Physical activity as a substitute for sedentary behavior in youth.

BACKGROUND

Youth may choose to be sedentary rather than physically active.

PURPOSE

The purpose of this study was to use behavioral economics methods to investigate how experimental changes in the amount of sedentary behaviors influenced physical activity.

METHODS

Fifty-eight 8- to 16-year-old youth were studied in a within-subject crossover design with three 3-week phases: baseline, increasing, and decreasing targeted sedentary behaviors by 25% to 50%.

RESULTS

At baseline, boys were more active than girls (518.9 vs. 401.2 accelerometer counts/min, p = .02), and obese youth more sedentary than nonobese youth (240.5 vs. 174.4 min/day, p = .003). During the increase sedentary behavior phase, targeted sedentary behaviors increased by 52.1%, with girls increasing sedentary behaviors more than boys (114.7 vs. 79.8 min/day, p = .04). Physical activity decreased (-48.3 counts/min, p < .01) when sedentary behaviors increased, with obese youth decreasing total and moderate to vigorous physical activity (MVPA) more than nonobese youth (-110.4 vs. 8.9 counts/min, p < .001; -3.3 vs. -.03 % MVPA, p = .013). During the decrease sedentary behavior phase, targeted sedentary behaviors decreased by 55.6% from baseline as nonobese youth increased physical activity, whereas obese youth decreased physical activity (55.8 vs. -48.0 counts/min, p = .042; 1.1 vs. -2.1% MVPA, p = .021). Youth who substituted physical activity when sedentary behaviors were increased had greater standardized body mass index (z-body mass index = 1.4 vs. 0.4, p = .018), whereas youth who substituted physical activity when sedentary behaviors were decreased were less active at baseline (396.1 vs. 513.7 counts/min, p = .035).

CONCLUSIONS

Behavioral economics provides a methodology to understand changes in physical activity when sedentary behaviors are modified and to identify factors associated with substitution of physically active for sedentary behaviors.