The researchers collected information about study participants' mental function, health, exercise, and lifestyle at the beginning of the study. The researchers asked participants to report the number of days per week during the past year that they did each of the following activities for at least 15 minutes: walking, hiking, aerobics or calisthenics, swimming, water aerobics, weight training, stretching, or other exercise. The researchers defined “regular exercisers” as those who reported exercising at least 3 days per week. They then evaluated participants every 2 years to determine if they had developed dementia by using a standard set of examinations done by physicians, nurses, and a neuropsychologist.