Abstract
Introduction Physical activity may enhance cognition in older adults, yet evidence from randomized controlled trials (RCTs) on mechanistic pathways remains inconclusive. Methods This single-blinded RCT examined the effects of an 8-week, online-guided, multicomponent physical activity intervention on cognitive function, resting-state functional brain connectivity (rsFC), and the gut microbiome in 92 healthy older adults (M age = 66.35). Participants were randomized to a physical activity group performing moderate-to-vigorous-intensity aerobic, coordination, and balance exercises, or to an active control group engaging in progressive muscle relaxation and listening to aging-related podcasts. The primary outcome was change in visual processing speed (items/s) from pre- to post-assessment. Secondary outcomes included changes in additional cognitive measures, rsFC, cardiorespiratory fitness (CRF), and the gut microbiome. Results The primary outcome showed no significant between-group differences. However, exploratory analyses revealed potential improvements in inhibition ( η 2 = 0.061; p = 0.025) and visual memory ( η 2 = 0.047; p = 0.040) in the physical activity group. This group also showed a potential increase in rsFC between visual and dorsal attention networks ( η 2 = 0.101; p = 0.009). Visual memory gains correlated with improvements in rsFC ( p = 0.013). No between-group differences were observed in CRF or gut microbiome composition. Discussion While the primary outcome (visual processing speed) and predefined mechanistic pathways (e.g., gut microbiome composition) remained unaffected, this may partly reflect the sample’s high baseline fitness, which likely limited observable improvements. Exploratory findings suggest potential cognitive and associated rsFC benefits in memory and attention-related networks. The online format enabled a structured, scalable intervention while minimizing potential confounding from social interaction. Trial registration https://drks.de/search/de/trial/DRKS00028022 (date of registration: 14.02.2022).