What Is Heart Rate Variability? How to Use and Monitor HRV (Brought to You by WHOOP)

Heart rate variability (HRV) is an incredibly useful tool for athletes assessing their performance and recovery.

This article is presented in paid partnership with WHOOP, a technology company dedicated to unlocking human potential. See our disclosure page for details. We may receive commissions on items purchased through our links.

Over the last five years, heart rate variability (HRV) has grown in popularity as a useful tool for assessing recovery and training readiness. If you’re new to the concept of HRV and how it can translate to performance, then you may be unaware of how useful this tool can be for progress.

“What exactly is heart rate variability (HRV)?”

In short, HRV is the variability our body experiences in between successive heart beats. More variability  between each heartbeat is a good thing when it comes to achieving a healthy balance of recovery and performance. The WHOOP Strap helps athletes everywhere assess their HRV on a daily basis with real-time analysis to better understand performance readiness and recovery needs.

In this HRV guide we’re going to cover a variety of topics, including:

  • What is HRV?
  • What is a good HRV number?
  • How to monitor HRV with WHOOP
  • How strength athletes can use WHOOP
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Optimize your performance and recovery with the WHOOP fitness tracker. Tracks and quantifies recovery, sleep, activity, heart rate, HRV, and more.

What Is HRV?

Heart Rate Variability Origins

In 1733, Rev. Stephen Hales became the first person to formally document that heart beats and arterial pressure levels vary during the respiratory cycle (1). Following Hales in 1847, Carl Ludwig became the first to record the variations and oscillations that occurred during the respiratory cycle, which eventually became known as respiratory sinus arrhythmia (RSA).

In the late 1800s and early 1900s, Dutch physician Willem Einthoven became the first to document the electrical current of the heart, which is known as electrocardiogram (ECG). After Einthoven’s discovery, ECG became standardized and developed over the following years, and in 1960 the ambulatory ECG was used in wide practice (1).

Willem Einthoven
Willem Einthoven / Source: CardioNetworks

In the 1970s, power spectral analysis was used to study the physiological differences in beat-to-beat variability, thus creating the birth of HRV. Multiple studies since have investigated the physiological components that could be at play and responsible for each individual’s HRV (2, 3).

In the early days of HRV research, many scientists speculated that there was some form of neural activity at play, but it was still too new to draw strong suggestions (4, 5). By the 2000s, research finally began to show that both the sympathetic and parasympathetic branches of the autonomic nervous system played a role in establishing an individual’s HRV. 

Defining HRV

Definition: HRV can be used as a non-invasive metric to assess the health and balance of the autonomic nervous system through analyzing the variability of one’s heartbeat.

In layman’s terms, our body’s heart beat is rarely the same from beat-to-beat. There are slight variations in the amount of time between beats.HRV is a measure of those variations, and is a product of the complex interactions between one’s sympathetic and parasympathetic nervous systems. 

HRV is a representation of how the body’s sympathetic and parasympathetic nervous systems are interacting with one another. Greater HRV is a good thing, as it suggests there’s a balance within the autonomic nervous system.

Sympathetic Vs. Parasympathetic

To truly understand HRV and the science that goes into WHOOP, one must first understand the nervous systems at play. The autonomic nervous system is made up of two branches,  the sympathetic and parasympathetic.

Autonomic Nervous System
Autonomic Nervous System

The sympathetic nervous system is responsible for creating the body’s “fight or flight” responses. It creates all of the stress responses to physical, physiological, and psychological triggers. A few scenarios where the sympathetic branch will come into play:

  • Preparing for a 1-RM squat
  • Finalizing a business proposal on a tight timeline
  • Jumping on a hike from the sight of a snake

While different in nature, all of these activities will typically result in a sympathetic nervous system response (fight or flight). A sympathetic nervous system response can create a few reactions in the body including increased heart rate and blood pressure, the release of norepinephrine, and vasoconstriction of the kidneys and digestive tract.

It’s worth pointing out that not every sympathetic nervous system reaction will create the same level of stress response within the body, as everyone will have their own hierarchy of what’s viewed and interpreted as a stressor.

The parasympathetic nervous system is typically described as creating the body’s “rest and digest” responses. The parasympathetic branch is generally heavily in play when the body is at rest and recovering. A few scenarios when the parasympathetic nervous system is more active include:

  • Lying down In bed at night
  • The time following sexual activity
  • Meditation
  • The time after a meal

The parasympathetic nervous system helps the body maintain and promote homeostasis when at rest, and plays a heavy role in our ability to rest and recovery.

In terms of HRV, the sympathetic and parasympathetic nervous systems continually dance in and out of the spotlight based on the acute stimulus at hand. If there’s an imbalance in one of the nervous systems,HRV can suggest that one should be attentive to the direction in which their systems are leaning. 

For example, if the sympathetic nervous system is always active, that’s usually a good indication that one is not recovering properly due to the parasympathetic nervous system lacking an equal response to stressors.

Why HRV Matters for Well-Being

For pretty much everyone, and especially athletes, HRV can be a useful method for assessing overall well-being. The WHOOP Strap uses HRV to help calculate your readiness to perform each day.

Over the last 40 years, there has been a ton of research produced relating HRV to overall health, including:

  • Risk and progression of certain diseases (6)
  • Psychological stress and health (7)
  • Potential injury risk predictor (8)
  • Mental performance (7)

HRV can also be taken a step further for athletes and active individuals and is related to performance factors like:

  • Overall fitness levels
  • Current stress levels
  • Training readiness
  • Recovery levels
  • Mental readiness

At the end of the day, the easiest way to understand HRV and its relationship to well-being is to remember how it correlates to our autonomic nervous system. Think of it like a scale:

The autonomic system plays a major role in digestion, metabolism, body temperature regulation, blood pressure, sexual responses, and fluid balance. If it’s functioning inefficiently, then performance can take a hit for a variety of reasons. For athletes and fitness enthusiasts, autonomic nervous system imbalances can wreak havoc on progress.

Why HRV Matters for Performance

To take HRV a step further, let’s take a closer look at how it can directly affect performance.

Athletes and fitness enthusiasts require higher energy levels on a daily basis. Workouts put strain and stress on the body, which help promote specific training adaptations. These training adaptations then create success for one within their sport or activity of choosing.

HRV can be useful in this setting because it can serve as a compass for pursuing these adaptations in a thoughtful and calculated manner. Frequent high levels of energy and stress produce a greater demand on the body for proper recovery. If one can understand how to interpret their HRV numbers, then they can thoughtfully use them to push the limits without overreaching. 

Below are two ways WHOOP helps relate HRV directly to performance on the field, in the gym, and on the court:

  • Recovery: Using HRV, WHOOP determines how recovered one’s body is each day.. This is useful for athletes who are following a periodized program or trying to peak for a competition.
  • Strain: Every activity produces different levels of strain on the body. WHOOP calculates strain from activities and then relates this strain to HRV, performance goals, and recovery needs.

WHOOP can make it easy for athletes to understand how much energy they have to push themselves and remain progressing, but also stay within their limits and avoid overreaching.

What Is a Good HRV Number?

Unlike heart rate, HRV varies greatly from individual to individual due to genetics (9). A good HRV number is relative to where an athlete’s rolling baseline is. This makes it incredibly tough to pinpoint a “good” HRV that will fit everyone. Many things can influence one’s HRV, including:

  • Genetics
  • Sex
  • Age
  • Environment
  • Health
  • Diet

While there is no ideal HRV number that will fit everyone, a higher HRV is generally considered to be a more positive indicator of overall wellness and suggests that the body’s sympathetic and parasympathetic nervous systems are highly responsive.


To help provide context, Mike Lombardi, Elite Performance Manager at WHOOP, shared examples of two WHOOP athletes who are equally “fit”, but with different HRVs:

“Let’s look at a couple anecdotal examples. My wife was a 2012 Olympian and she has an average HRV of about 60. Then on the other end of the spectrum, we have someone in the [WHOOP] office who does triathlons and half Ironman races, and her average HRV sits around 220. In reality, they’re probably equivalently fit in terms of capacity.”

What Lombardi is saying is that both of these athletes are incredibly fit, but their rolling baselines are very different. If athletes can understand where they normally sit on a day-to-day optimal training basis, then they can augment variables in their personal lives to facilitate the HRV responses they want.

So what exactly does it mean to augment other variables to increase HRV? Well, multiple variables can shift HRV in a positive direction. Things like nutrition, sleep habits, training, and much more can all play a role in HRV, resting heart rate, and sleep quality. It’s the summation of these variables that can provide a better understanding of one’s overall fitness, readiness, and recovery — and that’s exactly what WHOOP does.

Understanding HRV Numbers
Photo By sportpoint / Shutterstock

Since WHOOP tracks resting heart rate, HRV, and sleep quality, it can become much easier to assess the effects when an athlete makes changes to things like diet, training, or recovery modalities. The WHOOP data will reflect the changes in relation to one’s normal baseline — whether positive or negative. 

If HRV  varies so greatly, is there such a thing as a poor HRV?

Yes and no. If HRV is lower, that could be a sign of imbalance in one direction within the sympathetic and parasympathetic nervous systems. However, it’s important to remember that a lower, poor HRV number will be “low” in relation to one’s rolling baseline.

For example, if someone has an HRV that sits around 70 normally, but has an intense week of training and encounters a ton of stress at their job and records an HRV of 40 for a few days, then this number could be considered a “poor” HRV. This trend suggests that the body is having a harder time leaving a sympathetic state to rest and recover in a parasympathetic state.

Again, generally speaking, a lower HRV number is suggested to reflect poor overall wellness, but to be accurate with this reading one should relate a “low” HRV number and adapt it to their normal rolling baseline (10). 

“The goal is to always improve your own HRV relative to your rolling baseline,” Mike Lombardi.

Relating HRV to Resting Heart Rate

One of the more accurate ways to assess overall fitness is to relate HRV to resting heart rate. Due to HRV varying so greatly between individuals, resting heart rate can be a useful tool to understand a body’s efficiency.

Lombardi explains, “Genetically speaking, what we’ll typically see are athletes with a higher HRV and naturally lower resting heart rate have an innate ability to go, go, go. The way WHOOP calculates daily strain is based off of heart rate, so their prolonged high heart rate is accumulating a ton of strain, but the next day their heart rate and other variables typically return to normal.

A high HRV and low resting heart rate means that the body is incredibly efficient and has a great work economy. HRV is daily readiness and that includes all of the [body’s] inputs internally and externally and how you’re handling them, while resting heart rate indicates fitness level.”

That equation seems pretty clean cut, but what about an individual who has a lower HRV and low heart rate? For example, if someone has an HRV that sits around 45 and a heart rate that hovers in the 50s, what does that mean? After all, a resting heart rate in the 50s is generally considered fit.

Based on the trends he’s seen, Lombardi explains that this type of profile would likely be for a power-based athlete .

“A lower HRV with a middle of the road heart rate doesn’t mean someone isn’t efficient, but they’re more likely an athlete with higher top-end power, or they’re a strength based athlete.”

Powerlifting Meet
Photo By Jordan Jovkov / Shutterstock

In this particular scenario, the lower HRV could mean the athlete’s nervous system is likely more sympathetic, and the lower heart rate could suggest they’re physically fit. Thus, confirming the trends and analysis Lombardi provided above.

Tying HRV with resting heart rate becomes the most meaningful when one can relate the two to the context of their sport, lifestyle, and current training.

How to Monitor HRV With WHOOP

How the WHOOP Strap Works

The WHOOP Strap is designed  to be worn 24/7 to provide you with the best recordings possible. WHOOP has developed a proprietary and easy-to-learn system that is designed to help athletes, coaches, and fitness enthusiasts assess recovery and training readiness on a day-to-day basis. 

When first using a WHOOP Strap, activity levels and recovery needs are compared to those of the same age, sex, and activity level. Then after about four days, WHOOP will begin to learn and adapt to your own physiology, which helps with understanding what’s considered normal for your performance.

To assess recovery needs and training readiness, WHOOP compiles daily strain and workout strain, then relates these strains to how much recovery and sleep an individual needs to get by, perform, or peak.

Within the WHOOP app, there is a graph that presents daily strain in accordance to undertraining, optimal training, and overreaching. This is a useful system to help athletes avoid overreaching and setting themselves back due to burnout.

Why Strength Athletes Should Use HRV

To perform at the highest levels, strength athletes must adhere to multiple factors including intensity, volume, and loading. High neural drive is essential in heavy barbell sports and is present in every form of strength training (11, 12).

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Optimize your performance and recovery with the WHOOP fitness tracker. Tracks and quantifies recovery, sleep, activity, heart rate, HRV, and more.

WHOOP calculates strain data with an algorithm that tracks elevated heart rate, HRV levels, the previous day’s recovery, and much more. For most fitness enthusiasts, the strain system is straightforward, but strength athletes should look at the data slightly differently.

Why? Let’s say a powerlifter is training heavy with longer rest periods in-between sets and has a lower heart rate for the duration of their work out. Their strain will likely record differently compared to someone who does a 20-min HIIT workout with a higher prolonged elevated heart rate.

Lombardi explains, “People who live in the strength community are pushing the upper bounds of strength, and finding ways to maximize their body in various lifts. The strain that accumulates on WHOOP is not always the true indicator of readiness and recovery for them. Where these athletes will see the tax from their training is on the next day’s recovery recordings and HRV numbers.”

  • Example Scenario: Let’s say a powerlifter has an HRV that sits around 70 on a normal basis and has a heavy squat workout with 90% intensity for five doubles.
  • What It Means: If this athlete notices in the WHOOP app that their HRV is down the following day or two, then this could indicate that their sympathetic and parasympathetic nervous systems are fatigued and not balanced.

For strength athletes, this is incredibly vital information, especially when working at higher intensities and volumes. Strength athletes use autoregulation tactics like RPE all the time in their training. When used correctly, WHOOP can serve as another means for objectively calculating training fatigue and prospective readiness for days following heavy workouts.

At times, strength athletes may want to push when their body isn’t necessarily ready to do so. If a strength athlete can identify when their nervous system might be fatigued, then they can scale back volume and intensity to continue progressing without burning out and needing a deload.

HRV, WHOOP, and Continual Progress

The technology that goes into HRV and the WHOOP Strap continues to grow and improve. Over the last decade alone, HRV has proven to be a viable resource to assess one’s well-being, performance readiness, and recovery, and that’s exactly why WHOOP utilizes this key metric to help athletes push to new feats.

The WHOOP Strap adapts to an athlete’s physiology and lifestyle, which makes it a dynamic tool to assess readiness and recovery on a daily basis. If athletes can build a strong understanding of HRV and how to use it for their benefit, then training can be constantly scaled to one’s readiness without the fear of overtraining.


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  2. BM, S. (2019). Analysis of heart rate variability. – PubMed – NCBI . Ncbi.nlm.nih.gov. Retrieved 24 June 2019, from https://www.ncbi.nlm.nih.gov/pubmed/4702060
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  7. Lin, F., Ren, P., Cotton, K., Porsteinsson, A., Mapstone, M., & Heffner, K. (2016). Mental Fatigability and Heart Rate Variability in Mild Cognitive Impairment. The American Journal Of Geriatric Psychiatry, 24(5), 374-378. doi:10.1016/j.jagp.2015.12.012
  8. Gisselman AS, e. (2019). Musculoskeletal overuse injuries and heart rate variability: Is there a link? – PubMed – NCBI . Ncbi.nlm.nih.gov. Retrieved 24 June 2019, from https://www.ncbi.nlm.nih.gov/pubmed/26826630
  9. Golosheykin, S., Grant, J., Novak, O., Heath, A., & Anokhin, A. (2017). Genetic influences on heart rate variability. International Journal Of Psychophysiology, 115, 65-73. doi:10.1016/j.ijpsycho.2016.04.008
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  12. 12. Wang, X., Ding, X., Su, S., Li, Z., Riese, H., & Thayer, J. et al. (2009). Genetic influences on heart rate variability at rest and during stress. Psychophysiology, 46(3), 458-465. doi:10.1111/j.1469-8986.2009.00793.x