UC Irvine

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

Supervised in-class exercise, health education, and internet-based self-monitoring.

Measures

Physical activity by 3-day physical activity recall; 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.