Heart Rate Variability

What is Heart Rate Variability?

The human heart, unlike a metronome, beats at different intervals, as opposed to the constant interval of a metronome or clock. These intervals constantly change depending on the time of day and the amount and type of stimuli our body is experiencing from its environment. Heart Rate Variability (HRV) is the measure of the variation in time between consecutive heartbeats. These intervals are known as interbeat intervals, or IBIs. HRV allows the body to respond dynamically and better resist the physical challenges it experiences.

How is HRV measured?

The best way to analyze and determine HRV is by using an electrocardiogram machine that records the electric signals released from the heart; however, many wearable fitness trackers have begun to measure HRV, making it a more easily accessible metric that can be assessed daily.

HRV can be measured in periods as short as 5 minutes and as long as 24 hours. The measurements taken in shorter time periods are not interchangeable with those taken over the course of 24 hours. Assessing HRV in the context of longer time periods represents a wider range of processes occurring in the body and their subsequent effects.

Shorter time periods can be heavily influenced by the body reacting to a specific stimulus that may raise or lower the variability. Twenty-four-hour recordings of HRV are the best clinical representation and give the user the best data relating to their heart health. The longer time period allows the body’s circadian rhythms, core body temperature, metabolism, and sleep cycle to influence the measurement and for the user to receive a reading that more accurately encapsulates their overall health.

Factors that Affect Heart Rate Variability

Normal HRV allows the heart to self-regulate and adapt to environmental stimuli and challenges. There are a multitude of factors that can affect a person’s HRV:

  • Age → As a person gets older, their HRV naturally decreases as the body becomes less responsive to stimuli.

  • Sex → On average, women have higher HRV than men.

  • Cardiovascular Health and Fitness → Higher fitness levels condition the heart to be stronger and responsive to stimuli, therefore increasing HRV.

  • Cognitive Resilience → Higher resilience during stressful tasks is associated with higher HRV.

  • Time of day → HRV is generally higher during the night and in the early morning. The body has had a chance to fully recover overnight, and it is primed to respond well to stimuli. As the body tires throughout the day, HRV slowly declines.

The Importance of Heart Rate Variability

HRV is shown to be an indicator of both physical and mental health. Although high HRV generally shows good physical health, certain heart conditions can cause an increase in HRV, such as abnormalities in the contraction of the heart muscles. Another great metric of physical and aerobic fitness is VO2 Max. Learn more about VO2 Max here.

In addition to physical health, high levels of HRV are linked to better performance of the executive functions in the prefrontal cortex of the brain, such as our emotional reaction to stimuli, our ability to focus, and other elements of emotional processing. Examining our HRV can give clues to both the physical and mental health of our bodies.

To take the next step towards using HRV to learn more about your own health, find the fitness tracker that is right for you by taking our fitness tracker quiz here or explore devices that measure HRV.

Amazon:Halo View and Halo Band

Apple:Watch Ultra, Watch 8, and Watch SE

Coros:Apex 2 Pro, Apex 2, and Vertix 2

Fitbit:Sense 2, Versa 4, Charge 5, Versa 2, Inspire 3, and Luxe

Garmin:Enduro 2, Fenix 7, Epix, Forerunner 955, Forerunner 745, Forerunner 255, Forerunner 245, Forerunner 55, and Venu Sq

Oura Ring:Ring 3

Polar:Grit X Pro, Grit X, Vantage V2, Pacer Pro, Pacer, Ignite 3https://amzn.to/3CQa33P, Ignite 2, Vantage M2, and Unite

Suunto:9 Peak Pro, 9 Peak, and 9 Baro

Whoop:Whoop 4

You can find these fitness trackers on the products page.

This is for informational purposes only and should not be considered as medical advice. Go to the emergency room if you are experiencing a life-threatening medical emergency.

Disclaimer: Takeoff Health may make a small commission from some of the links above.

Blog written by Allie K and reviewed by Milos Tomovic.


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