Effects of high-intensity interval training on depressive symptoms in Hong Kong community-dwelling older adults with mild to moderate depressive symptoms: a study protocol for a cluster randomized controlled trial

Background: Older adults with mild to moderate depressive symptoms are at high risk of developing severe depression along with complications, disability, and mortality. Early intervention during mild to moderate stages of depressive symptoms is important to prevent further deterioration. Exercise as a readily available approach has been recognised for reducing depressive symptoms. High-intensity interval training (HIIT), a novel form of exercise that has the potential to improve both depressive symptoms and physical health, has garnered increasing attention. However, the application of HIIT to address depressive symptoms among older adults remains scarce. Aims: This proposed study aims to investigate the effects of HIIT on depressive symptoms, biomarkers of depressive symptoms, physical fitness, sleep quality, and quality of life in Hong Kong community-dwelling older adults with mild to moderate depressive symptoms. Methods: This study will be a single-blinded, cluster-randomised, controlled trial comprising three groups and three assessments. The three groups will consist of a HIIT group, a Baduanjin Qigong control group, and a recreation workshop non-exercise control group. The 144 eligible participants from 9 community centres (clusters) will be randomly allocated in a 1:1:1 ratio to three groups for 16 weeks through cluster randomisation. The primary outcome measure will be self-reported depressive symptoms. The secondary outcome measures will include salivary cortisol (a biomarker of depressive symptoms), physical fitness, sleep quality, and quality of life. The outcomes will be assessed at baseline, after completion of the intervention, and at a three-month follow-up. Discussion: This study will provide valuable evidence on whether older adults in the HIIT group could gain more improvement in depressive symptoms and other health-related benefits compared to the control groups. If HIIT demonstrates superiority, it could be prescribed as a new exercise regimen to benefit older adults with depressive symptoms in future studies. The research findings may have considerable impacts on the future prevention and treatment of mental disorders and may also contribute to promoting healthy aging among Hong Kong older adults. Clinical trial registration: ClinicalTrials.gov, identifier NCT06014294.