Comparing Methods to Identify Wear-Time Intervals for Physical Activity With the Fitbit Charge 2

• Published in: Journal of aging and physical activity 2021-06, Vol.29 (3), p.529-535
• Main Authors: Claudel, Sophie E, Tamura, Kosuke, Troendle, James, Andrews, Marcus R, Ceasar, Joniqua N, Mitchell, Valerie M, Vijayakumar, Nithya, Powell-Wiley, Tiffany M
• Format: Article
• Language: English
• Subjects: African Americans; Algorithms; Body Mass Index; Exercise; Female; Fitness Trackers; Heart Rate; Humans; Physical activity; Time use; Women
• ISSN: 1063-8652; 1543-267X
• DOI: 10.1123/JAPA.2020-0059

There is no established method for processing data from commercially available physical activity trackers. This study aims to develop a standardized approach to defining valid wear time for use in future interventions and analyses. Sixteen African American women (mean age = 62.1 years and mean body mass index = 35.5 kg/m2) wore the Fitbit Charge 2 for 20 days. Method 1 defined a valid day as ≥10-hr wear time with heart rate data. Method 2 removed minutes without heart rate data, minutes with heart rate ≤ mean - 2 SDs below mean and ≤2 steps, and nighttime. Linear regression modeled steps per day per week change. Using Method 1 (n = 292 person-days), participants had 20.5 (SD = 4.3) hr wear time per day compared with 16.3 (SD = 2.2) hr using Method 2 (n = 282) (p < .0001). With Method 1, participants took 7,436 (SD = 3,543) steps per day compared with 7,298 (SD = 3,501) steps per day with Method 2 (p = .64). The proposed algorithm represents a novel approach to standardizing data generated by physical activity trackers. Future studies are needed to improve the accuracy of physical activity data sets.