Purpose: The purpose of this study was to describe and compare the levels of tracking of physical activity and inactivity as assessed by self-report and accelerometry in middle school girls during a 2-yr period.
Methods: Participants (n = 951) were from the Trial of Activity for Adolescent Girls (TAAG). The TAAG intervention had minimal effect on physical activity; therefore, both intervention and control participants were included. Inactivity and physical activity were measured by accelerometry (MTI ActiGraph) and self-report (3-d physical activity recall).
Results: Weighted kappa statistics ranged from 0.14 to 0.17 across inactivity, moderate-to-vigorous physical activity (MVPA), and vigorous physical activity (VPA) for self-report, from 0.13 to 0.20 for 3-d accelerometry, and from 0.22 to 0.29 for a 6-d accelerometry. Intraclass correlations ranged from 0.17 to 0.22 for self-report, 0.06 to 0.23 for 3-d accelerometry, and 0.16 to 0.33 for a 6-d accelerometry. In general, the estimates from the 6-d accelerometry tended to be higher than those from self-report, whereas few differences were observed between 3-d accelerometry and self-report. Odds ratios (OR) for being in the highest quintile at eighth grade for those in the highest quintile at sixth grade compared with those in any other quintile at sixth grade were 3.26 (95% confidence interval = 2.28-4.67), 3.64 (2.55-5.20), and 3.45 (2.42-4.93) for the 6-d accelerometry-measured inactivity, MVPA, and VPA. Corresponding OR from self-report were 2.44 (1.66-3.58) for inactivity, 2.63 (1.83-3.79) for MVPA, and 2.23 (1.54-3.23) for VPA.
Conclusion: Tracking of inactivity and physical activity in middle school girls was fair to moderate. Our results suggest that physical activity and inactivity habits are dynamic for most girls during early adolescence. Population-based efforts should be made in this age group to promote physical activity and offer alternatives to inactivity for all girls.