What Is Heart Rate Variability (HRV) & 12 Things It Can Tell You
“Look to the nervous system as the key to maximum health.”
-Galen
We often think of stress as an abstract and binary thing. We tend to describe ourselves in “stressed” or “stress-free” states. Stress, however, is a series of physiological reactions constantly occurring in our bodies.
This stress, whether it’s perceived or real, lives on a spectrum and is constantly fluctuating toward one end or the other with every passing second. The problem is that we are only truly aware of our stress levels when they reach the polar ends. And this is bad news given how much of a role stress plays in our health.
Fortunately, there is a simple and objective way to measure your stress: heart rate variability (HRV). In recent years, HRV has not only become affordable and accessible to the average Joe but there is also so much research supporting its efficacy. While you may not need to measure your HRV when a crying baby is around, our sensitive nervous system is constantly reacting to internal and external stressors that play a role in our health including food, sleep, relationships, and your training. But I’m getting ahead of myself. Let’s take a step back and table the basics. What is heart rate variability?
What Is Heart Rate Variability?
Our peripheral nervous system (PNS) is responsible for, among other things, relaying information between the brain and other areas of the body. This nervous system is further broken down into the autonomic nervous system which has two parts: the sympathetic (fight, flight, freeze) and the parasympathetic (rest, digest, repair) branches.
These two parts work in tandem to constantly adjust our bodily functions--heart rate, blood pressure, digestion, breathing, etc.--to nearly every internal and external stimuli imaginable. A smile from a passing stranger, a bite of food, air pollution, the accumulated fatigue from workouts, and the mere thought of an upcoming deadline all influence our physiology through our very sensitive nervous system.
The CEO making these changes is the brain, more specifically the hypothalamus, which has a direct line to the heart in the vagus nerve. The heart receives the signal from the vagus nerve and the heart responds by changing its heartbeats and the variation between the heartbeats. The measurement of the variation of the time between heartbeats is called heart rate variability (HRV) and it’s considered the single best way to measure the state of your nervous system at any given moment. When we take our heart rate we measure the number of beats in a minute (“bpm”). This can tell us things like the general arousal of our body but HRV takes it many steps further and measures the milliseconds between heartbeats and compares those to the next heartbeat. For example, an HRV will compare the 982 milliseconds between two heartbeats to the 1,021 milliseconds between the next heartbeats, and so on.
HRV takes these slight differences, with the help of sophisticated algorithms, and spits out a number or a “score”. An HRV score that has more variability between heartbeats has a greater high-frequency score. This means that there is more parasympathetic activity and you are more relaxed and recovered. A score that has less variability means that your body is adapting to or recovering well from stress. A good HRV is one that’s adapting to its environment both internally and externally. A score that has less variability means that your body is adapting to or recovering well from stress. The topic of HRV can get pretty dense pretty quickly so if you want to take a deeper dive then check out this site for a thorough explanation.
The take-home message is that HRV is not only an extremely effective and cutting-edge tool but it is the most comprehensive, non-invasive biomarker that we have today. HRV was first noted back in 1733, however, it's only in recent years that it's become affordable and portable. I first used HRV as a way to optimize my race training plans but the ever-mounting research points to the fact that everyone can benefit from tracking their HRV for a period of time.
How To Measure HRV
In order to measure HRV, we need a device that’s sensitive and reliable enough to perceive the acute changes in our heart rate and then interpret that information and provide us with practical information that we can use. The two main ways to measure your HRV are snapshot measurements and 24/7 measurements.
Snapshot measurements typically consist of lying in a relaxed state (typically in bed once you wake up) and using one of the devices below for a 3-5 minute period to indicate your score. This approach uses an algorithm to determine your RMSSD (root mean square of successive differences between normal heartbeats) to indicate your HRV score.
The other way is through 24/7 monitoring which uses an algorithm to determine your SDNN (Standard deviation of normal-to-normal R-R-intervals). The 24/7 approach is both more reliable and it offers more insight into your body’s constantly-changing reaction to parts of your day (more to come below).
HRV Monitors
There are a lot of HRV monitors on the market that claim that they can do this but many of them are far from accurate. Here are some of the best ones:
Polar 10 HR strap. This is the most accurate wearable device. Pair it with an HRV app such as the EliteHRV app.
This is my preferred technique. Put the strap on for 5 minutes in the morning while laying in bed and just relax.
Important: The Apple watch alone is not an accurate HRV monitor, however, pairing the data to the breath app on the watch has been validated to be accurate.
Note: The tools above can do both snapshot and 24/7 monitoring.Key points to keep in mind about HRV:
It’s important to measure your HRV consistently. It’s best to use a tool that measures 24/7. If you don’t have access to this then I recommend measuring when you first wake up for a good baseline measurement for the day. This allows a consistent context while also reducing extraneous factors like caffeine and the inevitable onset of life stressors.
The same HRV score day in and day out is not the goal. Fluctuations in HRV are good just as fluctuations in training loads are good in order to elicit an adapted response.
Compare your scores only to yourself. Find patterns and build on them.
Remember that your HRV is a measure of how your body is performing and not necessarily how you feel.
What Can My HRV Tell Me?
HRV has gained popularity as a training tool for athletes but measuring your nervous system is important for more than just exercise. Here are some other ways to use HRV to tell us how our bodies respond to:
Alcohol. Alcohol is a neurotoxin that decreases your HRV when you consume enough of it. If you do drink, use HRV to determine the relationship alcohol has on your body. Do you recover better from wine or beer? How many drinks? How many nights? How late can you stop with a limited impact tomorrow?
Food. Less obvious things that may affect our sympathetic nervous system are the foods we’re always eating. Even if you don’t show any obvious symptoms to common problem foods. you may still have food sensitivities to nightshades, dairy, caffeine, gluten, FODMAPs, or a host of other things. These sensitivities or intolerances can lead to microstress which can cause brain fog, micronutrient deficiencies, or GI issues such as dysbiosis, IBS, or leaky gut. If you sense any abnormalities then start a food log and track which foods truly spike your HRV.
Sleep. Sleep plays an important role in your body’s stress management and overall health but sleep demands vary for different people. Older adults need as little as 5 or 6 hours while teens and athletes benefit from as many as 11 hours. HRV is a great tool for tracking sleep and helping to determine sleep disorders. (source). Track your nervous system to determine how long you should sleep, the best time to go to bed, and how to optimize your sleep hygiene.
Travel. The stress of packing, flying, planning, and changing time zones isn’t easy for our mind or body, no matter how well you claim to adapt. HRV can be a great tool to assess your stress level when you travel. When does your stress peak on your trip? Should you adapt to time zone changes or stay in your home time zone pattern? What tools can you use to mitigate these stressors?
Work & productivity. Tracking your nervous system can help you optimize your productivity. Do you perform better after a long weekend or at the end of the week? Morning time or afternoon? With breakfast or fasted? Long-distance truckers can even use it to determine if they should continue driving that last stretch. Know your peaks and troughs and plan your challenging tasks accordingly.
Recovery from injuries. Whether you had a musculoskeletal sports injury or a traumatic brain injury, using nervous system testing can be a great tool to help with your recovery. Share these findings with your doctor and therapist to make a plan for maximizing treatment interventions for a better recovery.
Breath. Whether it’s a state of relaxation or stress, our breath is a strong indicator of our current mindset, however, our breath is a two-way street. That is, you can be passively controlled by your breath (e.g. anxiety leading to shallow breaths) or you can actively manipulate your breathing (called pranayama breathing) to literally switch from a dominance of sympathetic activation to one of parasympathetic and vice versa. Practice breathwork strategies in relaxed states to induce automatic coping strategies when they’re more acutely needed in times of stress.
Air and noise. Air and noise pollution is known to play a major impact on your cardiovascular system. About 1 in 20 heart attacks are attributed to noise pollution. Another study found an association between air and noise pollution on your HRV. If you live near polluted areas then use an air filter inside, wear earplugs to bed, and make sure your house is insulated from noise.
Relationships. Our mammalian bodies require social support–regardless of whether we are introverted or extroverted. Having strong relationships with friends, family, and coworkers is important to our happiness and level of stress (). On the flip side, toxic relationships have a significant negative impact on our bodies. Drop the grudges, let go of friends who don’t have your best interest in mind, and prioritize time with those you actually like hanging out with the most.
Biofeedback. The purpose of biofeedback is to direct our awareness to our physiological state and gain insights into ourselves. It turns out that 49.,6% of the time we are “mind wandering.” How exactly do you feel when you are in rush hour, in new social situations, going for a walk, or playing with your dog? Use HRV to both identify the stressors throughout your day as well as using in-the-moment insights for your stress-reduction strategies such as meditation, cold showers, and doing yoga, Our body is sending us signals all the time. With the help of HRV testing, we can learn what these reactions are when they occur, and then we can adapt appropriately.
Exercise & training. Exercise is one of the best interventions to improve our mind and body. Whether you’re lifting, running, doing a HIIT workout, knowing out a yoga session, or simply walking, you can use HRV to improve both your performance as well as to decrease your post-workout stress levels through vagal modulation (source).
Medical conditions. A growing number of studies have linked significant changes in HRV with a variety of health conditions. Research is looking at ways to use HRV to prevent, diagnose, and treat a variety of conditions including depression, anxiety, stroke, heart attacks, cardiac arrhythmias, and traumatic brain injuries.
What I Do
I got into HRV as a way to improve my training but I quickly learned that its usefulness was vast. Here are a few things I learned while tracking my HRV and how I’ve adapted:
My body handles beer much better than wine and any more than 2 drinks has a direct impact on my body and my recovery the next day. And the earlier I have that last sip of alcohol the better I sleep and the better I recover the next day.
Going to bed after 9:30 limits my ability to bounce back (by limiting my deep sleep which I learned through sleep tracking).
Using the EliteHRV app with meditation in real time helped me determine the most effective breathwork strategies (double the exhale).
Cold showers and fasting show a little improvement but they don’t consistently move the dial.
Big meals make my numbers plummet.
I love coffee but some days I love it too much. Limiting my intake to a few cups and having my last sip by 11 am let me avoid any jitters and help me recover better through deeper sleep.
Leg workouts and sprints tank my HRV requiring more time to recover.
Takeaway
Regardless of your age, fitness level, or lifestyle you could benefit from tracking your nervous system for a stretch of time. HRV tracking can be a useful tool to improve your performance, mood, health, and longevity. I suggest everyone track their HRV for at least a month and learn a little bit more about what’s going on under the hood.
Start with a daily test for a week and look for patterns. The results are very contextual so find the context. Then throw the self-experimentation in. Start to upregulate your system by exercising or using breathwork strategies. Down-regulate with meditation and cold showers. Learn a little about your body and have fun with it.
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