Heart Rate Monitoring in the Age of Wearables

Written by Brooks Canavesi on October 4, 2018. Posted in Blog, IoT, Mobile App Development, Technology trends, Uncategorized

You don’t have to be a fitness fanatic to monitor your heart rate. This useful piece of data is an important marker of cardiovascular health and monitoring how it changes over time can help you maintain a healthy lifestyle and stay within the recommended resting heart rate (RHR) range for adults, which ranges from 60 to 100 beats per minute. “A high RHR could be a sign of an increased risk of cardiac risk in some situations, as the more beats your heart has to take eventually takes a toll on its overall function,” says Dr. Jason Wasfy, director of quality and analytics at Harvard-affiliated Massachusetts General Hospital Heart Center. According to a 2013 study published in the journal Heart tracked the cardiovascular health of about 3,000 men, even a slightly higher RHR can double the risk of premature death. Fortunately, we live in the age of wearables, and it has never been easier to monitor heart rate in all real-life situations. Modern wearables make heart rate monitoring convenient, affordable, and sometimes even fun. But can relatively inexpensive gadgets from young tech companies produce reliable heart rate data? Let’s find out the answer.

Multiple Options

There are two main types of modern wearables that can be used for heart rate monitoring: chest straps and wrist devices. Each of these two types uses a completely different technology to measure heart rate, and each is suitable for different applications.

Chest Straps

Heart rate monitoring chest straps, such as the Polar H10, have been around for a while, but they’ve never looked as sleek and haven’t been as feature-packed as they are today. Chest straps measure heart rate using a processed called electrocardiography (ECG or EKG). The same processed is used by heart rate monitors in hospitals, and it records the electrical activity of the heart over a period of time using electrodes placed over the skin. While ECG machines in hospitals use multiple electrodes placed on different spots on the chest, chest straps typically have only one or two electrodes placed either underneath the breastbone or on the inner portion of the rib cage. Even with only one or two electrodes, chest straps produce highly accurate data, which has made them the favorite heart rate monitoring wearable of serious athletes. The biggest downside of chest straps is how uncomfortable they can be after a while. Chest straps are designed to stay in place during strenuous physical activity, which means they are as tight as necessary to ensure they won’t move out of place.

Wrist Devices

On the other hand, wrist devices with heart rate monitoring capabilities are just as comfortable as traditional watches, so it’s easy to wear them all day long, even during sleep, without any discomfort. Unlike chest straps, wrist devices measure heart rate using a processed called photoplethysmography (PPG). “PPG is a simple and low-cost optical technique that can be used to detect blood volume changes in the microvascular bed of tissue. It is often used non-invasively to make measurements at the skin surface,” explains Dr. John Allen, lead clinical scientist and honorary reader in microcirculation and vascular optics at Freeman Hospital in the UK. In other words, wrist devices, such as the Fitbit Charge 3, use optical sensors to see the blood pulsing through veins. Some manufacturers of heart rate monitoring wrist devices claim that their products offer the same accuracy as leading chest straps, but many experts find this hard to believe. The good news is that there’s now a growing body of scientific research that can help us decide whether wrist devices are useful health and fitness tools or just gimmicks that produce inaccurate data and mislead their users.

Trusting the Numbers

A group of scientists from the University of Louisville conducted a study to compare the average heart rate readings of two different heart rate technologies (PPG vs. ECG) after an interval style cardio-based workout. After conducting a total of 30 trials, the scientists found no significant difference between the two technologies. A difference of plus or minus 5 beats per minutes appeared only around 155–160 beats per minute, with ECG being more accurate. This means that the only users of wearable heart rate monitoring devices who might benefit from ECG technology are committed athletes who frequently push their heart rate to over 160 beats per minute. “One potential cause for the inaccuracies could exist within how PPG technology works. LED lights are pulsed into the skin and are reflected to the sensor by the capillaries. Therefore, the LED rate could be an issue. If light is not being sent fast enough, and the refracted light gets absorbed or delayed in any way, then PPG would indicate a lower HR, which is what was observed around the 155 – 160 bpm thresholds,” the researchers commented. “A second potential cause for inaccuracies lies within the workout itself. The workout involved running, which has been noted to potentially lead to HR inaccuracies within PPG algorithms.” As accurate as modern wrist devices are, they are not intended to match medical devices or scientific measurement devices. Most manufacturers of fitness-oriented heart rate monitors even explicitly state that their products are not medical devices and are intended for recreational purposes only. When used with this in mind, wrist devices provide a very convenient way how to monitor heart rate throughout the day.

Conclusion

Medical professionals and even health and fitness experts are preaching the benefits of heart rate monitoring, and the wearables industry has a whole range of heart rate monitors that allow anyone to stay on top of this critical marker of cardiovascular health. In recent years, researchers have been able to confirm that wrist devices are just as accurate as chest bands for regular applications, but serious athletes should still stick with ECG technology.