Determinants of changes in sedentary time and breaks in sedentary time among 9 and 12 year old children

The current study aimed to identify the determinants of objectively measured changes in sedentary time and sedentary fragmentation from age 9 - to age 12 years. Data were collected as part of the Gateshead Millennium Birth Cohort study from September 2008 - August 2009 and from January 2012 - November 2012. Participants were 9.3 (±0.4) years at baseline (n=508) and 12.5 (±0.3) years at follow-up (n=427). Sedentary behaviour was measured using an ActiGraph GT1M accelerometer. Twenty potential determinants were measured, within a socio-ecological model, and tested for their association with changes in sedentary time and the extent to which sedentary behaviour is prolonged or interrupted (fragmentation index). Univariate and multivariate linear regression analysis were conducted. Measurements taken during winter and a greater decrease in moderate-to-vigorous intensity physical activity (MVPA) over time were associated with larger increases in sedentary time (seasonality β:-3.03; 95% CI:-4.52,-1.54; and change in MVPA β:-1.68; 95% CI:-1.94, -1.41). Attendance at sport clubs was associated with smaller increases in sedentary time (-1.99; -3.44, -0.54). Girls showed larger decreases in fragmentation index (-0.52; -1.01, -0.02). Interventions aimed at decreasing the decline in MVPA and increasing/maintaining sport club attendance may prevent the rise in sedentary time as children grow older. In addition, winter could be targeted to prevent an increase in sedentary time and reduction in sedentary fragmentation during this season