morbidity and mortality
  • Measure systemic inflammation
  • Track progress and guide treatment plans
  • Re-balance the nervous system with live biofeedback
  • Objectively understand motivation and willpower
  • Provide early warning signs for changes in health, overtraining or maladaptation

Now that you can accurately and conveniently track your nervous system, you can make better health, training, and recovery decisions to reach your goals.

Your Nervous System in a Nutshell

Your Autonomic Nervous System (ANS) controls your unconscious bodily processes and influences the functions of internal organs. Some internal processes regulated by the ANS include:

  • Heart rate
  • Blood pressure
  • Body temperature
  • Electrolyte balance
  • Digestion
  • Respiratory rate
  • Pupillary response
  • Urination
  • Sexual arousal

Parasympathetic vs. Sympathetic Nervous System

The ANS consists of two branches:

The Sympathetic Nervous System controls your body’s “fight or flight” reactions in response to internal or external stressors. It stimulates blood glucose (to fuel your muscles), pupil dilation (to see tigers better), slows digestion/peristalsis (to focus energy on the present danger), and increases heart rate (to ensure adequate blood circulation to run or fight). The SNS is ideally activated to overcome short term stress situations such as running from a tiger or fighting an intruder. But this same response also occurs when you exercise, perform challenging mental tasks, get into an argument, or even sit in traffic.

The Parasympathetic Nervous System controls your body’s “rest and digest” responses and is associated with recovery. Parasympathetic activation conserves energy, constricts pupils, aids digestion, and slows heart rate. The PSNS is meant to help build for the long term and is needed to grow faster, stronger, and healthier.

The SNS and PSNS control the same organs with opposite effects. Both branches are always working and both are needed to maintain homeostasis (balance or equilibrium) in your body. With every single heartbeat, your nervous system is saying “slow down – speed up” based on feedback from all your senses, emotions, etc. A healthy nervous system has a balanced but strong push and pull between the Sympathetic and Parasympathetic branches. Heart Rate Variability is an accurate, non-invasive measure of the ANS and the balance between the SNS and PSNS branches.

Why Does This Matter?

The Sympathetic Nervous System’s physiological response to stress focuses on short term survival in lieu of long term health. This acute response can become chronic (constant, long term) in the presence of stress from modern daily life such as work, relationships, financial, environmental, dietary, physical, lifestyle choices, etc. Chronically accumulated stress from multiple sources can all contribute to drastically reduced health and performance over the long term.

A significant amount of research published over the past 50 years correlates Heart Rate Variability to:

  • Disease risk and progression (diabetes, cardiovascular disease, respiratory diseases, gastrointestinal diseases, autoimmune conditions, etc.)
  • Morbidity and mortality
  • Biological aging and health
  • Mental health, mood, depression, anxiety, PTSD
  • Physical performance (HRV is heavily used in elite endurance and team sports to guide training and recovery)
  • Injury prevention
  • Guided rehabilitation
  • Mental cognition

Now that you can accurately and conveniently track your nervous system, you can make better health, training, and recovery decisions to reach your goals.

Low HRV vs. High HRV

Higher resting-state HRV scores signify the ability of the body to activate the Parasympathetic “rest-and-digest” response. Higher heart rate variability is correlated with:

  • Increased fitness level
  • Better health
  • Better resilience
  • Youthfulness
  • Willpower
  • Calm, positive emotions

Lower resting-state HRV scores signify an activated Sympathetic “fight-or-flight” response or suppressed Parasympathetic activity. This can indicate the body’s inability to engage recovery mode or an exhaustion of recovery capacity. This can be a temporary response to a previous day’s hard workout or poor night of sleep. Or this can be a chronic response to stress that results in reduced health and increased risk of disease. Lower resting-state HRV is tied to:

  • Reduced fitness level
  • Poor health
  • Increased disease risk and inflammation
  • Increased biological age
  • Negative emotions
  • Increased anxiety and depression

Luckily, we make analyzing and understanding your HRV score easy. The app lets you tag your HRV measurements with the important things going on in your life and then helps you analysis the results and provides daily HRV-based guidance.

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by Jason Moore

by Jason Moore


Jason has a passion for technology and drive to improve human wellbeing. He has personally helped thousands of people and hundreds of organizations successfully implement Heart Rate Variability into their life or practice.


Take a deeper look

Part 1

Age & Gender

Part 2

Fitness Level

Part 3

Health, Medication & Guidelines