Reading time: 5 min

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 Wrongand 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), 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.

Reading time: 4 min

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.

Reading time: 3 min

What’s more heartwarming in the wintertime than struggling up close to the fireplace, drinking a cup of hot cocoa while watching your favorite movie? Well, how about going for a run or hike in fresh, mountain snow, or taking a walk on your neighborhood parkway as snowflakes flutter down upon your eyelashes?

While wintery terrain may give you cold feet, it’s all warm and fuzzy when it comes to your heart. And here are six tips to help keep your heart warm this winter.

1. Winterize it

Cold weather can put a large strain on the heart, especially if you aren’t used to it. Cold temperatures cause your blood vessels and arteries to shrink, restricting blood flow and reducing oxygen to the heart. Due to this, your heart has to pump harder to move the blood through the narrowed vessels. When this happens, your blood pressure and heart rate increase.

And as we know, a sudden spike in blood pressure – especially when paired with outdoor exertion, can have scary, even life threatening consequences.

In order to avoid this, make sure that your heart is in good shape before winter by implementing a regular cardiovascular exercise regimen well before the winter months.

2. Dress appropriately

You wouldn’t wear a winter coat, gloves and hat in the middle of summer for the simple reason that it would cause your body to overheat. The same principle applies to wintertime. Shorts and a tank out in the freezing cold would cause your body temperature to plummet.

By dressing appropriately in moisture wicking layers with your head and hands covered, you will be able to last a lot longer out there in the cold, and your heart rate will be less variable.

3. Warm up

Temperature extremes are not good for the cardiovascular system. Both the extremes of heat and cold can cause changes in the body that may have lasting negative effects and could even lead to death.

This is why it is important to warm up before entering the cold so you can to get your heart pumping blood, easing the transition as you acclimate to the weather. Doing so will also lessen the shock to your cardiovascular system.

4. Drink fluids

Drinking plenty of water helps the heart pump blood through the blood vessels to the muscles more easily, according to the American Heart Association. Simply put, if you’re hydrated, your heart won’t need to work as hard.

And while you won’t sweat as much in the cold because your body is keeping water in to keep your body temperature up, rather than using it to cool you off, you still do sweat. Plus, the air that we breathe in the wintertime has less moisture in it, and our lungs need to use the water in our bodies to moisturize it, according to an Dr. Steven T. Devor – Director of Performance Physiology for MIT and OhioHealth.

So, continue to drink your water, and lots of it!

5. Eat heart healthy foods

Along with drinking plenty of water, it is important to eat heart healthy foods like fish, nuts, berries, and green vegetables to make sure that your heart is in tip-top shape as you exercise during the cold, winter months.

6. Know your limits and listen to your body

Exercising outdoors is awesome because you get to experience this time of year the best possible way. However, with extreme temperatures brings risks both to your heart and body. If you begin to shiver, it is time to bring things indoors because this is the first sign of hypothermia.

And there is nothing wrong with exercising in a temperature regulated room. Nothing at all.

Reading time: 5 min

From maintaining a healthy weight to living longer, eating healthy offers many benefits for our long-term wellbeing. The foods we eat also have a major impact on our heart — especially for those who suffer from a high heart rate.

Having a high heart rate is a dangerous condition that can increase a person’s risk for heart attack, stroke, and cardiovascular disease, all while shortening their life expectancy. Here’s what you should know about heart rate, plus the best foods that lower heart rate and improve quality of life.

Why Does Low Heart Rate Matter?

Heart rate fluctuates throughout the day depending on a person’s activity. According to Harvard Health Publishing’s Howard LeWine, M.D., walking around, lying down, and sitting all require different amounts of effort, which will cause the heart to beat at different rates.

Regardless of this change in activity level, a person’s resting heart rate — the number of heart beats per minute at rest — stays consistent over time. For example, a person’s resting heart rate will be consistent each night during sleep, regardless of the activity they engaged in that day.

Heart rate is an important predictor of health. Some people, such as athletes or pregnant women, are expected to have a lower or higher heart rate, respectively. Age and hormonal fluctuations also affect how fast a person’s heart beats.

When an average person’s resting heart rate falls outside the normal range — 60-90 beats per minute — it can signify a serious health problem. Having a high heart rate is called tachycardia, and there are many types of increased heart rates.

Perhaps the most common type of tachycardia is atrial fibrillation, which is caused by irregular electrical impulses in the upper heart chambers. Atrial fibrillation is a sign of weak contractions in the upper chamber of the heart (the atria). Atrial flutter is an associated condition marked by a rapidly beating atria and a normal heart rate.

A high heart rate doesn’t always cause symptoms, and seeking professional medical advice is sometimes the only way to diagnose this condition properly. When symptoms are present, they can include shortness of breath, lightheadedness, rapid pulse, heart palpitations, chest pain, and fainting. If you’re unable to exercise because of these factors, it’s a sign that it’s time to take control of your heart health. So what happens if you don’t intervene?

The Role of Heart Rate in Heart Attack and Disease


Having a high heart rate can affect everyday life by contributing to daytime fatigue, low fitness levels, and obesity. Yet it’s particularly dangerous because it puts people at higher risk for developing heart disease or suffering from additional cardiovascular disorders.

A high heart rate is linked to health issues like heart disease, stroke, and cardiac arrest. Research also shows that having an above-normal heart rate increases a person’s chance of death, regardless of whether they’re physically fit or generally deemed healthy. This study, which measured 3,000 middle-aged men, found that for every additional 10-22 beats per minute, a man’s chance of death increased by 16%.

Causes of High Heart Rate

The most common causes of high heart rate are hypertension (high blood pressure) and coronary artery disease — both of which can be controlled by lifestyle factors. In particular, things like chronic stress and excessive use of caffeine are all modern factors that contribute to high heart rate.

Additional risk factors that elevate resting heart rate include excessive alcohol consumption and alcoholism, taking certain medications, smoking cigarettes, and taking recreational drugs. High blood pressure is another common cause of high heart rate.

Medical professionals have understood the correlation between lifestyle and heart health for quite some time, but recent research shows that high heart rate can be caused by a variety of genetic factors.

For example, a heart study led by cardiologist Pim van der Harst found 64 gene locations that influence heart rate, suggesting that genes and gene location influence both heart rate and life expectancy more than previously thought. Congenital heart defects, which can be caused at birth or after heart surgery, can also cause the heart to beat irregularly.

Diet plays a significant role in high heart rate because the foods we eat affect our blood pressure. Alcohol and stimulants are especially hard on the heart because they cause dehydration and are considered toxic to the body. This means the heart has to work harder to remove them — leading to an increase in heart rate.

Foods high in fat and sugar also cause an increased heart rate, primarily because they contribute to being overweight or obese, which places more pressure on the heart.

Foods That Lower Heart Rate

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Despite the role of chronic and genetic factors in heart health, changing one’s diet to include more healthy foods is the quickest and most effective way a person can achieve a lower heart rate and improve overall healthLowering your heart rate can reduce the risk of heart disease, heart attack, and stroke while helping lower blood pressure. Here are the nutrient-dense foods that lower heart rate, reduce heart disease, and boost longevity.

Whole Grains

Whole grains are an important element of a heart healthy diet and offer many health benefits. A diet high in whole grains has been shown to reduce cholesterol, blood pressure, and blood sugar levels.

Whole grains have also been shown to reduce the risk of stroke, type 2 diabetes, and heart disease — all of which are associated with high heart rate. Whole grains also work to keep you full for longer. This can reduce the risk of overeating to help an overweight person lose extra pounds and reduce excess strain on the heart.

Simple, heart-healthy, whole-grain swaps and substitutes include choosing whole wheat flour instead of refined white flour, oatmeal, bulgur, whole wheat pasta, and barley. They are all examples of healthy whole grains to incorporate into your diet.

Green Vegetables, Leafy Greens, and Fruit

Green vegetables and leafy greens are especially beneficial for cardiovascular health because they contain vitamin K1. Eating high amounts of vitamin K1 can protect against high heart rate and an enlarged heart. It has also been shown to reduce high cholesterol. Fruits and vegetables are low-fat foods that contain fiber, which is known to lower both cholesterol and high blood pressure.

One study found that eating 10 servings of fruit and vegetables a day can lower your risk of cardiovascular disease by 28% while reducing the risk of premature death by 31%. Aside from leafy greens, apples, pears, citrus fruits, cruciferous vegetables, green beans, and peppers were shown to offer the best heart benefits.

Blueberries, which are high in anthocyanins (the phytochemicals that give blueberries their color) have also been shown to improve heart health. Specifically, blueberries have been shown to decrease blood pressure, improve blood vessel function, and reduce the risk of cardiovascular disease.

Omega-3 Fatty Acids


Omega-3s are healthy fats found in a variety of plant foods and fish. Omega-3 fatty acids are one of the best foods to lower heart rate and reduce the risk of cardiac arrest. There are three main types of Omega-3s. These include alpha-linolenic acid (ALA), which is found in plant oils, and eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), both of which are found in fish like salmon, mackerel, and tuna.

Omega-3s keep heart rate low while reducing the risk of irregular heartbeat, slowing down the buildup of artery plaque, and lowering blood pressure. Aside from eating fish, plant foods that contain essential fatty acids include ground flaxseeds, chia seeds, soybeans, and tofu. Walnuts also contain high amounts of Omega-3s, with almonds, macadamia nuts, hazelnuts, and pecans coming in second. Avocado, olives, and olive oil are also known to be high in ALA omega-3s.

Eating for a Healthy Heart

Heart rate plays a vital role in a person’s overall health. While athletes, pregnant women, and people with congenital heart defects are expected to have an abnormal heart rate, people outside of these categories should have a resting heart rate between 60-90 beats per minute. Having a heart rate above this range can put a person at risk for a variety of life-threatening diseases and conditions, including heart disease, heart failure, and heart attack.

Fortunately, eating healthier foods is one of the most effective ways a person can reduce their risk of disease and extend their life expectancy. Leafy greens, fruits, whole grains, and items rich in Omega-3s are all examples of foods that lower heart rate and improve overall quality of life.

Reading time: 4 min

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:

Depressed mood
Lack of motivation
Increased appetite
Carbohydrate cravings
Reduced sex drive
Inability to concentrate

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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.


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.

Reading time: 4 min

What is it?

Heart rate is defined as the number of contractions of the heart, expressed in beats per minute (bpm). The heart rate is a function of local electrical signals in the cardiac cells, neural inputs, and hormonal influence.

Heart rate changes in response to stressors in order to increase circulation of blood, often by increasing cardiac output. This increase in cardiac output helps meet the demands of physiological responses to stress.

Therefore, heart rate can be a valuable metric in understanding the cumulative stress (e.g. emotional and physical stress) that is placed on the body.

How it’s measured

Heart rate can be measured through palpation, electrocardiography (ECG), and photoplethysmography (PPG). Biostrap measures heart rate using PPG, which captures pulse waves of blood flow using red and infrared light. By using the count of pulse waves per unit of time, heart rate in bpm can be obtained.

Heart rate can be measured during activity (active heart rate). However, resting heart rate (RHR) is most often used to clinically assess cardiovascular health, since extra stress on the cardiovascular system is absent. RHR can be subject to acute stress, including observation bias. Therefore, passive collection of RHR through wearables, particularly during sleep, allows for minimizing error that may artificially raise RHR.

Correlation with health conditions

Chronically increased resting heart rate has been correlated with many diseases and their outcomes, particularly hypertension, obesity, cardiovascular diseases, cancer, and metabolic disorders, among others. In many cases, the increased heart rate is not itself a contributor to the disease progression, but rather a signal that there are down-stream effects of the underlying disease.

Acutely increased resting heart rate may be an indication of altered blood flow, reduced plasma volume, psychological stress, activity, infection, and thermal stress. Monitoring heart rate trends can alert when heart rate has changed acutely, but may not be indicative of the cause of the increase. In times where no change in RHR is expected such as during sleep, follow-up evaluation may be warranted.

What is a “normal” range?

<60 bpm = Bradycardia
60-100 bpm = “Normal”
>100 = Tachycardia

A “normal” RHR is considered to be 60-100 beats per minute. Factors that may influence resting heart rate values include:

  • Fitness level
  • Room temperature
  • Body position
  • Emotional stress
  • Body size and/or composition
  • Use of medications

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Interpreting trends

Resting heart rate, measured over time, provides insights into cardiovascular changes in response to lifestyle or disease progression. Since RHR responds relatively quickly to lifestyle changes, tracking resting heart rate over time is recommended in order to monitor positive and negative health adaptations.

Although RHR alone is not enough to diagnose any particular disease, the American Heart Association recommends lowering resting heart rate as much as possible. Exercise training, dietary changes, meditation, and reducing stress are examples of ways to reduce RHR. The decrease in heart rate reflects increased cardiovascular efficiency and decreased systemic stress.

Increases in RHR over time could be an indication of negative cardiovascular changes, and may warrant follow-up testing or lifestyle intervention.


In a clinical study, the Biostrap PPG-based resting heart rate measurement matched within 1 +/- BPM to the reference research grade ECG.

In a small real-world cohort of elderly people, the standalone Fibricheck AF algorithm can accurately detect AF using Wavelet wristband-derived PPG data. Results are comparable to the Alivecor Kardia one-lead ECG device, with an acceptable unclassifiable/bad quality rate. This opens the door for long-term AF screening and monitoring.


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  4. Sneddon G, Mourik R van, Law P, Dur O, Lowe D, Carlin C. P177 Cardiorespiratory physiology remotely monitored via wearable wristband photoplethysmography: feasibility and initial benchmarking. Thorax. 2018;73(Suppl 4):A197–A197. doi:10.1136/thorax-2018-212555.334
  5. Lequeux B, Uzan C, Rehman MB. Does resting heart rate measured by the physician reflect the patient’s true resting heart rate? White-coat heart rate. Indian Heart Journal. 2018;70(1):93–98. doi:10.1016/j.ihj.2017.07.015
  6. Paul Laura, Hastie Claire E., Li Weiling S., Harrow Craig, Muir Scott, Connell John M.C., Dominiczak Anna F., McInnes Gordon T., Padmanabhan Sandosh. Resting Heart Rate Pattern During Follow-Up and Mortality in Hypertensive Patients. Hypertension. 2010;55(2):567–574. doi:10.1161/HYPERTENSIONAHA.109.144808
  7. Aune D, Sen A, ó’Hartaigh B, Janszky I, Romundstad PR, Tonstad S, Vatten LJ. Resting heart rate and the risk of cardiovascular disease, total cancer, and all-cause mortality – A systematic review and dose-response meta-analysis of prospective studies. Nutrition, metabolism, and cardiovascular diseases: NMCD. 2017;27(6):504–517. doi:10.1016/j.numecd.2017.04.004
  8. Lee DH, Park S, Lim SM, Lee MK, Giovannucci EL, Kim JH, Kim SI, Jeon JY. Resting heart rate as a prognostic factor for mortality in patients with breast cancer. Breast Cancer Research and Treatment. 2016;159(2):375–384. doi:10.1007/s10549-016-3938-1
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  10. Jiang X, Liu X, Wu S, Zhang GQ, Peng M, Wu Y, Zheng X, Ruan C, Zhang W. Metabolic syndrome is associated with and predicted by resting heart rate: a cross-sectional and longitudinal study. Heart. 2015;101(1):44–49. doi:10.1136/heartjnl-2014-305685
  11. Lee B-A, Oh D-J. The effects of long-term aerobic exercise on cardiac structure, stroke volume of the left ventricle, and cardiac output. Journal of Exercise Rehabilitation. 2016;12(1):37–41. doi:10.12965/jer.150261
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  13. Reimers AK, Knapp G, Reimers C-D. Effects of Exercise on the Resting Heart Rate: A Systematic Review and Meta-Analysis of Interventional Studies. Journal of Clinical Medicine. 2018;7(12). doi:10.3390/jcm7120503
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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. Biostrap 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.


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


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  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
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  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:
  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:
  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.
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  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
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What is it?

Active heart rate is the rate at which the heart beats during activity or exercise. Heart rate is a highly responsive physiological measure. It is important to note that heart rate is a response variable to many factors. Therefore, the purpose of measuring heart rate is to measure the body’s physiological reaction to the work being performed.

How is it measured?

There are many ways to measure heart rate during physical activity, but some are more reliable than others. The typical ‘gold standard’ method is through electrocardiography, whether 12-lead or single-lead.

Additionally, photoplethysmography, or PPG, can be used to measure pulse waves to obtain heart rate. Due to the nature of different wavelengths utilized during PPG measurements, green light LED has been shown to be best at detecting pulse waveforms during exercise. Red and infrared light are motion intolerant and are not recommended for active heart rate monitoring.

The Biostrap ecosystem contains both a chest-worn ECG-based heart rate monitor as well as a green light PPG sensor worn on the arm. The Biostrap activity HRMs are recommended for use during activity to obtain proper active heart rate. The Biostrap EVO device, equipped with red and infrared PPG does not record during exercise due to motion artifacts; therefore, it’s best utilized for monitoring sleep and recovery metrics captured overnight.

Correlation with health

The use of heart rate during activity and exercise is not recommended for or capable of diagnosing medical conditions. However, heart rate during activity and exercise can provide a lot of information about heart health and performance.

Typically, when examining individuals during exercise, a lower heart rate at an equivalent workload suggests increased cardiovascular health.

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Normal Values

In theory, any value existing between resting heart rate and maximum heart rate, or MHR, are ‘typical’ values for exercising. MHR is considered the upper limit of what your cardiovascular system can handle during physical activity.

To roughly calculate your individual MHR, perform the following equation: 220 minus your age.

Interpreting Trends

In general, performing the same task, an individuals’ heart rate should be lower after cardiovascular fitness adaptations.

However, many variables can influence heart rate during exercise that may alter this trend. Heat, emotional stress, caffeine consumption, movement economy, and dehydration are just some of the factors that can influence day-to-day variation in exercise heart rate at the same workload. Cardiovascular adaptations may decrease the reactivity of heart rate to some of these influences, so a trend toward a lower heart rate should still be observed over time.

Note, this should not be confused with active heart rate during a single exercise bout. Heart rate should remain proportional to intensity, and thus depends on the workload applied to the activity.

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Resting Heart Rate can be a strong indicator of overall health and fitness—here are the essentials on why you should measure it and how to lower it. 

For decades, athletes and trainers have tracked Resting Heart Rate (RHR) as an indicator of athletic performance. However, RHR is an important biometric for everyone to track as it is an indicator of overall health.

Resting Heart Rate is a measure of how many times the heart beats per minute (bpm) while at rest. It is often measured while standing, sitting or lying down; however, it is best to track it passively while sleeping, as acute stress can highly influence it. 

What is a Normal Resting Heart Rate?

The average adult will have an RHR between 60-100 beats per minute, while athletes are likely to rest somewhere between 40-60 bpm. And the lower, the better, as RHR indicates the health of the heart leading to overall longevity, lower risk of heart attack, higher energy levels, metabolic efficiency and athletic endurance.

A resting heart rate below 60 bpm is considered “bradycardia”, but may be common, particularly in individuals with good cardiovascular fitness or individuals taking certain medications. Alternatively, this could be a result of problems with the sinoatrial node or damage to the heart as a result of a cardiovascular event or disease.

A resting heart rate over 100 is considered “tachycardia”, which is often correlated with increased risk for cardiovascular diseases. Increased HR at rest may result in increased work by the heart, as well as indicating an issue with other physiological pathways. If the RHR is closer to 150 bpm or higher, this may be indicative of a condition such as supra-ventricular tachycardia (SVT) requiring medical attention.

What Affects Resting Heart Rate?

  1. Regular Exercise: It’s important that whatever the exercise may be, it should increase heart rate for an extended period of time.
  1. Hydration: Staying hydrated helps with blood viscosity and allows the blood to flow through the body more easily, exerting less stress on the heart.
  2. Sleep: During consistent, uninterrupted sleep, the body rests, repairs, and recovers. Poor or inconsistent sleep can be a large contributor to elevated RHR, putting stress on the heart.
  3. Diet.:A balanced diet full of healthy fats, whole foods, good sources of protein and fiber as well low sodium, inflammatory oils and processed foods help keep the arteries clear, leading to lower RHR and less work for the heart.
  4. Stress: Both acute and chronic stress have a significant impact on the heart by increasing RHR. It’s important to incorporate healthy habits and routines to keep stress and anxiety at bay and help maintain a healthy RHR.
  5. Weight: Extra body weight puts stress on the body and heart. 
  6. Room Temperature: The hotter the body temperature, the faster the heart beats. 
  7. Use of Medications: Treatments for asthma, high blood pressure, thyroid and more can cause changes in heart rate and rhythm. 

Why Measure Resting Heart Rate?

As with most biometrics, Resting Heart Rate offers insights into your overall health, indicating general well-being as well as potential health risks which can inform your daily lifestyle choices.

Tracking consistently over time can be beneficial to watch for changes. As previously mentioned, working to lower your RHR is generally beneficial for overall health. This is because the decrease in heart rate reflects increased cardiovascular efficiency and decreased systemic stress. An increase in RHR over time could be an indication of negative cardiovascular changes, and may warrant follow-up testing or lifestyle intervention.

For athletes, knowing your RHR as well as your Maximum Heart Rate (MHR) can help dictate heart rate based training zones. Spikes in RHR can indicate when overtraining has occurred and an athlete should take a rest day, something else in a training regiment is amiss, or can even indicate an oncoming cold or illness.

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How to Lower RHR

It’s important to maintain an active lifestyle with regular aerobic exercise, a balanced diet, regular sleep and hydration. If your RHR is high, these are the first factors to assess. Beyond the basic lifestyle factors, a few other steps can be taken to significantly lower RHR:

  1. Smoking. Regular smoking increases stress on the heart and the cardiovascular system. Cutting back or eliminating this habit altogether may have a positive impact on not only reducing RHR, but on respiratory health and overall well-being as well.
  2. Manage Weight. Maintaining a healthy weight promotes increased metabolic and energy efficiency and decreases strain on the heart; hence lowering RHR.
  3. Meditation and breathwork. Controlled, long, and slow breathing can help regulate your heart rate and over time works to decrease RHR as well. 

Resting Heart Rate is an important measure of overall wellness for not only athletes but for anyone who wants to optimize their lifestyle. At Biostrap, we’re dedicated to putting you in control of your health by measuring biometrics at clinical-grade accuracy, so you can track and improve your performance and well-being better than ever.

Utilizing proprietary red and infrared photoplethysmography (PPG) sensors, Biostrap’s wrist-worn device captures high-integrity biometric measurements, including RHR, which have been successfully compared to gold standard medical devices.

We believe that the circumstances in which relevant biometrics are captured matter as well. Thus, our focus on nocturnal data collection. Sleep is when the body recovers from and adapts to daily stressors, which then dictates your resilience, recovery, and readiness to perform the following day. Measuring nocturnal RHR reflects some of these changes, providing you with the ultimate insight into how your daily choices impact your physical and mental health, and performance.

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There are a number of metrics we can use to get a snapshot of our health and well-being. From blood pressure to heart rate, doctors and researchers are more interested in our physiological data than ever before. 

There is one marker for resilience and well-being that researchers have just begun to utilize over the past two decades. It’s called heart rate variability, or HRV. This metric, once measured primarily in athletes and those with abnormal heart rhythms, has since become a key piece of data for individuals wanting insight into the state of their physiology and nervous system.

So what exactly is heart rate variability? How do we measure it? And what can it tell us about our overall health? Let’s break down the intricacies of this emerging physiological measurement.

What Is Heart Rate Variability?

Heart rate variability, or HRV for short, is a measure of the time between each heartbeat. 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. 

Regulated by a fundamental part of our nervous system called the autonomic nervous system (ANS), HRV is one of many functions that occurs without us even having to think about it. HRV has been shown to correlate with emotional and physical stress, sleep, and disease making it a common method for assessing the overall physiological state and the rate of adaptation to stressors. 

Generally, the higher the HRV the better, as high stress and poorer health outcomes have been associated with low values of HRV.

How Do We Measure Heart Rate Variability?

HRV can be measured by 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. More complex measures of HRV, including frequency domain analysis, can be used to get further information out of heart rate patterns and the state of one’s nervous system.

What Is a Normal Heart Rate Variability?

HRV has a large individual component that has yet to be understood clinically, and therefore is more often used to assess changes in health over time. HRV can fluctuate day-to-day based on exposure to stress, sleep quality, diet, exercise, and more. 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, but the inter-subject variability tends to be too high to suggest proper normative ranges.

Focusing On Trends

As previously mentioned, HRV is difficult to interpret and generally nonspecific using data 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 (coefficient of variation, CV%). The increase in HRV itself will not reduce risk and improve health over the long term, but rather, it reflects positive adaptations in an individual’s physiology.

For example, if we’re incorporating exercise or meditation into our daily routine, HRV should steadily increase. A downward trend, on the other hand, may be indicative of overtraining, poor sleep, illness, bad eating habits, increased exposure to stress, or failure to hydrate.

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What Factors Influence Heart Rate Variability?

Heart rate variability can be influenced by training, lifestyle, and biological factors.

Training factors that influence HRV include the intensity of a workout, exposure to unfamiliar stimuli, training load, and proper balance between rest days and training days. 

Lifestyle factors that influence HRV include diet and nutrition, stress, sleep habits, and alcohol consumption. Leading a healthy lifestyle that focuses on proper diet and physical fitness, while paying attention to mental health, is a valuable means of improving HRV.

Finally, biological factors such as age, gender, genetics, and health conditions can influence HRV as well. As we age, our HRV tends to decline, and men often have higher HRV than women. Genetics and health conditions such as cardiovascular disease are additional factors that may influence our heart’s ability to operate normally.

Should We Focus on Heart Rate Variability?

Measuring heart rate variability is a valuable form of analysis to monitor healthy individuals or to identify those who should seek improvement. The amount of information we get from HRV is making it a popular health data to assess physiological state, overall well-being and stress adaptation. You can track your HRV with clinical reliability with the Biostrap wrist-worn device and keep an eye on your nocturnal HRV as well as weekly, monthly and yearly trends. 

Reading time: 5 min

Do you know your sleeping heart rate, in other words nocturnal heart rate? If not, it might be time to find out. Several clinical studies have shown that resting heart rate is a key indicator of health, wellness, and longevity. Monitoring changes in your resting heart rate over time can also provide meaningful insight into changes in health.

Understanding your nocturnal heart rate is also important for determining your target heart rate zones, which can guide you to peak athletic performance. Here’s everything you need to know about your nocturnal heart rate — and how to improve it.

What Is Resting Heart Rate?

Heart rate is defined as the number of contractions of the heart, expressed in beats per minute (bpm). Heart rate can be measured during activity (active heart rate), but is most often clinically assessed at rest in the absence of extraneous stress and other factors. 

Resting heart rate is utilized to evaluate an individual’s cardiovascular health and function. While most healthy adults have a resting heart rate between 60 and 80 bpm, factors such as fitness level, body composition, room temperature, body position, stress, and use of certain medications can affect heart rate. 

‘Low’ Resting Heart Rate

A resting heart rate below 60 bpm is considered “bradycardia”, but may be common in individuals with good cardiovascular fitness or individuals taking certain medications. According to Dr. Jason Wasfy at Massachusetts General Hospital Heart Center. “In certain cases, a lower resting heart rate can mean a higher degree of physical fitness, which is associated with reduced rates of cardiac events like heart attacks.” In the case of individuals with good cardiovascular fitness, the stroke volume of the left ventricle is increased, meaning the heart rate may decrease while still maintaining adequate cardiac output.

In other cases, having a low resting heart rate could be indicative of an underlying health concern. According to the American Heart Association, bradycardia can lead to symptoms including lightheadedness, weakness, confusion, fatigue, and diminished exercise performance. Symptomatic bradycardia may indicate that an individual should seek immediate medical advice.

‘High’ Resting Heart Rate

A resting heart rate greater than 100 bpm is considered “tachycardia”, which is often correlated with increased risk of cardiovascular diseases due to chronic additional work placed on the heart. According to Healthline, tachycardia can be caused by anxiety, fatigue, electrolyte imbalance, overconsumption of alcohol or caffeine, drug use, or other underlying medical conditions.

The negative effects of a high resting heart rate were demonstrated in a study conducted by Copenhagen University Hospital. This study found a strong correlation between patients with higher resting heart rates (RHR) and risk of death, specifically a 10% increase risk of mortality for every additional 10 bpm.

Nocturnal Heart Rate

Unlike the traditional resting heart rate values obtained in normal clinical practice, nocturnal heart rate is obtained during sleep. It is normal for nocturnal heart rate values to be slightly lower than waking resting heart rate due to minimal factors impacting the value, and therefore represents a more valuable tool for trending over time to gain valuable insight into changes in your health and performance.

Your Heart Rate During Sleep and Sleep Apnea

Obstructive Sleep Apnea (OSA) is one of the most prevalent sleep disorders in the US with greater than 25 million confirmed cases and research suggesting a high prevalence of undiagnosed patients. During an apneic event, individuals experience a partial or complete collapse of their airway depriving them of oxygen for several seconds. In addition to sleep disturbances, this can lead to an acute change in heart rate and oxygen saturation. 

So what are some indications that you may have OSA? Kathleen Davis states that loud snoring, accompanied by restless sleep and daytime fatigue, could indicate the presence of sleep apnea.

According to Medline Plus, this sleep disorder can cause pauses in breathing that can last from a few seconds to several minutes, with a transition back to normal breathing marked by a gasp, snort or choke, which may startle the sleeper (and often their partner awake). These sleep disruptions have been credited for symptoms of daytime tiredness, even after a full night’s sleep, in patients with sleep apnea.

Fatigue and frustration aside, sleep apnea also affects nocturnal heart rate. “When you stop breathing while you sleep, your heart rate drops, and then your involuntary reflexes make you startle into a micro-arousal, which causes your heart rate to accelerate quickly,” says The National Sleep Foundation. In addition to elevated blood pressure, this rapid decrease and increase in heart rate may lead to an irregular heart rhythm, or cardiac arrhythmia.

Irregular Heart Rhythms and Risks

While irregular heartbeats can be caused by a variety of factors, more studies are revealing the direct relationship between cardiac arrhythmias and sleep disorders such as OSA. One of the most common types of arrhythmia, atrial fibrillation (AF) is marked by irregular contractions of the upper heart chambers.

According to a clinical study conducted at the University of Ottawa, researchers found that OSA may increase the risk of atrial fibrillation with secondary symptoms including palpitations, lightheadedness, weakness, fatigue, shortness of breath, and chest pain. Atrial fibrillation is also associated with stroke, heart failure, and other cardiovascular conditions. 

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Measuring Heart Rate

Maintaining a healthy cardiorespiratory system is important – but what are some ways you can measure your resting and nocturnal heart rate?

This can be accomplished with the old fashioned method of measuring your pulse rate with your fingertips placed on your wrist – just make sure you’ve had ample time to rest after a stressful event or exercise, and under controlled conditions. While this is cost effective (free) and can be done anywhere, there may be issues associated with reliability and these measurements cannot feasibly be performed during sleep. 

Electrocardiograms (ECG) are another method that are commonly used in clinical practice to measure electrical conductivity of the heart to measure its rate of contractions. While this is a relatively quick and very precise method for measuring heart rate and other important aspects of cardiovascular function, the most reliable form (12-lead ECG) is typically not available for the general population to track consistently over time.

Which brings us to perhaps the best solution for measuring resting and nocturnal heart rate in terms of cost, reliability, and availability- wearable technology. These cost-effective technologies unlock the ability for all to consistently track and monitor their heart rate over time to gain valuable insight into cardiovascular function. However, it is important that consumers seek a wearable technology that has proven accuracy compared to the gold standard ECG devices.

Improving Your Heart Rate

When it comes to improving your heart rate, maintaining a healthy body composition and regularly engaging in physical activity are key. According to Harvard Health Publishing, exercising within target heart rate zones can help to strengthen the heart and improve aerobic capacity. To safely and effectively train with heart rate zones, it is encouraged that individuals first seek clearance from their healthcare provider, and consider training under the guidance of a qualified fitness professional. 

Improve Your Nocturnal Heart Rate, Reduce Your Risks

Nocturnal heart rate is an important metric that helps quantify the efficiency of your cardiovascular system. Tracking your nocturnal heart rate over time and gaining knowledge of how certain behaviors are impacting trends can help develop an individualized lifestyle plan on the journey to optimal health and life performance.

Additionally, tracking heart rate may provide valuable insight or early detection of health conditions such as sleep disorders that can not impact your sleep quality, but may facilitate or exacerbate other health-related issues.

Maintaining positive habits such as consistently engaging in physical activity may help strengthen the body’s most vital muscle- the heart. 

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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 Biostrap

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.

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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 Biostrap.

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.

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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