Accuracy of commercially available heart rate monitors in athletes: a prospective study

Endurance athletes, particularly competitive runners, are using wrist worn devices with the heart rate (HR) feature to guide their training. However, few studies have assessed the effectiveness of these at high levels of exertion. The purpose of this study was to measure the accuracy of the HR monitor feature in four watches at six different treadmill speeds. This prospective study recruited 50 healthy, athletic adults (68% male, mean age of 29, and mean BMI of 23 kg/m²). All subjects wore a three lead ECG and Polar H7 chest strap monitor and two different randomly assigned wrist worn HR monitors. These included the Apple Watch III, Fitbit Iconic, Garmin Vivosmart HR, and Tom Tom Spark 3. Once all devices were on, they were asked to run at the following speeds on a treadmill (in mph): 4, 5, 6, 7, 8, and 9 for two min. HR was assessed on all devices and agreement among measurements determined with Lin's concordance correlation coefficient (CCC) (r_c). The Polar H7 chest strap had the greatest agreement with the ECG (r_c=98). This was followed by the Apple Watch III (r_c=96). The Fitbit Iconic, Garmin Vivosmart HR, and Tom Tom Spark 3 all had the same level of agreement (r_c=89). The Polar H7 chest strap was the most accurate, and the Apple Watch was superior among watches. For endurance athletes and their coaches, a chest strap device or Apple Watch may be the best choice for guiding workouts and performance.