Minutes, MET minutes, and METs: unpacking socio-economic gradients in physical activity in adolescents

There is conflicting evidence regarding the relationship between socio-economic position (SEP) and physical activity in adolescents. The aim of this study was to investigate associations between SEP and characteristics of physical activity in Australian adolescents using a high-resolution use-of-time tool.

Use-of-time and pedometer data were collected on a random sample of 2071 9-16-year-old Australian children. Use-of-time was recorded using a computerised 24-h use-of-time recall, the Multimedia Activity Recall for Children and Adults. Reported household income was used as a marker of SEP.

There were no differences in self-reported minutes of moderate to vigorous physical activity (MVPA) across the income bands and only very small differences in the number of daily steps. However, the mix of MVPA components varied across income bands, with adolescents from low-SEP families experiencing less sport but more active transport. Because the mean rate of energy expenditure was greater in sport than in other forms of MVPA (play, active transport or chores), there were significant differences in MVPA-related and total daily energy expenditure across income bands, with the lower bands having significantly lower values. Differences in total daily energy expenditure were almost entirely explained by differences in energy expenditure associated with sport.

Physical activity patterns vary across SEP bands in Australian adolescents, with sport being the major locus of differences. Instruments which do not account for the energy costs of various activities may fail to detect important relationships.