Objective measurements of physical activity in primary school children in UK Millineum Cohort (360G-Wellcome-084686_Z_08_Z)

We will measure physical activity using accelerometers at age 7 and again at age 9 in the ethnically diverse UK Millennium Cohort Study and, in a random sample, establish how activity varies by season of year by measuring activity on three further occasions, each a season apart. Two calibration studies will be carried out in 7 and 9 year olds to determine cut-offs defining moderate and vigorous physical activity (MVPA). We hypothesise that MVPA will be inversely related to fat mass, but that this may vary according to sex and ethnic group. We will test the following hypotheses: that children who are physically active have lower fat mass and less central fat; that children who are overweight or obese by school age are less active at primary school; that more active children have higher subsequent self esteem; that children who skip breakfast, drink sugary drinks or eat high energy snacks have higher fat mass and more centrally distributed fat at age 7; and that Body Mass Index is a not reliable indicator of fat mass at this age.