Professor of Health Psychology and Exercise Science, Associate Dean, Faculty of health and Behavioural Sciences, University of Wollongong, NSW 2522, Australia.

Population-wide strategies for the prevention of non-communicable diseases (particularly cardiovascular disease, diabetes and some cancers) rely on influencing patterns of behavior - primarily physical inactivity, dietary habits and cigarette smoking. A particularly important public-health goal is to curtail, in the aging populations of Asia, those disease processes that are determined by the interactions of habitual physical inactivity with prevailing dietary patterns.
The rising prevalence of overweight and obesity in the increasingly sedentary populations of our region is a compelling indicator of the important role of physical activity in health. Many national health policies (particularly for the prevention of cardiovascular disease and diabetes) now include physical activity targets and guidelines. These emphasize regular, moderate-intensity activity (1). There are also some broad policy commitments to develop the social and community infrastructure needed to make physical activity a more realistic and enjoyable option.
While the current imperatives to increase physical activity come from the health sector, much of the necessary implementation will require strong involvement and leadership from several other sectors of our societies - including education, sport and recreation, transport, local government, the food and other industries, religious organizations and community-service groups.
Improved concepts, methods and systems for monitoring, understanding and influencing physical inactivity and its determinants in whole populations are needed. Relevant domains of health-behavior research may be classified using a "behavioral epidemiology" framework (2). In the case of physical activity, five main phases of research and development may be identified:
Phase 1 - establish the links between physical activity and health.
Phase 2 - develop methods for accurately measuring physical activity.
Phase 3 - identify factors that influence level of physical activity.
Phase 4 - evaluate interventions to promote physical activity.
Phase 5 - translate research into practice.
Phases 2 and 3 study the types and amounts of physical activity that are identified as most closely associated with health in phase 1. Research in phase 4 targets the most sedentary groups, and tries to change influences found to be most related to physical activity that have been identified in phase 3. When interventions are shown to be effective in phase 4, it is hoped that they will be used in worksites, schools, health care settings, fitness facilities, and the broader community environment.
Examples from Australian and international studies of health-related physical activity illustrate the status of our current knowledge base in these areas. Strengthening research and development efforts in these latter phases can inform practical initiatives of population-health significance.
In order to proceed with evidence-based planning, initiatives and evaluations, the two central elements identified in the behavioral epidemiology framework are crucial:
o developing methods for accurately measuring physical activity; and,
o identifying those physical activity "determinants" that influence different population groups, in different settings and at different life stages.
While we now have some reasonably valid, reliable and practically useful measures of leisure-time physical activity, we need to know much more about how to assess occupational, domestic and "incidental" physical activity. These forms of activity are central to long-term energy balance and associated health outcomes. New measures are emerging from research using accelerometers to obtain direct measures of movement, physiological monitoring, observational and self-report techniques. Findings from these studies will greatly assist in deriving accurate prevalence estimates for levels of participation, facilitate the tracking of trends over time and will inform the evaluations of new policies and programs.
Understanding the determinants of physical activity will require some new research initiatives, particularly if we are to understand and influence the pervasive environmental factors that are leading to widespread inactivity (3). It seems highly likely that technological innovations in transportation, community, working, entertainment and information environments are contributing significantly to a new "epidemic" of sedentary behavior. This is a domain within which new theoretical frameworks, new measures of activity and physical activity environments, trials of innovative interventions and evaluations of large-scale policy initiatives will be highly informative.
These new directions should lead in a practical sense to more-effective campaigns to influence physical activity knowledge, attitudes and behaviors (4). Importantly, our strategies must also include concerted efforts to recruit stronger support from political, community and industry leaders and decision-makers. This is crucial for implementing the environmental, community and social innovations needed to make being physically active a natural, enjoyable and easy option (2, 3).
The challenge for research is to develop more-focussed yet comprehensive conceptual models and to assemble new research findings that will help us to better understand, measure and influence physical activity. With better concepts and measures relating to activities that influence long-term energy balance, we will be strongly placed to study interactions with dietary and nutritional factors. We will be able to proceed with innovative strategies and programs for particular groups and settings. We must then demonstrate that these efforts actually lead to more-active living and that they do result in healthier aging.

References

1. U.S. Department of Health and Human Services (USDHHS). Physical activity and health: A report of the Surgeon General. USDHHS, Centers for Disease Control and Prevention, Atlanta, 1996. <http://www.cdc.gov/nccdphp/sgr/sgr.htm>
2. Sallis J F, Owen N. Physical activity and behavioral medicine. Thousand Oaks, Ca., Sage, 1999. <http:/www.sagepub.com> (email: order@sagepub.com)
3. Sallis J F, Owen N. Ecological models. In K Glanz, F M Lewis, B K Rimer (eds.). Health behavior and health education: Theory, research and practice, Second Edition. (pp. 403-424). San Francisco, Jossey-Bass, 1997.
4. Marcus B H, Owen N, Forsyth L H, Cavill N A, Fridinger F. Interventions to promote physical activity using mass media, print media and information technology. Am J Prev Med 1998; 15: 362-378.