Background: Population-based studies directed at promoting physical activity in youth have shown limited success in obesity prevention. Objective: To assess whether an intervention integrating environmental changes to induce sustained changes in physical activity, prevents overweight in adolescents. Design: Four-year randomized trial started in 2002 in eight middle schools of Eastern France. The intervention, randomized at school level, was designed to promote physical activity by changing attitudes through debates and attractive activities, and by providing social support and environmental changes encouraging physical activity. Subjects: Nine hundred and fifty four 12-year-old six-graders. Measurements: Body mass index (BMI), body composition, physical activity by questionnaire, plasma lipids and glucose, insulin resistance. Results: Intervention students had a lower increase in BMI (P ¼ 0.01) and age-and gender-adjusted BMI (Po0.02) over time than controls. The differences across groups of the age-and gender-adjusted BMI changes (95% confidence interval (CI)) were À0.29 (À0.51; À0.07) kg/m 2 at 3 years, À0.25 (À0.51; 0.01) kg/m 2 at 4 years. An interaction with baseline weight status was noted. The intervention had a significant effect throughout the study in initially non-overweight adolescents (À0.36 (À0.60;À0.11) kg/m 2 for adjusted BMI at 4 years), corresponding to a lower increase in fat mass index (Po0.001). In initially overweight adolescents, the differences observed across groups at 2 years (-0.40 (À0.94; 0.13) kg/m 2 for adjusted BMI) did not persist over time. At 4 years, 4.2% of the initially non-overweight adolescents were overweight in the intervention schools, 9.8% in the controls (odds ratio ¼ 0.41 (0.22; 0.75); Po0.01). Independent of initial weight status, compared with controls, intervention adolescents had an increase in supervised physical activity (Po0.0001), a decrease of TV/video viewing (Po0.01) and an increase of high-density cholesterol concentrations (Po0.0001). Conclusion: Enhancing physical activity with a multilevel program prevents excessive weight gain in non-overweight adolescents. Our study provides evidence that prevention of obesity in youth is feasible.

OBJECTIVE:To evaluate the 6-month impact of a physical activity (PA) multilevel intervention on activity patterns and psychological predictors of PA among adolescents. The intervention was directed at changing knowledge and attitudes and at providing social support and environmental conditions that encourage PA of adolescents inside and outside school. SUBJECTS AND DESIGN: Randomised, controlled ongoing field trial (ICAPS) in middle-school's first-level adolescents from eight schools selected in the department of the Bas-Rhin (Eastern France) with a cohort of 954 adolescents (92% of the eligible students) initially aged 11.770.6 y. The 6-month changes in participation in leisure organised PA (LOPA), high sedentary (SED) behaviour (43h/day), self-efficacy (SELF) and intention (INTENT) towards PA were analysed after controlling for baseline measures and different covariables (age, overweight, socioprofessional occupation), taking into account the cluster randomisation design. RESULTS: The proportion of intervention adolescents not engaged in organised PA was reduced by 50% whereas it was unchanged among control students. After adjustment for baseline covariables, LOPA participation significantly increased among the intervention adolescents (odds ratio (95% confidence interval) (OR) ¼ 3.38 (1.42-8.05) in girls; 1.73 (1.12-2.66) in boys), while high SED was reduced (OR ¼ 0.54 (0.38-0.77) in girls; 0.52 (0.35-0.76) in boys). The intervention improved SELF in girls, whatever their baseline LOPA (Po10 À4 ) and INTENT in girls with no baseline LOPA (P ¼ 0.04). SELF tended to improve in boys with no baseline LOPA, without reaching statistical significance. When included in the regression, follow-up LOPA was associated with improvement of SELF in girls (P ¼ 0.02) and of INTENT in girls with no baseline PA (Po0.02). The intervention effect was then attenuated. CONCLUSION: After 6 months of intervention, ICAPS was associated with a significant improvement of activity patterns and psychological predictors, indicating a promising approach for modifying the long-term PA level of adolescents.

(ICAPS). Presence of a TV set in the bedroom (TV bedroom ) and leisure activities were obtained by questionnaire. There was annual assessment of BMI, waist circumference, and body fat by bioimpedance. Results: In boys but not girls, baseline TV bedroom was associated with higher TV/video viewing over time [odds ratio (OR) of high TV/video ϭ 1.87; 95% confidence interval, 1.2 to 2.8] and less no-sport club participation (OR ϭ 0.59; 95% confidence interval, 0.35 to 1.0). Both boys and girls with baseline TV bedroom had lower reading time (p Ͻ 0.0001 in boys; p ϭ 0.04 in girls), while PA did not differ according to TV bedroom for boys or for girls. For boys only, baseline TV bedroom was associated with higher BMI (mean BMI over time 20.5 Ϯ 0.5 vs. 19.0 Ϯ 0.5 kg/m 2 ; p ϭ 0.001), waist circumference (70.9 Ϯ 0.9 vs. 67.2 Ϯ 0.8 cm; p Ͻ 0.001), and body fat (15.9 Ϯ 0.9% vs. 13.5 Ϯ 0.9%; p Ͻ 0.001), without interaction with time. These relationships remained significant after adjustment for socioeconomic status. TV/video viewing explained 26%, 42%, and 36% of the relationships of TV bedroom with BMI, waist circumference, and body fat, respectively, while addition of other leisure activities in the models only marginally reduced the effects. Discussion: These results suggest the importance of keeping TV out of an adolescent's bedroom from an obesity prevention perspective but show gender differences.

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