The challenges of evaluating environmental interventions to increase population levels of physical activity: the case of the UK National Cycle Network

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 activity, such as media campaigns or primary care based "exercise on prescription schemes", have focused on individual behaviour 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) . . .