**Background:** The AGIL Barcelona (AGILBcn) program is a community-based multicomponent healthy aging intervention for frail older adults. During the COVID-19 pandemic, the need to transition to virtual or semi-virtual formats became urgent, but implementation strategies for mHealth physical activity programs in this population remain poorly defined. This study aimed to identify and prioritize implementation strategies to optimize the accessibility, acceptability, and adaptability of mHealth interventions for enhancing physical activity in frail older adults through a co-design process involving multiple stakeholders.
**Methods:** A mixed-methods study was conducted in two phases. In the qualitative phase (Phase 1), a method adapted from the World Café approach (termed "AGIL Café") was used across six virtual groups (two per stakeholder group) to identify strategies for facilitating a virtual physical activity program. Participants included older adults (OA, n=7, aged 70–90 years), health professionals (HP, n=13), and community and voluntary sector professionals (CVS, n=9). Sessions were conducted via Zoom between December 2020 and March 2021, lasting 1.5 hours each. In the quantitative phase (Phase 2), an ad hoc questionnaire with 27 strategies (grouped into 4 categories) was administered via LimeSurvey (HP, CVS) or computer-assisted telephone interviewing (OA) between May and June 2021, with a 100% response rate. Each strategy was rated on a 5-point Likert scale for priority (P1–P5) and feasibility (F1–F5). Scores were converted to numerical values (P1/F1=100, P5/F5=0). A "priority vs. feasibility score" (PvF score) was calculated as the average of priority and feasibility scores. Qualitative data were analyzed using summative content analysis; quantitative data used nonparametric descriptive analyses.
**Key Results:** Twenty-seven strategies were identified and grouped into four categories: (1) general strategies for reducing barriers (e.g., assess digital capacity, educational meetings, paper-based materials, continuous technological support); (2) specific strategies for facilitating use of a digital application (e.g., telephone feedback, gamification, expert user programs); (3) specific strategies for facilitating participation in virtual exercise groups (e.g., limit group size, personalize exercises, incorporate music, send reminders); and (4) specific strategies for facilitating external support (e.g., recruit local volunteers, peer support, intergenerational programs, social prescription). The top ten strategies by overall PvF score were: limit virtual group size (81), provide personalized exercises (75), conduct educational meetings on technology (74), establish a preferred video platform (73), implement reminder systems (73), provide continuous technological support (71), incorporate music (71), inform family about technology (69), assess need for external support (69), and provide telephone feedback on individual progress (69). The "must do" strategies identified through the prioritization matrix included: set up a preparation meeting, identify a support person for technology, assess need for external support, limit group size, personalize exercises, and provide weekly telephone follow-up. HP scored priority higher than feasibility for most items (average difference −12), while OA showed the highest coherence between priority and feasibility (average difference <1). CVS scored systematically lower on all items (average PvF 56 vs. 72 for HP and 66 for OA).
**Clinical Implications:** The study provides a practical, stakeholder-informed framework for implementing mHealth physical activity programs in frail older adults. Key actionable strategies include pre-program digital literacy training and capacity assessment, family involvement, small-group virtual sessions with personalized exercises, and regular telephone follow-up by health professionals. The findings highlight the importance of combining digital and non-digital support mechanisms to avoid exacerbating health inequalities. The co-design approach revealed divergent perspectives: older adults prioritized social interaction and personalized attention, health professionals focused on feasibility barriers, and community professionals emphasized leveraging existing local support networks. These strategies can inform policymakers, care providers, and practitioners designing technology-based programs for older populations, particularly in contexts where face-to-face delivery is limited.