This study expands on prior research conducted on serum biomarkers in CHAP.3 Examining the associations between AD biomarkers and health behaviors such as physical activity is a new area of research.25 We found only 1 study, the Multidomain Alzheimer Preventive Trial (MAPT),26 that evaluated associations between NfL concentrations in blood and physical activity over 4 years. This evidence concerns the gene NEFL and Alzheimer disease.