Efforts to increase energy expenditure deserve as much emphasis as those to reduce energy intake for the management of overweight/obesity. Yet, in the public mind, management seems dominated by ‘dieting’. This is surprising since data suggest that mean energy intakes for UK children under 15 years fell consistently over the latter half of the twentieth century (Gregory et al. 1995; Gregory and Lowe 2000). Some decline in energy expenditure as PA must have contributed at least in part to the increased prevalence of obesity. Multi-pronged approaches which include changes to both dietary habits and PA are now widely recognized as the ways to effective management in adults (Chief Medical Officer 2004; Lobstein et al. 2004). In children, both increased PA and reduced sedentary behaviour are effective in the treatment and prevention of childhood obesity (Summerbell et al. 2003, 2005).

What has changed?

Why has PA declined so much in children of many westernized countries? We list below some of the societal and environmental items which have led to falling PA levels in many present-day societies.

Urbanization

Roads are much busier with traffic than in the past and many play areas and open spaces in towns have been lost. The environment and the perceptions of the environment seem very important to the extent to which children are active outside the home (Davison and Lawson 2006; Evenson et al. 2006; Alton et al. 2007).