Background
Physical activity (PA) is one of the core components of healthy ageing. For older adults with intellectual disabilities (ID), PA is even more important because they often have a more sedentary and inactive lifestyle and more health problems than do older adults without ID. To promote PA, we explored personal and contextual barriers and facilitators to PA for this group.

Methods
We used a research-through-design approach with six older adults with ID in a specific care home facility. By applying co-design methods, older adults with ID, caregivers and other stakeholders were involved from the beginning in (1) listing barriers and facilitators, (2) exploring PA-promoting interventions and (3) adapting co-design methods to the target group.

Results
Our work resulted in a list of barriers and facilitators for the participants to perform PA, related to the personal characteristics of the participants, the provided PAs and the physical and social context. Further, a PA-stimulating intervention prototype and lessons learned regarding co-design with older adults with ID were developed. It became clear that a modular, adaptive intervention is necessary to accommodate the individual needs and wishes of older adults with ID. The same adaptive approach was required to meaningfully involve them in the research and design process.

Conclusions
Older adults with ID cannot be regarded as a homogeneous group, and there is no one-size-fits-all solution for promoting their PA. Basic components for an intervention can be provided, yet they always require adaptations to personal and contextual circumstances. The identified barriers and facilitators, intervention prototype and co-design lessons can provide guidance for creating tailored interventions.