Editors' introduction

Ways in which physical activity is influenced by social, cultural, economic and geographical factors in urban settings are discussed in this chapter. Urban populations and the environments they inhabit are highly diverse, this being largely related to position in the economic status system, and reflected in energy expenditure levels. Among urban populations, other factors become increasingly important as the need to work physically hard diminishes with the mechanisation of labor, and the increasing proportion of sedentary paid work. These can be disaggregated into those that operate in nested fashion at the individual, household, neighbourhood and institutional levels. Cultural and demographic factors may have an underlying effect on the way in which the interplay between these factors varies from place to place, although institutional influences may be quite idiosyncratic, and vary enormously within any sociocultural and geographic region. Thus far, there is little data from urban populations on human energetics in an ecological context, and there is a great need to study urban compexity in relation to physical activity. Energetics and physical activity are important to understand in relation to the increasing global prevalence of overweight and obesity (which has taken place predominantly among urban populations), and with respect to ovarian function, which Ellison, in chapter 6, indicates may be influenced by many factors in the urban environment.