Monitoring muscle oxygen saturation during forest trail hiking: a prospective open-label quasi-experimental study...

Forest-based physical activity has been proposed as a strategy to counteract age-associated declines in health, yet its mechanistic underpinnings remain unclear. Muscle oxygen saturation (SmO₂) may serve as a real-time marker of physiological adaptation during a physical activity. This study was conducted as an open-label intervention trial with facility-based allocation in 69 older adults (aged 66-78 years), comparing a forest trail hiking group (FTH, n = 34) with a control group (CON, n = 35). Participants in the FTH engaged in progressive low- to high-intensity hiking (120 min, twice weekly). SmO₂ of the vastus lateralis was continuously monitored, and pre- and post-intervention assessments included body composition, cardiopulmonary function, and immunological markers. During hiking, SmO₂ declined progressively, reaching a nadir at 60-90 min before partial recovery. After 12 weeks, the FTH showed reduced body fat, increased muscle mass, and improved VO₂max, FVC, FEV₁, and PEF, whereas the CON exhibited adverse trends. Immunological changes included decreased IL-6 and increased IL-10 and IL-12 in the FTH, alongside enhanced lymphocyte subsets. Ultimately, continuous SmO₂ monitoring provides an informative marker of muscle oxygen dynamics during prolonged outdoor activity. Forest trail hiking elicited broad physiological and immunological benefits in older adults, underscoring its therapeutic potential for healthy ageing. However, since the study did not incorporate functional immune assessments or specific biomarkers of immunosenescence, the findings should be interpreted cautiously and cannot be considered definitive evidence of immune function restoration.Trial registration: This study was retrospectively registered with the Clinical Research Information Service of the Korea Centers for Disease Control and Prevention under Clinical Trials KCT0008712 on 18/08/2023.