The overall health of the United States improved throughout the 20th Century (U.S. Department of Health and Human Services, 2001). The ten greatest public health achievements in the United States from 1900 to 1999 included improvements in the areas of vaccinations; motor vehicle safety; safer workplaces; control of infectious diseases; reduced deaths from coronary heart disease and stroke; safer and healthier foods; healthier mothers and babies; family planning; fluoridation of drinking water; and recognition of tobacco as a health hazard (Centers for Disease Control and Prevention, 2001a). The nation faces other health challenges in the 21st Century, including the noninfectious diseases of overweight and obesity. These diseases have reached epidemic proportions (U.S. Department of Health and Human Services, 2001). The prevalence of obesity increased from 12.0% in 1991 to 17.9% in 1998 (Mokdad, et al., 1999), and continued to increase to 19.8% in 2000 (Mokdad, et al., 2001), reaching 20.9% in 2001 (Mokdad, Stroup, & Giles, 2003).
Overweight and obesity are associated with increased health risks for certain chronic diseases, including coronary heart disease, type 2 (non-insulin dependent) diabetes, various cancers (e.g., endometrial, breast, and colon cancers), among other diseases and disorders (Mokdad, et al., 2003; Must, et al., 1999; Thompson, Edelsberg, Colditz, Bird, & Oster, 1999). The top five chronic disease killers, which include heart disease, cancer, stroke, chronic obstructive pulmonary disease, and diabetes, accounted for 68% of all deaths in the United States in 1999 (U.S. Department of Health and Human Services, 2002). Obesity has been estimated to lead to the death of 300,000 adults in the United States each year (Allison, Fontaine, Manson, Stevens, & VanItallie, 1999).
In addition, overweight and obesity impose substantial costs on the United States' health care system (Roux & Donaldson, 2004; U.S. Department of Health and Human Services, 2001). Direct health care costs of overweight and obesity include preventive, diagnostic, and treatment services (such as physician visits and hospital care). Indirect health care costs of overweight and obesity include lost wages due to an inability to function properly, and the value of future earnings due to premature death. Wolf and Colditz (1998) estimated the total costs of obesity to be $99 billion in 1995. Wolf (2001) estimated the total cost of obesity to be $117 billion in 2000, including $61 billion in direct costs and $56 billion in indirect costs. The costs of obesity are primarily due to its contribution to incidences of coronary heart disease, type 2 diabetes, and hypertension (Wolf, 1998).
Pronk, Goodman, O'Connor, and Martinson (1999) estimated a 1.9% increase in medical charges for every one-unit increase in body mass index (BMI). Thompson et al. (1999) estimated lifetime medical care costs are at least $10,000 higher for moderately obese (BMI of 32.5 kg/[m.sup.2]) as compared to non-obese (BMI of 22.5 kg/[m.sup.2]) 45-54 year old men in 1996. Severely obese (BMI 37.5 kg/[m.sup.2]) men in the same age group could expect $17,000 higher lifetime medical care costs as compared to non-obese men in 1996. Nearly half of their estimated lifetime medical care costs, regardless of degree of obesity, were due to coronary heart disease. They also reported similar results across other age groups and for women (Thompson et al., 1999). The relative magnitudes of excess lifetime medical care costs associated with increasing degrees of obesity were similar to estimates for smoking (Thompson et al., 1999).
Chronic diseases, including overweight and obesity, are not only the most prevalent and costly of all health problems, but they are also among the most preventable (U.S. Department of Health and Human Services, 2002). Many chronic diseases are a function of people's daily choices. The lack of physical activity and poor dietary habits are second only to tobacco use as leading causes of preventable death in the United States (McGinnis & Foege, 1993; U.S. Department of Health and Human Services, 2002). Further, physical inactivity is estimated to account for about 22% of colon cancer, 18% of osteoporotic fractures, 12% of diabetes and hypertension, and 5% of breast cancer or about $24 billion of total United States' health care costs each year (Colditz, 1999). Pratt, Macera, and Wang (2000) estimated that $29.2 billion to $76.6 billion (in 2000 dollars) in national health care costs could be reduced annually if the 88 million inactive Americans over the age of 15 increased their participation in moderate-intensity physical activity.
Emphasis on research that links behavioral choices, in particular regular physical activity, with health outcomes was initiated in 1992 (Dunn & Blair, 2002). Sustained activity levels are recommended for long-term health benefits, including moderate-intensity physical activity ([greater than or equal to] five times per week for [greater than or equal to] 30 minutes each time) and vigorous-intensity physical activity ([greater than or equal to] 3 times per week for [greater than or equal to] 20 minutes each time), the latter level being necessary for cardio-respiratory fitness (Centers for Disease Control and Prevention, 2001b; Pate et al., 1995).
In 1996, the director of the Centers for Disease Control and Prevention appointed the non-Federal Task Force on Community Preventive Services (Task Force). The Task Force reviewed and assessed scientific evidence on the effectiveness of community preventive health services and provided several recommendations to help improve the health state of the nation (Pappaioanou & Evans, 1998). The Task Force's review of scientific studies measuring the effectiveness of intervention programs, physical activity, and health found that regular physical activity is associated with improved health, including aerobic capacity, muscular strength, body agility and coordination, and metabolic functioning (Task Force on Community Preventive Services, 2002). Regular physical activity helps reduce risks of cardiovascular disease, stroke, type 2 diabetes, some cancers, and other diseases (Task Force on Community Preventive Services, 2002). There is also evidence that physical activity has an important role in improving self-confidence, self-esteem, and general feelings of well-being (Coleman & Iso-Ahola, 1993; Fletcher et al., 1996; Ponde & Santana, 2000). Therefore, eating healthy and engaging in regular physical activity are two behavioral changes people can make to help prevent obesity and reduce the risks of heart disease, hypertension, diabetes, colon cancer, and premature mortality (U.S. Department of Health and Human Services, 1996).
The dose-response function relating increases in physical activity with health benefits is generally positive and linear in shape (Bouchard, 2001). Small increases in activity for inactive people result in significant health gains. Pronk et al. (1999) estimated medical care costs to be 4.7% lower for people who were physically active for only one day per week as compared to people with no days of physical activity. The Task Force notes that "the largest public health benefit of physical activity interventions is a result of increased activity among sedentary populations, rather than increased activity among already active people" (Task Force on Community Preventive Services, 2002, 71-72). However, despite scientific evidence and health education campaigns, leisure time physical activity rates have remained relatively unchanged (Centers for Disease Control and Prevention, 2001b) while rates of overweight and obesity have continued to increase (Mokdad et al., 1999, 2001, 2003) from 1990 to 1998. Only about 25% of the United States' adult population engaged in leisure time physical activity at or above the recommended levels. Nearly half of the adult population (45%), while physically active in their leisure time pursuits, is active at an insufficient level for long-term health benefits. About 30% of the adult population in the United States gets no physical activity in their leisure time (Centers for Disease Control and Prevention, 2001b). The rates for leisure time physical inactivity were slightly lower in 2000 (27%) and in 2001 (26%) (Centers for Disease Control and Prevention, 2003).
The Task Force also evaluated 94 published studies on the effectiveness of various approaches for increasing physical activity (Kahn et al., 2002). They classified the physical activity intervention studies as (1) informational approaches; (2) behavioral and social approaches; or (3) environmental and policy approaches. Based on the evidence, the Task Force recommended six interventions for increasing physical activity: two informational approaches that include communitywide campaigns and point-of-decision prompts to encourage using stairs; three behavioral and social approaches that include school-based physical education, social support interventions in community settings, and individually adapted health behavior change; and one environmental and policy approach that includes creation of or enhanced …