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), 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.

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: 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:

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.

Reading time: 5 min

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.

Biostrap

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. 

References

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  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
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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
  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
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  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.
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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. 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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