Physical Activity Determinants Among Adolescents With Mild Intellectual Disability in Dutch Practical Education: Exploratory Sequential Mixed Methods Study.

Background: A sedentary lifestyle is a global health crisis that contributes to chronic disease and premature mortality. Adolescents with mild intellectual disability attending Dutch practical education (PrO) schools face elevated health risks due to low levels of physical activity (PA) and limited conceptual, social, and practical skills. Digital health interventions offer scalable solutions, but require contextual adaptation informed by formative research. However, understanding of PA behavior in this population and context remains limited because existing research relies on partial lenses and lacks integration of theory, participatory methods, and multistakeholder insights. Objective: We aimed to identify and prioritize PA determinants among adolescents with mild intellectual disability in Dutch PrO schools, using a theory-driven, participatory, and multistakeholder approach to inform the contextual adaptation of digital health interventions. Methods: We used an exploratory sequential mixed methods study design integrating context mapping and concept mapping. Inclusive participatory methods were co-designed with PrO schools for adolescents. In the first qualitative phase, PA determinants were identified through data collected from experts (n=13), teachers (n=8), and adolescents (n=83-90). Qualitative data from all stakeholder groups were integrated and analyzed using a framework approach grounded in the Theoretical Domains Framework and the Capability, Opportunity, Motivation-Behavior model. In the subsequent quantitative phase, the PA determinants identified across all data sources were translated into inclusive pictorial rating instruments and prioritized from the adolescents' perspectives using a 7-point Likert scale ranging from barriers to facilitators. Quantitative analyses included descriptive statistics and hierarchical clustering to examine perceived importance and consensus across determinants. Results: Qualitatively, 29 PA determinants were identified and mapped to Capability, Opportunity, Motivation-Behavior components: opportunity (n=15), motivation (n=8), and capability (n=6). Experts and teachers focused on capability and opportunity barriers (eg, impaired skills and cognitive fatigue), while adolescents emphasized motivation and social opportunity facilitators (eg, fun activities, enjoyment, and peer or family support). Quantitatively, adolescents' ratings showed a positive bias toward facilitators (mean 5.09/7, SD 1.72), and facilitators showed greater consensus than barriers ( Conclusions: Three meta-inferences informing future intervention adaptation were derived: (1) substantial individual variation exists in adolescents' perceptions of PA determinants, (2) school-related barriers are highly individualized, and (3) social and emotional facilitators tend to be relatively more shared across adolescents. Integrating findings suggests a dual approach to promoting PA in this population and context: personalized strategies for individual barriers and group-level strategies for shared facilitators. Digital health interventions seem promising to provide accessible and inclusive means of delivering this dual approach at scale.