Commercial Activity Trackers Overestimate Step Count: Implications for Ambulatory Activity Monitoring

Abstract

Guidelines for Physical Activity (PA) include a minimum of 150 min of moderate PA each week for adults, and at least 60 daily minutes of moderate-to-vigorous PA for youth aged 6–17 years. The burden to monitor self-compliance lies on the individual and involves tracking content, intensity, and temporal breakdown of daily activities while delineating these as light-, moderate-, or vigorous-intensity. Presenting PA recommendations as steps per day makes them more accessible. Inaccurate step counts can mislead individuals looking to meet recommendations using a step count paradigm. This research evaluated the degree to which wrist and hip worn activity trackers misattribute steps to non-ambulatory activities and overestimate total step count. An adult male (age: 41 years; height: 1.7 m; mass: 74 kg) wore a Fitbit Versa and Apple Watch on his wrist and a Withings Go and an Apple iPhone 7-deployed Pedometer++ application on his lateral hip. The participant walked and ran for a total of 84 and 100 steps, respectively, and performed 20 vertical jumps, 20 bilateral hops, 20 squats, and 20 sit-to-stand tasks. The mean step count and percent error between observed step count and total step count output from each device were calculated. Fitbit Versa, Apple Watch, Pedometer++, and Withings Go overestimated total step count by 110%, 126%, 48%, 97%, respectively. It was concluded that both low- and high-end commercial activity trackers attribute steps to non-ambulatory activities and consequently overestimate step count. This can mislead individuals who rely on these activity trackers to monitor their step count. Therefore, there is need for algorithms with improved activity recognition.