A Digitally Supported Outdoor Physical Activity Intervention for Mildly Frail Older Adults in Hong Kong

The aging population in Hong Kong is projected to reach 36.6% by 2046, with roughly 16.6% of older adults estimated to be mildly frail-a condition linked to higher risks of falls, hospitalization, and mortality. While physical activity (PA) is a key modifiable determinant of frailty, a major service gap exists for mildly frail older adults, who lack tailored support, resources, and long-term self-management programs. Although Hong Kong features over 440 public open spaces equipped with senior-friendly outdoor exercise facilities (OEFs), older adults often lack awareness and knowledge on how to utilize them safely for aerobic, strength, and balance training. Furthermore, existing PA interventions often overlook social-ecological perspectives and fail to optimize built environment resources or address digital literacy barriers to sustain long-term behavior change.

To bridge these gaps, our team developed and preliminary-tested OUTDOOR-FIT, a complex, theory-driven, socio-ecological mHealth intervention. OUTDOOR-FIT synergizes Hong Kong's built environment (OEFs), social and volunteer support, individual goal-setting, and digital health technology (a contextually tailored mobile Application) to empower mildly frail older adults to self-manage their PA habits. Building upon promising preliminary findings and qualitative feedback from our initial pilot RCT, the intervention has been refined to incorporate neighborhood OEF environmental audits, supervised outdoor experiential practice sessions, and a train-the-trainer volunteer model to support digital literacy and engagement.

The main objective of this study is to evaluate the clinical effectiveness and real-world implementation of the refined OUTDOOR-FIT intervention using a hybrid type 1 effectiveness-implementation design. Primary effectiveness outcomes include physical activity levels, exercise self-efficacy, mental well-being, chronic pain, and social loneliness measured immediately post-intervention, as well as at 3-month and 6-month follow-ups. Guided by the Reach, Effectiveness, Adoption, Implementation, and Maintenance (RE-AIM) framework, secondary implementation outcomes include Reach, Effectiveness, Adoption, Implementation fidelity, and Organizational Maintenance.

This study adopts a mixed-methods design embedded within a two-arm cluster randomized controlled trial (cluster RCT) involving community service units. Mildly frail older adults will be cluster-randomized into either (i) the OUTDOOR-FIT intervention group or (ii) a control group.

Quantitative analysis will be conducted to evaluate the immediate and sustained effectiveness of the intervention across the primary health outcomes. The qualitative component will consist of semi-structured interviews with older adult participants and community stakeholders to evaluate intervention adoption, implementation barriers, and long-term organizational maintenance.