Effect of Changing Sedentary Behavior in Youth (Effects)

The primary aim is to examine how reduction in sedentary behaviors influences physical activity and energy intake.

Many youth find television, videos and computer games to be very reinforcing, and they choose to be sedentary rather than physically active. Sedentary behaviors can influence energy balance and body weight by reducing physical activity and increasing energy intake. Research from our laboratory has shown that reducing sedentary behavior can increase physical activity and decrease energy intake, but there is substantial variability in the response of youth to reductions in sedentary behavior. The present proposal is designed to extend our research and explore theoretical models that may help understand why youth vary in their response to increase physical activity when targeted sedentary behaviors are reduced. We hypothesize that the increase in physical activity when sedentary behaviors are reduced is related to the relative reinforcing value (RRV) of physical activity to sedentary behaviors. The RRV of physical activity is a measure of the motivation to be active in youth, and overweight youth who are inactive find physical activity relatively less reinforcing than less overweight youth. We predict that RRV of physical activity will be positively related to the substitution of total physical activity and physical activity in the moderate to vigorous intensity range for sedentary behaviors when targeted sedentary behaviors are reduced. To test this hypothesis, we will study 60 overweight and at risk for overweight 8-12 year-old youth who differ in the RRV of physical activity to sedentary behavior, with equal numbers of boys and girls, in 3 phases: baseline, and reduce television watching from baseline by 25 percent and 50 percent. Each phase will be implemented for three weeks. Order of experimental phases will be counterbalanced across subjects. It is also predicted that reducing sedentary behavior will reduce energy intake and dietary fat intake, and the reduction in energy intake will be greatest for youth with stronger association between eating with television watching and other targeted sedentary behaviors. Liking and outcome expectancy of physical activity will be studied as additional predictors of substitution of physical activity for reductions in sedentary behaviors. Developing a better understanding of why obese youth increase physical activity or decrease energy intake when sedentary behaviors are reduced is important for the treatment of pediatric obesity.

The initial 3 weeks of the study, children were asked to maintain their usual targeted sedentary behaviors (TV, video game, computer use) measured by a television reduction device (TV Allowance). The following 3 weeks children were asked to reduce their targeted sedentary behaviors (TV, video game, computer use) by 25% from the usual sedentary condition using a television reduction device (TV Allowance). The final 3 weeks of the study, children were asked to reduce their targeted sedentary behaviors (TV, video game, computer use) by 50% from the usual sedentary condition using a television reduction device (TV Allowance)

Actigraph activity monitors were used to record physical activity over 3 days, in addition to a weekly physical activity diary. Acti-graph counts were used to estimate energy expenditure during waking hours. Counts per minute describes the average rate of counts, with 0 being at rest and higher numbers indicating more vigorous physical activity.

Resting metabolic rate was calculated using the activity data from accelerometer (Actigraph) collection. Resting metabolic rate was used to calculate estimated daily energy expenditure. Daily energy expenditure and weight change over the study period was used to estimate energy intake. If weight was stable of the nine weeks, assume energy intake = energy expenditure. A gain of a pound was estimated as equivalent to a positive balance of 3500 calories and a loss of a pound was estimated as equivalent to a negative balance of 3500 calories.

Inclusion Criteria: above the 85th BMI percentile reside in one primary household engage in at least 18 hours of sedentary behavior a week Exclusion Criteria: none

Epstein LH, Roemmich JN, Cavanaugh MD, Paluch RA. The motivation to be sedentary predicts weight change when sedentary behaviors are reduced. Int J Behav Nutr Phys Act. 2011 Feb 22;8:13. doi: 10.1186/1479-5868-8-13.