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

Abstract Background: Depression is a mental health problem often occurring in older adults. More attention has been paid to the benefits of green exercise on mental health in recent years. However, most existing studies of structured exercise on older adults’ depressive symptoms only encompassed one or two exercise components (aerobic/muscular strength/balance) in indoor setting. Considering the advantages of indoor exercise and the high relevance between nature and mental health, the combination of indoor and outdoor multicomponent structured exercise (MSE) programs might be able to maximize intervention effectiveness. The aim of this study is to develop and examine the effect of a blended indoor and outdoor MSE program on depressive symptoms, physical fitness and physical activity (PA) enjoyment in Hong Kong older adults with 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.