Influence of Two-Year Changes in Sedentary Behavior and Physical Activity on Adolescent Weight Status

Purpose: To examine whether change in SB and PA associated with a change in weight status over 24-months.

Methods: Data were from Identifying Determinants of Eating and Activity (IDEA), a 3-year longitudinal cohort study that assessed the etiology of adolescent obesity. PA and SB were assessed using the ActiGraph (Model 7164; Pensacola, FL) accelerometer, which participants wore over a 7 day period and baseline and follow-up. Activity change was defined as percent of time spent in SB, light, moderate, and vigorous PA at baseline subtracted from percentage of time spent in these activity intensities at follow-up. Multiple regression analysis, controlling for age, sex, race, SES, pubertal status, and diet, examined the association between the change in the percent of time spent in sedentary, light, moderate, and vigorous activity with change in BMI percentile from baseline to follow-up. Models were calculated separately for each activity change variable, while controlling for the other activity intensities.

Results: The sample consisted of 299 participants (15.38 ± 1.7 yrs, 50.2% males, 93% Caucasian). Multiple regression analysis of the entire sample as a whole showed that none of the activity change variables were significantly associated with change in BMI percentile, though there was a negative trend for change in time spent in light activity (p=0.09). As a result of a significant gender interaction with time spent in SB and PA (p<.05), gender-separated analyses were conducted, indicating that an increasing amount of time spent in SB (p<0.05) and a decrease in light PA (p<0.05) were both independently associated with an increase in BMI percentile in females. There were no significant associations for males.

Conclusions: An increase in sedentary time and a decrease in light PA over a 2 year period were associated with increases in BMI percentile in females. This research would indicate that SB does not necessarily have to be replaced with strenuous exercise to reduce excess weight gain.