Time Trends in Physical Activity Using Wearable Devices: A Systematic Review and Meta-analysis of Studies from 1995 to 2017.

INTRODUCTION Conflicting evidence exists on whether physical activity (PA) levels of humans have changed over the last quarter-century. The main objective of this study was to determine if there is evidence of time trends in PA, from cross-sectional studies that assessed PA at different time points using wearable devices (e.g., pedometers, accelerometers). A secondary objective was to quantify the rate of change in PA. METHODS A systematic literature review was conducted of English language studies indexed in PubMed, SPORTDiscus, and Web of Science (1960-2020) using search terms (time OR temporal OR secular) AND trends AND (steps per day OR pedometer OR accelerometer OR MVPA). Subsequently, a meta-analytic approach was used to aggregate data from multiple studies, and to examine specific factors (i.e. sex, age group, sex-and-age group, and PA metric). RESULTS Based on 16 peer-reviewed scientific studies conducted between 1995 and 2017, levels of ambulatory PA are trending downward in developed countries. Significant declines were seen in both males and females (p < 0.001) as well as in children (p = 0.020), adolescents (p < 0.001) and adults (p = 0.004). The average study duration was 9.4 yrs (accelerometer studies: 5.3 yrs, pedometer studies: 10.8 yrs). For studies that assessed steps, the average change in PA was -1,118 steps/day over the course of the study (p < 0.001) and adolescents had the greatest change in PA at -2,278 steps/day (p < 0.001). Adolescents also had the steepest rate of change over time, expressed in steps/day/decade. CONCLUSION Evidence from studies conducted in eight developed nations over a 22-yr period indicates that PA levels have declined overall, especially in adolescents. This study emphasizes the need for continued research tracking time trends in PA using wearable devices.