Television Viewing: Moderator or Mediator of an Adolescent Physical Activity Intervention?

Purpose. To determine whether the amount of television (TV) watched by participants enrolled in a physical activity intervention mediates or moderates program effectiveness. Design. Nine-month, controlled, school-based physical activity intervention. Setting. Public high school. Participants. One hundred twenty-two sedentary adolescent females (mean +/- standard deviation age = 15.04 +/- 0.79 years). Intervention. Supervise in-class exercise, health education, and internet-based self-monitoring. Measures. Physical activity by 3-day physical activity reacall; TV viewing by self-reports; cardiovascular fitness by cycle ergometer. Analysis. T-tests were conducted to examine between-group differences. Linear regression equations tested the mediating or moderating role of TV watching relative to the intervention. Results. TV viewing moderated the intervention's effect on vigorous activity; the intervention significantly predicted change in physical activity among high (beta = -.45; p < .001), but not among low (p > .05), TV watchers, TV viewing did not mediate the intervention effect. Conclusions. Consistent with displacement theory, adolescents who watched more TV prior to the intervention showed postintervention increases in vigorous physical activity and concomitant decreases in TV viewing, whereas those who watched less TV showed no change in physical activity or TV viewing. (Am J Health Promot 2008;23[2]:88-91.)