Fitness trackers are all the rage these days. Everyone seems to be wearing one—from an Apple watch, to a FitBit, to a Polar GPS watch, or simply an app on a smartphone. You can’t walk into a gym, yoga class, or CrossFit box without seeing at least half a dozen of them.
The effectiveness of fitness trackers has been debated in the past. Some studies have indicated they aren’t useful for weight loss, while others have shown they can make you more conscientious during the day. In the end, if they help you to improve your performance at the gym or while running, they’re worth it.
The addition of heart rate data is used by many people to estimate energy expenditure, which can be a huge help for those chasing body composition goals. But how accurate is the data your device is giving you?
A Fitness Tracker Showdown
There are two basic heart rate monitor designs: one uses a strap worn around your chest, and the other is a wristwatch-style tracker. A study conducted by the American College of Cardiology tested each to determine which was more effective. Fifty people volunteered for the study, roughly half men and half women. The participants were all fitted with an EKG, a chest monitor (strap), and an armband (Scosche Rhythm+). They were then given two of the other devices tested: the Apple Watch, TomTom Spark Cardio, Garmin Forerunner 235, and Fitbit Blaze. The volunteers were then put through their paces in a moderate, mild, and vigorous workout.
Throughout, the heart rate data from the EKG, chest strap, armband, and the various wristwatch trackers were recorded. As the volunteers ran, cycled, and trained on the elliptical, the researchers monitored the performance of the various fitness trackers to determine which was the most accurate (results closest to the EKG).
The chest strap proved the most accurate of the heartrate-measuring devices, with a 99.6% accuracy. The wrist-worn devices, however, proved to be far less accurate. The highest accuracy was 92%, but some devices scored as low as 67%. The errors ranged anywhere from 15 to 34 BPMs, depending on the intensity of the activity. The Apple watch proved the most accurate of all the wrist-worn devices, regardless of the type of exercise. The higher the intensity, the less accurate the rest of the devices become.
The concept of the wrist-worn devices are the same as the chest strap, but the difference is that the fitness wristbands are measuring the downstream flow of blood, rather than measuring the beats of the heart right at the source. If you’re looking for maximum accuracy, the chest strap is the least likely to be thrown off by sweat, wrist position, or even silly things like skin pigmentation.
