How should activity guidelines for young people be operationalised?

The subjects for this study were 885 13–19 year olds who recalled four days of activities using a computerised use-of-time instrument, the Multimedia Activity Recall for Children and Adolescents (MARCA). Daily minutes of moderate-to-vigorous physical activity (MVPA) and screen time were calculated. The prevalence of compliance to Australian guidelines (≥ 60 min/day of MVPA and ≤ 120 min/day of screen time outside of school hours) was calculated using the four methods.The four methods resulted in significantly different prevalence estimates for compliance to the MVPA guideline (20–68%), screen guideline (12–42%) and both guidelines (2–26%). Furthermore, different individuals were identified as compliant by the different methods.Clarification of how compliance to guidelines should be operationalised would assist in comparisons between studies, and in consistency in determining correlates of compliance.There has been increasing concern over the last decade at rapidly increasing levels of childhood overweight and obesity [1] and decreasing levels of fitness [2]. A number of strategies have been proposed to combat these trends, including increasing physical activity and reducing sedentary behaviour. As a result, a number of professional and government bodies around the world have issued recommendations for activity levels for young people [3,4]. These guidelines typically specify a minimum number of daily minutes of moderate-to-vigorous physical activity (MVPA), and/or a maximum number of daily minutes of exposure to television, computer and videogames (i.e. "screen time"). In late 2005, for example, the Australian Department of Health and Ageing recommended that children aged 5–18 years get a minimum of 60 minutes per day of MVPA and a maximum of 120 minutes a day of screen time for entertainment [5].In order to monitor compliance or the extent to which populations meet guidelines, there is a need for good operationalisation of such guidelines. This would in turn allow