Tag: heart rate variability

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Academy > article > Human Performance

Hacking Your Parasympathetic Nervous System

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A person lying face down on a massage table receives a back massage from a masseuse dressed in a white uniform, aiming to enhance stress resilience and promote ANS balance.

In assessing overall health, the role of the nervous system is often overlooked, but the Parasympathetic Nervous System is a key component in understanding and achieving optimal training and wellness goals.

The body’s Autonomic Nervous System (ANS) controls and influences internal organ function through largely automatic processes such as digestion, respiration, and heart rate. The larger ANS is divided into several systems including the more well-known “fight-or-flight” Sympathetic Nervous System (SNS) and lesser known “rest-and-digest” Parasympathetic Nervous System (PNS). These systems naturally counteract each other and work to achieve balance within the body.

Why It’s Important

The body should naturally remain in PNS most of the time, and only activate SNS in life-threatening situations; however, in the modern age, the body’s SNS response is often triggered by everyday stressors, including adrenaline rushes from caffeine, exercise, and anxiety.

Spending too much time in SNS can lead to a general weakening of the immune system as well as other serious health issues such as:

  • Cardiovascular issues. High blood pressure, hardening of the arteries, and heart attack
  • Gastrointestinal issues. IBS, chronic constipation or diarrhea
  • Endocrine System issues. Type 2 diabetes, sexual impotence, and decreased energy and longevity
  • Decreased exercise recovery. Muscle and training fatigue

Comparatively, some benefits from spending more time in PNS include:

  • Cardiovascular benefits. Higher Heart Rate Variability, lower blood pressure, decreased risk of heart attack
  • More stable blood sugar. Decreased risk of diabetes
  • Higher overall energy. Due to more balanced cortisol levels
  • Better sleep quality. SNS can negatively impact circadian rhythm

Activating the Parasympathetic Nervous System

While the average person spends too much time in SNS, there are ways to adjust your habits and thinking in order to increase time spent in PNS.

High Intensity Training

Change it up— high intensity exercise activates the SNS and studies have shown that repeated, intense training can decrease the ability to transition back to the PNS. Like most things in life, balance is key: take rest days and be sure to include lower intensity exercises throughout the week.

Aerobic Exercise

Studies have shown that light to moderate aerobic exercise such as walking or swimming for at least 30 minutes per day at least five days per week can improve the PNS response. Over time, the PNS response and Heart Rate Variability increase and Resting Heart Rate decreases. Mind-body centered exercise such as yoga and tai chi carry similar benefits.

Meditation & Massage

Stress relief and relaxation are hugely impactful in achieving the “rest-and-digest” mode of the PNS. Deep breathing and focus on relaxing the mind lead to less stress and less time spent in SNS.

Many of the metrics SENSR tracks— including HRV, RHR, SpO2, and sleep tracking— can be quality indicators of time spent in the SNS vs. PNS. By carefully tracking your body’s metrics, you can consciously control your Autonomic Nervous System and reap the benefits of the Parasympathetic Response.

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Academy > article > Human Performance

How to Utilize a Heart Rate Variability Monitor

Reading time: 5 min
A man in athletic wear runs on a paved road with a digital overlay showing fitness data, including his HRV and ANS Balance.

There are many ways in which we can measure the effects of stress on the body as it pertains to physical activity and fitness. In the past, we’ve discussed utilizing the Borg rate of perceived exertion scale to determine how hard you think your body is working. Or instead we’ve broken down the complexities of analyzing heart rate zones to determine how intense a bout of exercise is on your cardiovascular system.

Yet a relatively new method for assessing the effects of physical stress on the body has emerged in recent decades. We refer to this concept simply as heart rate variability, or HRV. While techniques such as the Borg scale utilize qualitative values to measure stress on the body, measuring heart rate variability requires wearable technology that can monitor, record and analyze sets of HRV measurement data. As a result, the data provided by a heart rate variability monitor can prove far more valuable than simply describing how fatigued you may feel.

All of this may seem a bit complex, but have no fear! In reality, measuring HRV only requires a heart rate monitor and a smartphone. Often times an iPhone, Android device, or other simple fitness wearable can get the job done.

But in order to measure HRV, it pays to understand what exactly HRV is, and why it’s so important. From there we can break down the various HRV monitors on the market today that seek to provide this important data. And finally, we can dig into what those HRV values really mean for your overall health. Let’s take a deep dive into the world of heart rate variability.

What Is Heart Rate Variability?

Though the term may sound complex, heart rate variability is simply defined as the time between your heart beats that varies as you breathe in and out. This small window of time is measured in milliseconds when using the RMSSD method, which is an intricate mode of calculation that stands for Root Mean Square of Successive Differences. It’s used to find the standard deviation of heartbeat to heartbeat differences.

Given this information, you may now be wondering why HRV is so important. After all, what can the milliseconds of time between heartbeats really disclose about your overall health?

As it turns out, those milliseconds can tell you a whole lot about your personal well-being. Research increasingly suggests that high HRV — that is to say, more variability between heartbeats — is linked to better overall health and a higher level of aerobic fitness. Low HRV, on the other hand, is linked to increased stress levels, fatigue, and even exhaustion.

HRV can be affected by everything from your mindset to air quality to age to exercise patterns. Because HRV is tied to our autonomic nervous system, it acts as an indicator for both the parasympathetic (rest) and sympathetic (activation) branches of our nervous system. With this information in mind, it’s time to examine the many ways in which HRV can be measured.

Measuring Heart Rate Variability

HRV was once utilized solely as a tool to assess cardiovascular risks for patients that suffered from heart attacks. To produce accurate HRV data at the time, an electrocardiogram was produced to analyze the heart’s voltage over a span of seconds. When medical television dramas depict a doctor staring inquisitively at a long sheet of paper with rising and falling lines, this is the electrocardiogram we speak of. Medical professionals analyze what’s referred to as the RR interval. They are studying the variation in beat-to-beat intervals as indicated by the time between two beats of the heart.

Eventually, however, HRV analysis became a standard tool for sports scientists that sought to monitor overtraining in athletes. Studies began to increasingly show that overtrained athletes had low HRV, and thus the usage of heart rate variability monitors began to rise. Both professional and amateur athletes sought the chance to monitor daily HRV values without stepping into the research lab. As a result, personal fitness devices that contained real-time HRV measurement capabilities rapidly increased as wearable technology advanced.

Wearable Technology for Measuring Heart Rate Variability

Today a number of fitness wearable companies offer biofeedback technology that produces real-time measurements of HRV.

Garmin, for instance, sports a full lineup of GPS-enabled watches that include a heart rate sensor in the watch itself. Apple’s Apple Watch does the very same by utilizing infrared technology that detects the heart beat by measuring reflected infrared light from tissue.

Other companies such as Polar offer products like the Polar H7, a heart rate monitor that takes the form of a chest strap worn across the torso, sitting directly above the heart. Wahoo’s TICKR heart rate monitoring chest strap does the very same.

And even SENSR’s wristband utilizes a heart rate sensor to monitor oxygen saturation, heart rate variability, resting heart rate, and more. Accessories such as a chest strap or shoe pod allow for even more data-driven capabilities that other fitness wearable companies don’t often provide. By tracking metrics associated with sleep, performance, and even recovery, SENSR’s technology makes a wealth of valuable personal information immediately available.

These devices monitor and record HRV information, but how does that data get to you? By utilizing Bluetooth 4.0, these devices can sync with most heart rate variability monitor apps available through Google’s Google Play store or Apple’s App Store. One of the most popular HRV apps is entitled “elite HRV,” and it syncs with most devices.

Other instruments, like Samsung’s Galaxy smartphone lineup, have implemented heart rate monitors into the phone itself via an infrared finger sensor. The user only has to place their index finger on the sensor to record their heart rate over an allotted period of time. From within these apps and devices, a physiological profile takes shape that seeks to illustrate your heart health over a longer span of time, such as weeks or months. In turn, you have access to powerful physiological information, right at your fingertips.

So What Can You Learn From HRV Data?

You have the device that contains HRV measurement capabilities. You’ve downloaded the necessary apps from the app store of your choice. And that important HRV data we keep referring to has finally synced to your phone. So what can you learn from the data?

It all starts by paying attention to your baseline HRV. This is your everyday HRV based on your resting heart rate when you’re not dripping with sweat after sprinting up a flight of stairs. Understanding your baseline HRV provides you with the perfect snapshot of everyday life. If you’re in good health, your HRV will likely be higher. And if you’re not, it may be lower (your heart rate variability monitor and app of choice can identify if your HRV values are high or low). Refer to the table below for a general idea of where your HRV values should fall.

From there, take time to understand how your lifestyle and health affect your HRV. Perhaps you’re stressed due to tight deadlines at work, or you haven’t slept very well over the past few nights, and your HRV is low as a result. Or instead you may be increasing your training load during exercise, and your HRV is high. Paying attention to your daily life and how it affects your HRV can provide you with a crucial snapshot of your overall health. It can additionally help you determine where improvements in your health should be made. And this all starts by utilizing a heart rate variability monitor.

Is Focusing on Heart Rate Variability Enough?

As with most forms of physiological analysis, focusing solely on HRV or any singular health statistic is not enough. By utilizing multiple forms of health-oriented analysis, a more thorough snapshot of your overall health can begin to take shape. Monitoring other vitals that may include blood pressure, heart rate, oxygen saturation, and more are all worth taking into consideration. With the help of wearable fitness trackers, like those designed by SENSR, such possibilities quickly become reality.

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Academy > article > Human Performance

Managing Stress With HRV, Resting Heart rate, & SPO2

Reading time: 4 min
Silhouette of a person performing a martial arts pose outdoors at sunset, embodying ANS balance and stress resilience.

Elite athletes use Heart Rate Variability (HRV), resting heart rate and other metrics to manage their training regimens and recovery time. Intense training stresses the muscles, hormones, heart and lungs. By tracking these biometrics, athletes optimize their mix of recovery time and training. They train smarter, not just harder. Exercise is a form of physical stress. Mental and emotional stress also affect your body.

Both mental and physical stress may disrupt homeostasis. This can lead to metabolism issues, insomnia, heart problems, hormonal imbalances, and chronic illness. Stress management and stress reduction improve both quality and quantity of life. You can use HRV and other key biometrics to track the success of your stress management program and to plan for “recovery” just like an elite athlete.

Before we discuss applications, it helps if you understand what these biometrics measure and how stress may alter these readings in the short and long term.

How Stress Affects Your Heart and Your Oxygen Levels

Heart Rate and Stress

Most health-conscious people recognize that stress impacts well-known metrics like heart rate and blood pressure. Have you ever found that your pulse and blood pressure were higher than normal at the dentist’s office? If so, you experienced this phenomenon.

Resting heart rate measures how fast your heart beats while you rest. Many people take a resting heart rate in the morning as a quick barometer to their cardiovascular health.  Your heart rate varies day to day, and moment to moment. The following factors may alter day-to-day resting heart rate:

  • Caffeine consumption
  • The previous day’s workout
  • Quality of sleep
  • Hydration levels
  • Hormone cycle fluctuations
  • A large meal or alcohol the night before
  • Stress levels

If you consistently follow a well-designed training plan you may find that your average resting heart rate decreases along with improvements in your physical fitness.

However, as a measure resting heart rate is limited. Due to genetics, some people just have faster resting heart rates than other people. Some hormone imbalances like low thyroid levels may decrease your average resting heart rate. Due to these reasons, you may benefit even more from tracking more sophisticated data points.

SPO2 and Stress

SpO2 stands for peripheral capillary oxygen saturation. It estimates how saturated your blood is with oxygen. A healthy, fit person usually sees a SpO2 between 95% – 100%. Illness, altitude, heart disease, smoke inhalation all affect SpO2.

Your SpO2 measure may not vary quite as much as your resting heart rate and HRV, but a sudden drop often indicates stress to your body. Traditionally athletes who train in higher elevations track SPO2 to help ensure they are getting enough oxygen. With the right device this is an easy metric to track along with resting pulse.

HRV and Stress

HRV measures time between your heart beats. When you are at an optimal state of rest and wellness, your heart is ready to respond to life’s demands. The space between heartbeats varies a little depending on your needs. When your system is “stressed,” your resting heart rate may appear the same, but there may be less variation between the heartbeats.

Tracking HRV informs you of subtle changes. For example, people sometimes find their HRV decreases a couple days before they notice cold or flu symptoms.

Factors that influence HRV include:

  • Quantity and quality of sleep
  • The previous day’s workout
  • Caffeine or alcohol consumption
  • Emotional and mental stress
  • Nutritional habits
  • Hormonal fluctuations
  • Illness or injury

To learn more about these metrics, download our free white paper “The Definitive Guide To A Healthy Heart.” In the meantime, the following tips and techniques help you manage your stress.

Five Techniques To Use Biometrics in Your Stress Management Program

Take Baseline Readings

Take regular, ideally daily, readings since many factors affect biomarkers like HRV and resting heart rate. Try to take the measurements at a consistent time under similar conditions. For example, you may take your baseline reading shortly after you wake up, before you eat or drink anything, and while relaxing. A higher HRV reflects a more optimal state than a lower HRV reading. A lower resting heart rate or pulse also reflects a more relaxed state.

If you notice your HRV and SPO2 trending upwards, this is a sign that your wellness and stress management efforts are working. If your resting heart rate and blood pressure trend downward, this is also a sign of success.

Look at the Big Picture

Have you ever heard the phrase “fighting fit”? In general, maintaining a high fitness level prepares your body to better deal with stress. However, the combination of acute emotional stress *and* physical stress from a vigorous workout may weaken your body and mind. Factor your stress levels with your workouts. Take it easy if you are dealing with major stress like a family emergency or a big deadline.

Light-to-moderate exercise like walking, yoga, dancing, or recreational sports may give you an outlet to recover from stress. Alternately, in some cases you may actually benefit more from a power nap or practicing relaxation techniques than a workout if your stress levels are very high.

Consider Yoga, Tai Chi, or Meditation

Since deep breathing and relaxation temporarily elevate HRV (and lower pulse) these markers may also help guide your practice. Emerging research indicates mindful practices like yoga and tai chi may increase HRV, SPO2 and decrease blood pressure and resting pulse. Some tech-friendly yogis even take an HRV reading during relaxation post at the end of their practice.

Reduce or Manage Your Life Stress

Athletes don’t want to overtrain as they prepare for either a marathon or a sprinting race. The same applies to you while working on big projects, moving, or experiencing another major life change. If possible, simplify your life. Learn to say no and avoid taking on too much.

Take Care of Yourself

Generally when you take good care of yourself, your HRV, SPO2, and resting heart rate tend to improve. Even better, your body and mind are ready to face life’s challenges. The following healthy choices may improve your HRV in both the short and long term:

  • Get enough sleep
  • Eat a healthy, balanced diet
  • Drink enough fluids
  • Enjoy moderate activity most days and improve or maintain your physical fitness
  • Avoid smoking
  • Spend a few minutes relaxing each day whether you prefer to meditate, pray, do yoga, or practice breathing exercises.

Take control of your stress levels and your fitness. You can customize your lifestyle and measure results by tracking key metrics like HRV, SPO2, and resting heart rate. In the past, only elite athletes had this opportunity, but now these tools are  available to you. Thanks to fitness wearables like SENSR you can easily take these metrics at home.

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Academy > article > Human Performance

How Well Does Heart Rate Variability Reflect Overall Health?

Reading time: 4 min
Two people in winter jackets and hats, holding trekking poles, stand outdoors. Snow-covered mountains and a clear blue sky form the backdrop, epitomizing stress resilience amidst nature's beauty.

Resting heart rate, or pulse — the number of times your heart beats per minute — is a standard medical vital sign. But what your doctor can’t measure from the office, or doesn’t, is the more obscure, but equally important heart rate variability (HRV).

Imagine the planets stretched from the sun to poor, beleaguered  ‘maybe I’m a planet, maybe I’m not’ Pluto.  Each planet is a heartbeat. But see how the space between them varies?

That’s heart rate variability.

Heart rate variability measures the space between each beat, and how much it varies from the other spaces. Does your heart go Thump. Space. Thump. Space? Or does it go Thump. Space. Space. Thump. Space. Thump. Space. Space. Space.

If some spaces are longer and others are shorter, you have high heart rate variability. If all the spaces are the same, without peaks and valleys, you have low heart rate variability.

Which is Better?

High heart rate variability is a sign of health. Low heart rate variability is associated with aging, decline, illness and mortality.

What’s our maximum heart rate during exercise?

Our heart rate varies in response  to what’s going on around us. As the energy needs of our body increase our heart rate quickens. It beats faster to increase the volume of oxygenated blood it can push to our muscles.

At rest a healthy heart beats between 50 and 90 times a minute. During exercise or activity it might double.

To find your maximum heart rate, subtract your age from 220.  You shouldn’t exceed that target. When you exercise, aim to stay within 60 to 85% of that maximum heart rate. (Ex. if you are 30 your maximum heart rate is 190. Stay in a target zone  between 114 and 161 BPM. For a 60 year old, the maximum heart rate is 160, so your target range is lower, 96 to 136.) Some physicians and trainers recommend staying within 50 to 75%. These are just guidelines. Individual goals should reflect your general fitness and heart health.

Why Does It Matter?

HRV measures your heart’s resilience. Its ability to bounce back from effort. High HRV lets you respond with speed and efficiency when your body demands more blood, more oxygen, more performance. High heart rate variability is a sign of flexibility, strength and responsiveness.

As such it is a key indicator of heart health and general fitness.

Stress, Aging and HRV

Decreasing heart rate variability has been inked with decline and is a predictor of mortality. Research links low HRV to illness, sexual problems, and reduced independence (our ability to perform everyday tasks with ease and confidence).

HRV is closely linked to stress and aging.

Humans engage in a constant cycle of stress and recovery. Our bodies are designed to mobilize when stressed, triggering various processes to restore balance. We fluctuate between homeostasis (balance) and allostasis (all the tricks our bodies use to respond to stressors and recover equilibrium).

HRV is a marker for two kinds of allostasis: acute (temporary stress) and cumulative (allostatic load). HRV is sensitive to acute stress. Mental effort such as complex decisions or speaking in public lower HRV. As a marker of cumulative wear and tear, our HRV has also been shown to decline with the aging process.

Our resting heart rate stays constant as we age but our HRV declines. Regular exercise slows aging and raises our HRV.

The more varied our heart rate (the space between the beats) the healthier we are. High HRV renders us better able to maintain balance (homeostasis), overcome stress, and slow down the aging process (the cumulative wear and tear or allostatic load).

Can We Improve our HRV?

The good news is yes, heart rate variability can be regained. HRV is a function of cardio health. The heart is a muscle. Like any other muscle, it gets stronger with exercise. Anything you do to improve your heart health will also improve its HRV.

Interval training

High Intensity Interval Training (HIIT) alternates microbursts of intense activity with moderate exercise. It’s especially beneficial for cardiovascular fitness, weight loss, and increasing HRV.  This training lets your heart  practice a cycle of maximum effort and recovery. It’s in this recovery that the heart strengthens and HRV increases.

Every week brings new research on the impact of HRV. Recent studies have shown just 10 weeks of HIIT improved insulin function. HIIT may protect sedentary women against diabetes.

A technical analysis of HRV includes measuring bands by frequencies, classified as very low frequency, high frequency and low frequency.  Each of these frequencies plays a special role in the autonomic nervous system and vagal health. High frequency bands reflect vagal activity. The low/high frequency ratio implicates sympathetic activity.

The very low frequency band indicates the balances between the vagal and sympathetic systems. New research shows that, unlike the other 2 bands, the very low frequency of HRV does not bounce back quickly after mental stress task. This underscores the link between stress, cognitive function, and HRV.

This research confirms that the low frequency is the “slow recovery” component of HRV and the other bands are the “quick recovery” components. This may shed light on the potential role of HRV on cardiovascular disease prevention.

HRV impacts multiples aspects of physical and mental healthy. Patients with depression and hostility  or depressive disorders have reduced heart rate variability and may be at higher risk for coronary heart disease. Reduced HRV is also linked to anxiety sexual problems and reduced capacity for independence and self care in older people.

Our Evolving Understanding

A new tennis ball bounces with vigor, almost quivering with potential energy. It bounces high. Bounces low. Thwangs off the racket.

Now think of an old spent tennis ball. Limp. Not much bounce.

A healthy heart is like a new tennis ball. It is strong and elastic.

HRV measures the elasticity of our hearts. It is a key measure of heart health, where high heart variability signifies vigor, and low HRV is a sign of diminishing health.

Tracking our heart rate and HRV lets us evaluate steps we take to improve health and fitness.

Fortunately, there is a direct correlation between exercise and heart health. All we need to do is get started.

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Academy > article > Human Performance

Finding Your Circadian Rhythm And Sleep Chronotype

Reading time: 3 min
A man in bed reaches to turn off an alarm clock on a bedside table while a woman sleeps beside him. A lamp and a smartphone, equipped with HRV tracking for better stress resilience, are also on the table.

You naturally have your own body rhythm that determines how much sleep you need and when your body prefers to sleep. One of the best things you can do for your health is to get enough sleep. Lack of sleep contributes to many health issues and also tends to lower your Heart Rate Variability scores.

By recognizing your natural rhythms, you may be able to plan your day to capitalize on your strengths. In addition, timing your rest and workouts may even help improve your heart rate variability (HRV).

What is Circadian Rhythm?

According to the National Sleep Foundation, your circadian rhythms reflect your cycle of alertness, drowsiness, and sleep. Do you feel drowsy between 1 pm and 3 pm? If so, this is part of an average circadian rhythm. The exact time varies depending on whether you are a morning lark or a night owl. If you are well rested you might not feel as drowsy as you would if sleep deprived.

Your brain’s hypothalamus controls your circadian rhythm. Usually, natural day and night patterns influence this resulting in people craving more sleep during darker winter months than they do during the long summer days. The modern lifestyle disrupts natural circadian rhythms.

Finding Your Circadian Rhythm

In addition to day and night patterns, lifestyle and personal preferences may come into play. Dr. Michael Breus wrote “The Power of When” about individual variations in circadian rhythms. He classes people into four sleep chronotypes types: bear, lion, dolphin, and wolf.

According to Dr. Breus, your chronotype determines when you are most energetic. You can live your best life by planning to work, exercise, make decisions, or sleep at the “right” times for your natural rhythm.

He developed a sleep rhythm quiz to help people determine which type best describes them.

Wolf:

The wolf is the proverbial night owl. If you are a wolf you tend to be drowsy if you need to wake up early in the morning. Wolves peak from noon to 2 pm and again in the evening.

Lion:

The lion is the early bird that gets the worm. If you are a lion then you are likely ready to seize the day early in the morning. Your most productive hours are in the early morning. You tend to feel exhausted at night and go to bed early.

Dolphin:

The dolphin is harder to categorize than the bear, lion, and wolf. If you are a dolphin, you may be a light sleeper and often feel sleep deprived. Dolphins tend to be most productive mid-morning to early afternoon.

Bear:

The bear is the most common chronotype. If you are a bear, then your waking and sleeping rhythms follow the sun and moon. You sleep well and are most alert mid-morning. You may feel a big energy dip during the mid-afternoon.

Tips:

We can’t always control which hours we need to be awake. Work schedules, family obligations, travel, and our social lives sometimes require us to be awake during less ideal times. Try these tips to make the best use of your natural rhythms:

  • Try to avoid accumulating sleep debt. If you are caught up on your sleep then staying up later one night or getting up too early doesn’t affect you as much.
  • Plan your day to prioritize getting 7-8 hours of sleep most nights.
  • Try to plan your challenging projects or meetings during your peak alertness and productivity hours as much as possible.
  • Pay attention to how you feel and to your daily HRV readings.
  • Be physically active or exercise daily, for many people outdoor activity helps balance their circadian rhythms.

Working with your body’s rhythm helps you stay productive while looking and feeling your best.

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Academy > article > Human Performance

Salt and its effects on resting heart rate and heart rate variability

Reading time: 5 min
Three bowls filled with coarse salt, colored white, purple, and pink, are placed on a white surface with scattered salt around them. These vibrant salts symbolize Stress Resilience and the balance of ANS in our lives.

Too much salt is bad for you. Everyone knows this. Lose the salt shaker, we’ve been told, by our doctors. Our mothers. The government. Our trainers. Turns out, maybe we should take this advice with, er, a grain of salt. That is, with skepticism.

In a new book The Salt Fix author James DiNicolantonio comes out swinging. Subtitled Why the Experts Got It All Wrong—and How Eating More Might Save Your Life, the book lays out the case that medicine has been ignoring its own research. Study after study, he says, shows the dangers of salt consumption are exaggerated, the risks of a low salt diet understated, and, when it comes to government recommendations? The numbers are just plain wrong.

What is Salt?

Salt (NaCl or sodium chloride) is a mineral made up of equal parts sodium and chloride. Most commercial salt is harvested through mining or solution mining existing salt deposits. Salt occurs naturally throughout the world and is necessary for all life.

Do a quick Google search on ‘tips for heart health”. Nearly every search result will tell you to reduce or eliminate the salt in your diet. Authorities firmly on the no-such-thing-as-good-salt bandwagon include Harvard the British National Health Service, the CDC Centers for Disease Controls and Prevention (CDC), Health.gov and the American Heart Association. The CDC has launched a Sodium Reduction Initiative.

And for people with existing high blood pressure, salt is a serious irritant. Salt reduces their kidneys’ ability to remove water. This extra fluid strains blood vessels and can elevate blood pressure further.

What’s the deal with blood pressure?

Blood pressure is the measurement of blood moving through the circulatory system. It is measured by two numbers: systolic (the top number, is the pressure in your blood vessels while your heart beats) and diastolic (the bottom number, is the pressure as your heart rests between beats). A normal range is systolic under 120 mmHg and diastolic reading under 80 mmHg. (120/80.) Hypertension (high blood pressure) is diagnosed when systolic exceeds 140 mmHg. Or diastolic tops 90 mmHg.

High blood pressure increases the long-term heart risk and stroke. Dangerously high blood pressure raises the immediate risk of stroke, heart attack, organ failure or death. Low blood pressure can also signify a problem. Plummeting blood pressure from any cause is a life-threatening emergency.

Blood pressure is affected by the heartbeat and the width and elasticity of our arteries. Salt and potassium also work together to regulate blood pressure and circulating blood volume.

Without salt, our bodies could not sustain blood volume. Our blood vessels would literally collapse, leading to circulatory collapse, hypovolemic shock and eventually death.

How Much Salt is Too Much?

Nutrition and health are closely related. Given the demonstrated connection between high blood pressure and poor cardiac outcomes, health officials have sought behavioral interventions to lower blood pressure. Salt, known to raise blood pressure in people with already high blood pressure, was an obvious target. Salt began to be seen as bad in general. The 2015-2020 Dietary Guidelines for Americans recommend less than 2.3 grams of sodium per day. The average American now eats 3.4 grams.

Some people are salt sensitive. High salt intake raises their blood pressure. A low salt diet decreases their blood pressure. Other folks are salt resistant. It’s not clear why. There is no unified theory of what causes high blood pressure. We do know that there is a connection between blood pressure and the ability to maintain core body temperature.

But for people who aren’t salt sensitive, restricting salt intake may not make sense. DiNicolantonio, author of The Salt Fix, says our relationship with salt is ancient as we “evolved from the briny sea”. He posits that healthy adults should actually be consuming 3 to 6 grams, more than double the current recommended limit.

Salt plays a key role in blood volume, hydration, electrolyte balance and general homeostasis.

Salt and our resting heart rate

When exercising, a healthy heart can even double its heart rate and still not cause an unhealthy rise in blood pressure. Blood vessels just get larger (dilate) to allow increased flow. But what about our resting heart rate?

Resting heart rate is a key measure of our overall health. The lower the better. DiNicolantonio is a cardiovascular research scientist and doctor of pharmacy, We reached out to him to ask about the impact of salt on our resting heart rates. “Low-salt diets have been found to increase heart rate in humans in several studies,” he said.

What about heart rate variability?

Heart rate variability (HRV) is the diversity of spacing between each heartbeat. High HRV is a marker of cardiac health. People with high blood pressure have decreased HRV. So what is the role of salt intake in HRV?

Sodium balance and related changes in plasma volume help determine our HRV. High salt diets might affect people with high blood pressure differently, including their HRV. “The data on heart rate variability are less consistent,” says DiNicolantonio, “but it is possible that by chronically stimulating the sympathetic nervous system low-salt diets may lead to altered heart rate variability.”

One study of heart rate variability centered on salt sensitivity and blood pressure. Researchers found that the body makes adjustments to regulate blood pressure. When salt intake is low, the heart and peripheral vasculature increase cardiac activity and vascular tone. When salt intake is high, the body decreases cardiac activity.

New areas of study

In 2014 The National Heart, Lung, and Blood Institute (NHLBI) convened to examine Salt’s Effect on Human Health. This working group “identified scientific gaps and challenges and highlighted some opportunities for scientific inquiry and technical development” concluding, “the initial research that implicated salt as a factor in important diseases points to the need to further illuminate the biological mechanisms and pathological processes to which salt may contribute”.

Specific areas for further study include the role of hypertension in autoimmune diseases; salt-sensitive hypertension; how we store salt in our skin; how to determine salt sensitivity at an individual level; new technologies to measure sodium concentrations in human tissue; and even a Sodium MRI to help reveal the role of salt in health and disease.

DiNicolantonio links low-sodium diets to medical risks including obesity, heart failure, and kidney disease, concluding “overconsumption of salt is not the primary cause of hypertension”.

“Salt restriction. “ he says, “may actually worsen overall cardiovascular health. and may lead to other unintended consequences (insulin resistance, type 2 diabetes, and obesity).”

He just performed an overview of existing research entitled, Is Salt a Culprit or an Innocent Bystander in Hypertension? A Hypothesis Challenging the Ancient Paradigm The study highlights a substantial body of peer-reviewed evidence, and concludes that high salt consumption is not always bad, and low salt diets are not always a panacea. Salt intake is a proven risk for folk who already have high blood pressure. The rest of us could be eating salt (within reason). A low salt diet, says DiNicolantonio, is even potentially heart harmful.

So who’s right? Looks like the debate will continue for a little while longer. In the meantime, know your risk factors, check your blood pressure, monitor your heart rate, get plenty of exercise, and don’t go overboard on the salt. But you might not need to skimp on it either.

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Academy > article > Human Performance

The Effects of Fasting on Heart Rate Variability

Reading time: 4 min
A plate with a blue alarm clock on it, flanked by a fork on the left and a knife on the right, set against a light blue background, subtly symbolizes the importance of timing in managing stress resilience.

Fasting is an age-old practice that is gaining speed in our modern-day world.

From intermittent fasting that can take place every few days or once in a while, to something that is a lifestyle, such as the one-meal-a-day, or OMAD, diet, fasting can take many forms.

Many formerly obese individual credit fasting for extreme weight loss. Others have said it improves overall health and wellness. And while the research backing up fasting regularly is mixed on all sides of the vein, the fact remains that when you don’t eat, things start to happen inside your body that affects your autonomic nervous system, and in turn, your heart rate variability.

Here is what happens to your body when you fast over a long period of time, and as a result, what role those changes play on your heart rate variability.

Your body will break down glycogen

In the beginning of your fast, your body will convert glycogen (sugar) into energy. This is entirely normal following a meal because it’s basically digestion (and your autonomic nervous system at its finest).  However, after about six hours, when you have “officially” begun you fast, your glycogen stores will begin to deplete, and you will become hungry.

Effect on HRV

Because of HRV levels being highly dependent on stress levels, in these beginning stages, your HRV could go high or low depending on your approach to the fast. If you are feeling stressed about being hungry, your HRV will likely be low. However, if you are feeling confident about the results of the fast, and even have the desired outcome, you are likely going to find that your HRV is high, indicating that you are handling the stress on your body quite well.

Your blood glucose level will rise

This may seem wrong because wouldn’t your body lose sugar if it doesn’t have the stores to break it down? And wouldn’t that mean that your blood sugar would go down?

You’d think so, but what actually happens when you fast, is that insulin levels start to drop, triggering a surge of hormones like including noradrenaline and growth hormone to fight against low blood sugar. This, in turn, concentrates the blood with sugar that it pulled from stored sugar that is usually in the liver.

Effect on HRV

According to research, high blood glucose concentration is associated with higher parasympathetic, but lower sympathetic CAM. This means that your body is under more stress to perform its normal functions of the nervous system. If you were to measure these using biometrics, you would likely find your HRV to be on the lower level.

Ketosis will begin

When your body doesn’t have the energy sources to break down new glycogen, it starts to starve and begin the hunt for other things to convert into energy. It will start breaking down fat into fatty acids in order to use them for energy rather than carbs. This is when those looking to use fasting for weight loss begin to see results.

However, due to the fact that the brain cannot use broken down fat for fuel, it turns to ketone bodies for energy. This works for a small time because ketone bodies can’t replace glucose. But after a few days, the ketone bodies build up and a volatile substance called acetone begins to form, lowering the pH of the blood. When this happens, a condition called acidosis develop and lead to coma or even death.

Effect on HRV

At this point — usually around the 48-hour mark —  your body is under stress as it searches for energy sources to survive.  Due to this, your HRV will lower. In fact, a study that took 16 young healthy female volunteers, and had them fast for 48 hours, found that parasympathetic withdrawal was induced with simultaneous sympathetic activation. These findings lead researchers to conclude that the changes in the women’s nervous systems appeared to reflect stress.

However, if your body is used to fasting, or if you have prepared yourself mentally and physically for the fast, the change may not be as significant as it could be otherwise.

If you do notice a significant drop in HRV and begin to feel considerably physical and mental stress, it might be best to abandon the fast at this point.

You’ll have cognitive function impairment

If you continue your fast, your body will be in the process of ketosis and quite possibly acidosis. During these stages, the body starts to break down protein to release amino acids that can convert into glucose. This is done to fuel your brain and suppress hunger.

For those who use fasting as a weight-loss measure, this is the next step that the body takes, and many experts — specifically as it relates to the keto diet —  say that ketosis is not entirely harmful. However, due to the strain on your brain, you may lose some simple brain functions that help you remember things, and carry out simple tasks.

Effect on HRV

The strain on many of your cognitive functions, and the continuing decline in your HRV levels will make it more difficult for your autonomic nervous system to work the way it needs to. You will be less alert and therefore unable to respond well to stressful situations

Fasting isn’t all bad …

The above may seem quite terrible and can be if taken to an extreme level. However, if you use fasting intermittently, your body will likely not have many or any of the negative side effects including those related to HRV.

Do your research on the right fasting approach for your health goals. And as always, check with a medical professional to make sure your body is able to handle the effects — whatever they may be — of a fasting regimen.

Categories
Academy > article > Human Performance

Not Getting Enough Sleep? How to Repay Your Sleep Debt

Reading time: 4 min
A person with glasses is resting their head on an open book, surrounded by several other books on a desk, perhaps finding a moment of ANS Balance amid the study session. Shelves filled with books are visible in the background.

Not getting enough sleep? You’re not alone. According to the CDC, more than one-third of adults don’t get the recommended seven hours of sleep they need to feel well-rested and energized the following day. When this occurs, we fall into what’s known as 6sleep debt.

Sleep debt, or sleep deprivation, occurs when you aren’t getting the sleep you need to feel awake, alert, and ready to go. And while one night of interrupted sleep may be a nuisance the following day, prolonged periods of sleep loss can lead to daytime sleepiness, emotional instability, weight gain, and several other health problems.

Why We Sleep

As human beings, our bodies require prolonged periods of rest not only to feel rejuvenated and refreshed but also to repair tissue, grow muscles, and synthesize hormones. We spend one-third of our lives asleep, and going without sleep can lead to psychosis or even death.

We can break down the stages of sleep into two primary categories: non-rapid eye movement and rapid eye movement (REM) sleep. Non-REM slow-wave deep sleep is characterized by slow brain waves and the release of growth hormones as our brain and many physiological systems enter a state of repair. REM sleep is similar to how our mind operates during the day, with one caveat — the brain is active and working, but our muscles are in a state of paralysis.

Beyond these realities, scientists don’t fully understand why we sleep. Some propose that sleep restores the brain’s energy while others hypothesize that sleep plays a major role in the connectivity and plasticity of the brain. The latter theory explains why individuals who are sleep-deprived suffer from memory loss and the inability to pay attention.

Regardless of the underlying reasons behind our need for sleep, we ultimately know that sleep is an extremely important aspect of our well-being. Without it, we suffer.

What Is Sleep Debt?

Sleep debt is the act of not getting enough sleep. You can often gauge whether or not you’re receiving enough sleep by monitoring how you feel the following day. If you’re tired, drowsy, and inattentive, chances are you’re suffering from short-term sleep debt. And if symptoms such as blood pressure changes, weight gain, or other serious health problems take shape over time, you may be suffering from the cumulative effects of chronic sleep debt.

The Symptoms of Sleep Debt

The primary short-term symptom of sleep debt is excessive daytime sleepiness. Other symptoms may include the following:

Irritability
Depressed mood
Forgetfulness
Clumsiness
Lack of motivation
Increased appetite
Carbohydrate cravings
Reduced sex drive
Inability to concentrate
Fatigue

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The Effects of Sleep Debt

Sleep loss in any form can come with serious side effects that will impact both your short-term and long-term health. Here’s a look at some of these effects.

Weight Gain

The hormones leptin and ghrelin control feelings of hunger and fullness. When you suffer from lack of sleep, leptin will decrease and lead to the constant feeling of hunger alongside a general slowdown of your metabolism, which may cause weight gain over time. Ghrelin will increase with lack of sleep increasing hunger levels.  Also, keep in mind that getting plenty of sleep can burn calories.

Blood Pressure & Heart Disease

During normal sleep, your blood pressure will naturally decrease. If you’re suffering from a sleep deficit, your blood pressure will stay higher for a longer period of time, just as it does during the day. Over time, this may lead to an increased risk of heart disease, thus illustrating the need for a normal sleep schedule.

Type 2 Diabetes

Diabetes is a disease that causes sugar to build up in your blood, which will damage your blood vessels over time. According to the National Sleep Foundation, when your sleep patterns are negatively impacted, less insulin is released into the bloodstream after you eat.

Meanwhile, your body may release other stress hormones to help you stay awake. These stress hormones impact the ability of insulin to do its job effectively. As a result, glucose will remain in your bloodstream and increase your risk of type 2 diabetes.

Sleep Debt Treatments

Treating sleep debt in any form is only required if you physically can’t go to sleep or suffer from a sleep disorder, such as sleep apnea. Oftentimes you can improve sleep debt by simply increasing the amount of time you’re asleep or by altering your sleep habits to further encourage healthy amounts of sleep.

If you physically can’t go to sleep or you suffer from a sleep disorder, two primary avenues exist that can treat your sleep deprivation: cognitive treatments and medications.

Cognitive Treatment

Cognitive treatments that seek to repay your sleep debt are available in abundance. For instance, relaxation and meditation techniques utilize guided breathing and mindfulness approaches that encourage your body and mind to fall asleep naturally.

Other cognitive treatments include controlling pre-bedtime activities and optimizing your sleep environment to increase your sleep duration. This may include limiting social media usage before bed and removing other distractions like bright lights or screens.

Medications

If the cognitive or non-medical intervention proves to be ineffective, sleep medicines are available that can help induce sleep. Some of these medications are available over-the-counter while others require a prescription.

Some individuals may form a dependence on sleeping medications, meaning they can’t go to sleep without taking medication. For this reason, it’s important to speak with your healthcare provider and review all your options before determining if sleep medication is right for you.

Habits for Healthy Sleep

Getting a good night’s sleep is dependent upon your sleeping habits and nightly routines. Also known as sleep hygiene, healthy sleep habits will leave you feeling rested and refreshed each morning.

Some good sleep habits include:

Going to bed when you feel tired
Not eating 2-3 hours before bed
Engaging in regular, daily exercise
Keeping the bedroom quiet and cool
Turning off electronic devices
Using an alarm clock to regulate when you wake up

Paying off sleep debt

If you fail to get your recommended amount of sleep, you’ll begin accumulating a sleep debt. For instance, if you need eight hours of sleep but only get five, you’ll have a sleep debt of three hours. If this pattern continues throughout the week, your sleep debt will climb, and the effects of sleep deprivation will quickly take hold.

The only way to pay off your sleep debt is to start getting the sleep you need, along with some extra time each night, or with naps, until the debt is fully ”paid off”. Once you’ve paid off the sleep debt, you can resume your normal sleeping schedule. 

Even if paying off your sleep debt seems impossible, remember that it can be done with conscious effort. While repaying tens or even hundreds of hours of sleep debt may seem out of reach, it can be accomplished by reflecting on your current sleep habits and making adjustments whenever necessary.

Consider using a sleep tracker to fully understand your sleeping habits. Once you’ve finally woken up feeling refreshed and recovered, you’ll have paid off your sleep debt in full.

Categories
Academy > Biometrics 101 > whitepaper

Heart Rate Variability: how to measure it, why it’s relevant to many aspects of health

Reading time: 5 min
Illustration of a human body with a visible heart and blood vessels, highlighting HRV. A green electrocardiogram line runs horizontally across the image, symbolizing stress resilience and ANS balance.

What is it?

Heart rate variability (HRV) is a measure of differences in the time intervals between heart beats. Heart rate by itself is the expression of how many contractions of the heart there are in a given unit of time; however, the rate itself is not constant. There is normal fluctuation of time between heartbeats, in a manner that speeds up and slows down heart rate. Therefore, HRV is a quantifiable measure that assesses these differences.

This variation in the time between heartbeats is thought to be a composite measure of parasympathetic and sympathetic neural inputs and hormonal inputs as regulated by the autonomic nervous system. Much is still unknown about the mechanism of action causing variability changes. However, many studies have shown correlations between HRV and diseased states, such as heart disease, Parkinson disease, and cardiovascular disease; emotional stress, such as depression; physical/mechanical stress, such as high-intensity or resistance training; sleep in the context of both acute stress and chronic stress; and meditation whether it’s “inward- attention” or Vipassana meditation. Therefore, HRV is becoming a more common non-invasive measure to examine the physiological state and responses.

How it’s measured

HRV can be measured by use of an electrocardiogram (ECG) or photoplethysmography (PPG). By referencing a common point in the ECG or PPG waveform, the time between each heart beat can be recorded in milliseconds (ms). Collecting each beat-to-beat interval in ms allows us to compute HRV, most commonly reported as rMSSD (root mean square of successive differences). 

The rMSSD method of calculation takes each interval, squares the interval, takes the overall mean, and then the square root of that mean is taken. SENSR computes the rMSSD using this method and remains the standard computational method for HRV. 

More complex measures of HRV, including frequency domain analysis can be performed to get further information out of heart rate patterns, which will be covered in another review. 

Correlation with health conditions

HRV is most notably correlated with stress conditions, such as anxiety disorders, depression, PTSD, and other psychological states, with lower HRV indicating higher-stressed states. The suggested mechanism is an increased sympathetic arousal, which affects HRV; HRV alone does not cause these states, but reflects and provides insight into the heightened stress on the physiological systems, which in turn have effects on other bodily systems, particularly the cardiovascular and endocrine systems. 

Because of the chronic effects of stress, as previously mentioned, HRV has been noted to be a predictor of all-cause mortality and correlated with obesity, cardiovascular disease, cancer, and neurodegenerative diseases, among other health conditions.

What is a “normal” range?

Heart rate variability has a large individual component and is often used to assess changes in health over time (see “Interpreting Trends” below).

Heart rate variability can fluctuate day-to-day based on exposure to stress, sleep quality, diet, and exercise. This leads to low repeatability, and therefore makes normative data difficult to collect.

In general, younger individuals, males, and more active individuals tend to have higher heart rate variability. However, the inter-subject variability tends to be too high to suggest proper normative ranges. This demonstrates a need to track HRV over time to understand the ‘profile’ of an individual.

When considering a normal range, there is not a normal scale of 0-100. HRV scale is 0-255. Many factors influence where your HRV sits on this scale, including; genetics, lifestyle, and age. Once you track HRV over a period of time you will have a baseline HRV. Once a baseline is established you will be able to see how day-to-day internal and external stressors influence your HRV, upward or downward.

Watching your HRV deviate positively or negatively from your baseline is the most important factor to observe. The actual HRV number matters less than how much it has varied from your “normal” baseline.

Interpreting trends

As previously mentioned, HRV is difficult to interpret and generally a nonspecific data point from a single spot check. However, since it is a dynamic measure that responds to various lifestyle factors, tracking HRV over time allows for non-invasive insight into changes in health status or efficacy of certain interventions.

In general, since higher HRV is preferable, a greater ability to manage stress results in an increased HRV. The results of the studies demonstrating the relationship between stress and HRV suggest that interventions aimed at reducing mental and physical stress could increase HRV and minimize day-to-day fluctuations. The increase in HRV itself will not reduce risk and improve health over the long term, but rather, it reflects positive changes in an individual’s physiology.

SENSR

In a 2018 study, the SENSR sensor as a wrist-worn device was shown to produce high-quality signals which are useful for the estimation of heart rate variability. 

References

  1. Mccraty R, Shaffer F. Heart Rate Variability: New Perspectives on Physiological Mechanisms, Assessment of Self-regulatory Capacity, and Health Risk. Global Advances in Health and Medicine. 2015;4(1):46–61. doi:10.7453/gahmj.2014.073
  2. Silva LEV, Silva CAA, Salgado HC, Fazan R. The role of sympathetic and vagal cardiac control on complexity of heart rate dynamics. American Journal of Physiology-Heart and Circulatory Physiology. 2016;312(3):H469–H477. doi:10.1152/ajpheart.00507.2016
  3. Dobrek Ł, Skowron B, Baranowska A, Malska-Woźniak A, Ciesielczyk K, Thor PJ. Spectral heart rate variability and selected biochemical markers for autonomic activity in rats under pentobarbital anesthesia. Polish Annals of Medicine. 2017;24(2):180–187. doi:10.1016/j.poamed.2017.01.001
  4. Huikuri HV, Mäkikallio TH. Heart rate variability in ischemic heart disease. Autonomic Neuroscience. 2001;90(1):95–101. (Neural Regulation of Cardiovascular Function Explored in the Frequency Domain). doi:10.1016/S1566-0702(01)00273-9
  5. Alonso A, Huang X, Mosley TH, Heiss G, Chen H. Heart rate variability and the risk of Parkinson disease: The Atherosclerosis Risk in Communities study. Annals of Neurology. 2015;77(5):877–883. doi:https://doi.org/10.1002/ana.24393
  6. Thayer JF, Yamamoto SS, Brosschot JF. The relationship of autonomic imbalance, heart rate variability and cardiovascular disease risk factors. International Journal of Cardiology. 2010;141(2):122–131. doi:10.1016/j.ijcard.2009.09.543
  7. McCraty R, Atkinson M, Tiller WA, Rein G, Watkins AD. The effects of emotions on short-term power spectrum analysis of heart rate variability. The American Journal of Cardiology. 1995;76(14):1089–1093. doi:10.1016/S0002-9149(99)80309-9
  8. CARNEY RM, FREEDLAND KE. Depression and heart rate variability in patients with coronary heart disease. Cleveland Clinic journal of medicine. 2009;76(Suppl 2):S13–S17. doi:10.3949/ccjm.76.s2.03
  9. Sarmiento S, García-Manso JM, Martín-González JM, Vaamonde D, Calderón J, Da Silva-Grigoletto ME. Heart rate variability during high-intensity exercise. Journal of Systems Science and Complexity. 2013;26(1):104–116. doi:10.1007/s11424-013-2287-y
  10. Kingsley JD, Figueroa A. Acute and training effects of resistance exercise on heart rate variability. Clinical Physiology and Functional Imaging. 2016;36(3):179–187. doi:https://doi.org/10.1111/cpf.12223
  11. Hall M, Vasko R, Buysse D, Ombao H, Chen Q, Cashmere JD, Kupfer D, Thayer JF. Acute Stress Affects Heart Rate Variability During Sleep. Psychosomatic Medicine. 2004;66(1):56–62. doi:10.1097/01.PSY.0000106884.58744.09
  12. da Estrela C, McGrath J, Booij L, Gouin J-P. Heart Rate Variability, Sleep Quality, and Depression in the Context of Chronic Stress. Annals of Behavioral Medicine. 2021;55(2):155–164. doi:10.1093/abm/kaaa039
  13. Busek P, Vanková J, Opavsky J, Salinger J, Nevsimalova S. Spectral analysis of heart rate variability in sleep. Physiological research / Academia Scientiarum Bohemoslovaca. 2005;54:369–76.
  14. Krygier JR, Heathers JAJ, Shahrestani S, Abbott M, Gross JJ, Kemp AH. Mindfulness meditation, well-being, and heart rate variability: A preliminary investigation into the impact of intensive Vipassana meditation. International Journal of Psychophysiology. 2013;89(3):305–313. (Psychophysiology in Australasia – ASP conference – November 28-30 2012). doi:10.1016/j.ijpsycho.2013.06.017
  15. Wu S-D, Lo P-C. Inward-attention meditation increases parasympathetic activity: a study based on heart rate variability. Biomedical Research. 2008;29(5):245–250. doi:10.2220/biomedres.29.245
  16. Jarchi D, Salvi D, Velardo C, Mahdi A, Tarassenko L, Clifton DA. Estimation of HRV and SpO2 from wrist-worn commercial sensors for clinical settings. In: 2018 IEEE 15th International Conference on Wearable and Implantable Body Sensor Networks (BSN). 2018. p. 144–147. doi:10.1109/BSN.2018.8329679
  17. Shaffer F, Ginsberg JP. An Overview of Heart Rate Variability Metrics and Norms. Frontiers in Public Health. 2017 [accessed 2021 Apr 14];5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5624990/. doi:10.3389/fpubh.2017.00258
  18. Chalmers JA, Quintana DS, Abbott MJ-A, Kemp AH. Anxiety Disorders are Associated with Reduced Heart Rate Variability: A Meta-Analysis. Frontiers in Psychiatry. 2014 [accessed 2021 Apr 21];5. https://www.frontiersin.org/articles/10.3389/fpsyt.2014.00080/full. doi:10.3389/fpsyt.2014.00080
  19. Hauschildt M, Peters MJV, Moritz S, Jelinek L. Heart rate variability in response to affective scenes in posttraumatic stress disorder. Biological Psychology. 2011;88(2):215–222. doi:10.1016/j.biopsycho.2011.08.004
  20. Cohen H, Kotler M, Matar MA, Kaplan Z, Miodownik H, Cassuto Y. Power spectral analysis of heart rate variability in posttraumatic stress disorder patients. Biological Psychiatry. 1997;41(5):627–629. doi:10.1016/S0006-3223(96)00525-2
  21. Tsuji H, Venditti F J, Manders E S, Evans J C, Larson M G, Feldman C L, Levy D. Reduced heart rate variability and mortality risk in an elderly cohort. The Framingham Heart Study. Circulation. 1994;90(2):878–883. doi:10.1161/01.CIR.90.2.878
  22. Karason K, Mølgaard H, Wikstrand J, Sjöström L. Heart rate variability in obesity and the effect of weight loss. The American Journal of Cardiology. 1999;83(8):1242–1247. doi:10.1016/S0002-9149(99)00066-1
  23. Stein PK, Reddy A. Non-Linear Heart Rate Variability and Risk Stratification in Cardiovascular Disease. Indian Pacing and Electrophysiology Journal. 2005;5(3):210–220.
  24. Sandercock G. Normative values, reliability and sample size estimates in heart rate variability. Clinical Science. 2007;113(3):129–130. doi:10.1042/CS20070137

 

Categories
Academy > article > Human Performance

Should you trust HRV values your wearable gives you?

Reading time: 5 min
Cyclist riding on a curved mountain road with a scenic backdrop and the sun shining brightly in the sky, embodying stress resilience amidst nature's tranquility.

My experience as an athlete

As a health coach and fitness trainer and being 53, I place a huge importance on the optimization of my health. I also love to challenge what I call conventional stupidity approach to health, fitness and life. I do things a bit differently than most Triathletes and Marathoners and Personal Trainers. I fundamentally believe we need to rest more, reduce chronic stress, and connect more with what is going on in our bodies.

I use a wide range of subjective measures in relation to my health and fitness. Subjective measures such as how I feel, my energy levels, my bowel movements, my mood, my ability to think and make decisions, and of course how I feel when I am in the gym, the pool, the track or on the bike. Some people place a lot of importance on Objective metrics and numbers and tend to negate the Subjective measures.

I think it is very important to have a good balance between both.

I recently found this to be important when I started looking at biometrics. I was looking at my RHR, O2 Saturation, Respiration and HRV all from a nocturnal measurement lens. I found there was a trend for my HRV to be quite low and I mean low 32, 41, 35, and it did not vary much regardless of if I had had a 5 hr training day or a rest day. It also did not vary based on my RHR, or how I felt. I was very confused. I was worried, I was starting to think something was wrong. There was a huge disconnect between the subjective rating I would give myself for my state and the objective numbers provided by the HRV tool I was using.

So I tried several HRV devices/applications and tools and they all seemed to show the same result. I was desperate for a deeper understanding of what was going on.

My experience with SENSR

So why is this so important? Well I am a serious AG athlete. Last year I raced in the 70.3 Ironman World Championships and I train about 13 hrs a week and I am serious about my sport. This was important to me. I also feel that recovery is one of the key pillars of health and fitness.

5ba48dd8e460730759184bc2 andre2

The last thing I want to do is cause further stress to my body that would impact my ability to recover, ie doing a solid training session when not fully recovered.

I started looking at a system for biometrics that to me appeared to be more focussed on HRV than simple fitness tracking, it also provided the ability to do a 2 minute biometric scan. I decided to give this a trial. It is called SENSR.

I had been hearing a lot about the fact that nocturnal HRV reading for elite athletes could be not effective due to a phenomenon called “parasympathetic saturation”

My understanding is that this has been reported in high level ultra-marathoners, triathletes and endurance athletes that are more susceptible to it in the supine position simply because you’re in a more rested or relaxed state where our heart is not being challenged to overcome gravity, to pump blood upwards and so forth. When you already have a very low RHR lying down makes it even worse.

Andrew Flatt PhD, CSCS

Andrew is a highly qualified practitioner in this field and writes fantastic content around biometrics. Flatt explains in more detail:

“Parasympathetic saturation, the results of would be having decreased heart rate variability despite having a very low resting heart rate, which is counterintuitive because typically, the lower your resting heart rate, the higher your heart rate variability is. There tends to be an inverse relationship there. But what’s happening kind of physiologically is that the acetylcholine receptors on the heart that respond to vagal stimulation, the vagus nerve is going to release acetylcholine which will bind to the muscarinic cholinergic receptors on the heart, and that tends to slow heart rate down”

So after reading all of this one morning before training I decided to conduct a Sitting biometric scan.

“Kiviniemi et al. (2007) provides a very thorough explanation of why HRV might be better measured in a standing position as opposed to seated or supine. Essentially, HRV is susceptible to saturation of the parasympathetic nervous system in subjects with low heart rates”

Yes, this is me at 36-41 RHR.  I got excited maybe I found the reason why my Nocturnal HRV was so low. He further explains:

“Mourout et al (2004) saw decreased HRV in overtrained athletes compared to not overtrained athletes in the supine position. Similar results were found when HRV was measured after 60 degree tilt. The non-OT group always had higher HRV in the standing position and saw greater reactivity to the postural change. Therefore, pick a position and stick to it 100% of the time for your values to be meaningful. Switching positions from day to day will provide skewed data.”

Endurance athletes and athletes with low resting heart rates (yes that’s me) are probably better off measuring HRV in a standing position. We understand that when an elite athlete has a very low RHR then they are likely to be in a state of parasympathetic saturation. Andrew Flatt Explains this as follows:

“This is when vagal HRV markers (e.g., lnRMSSD) are low despite a low resting heart rate. This has to do with excess acetylcholine within the myocardium that maintains inhibitory actions on the SA node, and thus limits the typical arrhythmia observed from respiration. See below”

“There are several potential explanations for the decrease in HRV with increasing parasympathetic effect. If with increasing blood pressure there is higher-frequency vagal discharge and inspiratory suppression is maintained,18 23 then there must be persistent parasympathetic effect during inspiration despite the suppression of vagal nerve discharge. In in vitro preparations, the dose-response curve to acetylcholine has a rapidly rising portion and at higher concentrations is flat,24 25 displaying a simple saturation relationship. High-intensity vagal nerve discharges during expiration may release enough acetylcholine to result in saturation of the parasympathetic effect during expiration. If acetylcholine concentrations during expiration are high enough, the expected decline in acetylcholine concentrations in the region of the sinus node during inspiration may not be enough to significantly diminish the parasympathetic effect. Alternatively, it is possible that with increasing blood pressure, there is loss of phasic respiratory changes in vagal nerve discharges,26 resulting in a loss of phasic effect and a decrease in HRV. It is unclear which mechanism is operative in humans.”

 

Goldberger, J. J., Challapalli, S., Tung, R., Parker, M. A., & Kadish, A. H. (2001). Relationship of heart rate variability to parasympathetic effect. Circulation, 103(15), 1977-1983. http://circ.ahajournals.org/content/103/15/1977.full.html

So if you are using an HRV device, and you have a low RHR  maybe you should do a self check and consider are your Objective numbers from your HRV app lining up with the Subjective measures and, if not, consider using a device that allows you to do a sitting or standing biometric scan.

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