Monitoring muscle oxygen saturation during forest trail hiking: A randomized controlled trial of physiological and immunological observations in older adults

Forest-based physical activity (PA) 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 PA. We conducted a 12-week randomized controlled trial in 69 older adults (aged 66–78 years), comparing forest trail hiking (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 performance, and immunological markers. During hiking, SmO₂ declined progressively, reaching a nadir at 60–90 min before partial recovery. After 12 weeks, the FTH group showed reduced body fat, increased muscle mass, and improved VO₂max, FVC, FEV₁, and PEF, whereas the CON group 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. 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.