Measurement and surveillance of physical activity and sedentary behaviours

We believe it is important to assess both physically active and sedentary behaviours. Indeed, although studying sedentary behaviour as a concept distinct from physical activity has been advocated recently (Owen et al. 2000), one factor that has confounded our understanding is the conceptual and definitional ambiguity over what inactivity actually is. Many large-scale epidemiologic surveys have attempted to assess the prevalence of sedentariness in a population by measuring against a minimum criterion for physical activity or energy expenditure thought necessary to obtain health benefits. While a central function of these surveys is simply to provide a description of patterns of (in)activity in a population,

these measures often fail to capture the diversity of physical inactivity behaviour and tell us nothing about what inactive people are actually doing. It is therefore proposed that ‘physical inactivity’ is an inadequate label to describe patterns of sedentariness because the definitional premise is one of ‘activity absence’, thus failing to capture the complexity of sedentary behaviour. It is suggested that a typology of sedentary behaviour be developed and conceptualised as a distinct class of behaviours characterised by low energy expenditure.

This definition acknowledges that both the topography of movement (what they are actually doing) and the energy cost are equally important features for understanding behaviour (Marshall et al. 2002).

Few studies have assessed physical activity and sedentary behaviours, although a metaanalysis suggests that for children and adolescents the relationship between physical activity and TV viewing (the most prevalent sedentary behaviour) is very small, suggesting that the two behaviours may be able to co-exist (Marshall et al. 2004).

The problems in determining the activity levels of the population should not be underestimated. The measurement of physical activity becomes less reliable as techniques more suited to large-scale surveys are used (Sallis and Saelens 2000). In a review of physical activity assessment in epidemiological research, LaPorte, Montoye and Caspersen (1985)

identified over thirty different techniques. For large-scale population-based research, however, the use of some variation on survey recall of activity is inevitable. However, so-called ‘objective’ measures, such as heart rate monitors or movement sensors, are possible in smaller samples, although with the development of cheap pedometers, larger cohorts can now be assessed (Tudor-Locke and Bassett 2004). There is no agreed ‘gold standard’ technique for assessing physical activity (Ainsworth, Montoye and Leon 1994). In an effort to obtain greater standardisation of self-reported physical activity levels across countries, a group of researchers have developed the International Physical Activity Questionnaire (IPAQ) for both international surveillance trends monitoring and more focused research projects (Craig et al. 2003). In the late 1990s, an international group of physical activity specialists developed several forms of the IPAQ. These included long and short forms, self-administered and those administered by telephone, and those that referred to the ‘last seven days’ and a ‘usual week’. The long form of IPAQ allows for assessment of different types of activity, including occupational, transport, yard/garden, household, leisure and sitting. Satisfactory reliability and validity, at least comparable with other self-report measures, were reported and it was recommended that the short form (seven-day version) be used for national physical activity monitoring purposes. In addition, it was proposed that the long form be used for research purposes where more detailed assessing is required (Craig et al. 2003). Further details are available at www.ipaq.ki.se.