PHYSICAL ACTIVITY AND PUBLIC HEALTH

Regular, physical activity is associated with increased life expectancy and reduced risk of coronary heart disease, stroke, diabetes, hypertension, obesity, and osteoporosis.1–3 It has been suggested that promoting physical activity is “public health’s best buy”.4 However, most people are not regularly active and the challenge remains as to how “more people ” can be encouraged to be “more active, more often”.5 To date, most public health interventions to increase levels of physical activ-ity, such as media campaigns or primary care based “exercise on prescription schemes”, have focused on individual behav-iour change. At worst these have no overall effect and at best they result in increased levels of activity in only a small proportion of the population and that are seldom maintained long term.6–9 This may not be surprising as these interventions are in effect trying to persuade individuals to participate in activities in environments that are (or are perceived to be) hostile to the very activities they promote.10 11 Modification of social, economic, and environmental factors may yield greater population health dividends than individual lifestyle approaches.12 Indeed such interventions may be necessary before individual lifestyle approaches can be effective.10 In this paper we will discuss the potential role of environmental strategies to increase population levels of cycling and walking; describe one such UK intervention—the UK National Cycle Network; discuss the challenges of evaluating this project and suggest appropriate ways of assessing its effect on population levels of physical activity. THE POTENTIAL PUBLIC HEALTH IMPORTANCE OF CYCLING AND WALKIN