Have you ever wondered what the health impact of a stressful day was? Will you perform well during your long run or training session tomorrow morning? Is there anything you can do today that would improve your ability to have a better day tomorrow? HRV may be a piece of data that could help you answer these questions.
What is HRV?
HRV is simply a measure of the variation in time between each heartbeat, also known as the RR interval. This variation is controlled by a primitive part of the nervous system called the autonomic nervous system (ANS). The ANS works regardless of our desire and regulates, among other things, our heart rate, blood pressure, breathing, and digestion. The ANS is subdivided into two large components, the sympathetic and the parasympathetic nervous system, also known as the fight-or-flight mechanism and the relaxation response.
The brain is constantly processing information in a region called the hypothalamus. The hypothalamus, through the ANS, sends signals to the rest of the body either to stimulate or to relax different functions. It responds not only to a poor night of sleep, or that sour interaction with your boss, but also to the exciting news that you got engaged, or to that delicious healthy meal you had for lunch. Our body handles all kinds of stimuli and life goes on. However, if we have persistent instigators such as stress, poor sleep, unhealthy diet, dysfunctional relationships, isolation or solitude, and lack of exercise, this balance may be disrupted, and your fight-or-flight response can shift into overdrive.
Why Monitor HRV?
HRV is a noninvasive way to identify these ANS imbalances. If a person’s system is in more of a fight-or-flight mode, the variation between subsequent heartbeats is low. If one is in a more relaxed state, the variation between beats is high. In other words, the healthier the ANS the faster you are able to switch gears, showing more resilience and flexibility. Over the past few decades, research has shown a relationship between low HRV and worsening depression or anxiety. A low HRV is even associated with an increased risk of death and cardiovascular disease (Buccelletti et al., 2009; Tsuji et al., 1994).
People who have a high HRV may have greater cardiovascular fitness and be more resilient to stress. HRV may also provide personal feedback about your lifestyle and help motivate those who are considering taking steps toward a healthier life. It is fascinating to see how HRV changes as you incorporate more mindfulness, meditation, sleep, and especially physical activity into your life. For those who love data and numbers, this can be a convenient way to track how your nervous system is reacting not only to the environment, but also to your emotions, thoughts, and feelings.
The gold standard to measure HRV is to analyze a long strip of an electrocardiogram, the test that occurs frequently in medical offices where wires are attached to the chest. But over the past few years, several companies have created heart rate monitors that sync with apps that do something similar. The accuracy of these methods is still under scrutiny, but the technology is improving substantially. A word of caution is that there are no agencies regulating these devices, thus they may not be as accurate as claimed to be. With that said, the easiest and cheapest way to check HRV is to buy a chest strap heart monitor (e.g., Polar H10) and download a free app (e.g., Elite HRV) to analyze the data. The chest strap monitor tends to be more accurate than wrist or finger devices. Check your HRV in the mornings after you wake up, a few times a week, and track for changes as you incorporate healthier interventions.
Tracking HRV may be a great tool to motivate behavioral change for some. HRV measurements can help create more awareness of how you live and think, and how your behavior affects your nervous system and bodily functions. While it obviously can’t help you avoid stress, it could help you understand how to respond to stress in a healthier way. While there are questions about measurement accuracy and reliability, if you decide to use HRV as another piece of data, do not get too confident if you have a high HRV, or too scared if your HRV is low. Think of HRV as a preventive tool, a visual insight into the most primitive part of your brain.
Far from the metronome we might assume it to be, the healthiest heart beat follows a fractal pattern, with varying lengths of time separating each pulse (Tapanainen et al., 2002; Yaniv, Y., Lyashkov, A. E., Lakatta, E. G., 2013). A higher HRV suggests a relaxed, low-stress physiological milieu, while a lower HRV indicates a need for recovery, rest, and sleep. Therefore, in order to increase HRV, generally speaking, a more relaxed, low-stress environment is desirable. While there are a number of ways to reduce stress and increase relaxation, here are some examples that have been observed to increase HRV:
The only other strategy that has so many research-baked benefits for longevity is long-term calorie restriction, which requires a significant long-term reduction in the amount of food you eat so that you are essentially living on the brink of starvation. Compliance with calorie-restricted diets is abysmal. Fortunately, there are many ways to fast, and there is likely a form of fasting out there that you will be able to tolerate and incorporate into your life. It's important for you to remember that fasting can provide nearly identical benefits without the pain, suffering, and compliance challenges of calorie restriction.
Instead of regulating how much food you eat, as with long-term calorie restriction, you only need to modify when you eat - and of course wisely choose the foods you do eat.Simply cycling between periods of eating and fasting on a daily, weekly, or monthly schedule has been shown to provide many of the same benefits as long-term calorie restriction. Choosing when to eat and when to fast in this way is known as "intermittent fasting."
"Don't eat less - eat less often."
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