Is Heart Rate Variability Really a Useful Metric?

The Caeden Sona with Valencell technology tracks HRV.
The Caeden Sona with Valencell technology tracks HRV.

Heart rate variability (HRV) has recently become a popular biomarker with wearable manufacturers. Perceived as a promising health measurement among some researchers, this quantitative marker tells us about the functioning of our autonomic nervous system. It is believed that measuring the time variation in the intervals between adjacent heartbeats might be an indicator of general health and well-being.

Put simply, by monitoring one’s HRV, the promise is a user can get insight into the functioning of his or her nervous system and predict (or avoid) various health risks.

HRV is becoming more popular among athletes as well as the general public. Systems such as BioForce and ithlete have further popularized its use and enabled people to relatively easily measure their HRV. Also, many free applications for Android and iOS are now available, which can be linked to existing heart rate monitors. People often decide on different ways, frequencies, and durations of testing HRV, and they frequently report positive experiences. Some athletes also use their HRV scores as guidelines for their training and resting periods.

But, is measuring HRV really as straightforward as it seems?

More Complex than Generally Appreciated

Although HRV is indeed a useful metric that can provide a lot of information on health, body recovery and risk factors, it might not always be fully understood.

Research on HRV is ongoing and many developments have been made since 1965 when it first started being recognized as an important health metric.

The European Society of Cardiology and the North American Society of Pacing and Electrophysiology felt it necessarily to assemble a task force that would develop some standards and recommendations regarding HRV measurement and equipment that is commercially used.

In their report, they emphasize that there are many different measures of HRV. Therefore, potential for wrong interpretations or erroneous estimations exists.

For instance, HRV can be recorded over short or long time periods. Short-term measurement is more commonly used due to practical reasons. However, long-term recordings might be a better option in certain cases, or when specific conditions exist. A study published in the International Heart Journal showed that although there was a correlation between the 24-hour and 5-minute HRV, it was not strong in all the domains that were measured. Nonetheless, according to the European Society of Cardiology and the North American Society of Pacing and Electrophysiology, both “short-term 5-minute recordings and nominal 24-hour long-term recordings appear to be appropriate options” when choosing the duration of testing.

Dr. Steven LeBoeuf is president and co-founder of Valencell, a company that has pioneered some of the technology that tracks HRV. According to LeBoeuf, “In terms of technology, HRV is an ancient, yet powerful tool for assessing overall stress and health, and with the recent advent of accurate biometric wearables (in popular form-factors such as wristbands and earbuds), HRV will soon be hitting the mainstream.

However, it's important to remember that all HRV assessments require the appropriate context in order to make a meaningful assessment. For example, we identified atrial fibrillation in one participant during our HRV demo at CES 2016, but that assessment required knowing the person's activity status in order to make the diagnosis truly meaningful.”

A Counterintuitive Measurement

Initially, scientists believed that the more stable and static the body, the better. This assumption has now been updated. It appears more likely that the optimal state of our bodies involves constant balancing and variation to meet current needs and demands that are placed on us.

The same goes for the heart — it should not be beating monotonously. It is expected that the normal resting heart rhythm should be highly variable and inconsistent.

So, contrary to what one might find normal, a high HRV value is what is actually desired. It suggests that our parasympathetic nervous system, which is associated with a more relaxed and functional state of being, is in a dominant position. In contrast, low HRV indicates the dominance of the sympathetic nervous system, which is responsible for the fight or flight reactions. Low HRV is often detected in patients who have had heart attacks and has been associated with higher mortality. High HRV, on the other hand, can suggest a better chance of longevity and healthy existence for years to come. That said, there should not be excessive variability in heart rhythms either. According to Rollin McCraty and Fred Shaffer, authors of the article on the importance of heart rate variability published in Global Advances in Health and Medicine, too much variability can become detrimental to health. Therefore, endlessly increasing your HRV should possibly not always be the goal.

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