• body-mass index [ Time Frame: at the end of the second, third and fourth school years of intervention ]
  

• fat mass (impedancemetry) [ Time Frame: at the end of the second, third and fourth school years of intervention ]
  
• physical activity (MOSPA) [ Time Frame: at the end of the second, third and fourth school years of intervention ]
  
• Attitudes and motivation toward physical activity [ Time Frame: at the end of the second, third and fourth school years of intervention ]
  
• clinical and biological cardiovascular risk factors [ Time Frame: at the end of the second, and fourth school years of intervention ]
  

Background

Physical activity is thought to be a key element in preventing the obesity epidemic and the associated cardiovascular and metabolic diseases. However population-based studies directed at promoting physical activity in youth have shown limited success in obesity prevention. The aim of this study is to assess whether an intervention integrating socioecological changes, which has the potential to induce sustained changes in physical activity, prevents overweight and cardiovascular risk in adolescents.

Methods

Population and design: The Intervention Centered on Adolescents’ Physical activity and Sedentary behavior (ICAPS) is a 4-year randomized prevention study targeting 6th graders (e.g. 12 year old adolescents). The study design is based on a randomization at school level and follows the intention-to-treat principle. Eight schools (four intervention schools and four controls) are randomly selected out of the 77 public middle schools of the Department of Bas-Rhin (Eastern France). To balance potential confounding factors and to ensure a broad socioeconomic context, randomization is done after stratification on sociogeographical criteria. Intervention status of the schools is randomized in each pair of matched schools. All initially first-level students of the randomized schools are eligible to participate.

Intervention: The 4-year intervention program is designed to promote physical activity by changing attitudes through debates and access to attractive activities, and by providing social support and environmental changes encouraging physical activity. The students of the control schools follow their usual school curriculum and physical education classes and are not be submitted to any intervention.

Outcomes and follow-up: The primary outcome is the subjects’ body mass index (BMI). Prespecified secondary end points include body composition, physical activity and sedentary behaviors, attitudes towards physical activity, and various cardiovascular risk factors. Surveys take place at baseline and annually at the end of each school year. Fasting blood is sampled at baseline and every two years. Physical examinations are performed by qualified professionals and questionnaires are administered to small groups of 3 to 6 students. All the procedures are standardized among schools and the interviewers are be regularly trained to assure the reliability of the measurements.

Statistical analysis: Outcome data are analyzed using mixed linear models taking into account the cluster randomization design and the repeated individual data. Random effects are schools within intervention group and individuals within schools. Possible heterogeneity of the intervention’s effect according to gender and initial weight status will be tested.

Perspectives This study will assess the feasibility and the efficacy of a multilevel multipartnership prevention program targeting adolescents’ physical activity.

Inclusion Criteria:

• 6th graders (in 2002) in one of the eight randomised middle school (four pairs of middle-school located in Bas-Rhin, France)