Heart rate variability is one of the most important variables to measure when optimizing mental performance.
HRV is your heart’s interpretation of the influence of stress on your body and your ability to adapt to it.1Marek Malik, et al. Heart rate variability: Standards of measurement, physiological interpretation, and clinical use European Heart Journal. 1996
To truly optimize your mind, you must eliminate as many stressors in your life as possible.
Knowing your HRV allows you to track your body’s ability to overcome mental and physical hurdles and shift into high performance.2Hye-Geum Kim, Eun-Jin Cheon, Dai-Seg Bai, Young Hwan Lee, and Bon-Hoon Koo. Stress and Heart Rate Variability: A Meta-Analysis and Review of the Literature Psychiatry Investig. 2018
In this article, I’ll explain what HRV is, its effects on cognition, and the best tools for tracking and optimization.
What is Heart Rate Variability
Heart rate variability or HRV measures the variation of the period between consecutive heartbeats over time.3U Rajendra Acharya, K Paul Joseph, N Kannathal, Choo Min Lim, Jasjit S Suri. Heart rate variability: a review Med Biol Eng Comput. 2006
In other words, the fluctuation of the length of heartbeat intervals.
It’s important to understand that the heart is not a metronome, and its rhythm fluctuates throughout the day.
This happens due to the autonomic nervous system’s direct influence on the heart.
In fact, HRV is a great quantitative marker for depicting the activity of the autonomous nervous system.
This is because HRV represents the heart’s ability to respond to physiological and environmental events, including:4B Caruana-Montaldo, K Gleeson, C W Zwillich. The control of breathing in clinical practice Chest. 2000
- Physical exercise
- Mental/emotional stress
- Metabolic changes
- Environmental toxicity
HRV data gives insight into whether your body is in parasympathetic (rest and digest) or sympathetic (fight or flight) nervous system.5JP Saul. Beat-To-Beat Variations of Heart Rate Reflect Modulation of Cardiac Autonomic Outflow Physiology. 1990
Ultimately this helps you understand how your body is reacting to stress and your overall health status.
HRV and Cardiovascular Health
This metric is also incredibly useful for analyzing overall cardiovascular health as well.
For example, it can assess the risk of sudden cardiac death in post-infarction and diabetic patients.6Dingfei Ge, Narayanan Srinivasan, Shankar M Krishnan. Cardiac arrhythmia classification using autoregressive modeling Biomed Eng Online. 2002
For simplicity’s sake (as HRV can be a deep rabbit hole), we will focus on using HRV strictly for cognitive enhancement purposes throughout this article.
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What Is A Good HRV?
It’s generally accepted that a higher HRV is considered better than a lower HRV.
Good HRV’s are as follows: [table id=18 /]
Keep in mind that the above values are averages. When tracking your HRV, you will see peaks and valleys. The higher the peaks, the better.
It’s important to remember that age is one of the biggest determinants of HRV:7Eduardo Miranda Dantas, et al. Reference values for short-term resting-state heart rate variability in healthy adults: Results from the Brazilian Longitudinal Study of Adult Health-ELSA-Brasil study Psychophysiology. 2018
As you age, the average lowers. However, HRV’s start trending up around 70 years old.
HRV and Mental Health
The balance between parasympathetic and sympathetic nervous system states can have profound effects on your mental wellness.
In the brain, the amygdala interprets the severity of threats and ultimately calls on the HPA Axis to respond accordingly with stress hormones.8James P Herman, Michelle M Ostrander, Nancy K Mueller, Helmer Figueiredo. Limbic system mechanisms of stress regulation: hypothalamo-pituitary-adrenocortical axis Prog Neuropsychopharmacol Biol Psychiatry. 2005
The prefrontal cortex (PFC) and medial PFC (mPFC) regulate your amygdala’s interpretation of threat severity, and when the mind feels safe, the amygdala is inhibited by the ventromedial PFC (vmPFC).9Julian F Thayer, Fredrik Ahs, Mats Fredrikson, John J Sollers 3rd, Tor D Wager. A meta-analysis of heart rate variability and neuroimaging studies: implications for heart rate variability as a marker of stress and health Neurosci Biobehav Rev. 2012
In fact, it’s been shown that HRV can measure the integration of the vmPFC, brainstem, and autonomic nervous system’s influence on the body.
This is useful since we know that heightened threat perception is at the heart of anxiety, PTSD, and depression.10Constance Hammen, Eunice Y Kim, Nicole K Eberhart, Patricia A Brennan. Chronic and acute stress and the prediction of major depression in women JDepress Anxiety. 200911V C Goessl, J E Curtiss, SG Hofmann. The effect of heart rate variability biofeedback training on stress and anxiety: a meta-analysis Psychol Med. 2017
Why HRV Is Not A Mental Health Parameter
It is important to remember that HRV is not a tool for diagnosing specific mental health conditions.
Many studies show associations between HRV and cognition. However, these studies have not been interpreted for application in mental health treatment.
Using HRV can be a useful tool to identify the state of your autonomic nervous system and begin the work of tuning it properly.
HRV and Autonomic Nervous System: Parasympathetic vs. Sympathetic
HRV is the best indicator of your body’s internal stress response.
This is because HRV measures your autonomic nervous system, which is coordinated with your HPA axis.12Sivan Rotenberg, Jennifer J McGrath. Inter-relation between autonomic and HPA axis activity in children and adolescents Biol Psychol. 2016
The HPA axis is your body’s internal emergency system that interprets stress and responds by releasing stress hormones.13Andrea H Marques, Marni N Silverman, Esther M Sternberg. Evaluation of stress systems by applying noninvasive methodologies: measurements of neuroimmune biomarkers in the sweat, heart rate variability, and salivary cortisol Neuroimmunomodulation. 2010
This stress response manipulates your autonomic nervous system (ANS) to promote physiological changes through the sympathetic nervous system (SNS) and parasympathetic nervous system (PNS).
Essentially, this is how your body maintains homeostasis and ultimately survives.
A low HRV indicates sympathetic nervous system dominance. Higher HRV indicates more parasympathetic activity.
You typically experience both as your body’s HRV fluctuates throughout the day.
However, your body should spend more time in the parasympathetic nervous system and higher average HRV.
Sympathetic Nervous System
The sympathetic nervous response, also known as fight or flight, is your body’s physiological response to keep itself safe from stress.
Your internal fight or flight response evolved to protect you in dangerous situations.
We know this as the classic “running from a tiger” example.
Nowadays, stress comes in many forms, both physical and emotional, from internal and external stimuli.
Some examples of things that turn on the sympathetic nervous system include:
- Competitive sports
- Fights and arguments
- Toxic foods
- Environmental chemicals
- Stressful relationships
- Social media
- Stressful news
The release of epinephrine and norepinephrine mediates the sympathetic nervous system’s influence on heart rate.14H F Brown, D DiFrancesco, S J Noble. How does adrenaline accelerate the heart? Nature. 1979.
This increases cardiac excitation frequency, excitation conduction velocity, and excitability of the sinoatrial (SA) node.
Using HRV can help you discover how you react to different stimuli like the above examples.
If your HRV trends low, you know your body is feeling the stress, which can be detrimental to your physical and mental health.
The most common stress-related diseases are cardiovascular diseases, metabolic diseases, psychotic and neurodegenerative disorders, and cancer.15Sheldon Cohen, Denise Janicki-Deverts, Gregory E Miller. Psychological stress and disease JAMA. 2007
Parasympathetic Nervous System
The parasympathetic nervous system, also known as rest and digest, is your body’s way of alleviating the stress response and lowering HPA axis activity.
In a parasympathetic state, your body can relax and promote important physiological processes like digestion, recovery, and sex hormone production.
and serotonin production.17Hannah Weinberg-Wolf, et al. The effects of 5-hydroxytryptophan on attention and central serotonin neurochemistry in the rhesus macaque Neuropsychopharmacology. 2018
How Is Heart Rate Variability Measured?
HRV is a measure of the variation in beat-to-beat time intervals of the heartbeat. Specifically the variability in the time series containing the time intervals between 2 successive “R” peaks of the QRS pattern on an electrocardiogram.18M J Cowan. Measurement of heart rate variability West J Nurs Res. 1995
The variability in R to R intervals is calculated in 2 domains: time and frequency domains.
This is important to understand since the heart does not beat in perfect rhythm, and understanding the time difference from one beat to the next can reveal much about your overall health.
The time-domain represents the variation in the R-R intervals by computing indices such as the standard deviation of the intervals (SDNN) or root mean square of successive heartbeat interval differences (RMSSD).
Many popular wearables use RMSSD metrics as their HRV number.
Higher values in time-domain measures are considered indicative of overall heart function resilience in adults.20C.K. Chen ; S.L. Lin; C.Y. Huang; T.C. Wang; T.Y. Yao; C.L. Wu. Analysis of Dynamic Cardiopulmonary Signals and Heart Rate Variability for Distinct Cardiopulmonary Fitness Norms under Graded Exercise and Recovery Periods IEEE Eurasia Conference on Biomedical Engineering, Healthcare and Sustainability (ECBIOS). 2019
The frequency-domain is based on a power spectrum analysis that examines R-R interval time series to provide a portion of the time series’ power falling within given frequency spans.
These spans include very low, low, and high-frequency spectra of oscillations.
- High Frequency (0.15-0.4 Hz)
- Low Frequency (0.04 to 0.15 Hz)
High frequency (HF) power in the heart rhythm spectra is consistently considered a marker of vagal dominance or vagal “tone,” a factor often associated with reduced physiological stress reactivity and/or improved emotional stability.21DeWayne P Williams, et al. Resting heart rate variability predicts self-reported difficulties in emotion regulation: a focus on different facets of emotion regulation Front Psychol. 2015
There is also Resonance frequency (RF), which is tied to a complex set of psychophysiological interacting influences.
RF factors include:
- arterial trunk and aorta response
- blood pressure
- respiratory rate
These factors reflect an optimum state of function for oxygen uptake as well as emotional self-regulation.22Patrick R. Steffen, Tara Austin, Andrea DeBarros, and Tracy Brown. The Impact of Resonance Frequency Breathing on Measures of Heart Rate Variability, Blood Pressure, and Mood Front Public Health. 2017
Heart Rate Variability vs. Heart Rate
Heart rate variability measures:
- the number of HR fluctuations around the mean HR
- gut, heart, and vascular tone
- regulation of autonomic balance
- gastrointestinal tone23Johannes Enevoldsen, et al. Gastrointestinal transit time and heart rate variability in patients with mild acquired brain injury PeerJ. 2018
- heart and vascular tone (aka the diameter of the blood vessels that regulate BP) 24 Mark S. Schwartz, Frank AndrasikBiofeedback, Fourth Edition: A Practitioner’s GuideGuilford Publications
- pulmonary gas exchange efficiency25Peter Y W Sin, et al. Interactions between heart rate variability and pulmonary gas exchange efficiency in humans Exp Physiol. 2010
Heart rate measures how many times your heart beats per minute
Both HRV and HR can be strong indicators of cardiovascular and overall health.
HRV is inextricably linked to heart rate since the autonomic nervous system directly influences your heart rate.
Heart rate is a reflection of the balance between the sympathetic and parasympathetic branches of the autonomic nervous systems.
For example, increased sympathetic nervous system activity or diminished parasympathetic nervous system activity results in accelerated cardiovascular activity.26J Malcolm Arnold, MD FRCPC, et al. Resting heart rate: A modifiable prognostic indicator of cardiovascular risk and outcomes? Can J Cardiol. 2008
On the other hand, increased parasympathetic and decreased sympathetic nervous system activity can lead to a slower cardio response.
HRV provides information about the functioning of your nervous system’s control on the HR and the heart’s ability to respond.
How To Improve Heart Rate Variability
Ultimately you want your autonomic nervous system to shift into the parasympathetic mode as much as possible.
Because of unavoidable factors in the modern world, you have to accept that your sympathetic nervous system will be used throughout the day.
The key is to instill practices and habits that allow your heart rate variability to rise and train your body to use the fight or flight mode when necessary.
Some practices that can help include:
- Breathing practices
- Sleep optimization
- Clean diet
- Regular exercise
- Acupuncture27Beate Wild, et al. Acupuncture in persons with an increased stress level—Results from a randomized-controlled pilot trial PLoS One. 2020
- Time away from work
Best HRV Monitor
As the importance of regularly monitoring HRV has become more mainstream, so have HRV monitors.
Many high-quality devices on the market can monitor HRV. These include:
- Oura Ring
- Whoop Band
- Apple Watch
These monitors can be expensive, and some come with monthly fees.
Not to mention you have to wear them throughout the day and while you sleep.
A good, affordable, non-invasive option is the Coresense finger clip monitor by Elite HRV.
This monitor is only worn a few times throughout the day for spot tracking. It’s the least expensive out of all other HRV options and gives you a ton of value for the low price.
Heart rate variability, aka HRV, is one of the most important metrics to use for mind/body health.
Knowing how your heart is responding to your daily life can be a powerful tool for optimizing cognition.
Eliminating things that cause stress and getting more of the things that relax you allows your nervous system to make the right hormones and neurotransmitters that boost your brain.