June 9, 2020
If the name Dr. Jay T. Wiles sounds familiar to you, it's probably because he's my right-hand man on the wildly popular Ben Greenfield Fitness Podcast “Q&A” episodes. But something you may not know about him is that he's an expert in all things heart rate variability (HRV)…
…a topic near and dear to my heart, since it's the primary daily quantification method via which I track my readiness to train, nervous system health, and overall wellness of myself and all my clients.
Dr. Wiles is a clinical health psychologist who is board-certified in biofeedback, HRV biofeedback, and Tai Chi for rehabilitation. He has a passion for helping others reach their full potential from an integrative and holistic perspective and has worked closely with elite athletes and executives on enhancing peak performance through training and regulating psychophysiology.
In today's article, a guest post by Dr. Wiles, you'll discover the single biggest contributor to poor health, a short primer on HRV, how HRV training can be life-changing in modifying your response to stress, HRV devices that Dr. Wiles has found to be the most accurate and effective, how to hack HRV, and much more!
The Single Biggest Contributor to Poor Health
There is an insidious force that has run rampant on our society, whose intention is to halt progress, reduce recovery, cause you to socially isolate, and is wearing out your mind and body. We hear of politicians referring to “the media” and other outlets as the “enemy of the people,” but they are all incredibly wrong.
This is because the force that I am referring to is one that can be unrelenting and tears you down to your core. It is the predatory lion that hunts endlessly for its prey, resulting in a perceived inability to escape. And, when you experience this constant state of attempts at fleeing, you are left feeling drained and helpless. I am talking about the single biggest contributor to poor health…
I know what you’re thinking, “Not another stress article.” However, this one is unique and not your “conventional” stress article, so bear with me. I know from experience—working with professional athletes, executives, high performers, and also from using these strategies myself—that sometimes the “conventional” is a waste of time and money. This caused me, as a clinical health psychologist, to seek out wisdom from research on stress mitigation strategies that are effective, sustainable, and don't take up all of my time and money.
See, there is a window into your nervous system functioning and subsequently your stress response. This window gives you the single greatest indicator of in-the-moment information regarding the functioning of your nervous system. I am referring to heart rate variability (HRV), a psychophysiological marker that provides extremely valuable insight into the underpinnings of your autonomic nervous system that can be used as a determinant, not only for your stress response but also for your recovery and performance outcomes.
If you haven’t done so already, check out the podcast I released recently on all things HRV. This will give you an in-depth look at the metric of HRV that will help to guide the article you are about to take on! Through HRV training, you can gain a better level of self-awareness and self-regulation of your stress response. Also, after thousands of hours engaging in HRV training both personally and with clientele, I have found some effective ways to “hack” this metric and improve well-being.
The Relationship Between Stress & Our Physiological Response
Stress is linked with every identifiable mental and physical ailment and can actually be the root cause of many ailments, ranging from the inflammatory response that increases cortisol and glucocorticoid production to dysregulation in the microbiome.
If it is not the root cause of a particular ailment, excessive stress will certainly exacerbate the symptoms of the ailment.
There is an inextricable bidirectional relationship between stress and your body's physiological response. When you experience stress, this will inevitably represent itself in a physiological response, and vice versa. When I talk about the deleterious effects of stress, I am not talking about when you experience inevitable acute and transient stress. From an evolutionary perspective, this is what your body is used to experiencing. Our ancestors hunted and foraged for food and encountered threats along the way, like the mountain lion. They either fought or fled from this danger and then returned to camp. During the acute stressor, a cascade of events occurs that results in turning on the sympathetic branch of the autonomic nervous system to help humans kick into high gear in an effort to get out of there and self-preserve. This is good, you need this. But, what happens if you always perceive the mountain lion is chasing you? What might this do to your overall mental and physical framework? Hint: it’s not good.
The reoccurring experience of stressors sends a message to the more primitive parts of your brain and physiology that you are constantly being chased by the mountain lion (even if you aren’t). There are some stressors that are going to be out of your control (worldwide pandemics, finances, work-related stress, etc.), but it is not an avoidance of stressors that is necessary, it is learning how to control and modulate your response to stress. This is one great thing about being a human; you can adapt to just about anything, and better yet, you can optimally adapt.
Your body has a primary goal of self-preservation and does so through maintaining homeostasis. In order to self-preserve, it is going to attempt to find ways of adapting to your environment; however, some adaptations are more beneficial than others. For instance, after repeated exposure to stressors, an adaptation could manifest as avoidance or isolation. You can adapt to the perceived threat by completely avoiding it, both physically and cognitively. This is what I see in working with individuals with PTSD. It becomes adaptive and protective to stay away from the triggers of trauma but ultimately results in a cascade of psychological and physiological problems.
An example of a more beneficial adaptation towards self-preservation would be through the usage of HRV training to better control and regulate the stress response. Practically, this would manifest in reduced emotional reactivity and improved resilience to stress. This equates to more energy, more time, and improved mental and physical well-being.
The Autonomic Nervous System
There is no need for me to bore you with another in-depth explanation of the autonomic nervous system (ANS) (go listen to my HRV podcast), but there are some important details worth repeating.
There are two branches of the ANS: the sympathetic nervous system (SNS, “fight or flight” response) and the parasympathetic nervous system (PNS, “relaxation” response).
There still seems to be confusion about the interconnection between these two systems. Please note, these are NOT linear systems. Indeed, you cannot turn one on and turn one off, but rather, think of them operating like a left-foot braking system. In Formula One racing, when a driver is taking a turn, they do not relinquish all pressure off of the gas pedal (SNS) when they begin to brake (PNS). Instead, unlike conventional one-footed driving, they will use the right foot to sustain power but also use the brake to exhibit control. This is the interconnection between the SNS and PNS. Dr. Gharbo states, “Once it appears that the turn will be managed safely, the braking system is released and more fuel is given for more speed through the next straightaway.”
Essentially, you do not need to (nor will you) “turn on” the SNS and “shut down” the PNS. What you need is to be able to exhibit pinpoint control of these systems. When you are encountering a perceived threat (stressor), you need to be able to modulate both systems at will. So often, I see many, if not most, with substantial difficulty in performing this task. This is typically for two reasons:
- They have limited self-awareness of how stress is manifesting both physically and psychologically.
- Their “thermostat” (more about this term later) is conditioned to be more emotionally reactive. (In other words, their baseline is to react, rather than to regulate.)
Every human has the ability to regulate—but, with compounding stress, you can lose control of it. This is where HRV training comes into play for stress mitigation. If you are constantly bombarded with messages to turn on the SNS, you are going to pay for it. But the great thing is, even if you do not have awareness of how stress has impacted and continues to impact your nervous system, you can (relatively easily) assess and modify this.
Short Primer on Heart Rate Variability
Okay, so I sound like a broken record, but I didn’t intend for this article to be a deep dive into the metrics and physiology of HRV that I discuss on my podcast (what number is this for shameless podcast plugs?). With that said, it still warrants some discussion of metrics, physiology, and evidence-based research.
If you have never heard of HRV or are still a little confused about what it is, let me clarify. HRV refers to the variability in time between heartbeats.
Your heart does not work like a metronome. It has to adapt (or should) to its environment and all of the billions of processes that are occurring in your body. In an effort to keep up with all of these demands, it will speed up or slow down accordingly; however, when it starts to detect significant threats, both psychologically and physiologically, it will begin to regulate itself, resulting in less variability.
Your heart does this as a sort of warning sign. It is an evolutionary mechanism that provides you with input about something that may be a threat to your survival. (Remember the mountain lion?) When you become more self-aware of what your heart is doing, you will begin to feel when it regulates itself, and this will ultimately become a warning of potential internal or external danger.
When there is chaos, both psychologically and physically, your heart does what it can to try and regulate the system in an effort to return to homeostasis. Again, this is why it is so incredibly important to learn how to appropriately self-monitor and, subsequently, self-regulate.
HRV is one of the, if not the, best metrics out there for providing insight into your ever-changing stress response. It can be used as a metric for determining your ability to recover and perform but is most researched from a stress mitigation perspective. A meta-analysis in 2018 indicated that HRV is very sensitive to changes in ANS activity and is closely associated with stress. Stress regulates two main pathways: the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system (SNS), and when there is a dysregulation in these areas, you will see changes in your HRV measurements.
HRV is also a great representative measure of homeostatic functions. Through a process called the baroreflex mechanism (which is a feedback loop for regulating blood pressure), HRV training can be used to directly communicate safety to the ANS and regulate homeostasis. The nemesis to homeostasis, which many people encounter quite frequently, is referred to as allostatic load. This is when your body and mind perceive an inability to handle certain threats, which results in sympathetic overload and a cascade of negative side effects.
If you want insight into your autonomic functioning that is the window of your stress response, then you can use HRV as a valuable metric. If you want to then regulate the stress response, you can use HRV training as a catalyst. Physiology is a great way to quantify stress load. When the subjective experience of stress meets quantified stress, that’s the perfect recipe for moving the thermostat in the right direction.
Heart Rate Variability Metrics and Measurement
I could write about HRV metrics for days, so I will keep it short and sweet. If you have an HRV measuring device, it is likely that you have seen that the devices calculate HRV via means of SDNN or rMSSD or measures low-frequency and high frequency…
…and it is likely that you have no idea what that means or have had to look it up and still do not understand what it means.
I want to clarify these measurements and give you my opinion on what you should be looking for and how to base your numbers on the norms and your own baselines. There are two predominant types of HRV measurements. One is a time domain measurement and the other is a frequency band or frequency domain measurement. Both of these look at different metrics.
Time Domain Measurement
When you see a time domain HRV measurement (you'll see examples of this in charts below), this is referring to a measurement that is calculated based on time intervals between adjacent heartbeats. As I mentioned earlier, your heart does not function as a metronome. There are different time intervals in between each adjacent heartbeat (one heartbeat to another may be 800ms and then to the next adjacent heartbeat might only be 750ms); this shows variability in the time intervals. The difference between these two is 50ms, so there were 50ms of variability between these two sets of heartbeats.
Now, as with anything in science, you can't base your HRV score on two sets of inter-beat intervals, as this is much too small of a sample size to give you any relevant or usable data. This is why HRV needs to be assessed over a period of time intervals.
The amount of time needed for different calculations is going to vary depending on the type of time domain index you are interested in examining. For instance, the two primary usable time domain indices are SDNN and rMSSD. These both require different time domains to get an accurate measurement or usable data. SDNN, for example, requires a minimum of 5 minutes (but is really only clinically relevant when assessed over a 24 hour period), while rMSSD has actually been shown to provide valuable interpretations at as low as 10 seconds, 30 seconds, and 180 seconds. However, like SDNN, rMSSD is most accurate over a 5-minute recording. So, it will be important for you to know what you are calculating and what time-frame you need to ensure accurate measurement.
Primary Time Domain Measurements:
- SDNN: Standard deviation of all NN (normal; removed artifact) intervals. The term “NN” is used in place of RR to emphasize the fact that the processed beats are “normal” beats.
- RMSSD: The square root of the mean of the sum of the squares of differences between adjacent NN intervals
- SDRR: Standard deviation of all RR intervals (all beats, including artifact)
- NN50: Number of pairs of adjacent NN intervals different by more than 50ms during recording
- pNN50: Percentile of NN50 during recording
There are more time domain indices, but these are the most common and more importantly, the SDNN measure and RMSSD measure are the gold standard measurements. A bulk majority of wearables (Oura Ring, Whoop strap, etc.) are going to use either of these.
I personally use the RMSSD for HRV biofeedback, as it a more true representation of HRV that is not modulated by a process called respiratory sinus arrhythmia (RSA), which is the fluctuation of heart rate across a breath cycle.
Frequency Domain Measurement
Frequency domain measurements quantify the distribution of absolute or relative power into different frequency bands. For example, an EEG measures individual brainwave domains. The slowest brainwave, which is associated with sleep, is called Delta, the next waveband Theta, then Alpha, and then the Beta. This is an example of how the process of something called a power spectral analysis can separate brainwaves into their own component rhythms that operate within different frequency ranges.
The same thing can be done with HRV. A great way to think about this is to think about a light shining through a prism. The prism will reflect white light into its component wavelengths. Through a mathematical process called the fast Fourier power spectral analysis, HRV is broken into its component wavelengths and each of these wavelengths provides insight into autonomic functioning. Want a deep dive into this? Check out Dr. Fred Shaffer’s article on HRV norms and metrics. Here is the breakdown of the most commonly used frequency bands:
- Very-Low Frequency (VLF: 0.004~0.04hz): Receives contributions from the SNS and PNS, but when there is a PNS blockade, it will almost completely abolish this metric. In other words, high VLF is representative of sympathetic load (stress).
- Low-Frequency (LF: 0.04~0.15hz): Receives contributions from the SNS and PNS and the baroreflex activity. This is referred to as the “meditators peak” and is seen when breathing at slow rates. This demonstrates good control of the ANS.
- High-Frequency (HF: 0.15~0.40hz): Inhibition and activation of the vagus nerve by breathing. Lower HF power is associated with increased stress, panic, anxiety, and worry.
So what is the goal for being within these domains?
If you find yourself, at resting conditions, having extremely high VLF power, this can be indicative of sympathetic activation. If you are meditating and breathing at a rate lower than 9 breaths/minute, you will likely see a peak at the 0.1 range or the LF band, which great representation of baroreflex activity and ANS control. This is what I teach through a process called resonance frequency breathing. At resting conditions, if most of the power if falling in the HF condition, this is representative of parasympathetic activity, but not necessarily vagal tone.
How HRV Training Can Modify Your Response To Stress
The single biggest misconception about HRV training is that it is all about one number. So many times I am asked, “How can I raise my HRV?” (speaking in terms of one number), but this shouldn’t be the main focus, just a side effect.
This is because it is not how high HRV is that is important, it is how well you can modulate HRV that demonstrates having control of your nervous system.
For some, changes in HRV may not manifest in the form of changes in the time domain indices (SDNN or RMSSD) but may be more evident in the frequency domain bands (VLF, LF, and HF). Unfortunately, many of the wearables only provide one HRV metric, normally a time domain index like SDNN or RMSSD. This can provide you with some valuable information, but it doesn’t paint the whole picture.
This is why I always tell my clients that they need to modify their paradigm of changing their HRV. Instead, view it as learning how to better regulate and control your nervous system at will. I’ll talk more about the devices I have found to be helpful later, but I will say, avoid the hype of many HRV wearables as many of them are not great. (I listed my two “go-to” devices down below.)
HRV biofeedback and training are not new, nor should these topics be approached with intimidation. Yes, all of the stuff I mentioned above can be intimidating, but HRV training is all about going back to the foundations of health and what it is to be human. It is simply a leveraging of technology and information to help guide that path. Think of HRV biofeedback as information, because in the end, that is all that it is; it just so happens to be extremely valuable information. When you train HRV through the use of biofeedback, the information itself is not the change agent. It is not the catalyst. You are! Just bear with me and watch.
In order to modulate HRV (self-regulation), you must become more self-aware. This is what biofeedback can do for you: increase your level of self-awareness while also providing information on the changes you are making.
If you are a baseball pitcher and the catcher sets his glove for the position he wants you to throw it and you miss that mark, what do you do? You readjust and try a different arm angle, release point, etc. This is HRV training and biofeedback. You adjust, given the results and information.
The intention behind HRV training is that it teaches you how to regulate your physiology in order to reduce stress. It is as simple as that. Remember when I spoke of the primitive brain? The primitive brain is giving you information about how you are constantly being chased by a mountain lion. No, really, it is! But you have to retrain it, and the way you do that is through HRV training and biofeedback. The brain will listen to the body.
Let me clarify this with an example: If you are being chased by a mountain lion, you need all of your physical and mental faculties to fight, or flee from, that threat in order to preserve your life. It would make no sense for you to press the brakes (PNS) because that ultimately means your life. However, if your brain is being told it is being chased by a mountain lion, but it is not (modern-day stressors), it is to your advantage to communicate to your brain that you are safe by pressing the brake. When you communicate to your brain via your nervous system that you are in a safe environment, you are able to turn down the volume on your HPA-axis and SNS.
So, how do you do this?
The primary tool in biofeedback that I teach is breathwork—and more specifically resonance frequency breathing. This is one of the key regulators of your ANS. If you are able to take the time to switch your breath mechanics to be centered in your belly (diaphragmatic breathing), then your are able to communicate to your brain (via the vagus nerve) that your safe and protected. If the mountain lion were chasing you, you wouldn’t be able to stop and breathe, and the brain knows that.
Over time, through the process of conditioning, your body’s and brain’s thermostat begins to change. You start to see the baseline of your ANS become more able to modulate in and out of a fight or flight response (when you need it) and the relaxation response (when you need it). Think of HRV biofeedback as a way to take information on your stress response and condition a new response.
I teach this to my clients via biofeedback wearables and clinical-grade devices (more about this later), but in the end, they do the work because it is much more potent for sustained change to your physiology than having something done to you (passive). This is not to say you cannot hack this in ways, but trying to “biohack” HRV will go nowhere if you have not already laid the groundwork. This is why having an HRV coach is so incredibly important as a primary step, as opposed to trying to use something exogenous to do the work for you. You can check out my HRV and biofeedback coaching services here.
So what are the tools needed for solid HRV training for stress mitigation?:
- Someone who knows what they are doing. Preferably, someone board-certified in HRV biofeedback or peripheral biofeedback.
- Quality consumer or clinical-grade device for measurement, in real-time. Devices that do not provide accurate, fast, real-time data are not nearly as effective. This is why, when I coach, I almost always suggest the Lief Therapeutics Device (use code GREENFIELD for a 20% discount).
- Learning and using proper breathwork techniques and assessing resonance frequency.
- Learning and integrating proper mindfulness techniques for HRV. (Check out Dr. Inna Khazan’s, Biofeedback and Mindfulness in Everyday Life.)
- Train, train, and train. It is all about conditioning!
In the end, after you have trained HRV with these biofeedback devices for a while, you should become your own biofeedback and HRV device. I train my clients to become so in tune with their HRV that they can modulate their HRV to demonstrate vagal tone at the snap of a finger (or within a few breaths). This is what I train my tennis players to use before they hit a big serve, or golfers before they take a swing. I could get into HRV for sports performance and spend another 10 pages on this, but I will save that for another article. Below you'll see data from one of my clients exhibiting what both stressed and relaxed responses look like in terms of HRV.
Example of “Client A” exhibiting a stress response during HRV biofeedback:
Below is a power spectrum graph of the individual during a stress response. Significant power is found in the VLF band and LF band, indicative of a stress response. Note also the low RMSSD value of 14.61.
Next, you will see a lack of “rolling hills” in the heart rate data (shown in red). You will also see that the individual, while still pacing breathing, has an elevated heart rate, reduced HRV, and subjectively reported being stressed.
Example of “Client A” exhibiting heightened HRV and a relaxation response during HRV Biofeedback:
Below is a power spectrum graph of the individual during a relaxation response. Significant power is found in the LF band, indicative of a good vagal response. We also see a higher RMSSD value of 64.46. When you see a tall peak in the LF band, as you do here, this is representative of a “meditators peak.” It demonstrates strong control of the stress response and is consistent with slower breathing/resonance breathing patterns. When you see this, you know that the mind and body are in sync!
Next, you can see nice “rolling hills” in the heart rate data (red). This is indicative of respiratory sinus arrhythmia (RSA), which is interconnected with the baroreflex response and contributes to high HRV. There is also a synchrony between respiration and heart rate. When I see this pattern of coherence, it is almost always accompanied by the subjective experience of relaxation and reduced stress.
Here is a short list of my favorite HRV devices and apps for HRV training and biofeedback (no order of preference):
- Lief Therapeutics (use code GREENFIELD for a 20% discount): Okay, so this is actually my favorite because it is a true, real-time wearable for HRV biofeedback and offers resonance frequency training! This is my go-to for both my own personal use and training with virtual clients, as I can view all of their real-time data.
- Viiiiva Heart Rate Monitor with NatureBeat app
- Oura Ring
- Whoop Band (use code BEN for a $30 discount)
- HeartMath EmWave 2 and InnerBalance
- EliteHRV CorSense
The end goal is gaining control of your physiology. When you are able to access that pathway, you will find yourself experiencing less stress, less anxiety, less depression, enhanced energy, and the ability to get back to the life you deserve.
Hacking HRV (After You Have Dialed in the Other Areas)
You are no doubt here because you are a fan of Ben Greenfield, so you probably want some “next level shit.” I’ve got it, but with the caveat that it makes no sense to try these or rely on these if you do not have the other areas dialed in first.
So, get a biofeedback coach and work on the basics first, and then give these a try.
As a “biohacker” and someone who is deeply invested in my psychological, physical, and spiritual health, I have tried almost everything under the sun to modulate my HRV. Some have worked and others were a waste of my time. However, I have found that what works for me may not work for others and vice versa. When you have seen thousands of hours of biofeedback recordings and data, you tend to pick up on a few things.
Here is my list of trusted hacks that have been effective for me and my clients. Remember, while this may not show demonstrable changes in the single number HRV, this does not mean that it is not affecting other areas (e.g., frequency bands).
Dr. Jay’s HRV Hacks (in no order of preference, but the wearables and biohacking gear are secondary):
- Cold Exposure or hot/cold contrast: This is an amazing hormetic stressor for the nervous system that helps to build nervous system resilience.
- Meditation and Gratitude Practices: I use different mindfulness strategies and a daily gratitude journal like the Christian Gratitude Journal
- Yoga, Tai Chi, and Qi Gong: These work WONDERS for some!
- Patrick McKeown’s Oxygen Advantage Protocol and Training: Helps you breathe more efficiently.
- Wim Hof Method: A combination of breathwork and cold therapy that rebalances your nervous system and strengthens your immune system.
- Box Breathing: Close your mouth and slowly breathe in through your nose for four counts. Hold your breath for four seconds. Then slowly exhale through your mouth for a count of four. Hold the exhale for another four counts. Repeat!
- Holotropic Breathwork: Allows you to achieve a relaxed, sort of “spiritual high.”
- NuCalm: Such a great device for many people for regulating HRV! (discount applied at checkout, 65% off first month of monthly subscription).
- Apollo Neuroscience: This sends a signal to the nervous system through vibratory patterns. It sends a signal of gentleness and safety, resulting in enhance vagal tone – click here for Ben's Apollo Neuroscience podcast with Dr. David Rabin. (15% automatically applied at checkout when you get the Apollo here).
- Infrared Sauna (use code BENGREENFIELD for $500 off regular prices and a free gift): I have even seen amazing results with my sauna blanket by Higher Dose (use code BEN for a 15% discount).
- Sunlight Exposure and Photobiomodulation: I use my Joovv (use code BEN for a gift at checkout) panel for this, but also make sure that I am getting a minimum of 30 minutes of sunlight exposure each day.
- Grounding: A minimum of 30 minutes daily, barefoot on grass (Click here for Ben's grounding podcast with Clint Ober.)
- Supplements that can enhance HRV:
- Ashwagandha (especially at night)
- Phosphatidylserine (PS)
- Qualia Mind (use code GREENFIELD2019 for 15% off): I use the caffeine-free version…some have had this raise HRV by 20 or 30 points!
- A quality fish oil, like LivingFuel SuperEssentials Fish Oil (Check out this article on fish oil supplements and HRV.)
- Exercise, especially high-intensity interval training (HIIT)
- Dialing in nutrition: This is going to look different for everyone, but if you are eating foods that are resulting in a stress (inflammatory) response, your HRV will be lowered.
There are many other things that can be effective like making sure you hone in on quality sleep, but, as Ben likes to say, “I am running a little long in the tooth,” so I will save them for another article.
Well, there you have it. Hopefully, this article has shed some light on the importance of HRV training and why I believe everyone should engage in training their nervous systems.
If you want to reduce stress, enhance energy, and truly live life at the peak, then I would highly consider hiring an HRV coach and/or biofeedback clinician who has the training and background to provide quality care.
Again, here are my favorite HRV devices:
- Lief Therapeutics (use code GREENFIELD for a 20% discount)
- Viiiiva Heart Rate Monitor with NatureBeat app
- Oura Ring
- Whoop Band (use code BEN for a $30 discount)
- HeartMath EmWave 2 and InnerBalance
- EliteHRV CorSense
…and here are some more resources on HRV for you to check out:
- A Deep Dive Into HRV: How To Use Heart Rate Variability To Optimize Your Sleep, Stress, Recovery, Performance, Nervous System Balance & Much More!
- How I Track My Heart Rate Variability, Recovery Status, And Training Readiness (And Why These Metrics Are So Important).
- The Best Way To Know How Stress, Supplements, Sleep, Sex & More Affects Your Nervous System: The Latest News About Heart Rate Variability (HRV) Training.
- A Deep Dive Into HRV: The Myths & Truths of Heart Rate Variability Testing.
- HRV: The Single, Next Big Trend In Biohacking And Self-Quantification And How To Use It.
- Everything You Need To Know About Heart Rate Variability Testing.
I also encourage you to take a look at my consulting practice, Thrive Wellness and Performance, (get 10% off, plus free HRV informational material, when you use that link) or my personal website to learn more or to get started on HRV training.
If you have any thoughts, questions, or comments on HRV training, please leave them below and I'll be happy to respond!