BackgroundDepression earlier in life is a risk factor for dementia later in life. Physical activity is associated with less risk of depression and dementia. However, prevention of Alzheimer's disease may be most effective before the onset of brain pathology, which precedes dementia symptoms by 20 + years, requiring the measure of physical activity across the life course.ObjectiveAssess the reliability and validity of the Lifetime Total Physical Activity Questionnaire (LTPAQ) in community-dwelling cognitively intact adults with and without a history of depression.MethodsTest-retest reliability was assessed with intraclass correlations (ICC). Evidence of construct validity was assessed with descriptive statistics using the contrasted group approach and a priori hypotheses testing with each intensity (sedentary, light, moderate, vigorous) within each domain (school/occupation, transportation, household, leisure-time) across the life course (school-age, adolescence, young adult, middle adult).ResultsEvidence of test-retest reliability and construct validity was found during school-age and adolescence for moderate school/occupation (ICC = 0.562,