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Did you know that it is thought that HRV is the only way to measure how our bodies respond to stress unconsciously?

I have a special interest in heart rate/HRV and the data from wearables and smart watches. I’m no cardiovascular specialist but did do some research for a paper I had to write and thought I would simplify it for the purpose of this blog 😊

What is HRV?
Heart rate variability is the variation in time between heart beats i.e. beat to beat fluctuations in the rhythm of the heart. The variation should be constant and is measured in milliseconds. This is regulated by the Autonomic Nervous System (ANS) and can be used as a reliable indicator of our state of health. A higher HRV is associated with “rest and digest” i.e. parasympathetic state and lower HRV with stress or illness. HRV is unique to every individual. HRV can be said to be related to the overall state of the central nervous system. We can’t measure stress or ANS function, so variability gives us a good indication as it is the only figure of measurement available at present.

How is HRV measured?
HRV can be measured with ECG devices and modern computer technology including smart watches and wearables (Garmin, Whoop, Oura Ring).
The best way to determine your normal level is to use a wearable that measures your HRV in a controlled setting, like sleep, and establishes a baseline over a few weeks. This baseline range will never change.

What is a wearable?
Compact electronic and computing devices that can be worn on an individuals’ body. They have empowered individuals to monitor, store, and transfer personal information about health, physical activity, and surrounding such as body temperature, blood pressure, heart rate, calories intake, calories burned, steps counters, sleep pattern, location etc. Examples are, smart watches such as Garmin, Apple Polar, Suunto and other wearables such as the Whoop band or Oura ring. They are very popular amongst active individuals, as many of the latest devices can also help track recovery, fitness and HRV. Giving an indication of the body’s ability to handle further stress (such as being able to increase training load, frequency, or intensity) or whether the body needs more time to recover (sickness, over trained, needing more sleep). Therefore, it is safe to say that athletes may also be able to use their HRV to optimize their training, performance and endurance.

What is a good HRV?
A normal HRV for adults can range anywhere from below 20 to over 200 milliseconds.

HRV and the Nervous System?
The hypothalamus, a small region located above the brain stem, constantly processes information and transmits signals to the rest of the body through the ANS. The signals can either relax or stimulate different functions in your body, including your HRV. HRV is the most effective way of estimating your ANS balance, as it directly impacts your heart’s activity. Therefore, HRV reflects the balance between the parasympathetic nervous system (PNS or rest-and-digest branch) and the sympathetic nervous system (SNS or fight-or-flight branch). By these two being in balance, it helps you to respond to daily stressors and regulate some of your body’s most important systems, including heart rate, respiration, and digestion. PNS regulates your heart to slow down, making room for variability between beats (higher HRV). Your SNS system tells your heart to speed up, limiting space for variability (lower HRV) (5).

  • Higher HRV is associated with rest-and-digest, general fitness, and good recovery.
  • Lower HRV is associated with fight-or-flight responses, stress, illness, or over training.

What affects HRV and why is it good to check it?

Being aware of your HRV allows you to identify ANS imbalances, it can help you to understand how to respond to stress in a healthier way. It may increase your awareness of your lifestyle habits.  It can detect your reaction to the environment, and your emotions. HRV measurements can also help increase your awareness of how you live and think, and how your behaviour affects your nervous system and bodily functions.

Various medications and substances can influence the autonomic nervous system and, consequently, HRV. For instance, stimulants like caffeine or certain drugs may increase sympathetic activity and reduce HRV. Alcohol also has a massive affect on HRV.

Many athletes tend to have greater degrees of cardiovascular fitness since exercise training improves the heart’s efficiency. Because of this, they also tend to have higher HRVs. However, a higher HRV doesn’t always mean better heart health. For example, arrhythmias, which are potentially serious irregular heartbeats, can cause high HRV.

Generally, a prolonged reduced HRV may be associated with an increased risk of death, arrhythmias, and heart attack.

HRV has also been found to be lower in people who suffer with psychiatric diseases (anxiety disorder, panic attacks, posttraumatic stress disorders, epilepsy, anorexia, borderline personality disorder, and depression).

A single nightly HRV reading can provide insights, like:

  • A higher HRV score that reflects a rest day, cool bedroom, or “mindful” low/moderate intensity activities such as hiking or yoga.
  • A lower HRV score that results from dehydration, alcohol, late meal or exercise, illness, a high-intensity workout, acute stress, or a hot bedroom.

Exercising is still the best way to improve heart rate variability, and it can pay off in as little as two months. Moderate exercise for 150 minutes a week total should be the goal. Do cardio, resistance training, or HIIT workouts, whatever you love enough to do consistently.

How can you improve your HRV?

  • Exercise and proper training. Regular exercise is one of the most effective ways to improve HRV. However, athletes should avoid over training, however, since strenuous exercise lowers HRV in the short term. Therefore, it is important not to put the body under too much strain without allowing it enough time to recuperate.
  • Eat healthy food at the right times. While eating a nutritious diet is good for your HRV, it’s also important to keep in mind that having regular eating patterns will also help your circadian rhythm. Not eating 3-4 hours before bedtime can enhance the quality of your sleep by enabling your body to focus on other restorative processes instead of digesting food.
  • Stay hydrated. The amount of blood in your body is determined by your level of hydration. So the more liquid in your system, the easier it is for your blood to circulate throughout your body and supply it with oxygen and nutrients. Make it a goal to drink an ounce of water per pound of body weight every day.
  • Avoid alcohol. According to some studies, drinking alcohol can lower HRV by an average of 22 milliseconds the following day, and lingering effects of alcohol in your system may even reduce your HRV for up to 4-5 days.
  • Get good, consistent sleep. In addition to getting enough quality sleep, it’s also important to maintain a consistent sleep schedule. Consistent sleep helps you have more REM and deep sleep, thus improving your circadian rhythm and increasing your HRV.
  • Be exposed to natural light. Biological processes that regulate sleep-wake times, energy levels, and hormone synthesis are triggered when you are outside in natural sunlight, especially in the morning.
  • Take a cold shower. The vagus nerve, which activates the parasympathetic branch of your ANS and controls HRV, is stimulated by exposing your body to low temperatures for brief periods of time (cold showers, ice baths, etc.)
  • Breathing exercises. Slow, controlled breathing has been shown to boost HRV and help fight stress, which can decrease HRV.
  • Practice mindfulness. For some people, practicing meditation or other mindfulness techniques can have a positive impact on HRV, helping with relaxation and stress reduction.

I have always been fascinated with HRV since suffering with a heart condition at the age of 29. I am 100% tuned in with mine and believe that if more people were too, it could greatly benefit their overall health and wellness. As discussed above, awareness of your HRV can help in so many ways. Predicting illness and over training, indicating recovery, detecting the affect of stress on your nervous system etc. As a health care practitioner, being able to have access to this data when working with a patient could be greatly beneficial. You could track nervous system responses to treatment and also see whether certain lifestyle factors are affecting a patient’s well being, as well as holding them back from reaching their true health and fitness potentials.

It may also be a very useful tool when dealing with pain and therapy response to pain. If a patient is not recovering as you may expect or not responding to treatment, you could look at their HRV (if measured), as a tool to look into their nervous system. As mentioned above, if someone’s nervous system is stressed, it may contribute to delayed healing, therefore a longer recovery time will be needed towards a patient’s function and/or pain.
References on request

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