Effect of a blended indoor and outdoor multicomponent structured exercise on depressive symptoms in Hong Kong older adults: study protocol of a randomized controlled trial

Background: Depression is a common mental health issue among older adults. Although green exercise has been shown to be beneficial for mental health, most existing studies on structured exercise for older adults’ depressive symptoms focus on indoor settings and involve limited exercise components. By integrating the outdoor elements into an indoor multicomponent structured exercise (MSE) program, this blended indoor and outdoor approach may maximize the effectiveness of interventions on older adults’ mental health. The aims of this study are 1) to examine the effectiveness of a blended indoor and outdoor MSE program on depressive symptoms, physical fitness and physical activity (PA) enjoyment in Hong Kong older adults. 2) to explore the mediating role of connectedness to nature (CN) between the MSE program and depressive symptoms. Methods: The 16-week single-blinded randomized controlled trial (RCT) (2 sessions/week, 90 min/session) will include 129 community-dwelling older adults aged 60 to 74 years old with depressive symptoms. Participants will be randomized to one of three groups (IG-1: a blended indoor and outdoor MSE group; IG-2: an indoor-only MSE group; CG: a control group) using 1:1:1 allocation ratio. The MSE program (aerobic + muscular strength + balance) will be conducted in IG-1 and IG-2. Primary outcome will be depressive symptoms. Secondary outcomes will include salivary cortisol, physical fitness, physical activity (PA) enjoyment. In addition, the mediating role of connectedness to nature (CN) will be examined to reveal the psychological mechanism of intervention. All measured data will be collected at the pre-intervention, post-intervention, and 3-month follow up stages. Discussion: This study will take the initiative to implement the blended indoor and outdoor MSE intervention catering older adults with depressive symptoms. The results will provide more comprehensive evidence support for non-pharmacological interventions and guide future relevant public health policies for the improvement of older adults’ depressive symptoms. Trial registration: This trial is prospectively registered in the ClinicalTrials.gov. Trial registration number NCT06190327 registered 19 December 2023.