From March to September 2024, experts and school managers were recruited via email and through convenience sampling via the LIFTS network [47]. They had a consulting role by providing their preconceptions of PA determinants among adolescents with mild intellectual disability in the PrO context. Additionally, school managers partnered with researchers to cocreate inclusive research methods for the adolescents.

In September 2024, teachers were recruited face-to-face via purposive sampling through their school managers. Teachers had both a role as consultants and partners, providing preconceptions on PA determinants and cofacilitating inclusive research activities with the adolescents (eg, helping with classroom management, student support, and instruction clarification). Researchers conducted a series of in-person and online meetings with the teachers to frame this study’s aim and explain the procedure. This study’s protocols cocreated with the school managers were provided to the teachers, including a study guide explaining activities, materials, and information letters.

From October to November 2024, adolescents enrolled in PrO schools in the LIFTS network, aged 12 to 17 years, were recruited via class-based purposive sampling with the support of school managers. They were involved as consultants on their own perceived PA determinants. Intact class groups of up to 16 students from years 1 to 4 of PrO schools were selected. While research guidelines recommend 10 to 12 participants per group, the existing class structure and staffing limitations made it impractical to divide classes into smaller groups [48]. The sample size was defined to offer sufficient diversity within the target population.

In line with the participatory lens, qualitative data collection was informed by Context Mapping, a user-centered design framework that uses creative and visual techniques to elicit tacit knowledge of user needs [54]. We adapted the sensitizing and generation phases in this framework in collaboration with PrO schools to make participation inclusive for the adolescents by priming their awareness of PA behavior and providing design artifacts to express this tacit knowledge.

The qualitative data collection process comprised 3 stages: preparation, sensitizing, and generation.

The quantitative phase built directly on the qualitative findings: PA determinants identified qualitatively by experts, teachers, and adolescents were translated into inclusive, pictorial quantitative instruments that adolescents could rate and discuss. In line with the participatory lens of this study, this phase used concept mapping, a framework widely used in public health and health promotion [64-66]. It comprised three stages: structuring, representation, and interpretation of identified PA determinants. Structuring and interpretation were implemented during data collection with adolescents, whereas representation was conducted during quantitative analysis by the research team. To support inclusivity, adolescents rated PA determinants on a pictorial Likert scale rather than engaging in abstract sorting tasks, which are difficult for people with intellectual disability [67,68]. Then, a gamified quiz confirmed researchers’ interpretations of adolescents’ perceptions rather than asking students to verify a complex concept representation, which researchers used for analysis.

This study received approval from the Ethical Review Board of the Technical University of Eindhoven (ERB2024IEIS69). The ethical review and approval covered this study’s protocol, including the consent procedures, privacy and confidentiality measures, and participatory ethics considerations described below.

Teachers and experts provided written informed consent; adolescents gave oral informed consent, witnessed by their teachers. All information was provided orally and in writing in plain B1-level Dutch with visual supports, in line with the Web Content Accessibility Guidelines [71]. Research activities with adolescents were not audio-recorded because school representatives feared this might discourage participation and limit their freedom to speak. Passive consent was used for caregivers in accordance with Dutch ethical guidelines for low-risk research [72]. No compensation was offered to participants.

Only limited personal data were collected (eg, for adolescents, age and gender; for other stakeholders, contact information, main expertise, and audio recordings). Adolescents’ postcards were anonymous, and all other materials were deidentified; physical materials were digitized and destroyed, adults’ audio recordings were deleted after transcription, and only deidentified data were stored in secure restricted-access systems.

Participatory research ethics guided the study: building trust, minimizing harm, offering inclusive methods, ensuring confidentiality and informed consent, and creating a safe environment for equal participation [73]. While PrO students may be labeled as a vulnerable population, the adolescents were not treated as inherently vulnerable. Instead, this study sought to enable their participation through inclusive methods that reduced barriers.

We identified 29 PA determinants (codes) indexed to COM-B components (themes) and TDF domains (subthemes), as illustrated in Figure 4. Each determinant was assigned to a primary TDF domain, with some also linked to secondary domains (Table S1 in Multimedia Appendix 6). To facilitate comparison across stakeholder groups, data from experts, teachers, and adolescents were synthesized in a framework matrix, summarizing data extracts, participant quotations, and researcher observations for each determinant (Table S2 in Multimedia Appendix 6).

Overall, PA determinants identified in all data sources were distributed across COM-B components as follows: opportunity (n=15), motivation (n=8), and capability (n=6). Comparing preconceptions from experts and teachers and perceptions from adolescents revealed both convergence and divergence across PA determinants. Experts and teachers emphasized capability and motivation barriers, prominently featuring the TDF domains of skills, reinforcement, and goals. These domains closely aligned with the impairments characteristic of mild intellectual disability. Conversely, adolescents consistently highlighted motivation and opportunity facilitators, particularly within the TDF domains of emotions and social influences.

Below, the PA determinants are described and organized based on the COM-B components and TDF domains, comparing experts’ and teachers’ preconceptions with adolescents’ perceptions.

Three main contexts emerged from participants’ input: home, school, and external environments, as described below.

Regarding the home, experts and teachers mentioned that financial difficulties (D7) and lack of parental knowledge (D8) often restrict adolescents from participating in organized PA opportunities. For example:

The adolescents rarely mentioned financial barriers, and only did it in anonymous formats (eg, postcards). Experts and teachers identified local and governmental programs, such as subsidies and information dissemination, as facilitators for accessing PA opportunities. Next, they noted that the home environment lacks the social support adolescents need for PA, making the home environment unsuitable for individual and home-based formats such as online workouts. Consistently, adolescents themselves did not mention the home environment in their timeline boards as a setting where they currently engage in PA.

Regarding the school, experts and teachers consistently appointed the school as a key environment for inclusive and tailored PA opportunities. Facilitators included active commutes to school (D9), inclusive physical education (PE) curricula, and additional organized (eg, class tournaments between classes and regular walk programs) or nudged (eg, available equipment and facilities during the breaks) activities at school (D10). Teachers added that PrO classes encourage natural movement throughout the day, which may lead to tiredness affecting students’ capability and motivation to engage in PA after school. Despite these opportunities, schools often lacked the staff and resources needed to sustain PA initiatives. Stronger school health policies and government support were identified as facilitators to institutionalize PA efforts. Consistently, many adolescents identified PA related to school on their timeline boards via active commutes, PE classes, and breaks. However, many did not mark the school period as active in the timeline (Figure 5) and thus viewed the school environment as sedentary. Older adolescents reported that PE classes were removed from their curriculum, reducing their chances for structured PA at school. Organized or nudged activities were rarely mentioned, and the PrO classes were not recognized as active.

Regarding the external environment, experts and teachers indicated that the external environment, outside the home and school contexts, is less inclusive than the PrO school environment, which caters to adolescents’ needs. These adolescents often struggle to integrate into local sport clubs and neighborhood activities (D11), where the setting is often performance-oriented and competition-driven (D12). Their skill impairments seem to lead to a mismatch and early dropout, as many fail to perform at the same level and feel isolated. It seems that, outside of school, adolescents face additional logistical barriers, such as transportation and distance to sport facilities (D13).

While experts and teachers emphasized the need for dedicated, inclusive, and local sport programs, they noted that such programs often lack sufficient funding, governmental commitment, and a systems-thinking approach to social and environmental factors. These external challenges were reflected in adolescents’ input. While many mentioned participation in sport clubs, others reported engaging in individual and flexible sports such as kickboxing, swimming, fitness, and spontaneous PA outside after school hours among peers. These opportunities seem to emphasize participation over competition (D12), making them more inclusive.

Across environmental contexts, participants described time-related determinants. Experts and teachers viewed structured PA during school hours (D10) as a facilitator and suggested embedding PA into the school day (eg, active breaks or movement-based educational tools). In contrast, PA after school hours (D14) was often constrained because experts and teachers mentioned competing priorities, such as rest and responsibilities such as part-time jobs or household chores. Similarly, adolescents’ timeline boards showed that many preferred resting, and some had part-time jobs after school, reflecting these competing demands later in the day. To address this, experts proposed low-threshold PA opportunities immediately after the last school hour, leveraging the school setting after school hours (D15) while motivation and structure remain. Additionally, commercial gyms and other flexible options were recommended to fit adolescents’ diverse schedules and responsibilities.

Experts and teachers consistently emphasized that social influences from family, peers, and professionals are key PA determinants among these adolescents. Preconceived barriers related to family social support (D16) included financial stresses, unstable households, lack of parental knowledge, inability to provide practical aspects (eg, transportation), social segregation, and overprotection of adolescents.

Regarding social support from school teachers (D17) and PA professionals (eg, coaches and neighborhood coaches) (D18), the focus on performance, competition, and lack of training on special needs were indicated as barriers. In contrast, child-centered coaching, inclusive activities in a safe environment, and specialized professionals were highlighted as facilitators. Even though it was indicated that these adolescents struggle to form social connections and networks, support and joint participation with friends and peers (D19) was mentioned as a significant facilitator for enjoying PA by promoting a sense of belonging through connection and teamwork.

These social circles also influence PA participation through role modeling and group norms, where “seeing movement is moving.” Experts and teachers mentioned that the lack of active role models (D20) is a significant barrier to participation. Moreover, in many social circles (eg, groups of friends and neighborhood), a sedentary lifestyle is the norm, and PA may even be discouraged. Conversely, when being active is the norm, it can strongly promote PA:

Visible role models and social media influencers (D21) were mentioned as potential facilitators by experts and teachers.

Despite the stakeholders’ emphasis on social barriers, adolescents generally seemed positive about social support and occasionally expressed a desire for competition (D12). Adolescents often mentioned family in their postcards and timeline boards as motivating and supportive for PA. Figure 6 gives 2 examples of postcards illustrating common themes of social connection and enjoyment. The desire to participate in PA with friends was a recurring theme across data collection activities. When asked why they think PA is fun, they often replied, “Het is gezellig met vrienden” (a common Dutch expression about social connectedness).

However, this positive attitude was not universal. Many adolescents perceived their teachers as unsupportive and sedentary role models. In postcards, only a few adolescents spontaneously mentioned their coaches or PE teachers as people who make them enthusiastic about PA. Importantly, some adolescents reported limited social support or that nobody makes them enthusiastic about PA. The timeline boards revealed that many students spend a lot of time alone at home after school, indicating a lack of social support, connectedness, and network.

Experts and teachers highlighted positive emotions (D22) as a central motivator for PA, both in terms of experienced and anticipated feelings. Enjoyment and having fun (D23) were consistently noted as key facilitators of PA. This was linked to participation in preferred PA options, which can be related to gender preferences and segregation (D25). In agreement, these PA determinants were reported by the adolescents. Across data collection activities, adolescents consistently described sports and exercise as “fun.” An overall positive and energetic feeling was also expressed by many adolescents, with some highlighting that PA has mental health benefits (eg, feeling calm, occupied, and distracted from other issues). Often linked to the enjoyment of PA, it seems that when sports and movement are part of adolescents’ identity, they are more likely to participate in PA. Conversely, when adolescents identify with sedentary activities and not as “sportive” individuals, PA participation seems difficult. Similarly, personal sport preferences among adolescents seem to be a barrier if they diverge from the popular options (D24).

In addition, experts and teachers also identified negative emotions related to PA, including general tiredness, anxiety, and disappointment in competitive environments (D12), fear and shame of participating due to a perceived lack of skills, and disgust related to sweating. It seems that these adolescents with impaired adaptive behavior skills find it harder to regulate emotions than their typically developing peers. Negative emotions were less frequently reported by the adolescents themselves.

Experts and teachers consistently identified low self-efficacy (D26) and self-esteem (D27), particularly regarding body image, and overall capabilities, as barriers to PA participation. These preconceptions are linked to the adolescents’ skill impairments relative to their peers, and past negative experiences in performance-focused settings, including at other nontailored school settings. Experts and teachers emphasized that enabling small successes through scaffolding, safe environments, and positive reinforcement could facilitate skill development and increased self-efficacy. Experts and teachers added that enabling adolescents to participate in PA voluntarily is relevant, as opposed to a top-down enforcement that may have a negative impact. Conversely, adolescents did not explicitly report low self-efficacy, but some expressed concerns about body image, linking PA only to weight loss.

Experts and teachers consistently noted that these adolescents often struggle to set long-term or abstract goals for PA (D28) due to their cognitive impairments. Instead, they mentioned that adolescents benefit from short-term, concrete goals that offer immediate outcomes, such as feeling stronger or more energetic. They emphasized that these goals should be voluntary (D29), aligning with the adolescent’s interests and emotional drivers.

Consistently, the adolescents did not explicitly express long-term goals related to PA in their postcards or timeline boards.

Table S1 in Multimedia Appendix 5 describes the adolescents’ ratings (from strong barriers to strong facilitators; 1 to 7) of the PA determinants identified in the qualitative phase from experts, teachers, and adolescents’ input. Ratings exhibit a positive trend (mean 5.09; SD 1.72), suggesting that the determinants are predominantly perceived by the adolescents as facilitators rather than barriers. Additionally, results show weak within-group agreement (r_wg<0.7) across all determinants, indicating that there is a substantial variation in perceptions between adolescents.

Figure 7 displays the hierarchical clustering of PA determinants, derived from the mean ratings and the within-group agreement indices (r_wg). The variation in agreement appears to be partially explained by the mean rating of the determinants. A Spearman correlation analysis confirmed a significant positive relationship between mean rating and agreement (ρ=0.74, P<.001). This indicates that determinants that are more frequently perceived as facilitators tend to elicit greater consensus among adolescents’ perceptions.

Table 3 shows 4 clusters of PA determinants from hierarchical clustering. One cluster is a singleton with the lowest agreement, while the remaining clusters indicate a good structure. We describe and interpret these clusters below.

Clusters 1 and 2 represent determinants perceived as barriers to PA by adolescents with centroids below the overall mean rating and lower within-group agreement. Cluster 1 is a singleton of a determinant with the lowest agreement level. Both clusters encompass school-related barriers, including after-school activities at the school premises (D15), inclusive activities during regular school hours (D10), cognitive tiredness after school (D6), and perceived lack of support from school staff (D17).

Cluster 3 represents determinants that are less often perceived as facilitators to PA, including habits and routines (D3), financial resources of household (D7), commuting to school (D9), activities outside school after school (D11), competition (D12), transportation and distance to sport facilities (D13), social support from sport professionals (D18), social media (D21), and gender-specific activities (D25).

Cluster 4 contained the most often perceived facilitators to PA. This cluster includes expected determinants related to emotions (D22), fun activities (D23), popular vs personal sport preferences (D24), social support from family and friends (D19), positive role models (D20), and parental knowledge (D8). Additionally, this cluster also includes knowledge (D1), physical skills and fitness (D2), early initiation (D4), ability to navigate social dynamics in sports (D5), self-efficacy (D26), self-esteem (D27), goals (D28), and voluntary participation (D29).

The quantitative phase examined how adolescents perceived the PA determinants identified across adolescents, teachers, and experts, prioritizing these from barriers to facilitators. Integrating the adolescents’ ratings with the qualitative findings generated 3 key meta-inferences for intervention adaptation.

The systematic weak within-group agreement of adolescents’ ratings indicates that they perceive PA determinants individually and differently, despite sharing the mild intellectual disability characteristics and a similar school environment. This finding aligns with behavior sciences frameworks emphasizing that behavior is shaped by its dynamic context and shows individual variability [17,74]. Variation was also evident in the determinants emphasized by each expert and teacher, while literature similarly shows inconsistencies in the determinants identified in comparable groups [19]. This evidence suggests that individual variation in perceived PA determinants among the adolescents is genuine rather than a research artifact.

A related finding was that determinants perceived as facilitators achieved relatively higher consensus, whereas barriers showed particularly weak within-group agreement. The integrated meta-inference is, therefore, that PA interventions should offer a dual strategy: personalized components to address highly individualized barriers and group-level components to enhance more shared facilitators. This duality seems overlooked in prior research, which has focused on the qualitative prevalence of themes in target groups [21,22,30-34] or on statistical comparisons between demographic groups rather than individual variation [24-29]. Modern digital health tools offer unprecedented opportunities to operationalize this dual approach, while being inclusive and scalable [11,75]. For example, cognitive tiredness after school, identified in this study as a barrier, manifests as habitual sedentary periods for some adolescents. Digital tools could identify these opportune moments to promote enjoyable or socially supported forms of PA.

Determinants that tended to be perceived as barriers by adolescents (clusters 1 and 2) showed weak agreement and primarily related to the school environment, including activities during or after school hours, cognitive tiredness after school, and limited support from school staff. The validation quiz reinforced this finding by showing that many adolescents preferred going home or resting rather than participating in PA at school after school hours. However, experts and teachers viewed the school environment as promising for inclusive PA opportunities. This is consistent with evidence of school-related determinants found in literature for adolescents with mild intellectual disability [21,24-26,28,31] and prior studies evaluating school-based interventions [76,77].

Integrating these findings, the key meta-inference is that, although schools are a promising setting for inclusive PA interventions, school-based PA opportunities may not align with every adolescent’s individual needs, lived experiences, and wishes. Therefore, interventions should combine the strengths of the school setting with tailored support for individual barriers, particularly focusing on unstructured time (eg, during breaks and after school hours) [78]. For example, one approach could be to use school-led digital interventions that extend beyond the school premises, enabling teachers and staff to support PA participation in settings such as the home or local parks when these better fit adolescents’ needs and daily lives.

Adolescents rated some determinants as facilitators, aligning with qualitative input from experts and teachers, including emotions, fun activities, popular vs personal sport preferences, social support from family and friends, positive role models, and parental knowledge. These determinants were clustered among the highest-rated facilitators and demonstrated relatively greater consensus across adolescents (clusters 3 and 4). However, adolescents rated several determinants as facilitators that experts and teachers emphasized as barriers, particularly those related to impaired skills and self-efficacy. In addition to the qualitative phase explanations above, three other factors may account for this discrepancy in the quantitative phase. First, adolescents rated PA determinants more often as facilitators than barriers (mean 5.1/7, SD 1.72), suggesting that they answered based on what they believe matters for PA participation rather than their own experiences. For example, self-efficacy was often rated as a facilitator, indicating adolescents know it helps participation even if they do not feel confident themselves. Second, social desirability bias may have led adolescents to underreport personal struggles. Third, adolescents may genuinely view PA barriers and facilitators differently, emphasizing emotional and social aspects meaningful to them.

The integrated meta-inference is that PA interventions should prioritize shared facilitators as core group-level targets. In other words, interventions should target adolescents’ positive meaning of PA participation, such as enjoyment and social influences. At the same time, teacher and expert perspectives suggest that impairment-related determinants may still influence adolescents’ ability to benefit from the shared facilitators. Therefore, while interventions should avoid being driven solely by an impairment-based lens, such considerations remain important for ensuring that shared facilitators are accessible and meaningful for adolescents with mild intellectual disability.

Research on typically developing adolescents has consistently shown that social influences and enjoyment are primary facilitators of PA participation [79]. This is consistent with our findings in adolescents with mild intellectual disability, suggesting that these facilitators are shared across adolescents’ populations regardless of cognitive ability. Nevertheless, experts and teachers in this study mentioned barriers specific to adolescents with mild intellectual disability, such as impaired capabilities, cognitive tiredness, struggles in competitive activities, and the need for structured support. These barriers underscore the need for tailored interventions in the PrO context, although adaptations may be less extensive than those needed for adolescents with more severe intellectual disability who experience greater barriers to PA participation [19,80,81].

A larger proportion of adolescents attending PrO schools in the Netherlands comes from families with low socioeconomic status (SES) compared to other education tracks [82]. Previous research has identified barriers to PA among low-SES adolescents that are consistent with those identified by experts and teachers in this study, including limited household resources, low family support due to competing priorities, and difficulties accessing PA opportunities [83]. Similarly, social support from friends and enjoyment have been identified as facilitators across all SES groups, which is consistent with our findings [83]. This suggests that barriers may be more dependent on individual circumstances, including SES, while facilitators such as enjoyment and social support appear to be shared across adolescents.