Relationship Among Changes in Sedentary Time, Physical Activity, and Body Mass Index in Young Schoolchildren: A 3-Year Longitudinal Study

Purposes: To examine the association between sedentary time (ST) and light physical activity (LPA), moderate- to vigorous-intensity physical activity (MVPA), and body mass index (BMI), and to track these behaviors over a 3-year follow-up in young schoolchildren. Methods: The final sample was 64 children (female: n= 36 or 56.3%), enrolled in schools in Porto, Portugal. Height and mass of children were measured by standard methods, and BMI was then calculated. ST, LPA, and MVPA were measured by accelerometer. Changes (Delta) and relative changes (Delta%) between 2009/2010 and 2012/2013 of ST, LPA, MVPA, and BMI were computed. Multiple linear regression analyses were fit to predict Delta%ST (outcome variable), by Delta%LPA, Delta%MVPA, and Delta%BMI (exposure variables). Results: ST increased and LPA decreased significantly for whole sample (both Ps < .05). No statistically significant difference was found for MVPA over time. There were no differences for Delta ST, Delta LPA, Delta MVPA, and Delta BMI between boys and girls. The Delta%LPA and Delta%MVPA were negatively associated with Delta%ST, whereas Delta%BMI was positively associated. Tracking coefficients varied from moderate to strong. Conclusions: Time spent in ST increases due to displacement of time in LPA. This reinforces public health measures and suggests the need for interventions focusing on offsetting the decline ST and increasing MVPA during childhood.