Abstract
This study assessed the efficacy of a co-designed, school-based intervention meant to promote physical activity
and fitness among Dutch prevocational secondary students. In a two-year clustered randomized controlled trial,
students’ physical activity and fitness was measured by indirect and direct methods. In the intervention group,
we used the triple-I procedure, a participatory action research method, to co-design the intervention together with
the students and schools. This procedure involved focus group discussions by interviewing and imaging
techniques, followed by a co-design process to align the intervention content and implementation processes with
students’ preferences. The study involved 22 Dutch schools, with a total of 2685 13-to-14-year-old prevocational
secondary students. Schools were randomly assigned to either intervention (11 schools, 1446 students) or control
group (11 schools, 1239 students).There were no significant intervention differences between students’ overall
physical activity behavior on intervention versus control schools. However, with regards to various specific
physical fitness indicators, such as the long jump, handgrip strength, shuttle run test, and the sum of skinfolds,
intervention school students performed significantly better than the control group students. Furthermore, when
taking into account student participation, i.e. the success of the co-design process, schools with higher levels of
student participation showed higher shuttle run scores. However, such graded effects were not similarly apparent
with regards to students’ physical fitness indicators. This study showed that co-designing a comprehensive
physical activity intervention on numerous Dutch high schools via the Triple-I Interactive Method was feasible.
Moreover, results showed that certain aspects of physical fitness were improved after two years of intervention,
although taken together with the lack of effects on physical activity, results were mixed.