Watts A, et al. - Physical activity may preserve cognitive function in older adults, but benefits vary by sex and genetic factors. Herein, the longitudinal link between physical activity and cognitive performance was tested to determine if a common genetic polymorphism for brain-derived neurotrophic factor (BDNF Val66Met) moderated this impact. Findings demonstrated longitudinal, but not cross-sectional, influences of physical activity on cognitive performance. These data highlight the importance of longitudinal follow-up and consideration of sex differences in the links between physical activity, BDNF genotype, and cognitive decline.