For participants with high NfL concentrations, global cognitive decline was 12% slower for medium physical activity (β, –0.065; 95% CI, −0.099 to −0.032) and 36% slower for high physical activity (β, –0.048; 95% CI, −0.080 to −0.016) than for low physical activity (β, –0.075; 95% CI, −0.108 to −0.041). The gene discussed is NEFL; the disease is Mental deterioration.