The optimal intensity of physical activity for alleviating depression in middle-aged and older adults remains unclear. The World Health Organization (WHO) physical activity guidelines recommend adults and older adults to accumulate at least 150-300 minutes of moderate or 75-150 minutes of vigorous aerobic-type physical activity weekly or an equivalent combination of both for health benefits including reduced risk of depression. This parallel, assessor-blinded, pilot randomized controlled trial preliminarily compared the effectiveness of the minimal volume of aerobic-type physical activity at different intensities as recommended by WHO (150 minutes of moderate walking exercise and 75 minutes of vigorous walking exercise weekly) on alleviating depression in middle-aged and older adults. Thirty-five participants were randomized to the control group (CON), moderate walking exercise group (MOD), or vigorous walking exercise group (VIG). The exercise frequency was three times a week and the intervention duration was 12 weeks. The primary outcome was the severity of depression assessed by Beck Depression Inventory. Secondary outcomes included severity of anxiety, sleep quality, quality of life, and cardiorespiratory fitness. Thirty participants completed the study (CON: n = 10, MOD: n = 10, VIG: n = 10). Participants in both MOD and VIG had significantly decreased depression severity after the intervention compared to CON (both p < 0.001). There was no significant difference between MOD and VIG (p = 0.92). Both MOD and VIG interventions also mitigated anxiety severity, improved quality of life and cardiorespiratory fitness. The minimum volume of walking exercise at either moderate or vigorous intensity was found to alleviate depression in middle-aged and older adults.Trial registration: ClinicalTrials.gov identifier: NCT04403373.HighlightsThe 12-week 150-minute moderate walking exercise and 75-minute vigorous walking exercise (the minimal weekly volumes of aerobic-type physical activity recommended by WHO guidelines) similarly reduced the severity of depression in middle-aged and older adults.The 12-week walking exercise interventions significantly reduced anxiety severity concomitant with improved quality of life and cardiorespiratory fitness in middle-aged and older adults with depression.

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