Wearable fitness trackers are increasingly popular. Why? Data. Active people want to know the effectiveness of their training. They want to chart the quantity and quality of their hard work and dedication so they can use that information to improve their workouts. One of the measurements calculated by these devices is caloric expenditure both at rest and during physical activity. The purpose of this study was to examine the accuracy of two wearable tracking devices—the FitBit Ionic and Garmin Vivoactive 3 in determining resting energy expenditure (REE). REE is defined as the amount of energy (calories) used during sedentary, every day activities. A secondary purpose was to determine if the accuracy varies by training status of the individual wearing the device. Each participant completed a maximal aerobic capacity (VO2max) test to determine training status.They were then placed into one of three fitness groups based on their VO2max measures: highly trained, moderately trained, and untrained. In a separate session, REE of each participant was measured using a laboratory-grade metabolic cart and measures of gas exchange. During the same REE test, each wearable fitness tracking device was worn to obtain a predicted REE. The predicted REE from each device and measured REE were then compared with ANOVA, with statistical significance set at p
