large, so we draw on two recent comprehensive reports that have reviewed this work, namely the 2008 report of the Physical Activity Guidelines Advisory Committee (2008) and the position stand on physical activity for older adults from the American College of Sports Medicine (Chodzko-Zajko et al., 2009). A particular difficulty of studying the health benefits of physical activity at older ages is establishing an incontrovertible level of proof. Intervention studies with disease outcomes are rare, so much of the evidence is based on observational studies or short-term interventions with intermediate health endpoints. Nevertheless, the weight of the data indicates that physical activity is associated both with an enhanced life span and good health and functioning at older ages.

Any discussion of the contribution of physical activity to divergent trends in longevity across countries depends on accurate assessment. The second section of the chapter therefore addresses the strengths and limitations of self-report and objective measures and suggests ways in which self-report assessments might be improved. Third, we review the current literature concerning physical activity levels in developed countries in relation to longevity. A key issue in these cross-country comparisons is whether countries should be judged in terms of the proportion of their population attaining recommended levels of physical activity, or the proportion that is sedentary and does no activity at all. Population rates of physical activity and sedentary behavior do not have a simple reciprocal relationship, and country rankings vary depending on which measure is used. While monitoring adherence to physical activity guidelines is valuable for public health promotion, many of the adverse effects of being inactive are likely to occur at the lower end of the activity/inactivity distribution. The timing of important relationships is also poorly understood. Is it the current level of physical activity or sedentary behavior among older adults that is important, or the levels of activity that were present in the country when these individuals were in middle age?

Regular physical activity is thought to be among the most important lifestyle factors for the maintenance of health and prevention of premature disease and mortality. Across developed regions of the world, inactivity ranks alongside tobacco, alcohol, and adiposity as a leading cause of reduced healthy life expectancy (Ezzati et al., 2003). An analysis of the Nurses’ Health Study estimated that the population attributable risk (PAR) for physical inactivity was 16.5 percent of deaths from any cause, 27.7 percent of cardiovascular deaths, and 9.3 percent of cancer deaths (van Dam et al., 2008). In the INTERHEART study of myocardial infarction in 52 countries, the PAR for inactivity was 12.2 percent across all regions of the