The research proposed compares several methods of evaluating level of habitual physical activity (PA) and fitness in athletic and 100 nonathletic men and women age, 20 to 59. This research will determine the reliability and validity of a variety of evaluation tools for assessing PA and fitness. PA will be assessed repeatedly by the comprehensive Minnesota Leisure Time PA questionnaire and shorter questionnaires; the results of these questionnaires will be compared with those from 24 hour PA and food diary records and mechanical motion detectors (Caltrac). The PA and diet diary and the motion detectors data will be collected 21 times per year (3 times for each day of the week). Physical fitness will be assessed by treadmill exercise testing using the Bruce Protocol and the Beckman Metabolic Measurement Cart for determining maximal oxygen uptak (VO2 max). The results will be compared with estimated VO2 max. values obtained with simpler submaximal step and bicycle ergometer tests; and anthrophometric measurements, including relative body weight, multiple skinfold thickness, body circumferences, and underwater weighing determination of body density and percent body fat. Two years will be required to complete the assessments of the 100 subjects (50 per year). The ultimate goal is to provide researchers in epidemiologic studies and clinical trials guidelines about the relative merit of various procedures for assessing PA and fitness in terms of reliability, validity, practicality, costs and implementation requirements.