Fitness Trackers: Do Their Heart Rate Monitors Really Work?

Which fitness trackers worked, and which didn't- the answer might surprise you.

A new study has found that wrist-worn heart monitors are less accurate than the old-fashioned chest strap.

Researchers at the Cleveland Clinic fitted 50 different volunteers (mostly women Cleveland Clinic employees who were healthy and in pretty good shape) with an EKG, a chest strap monitor, and an armband along with two of four different wearable fitness trackers (the brands tested were the Fitbit Blaze, the Garmin Forerunner 235, the TomTom SparkCardio, and the Apple Watch) to find out how accurately each tracker measured heart rate after various types of exercise.

After testing the volunteers’ heart rates after 18 minutes of light, moderate, and intense exercise on a stationary bike, treadmill, and elliptical (both with and without arm levers), the researchers found that the chest strap monitor most closely matched the readings from the EKG, while the wrist-worn trackers didn’t match the EKG very well at all, especially when it came to the elliptical and bike. However, the researchers noted that the watch-style trackers were fairly accurate when it came to the treadmill. The researchers also found that as exercise intensity increased, the accuracy of the wrist-worn trackers dropped.

Related: Fitter & Healthier With Wearable Tech

One exception: the Apple Watch was the only wearable fitness tracker that provided an accurate heart rate reading when the participants switched from the elliptical with arm levers to one without arm levers, and it was the only tracker whose accuracy didn’t decrease as the workouts increased.

Why all the variation? The traditional chest strap, much like an EKG, measures the electrical activity of your heart, while the wrist-worn trackers use light or optical sensing to measure blood flow. The problem with the wrist trackers is that factors like sweating and poor fit can all lead to an inaccurate reading of blood flow.

The researchers say that more, and larger, studies need to be done, but in the meantime, if you have a heart problem that makes tracking your heart rate important, you might want to stick with a traditional chest strap while working out.

Related: Why Fitness Trackers Will Stay On Your Wrist

By Alanna Nunez

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