Objective methods are being used increasingly for the quantification of the amount of physical activity, intensity of physical activity and amount of sedentary behaviour in children. The accelerometer is currently the objective method of choice. In this review we address the advantages of objective measurement compared with more traditional subjective methods, notably the avoidance of bias, greater confidence in the amount of activity and sedentary behaviour measured, and improved ability to relate variation in physical activity and sedentary behaviour to variation in health outcomes. We also consider unresolved practical issues in paediatric accelerometry by critically reviewing the existing evidence and by providing new evidence.

In this sample and setting, fundamental movement skills were significantly associated with habitual physical activity, but the association between the two variables was weak. The present study questions whether the widely assumed relationships between motor skills and habitual physical activity actually exist in young children.

Objective To assess whether a physical activity intervention reduces body mass index in young children. Design Cluster randomised controlled single blinded trial over 12 months. Setting Thirty six nurseries in Glasgow, Scotland. Participants 545 children in their preschool year, mean age 4.2 years (SD 0.2) at baseline. Intervention Enhanced physical activity programme in nursery (three 30 minute sessions a week over 24 weeks) plus home based health education aimed at increasing physical activity through play and reducing sedentary behaviour. Main outcome measure Body mass index, expressed as a standard deviation score relative to UK 1990 reference data. Secondary measures were objectively measured physical activity and sedentary behaviour; fundamental movement skills; and evaluation of the process. Results Group allocation had no significant effect on the primary outcome measure at six and 12 months or on measures of physical activity and sedentary behaviour by accelerometry. Children in the intervention group had significantly higher performance in movement skills tests than control children at six month follow-up (P = 0.0027; 95% confidence interval 0.3 to 1.3) after adjustment for sex and baseline performance. Conclusions Physical activity can significantly improve motor skills but did not reduce body mass index in young children in this trial. Trial registration Current Controlled Trials ISRCTN36363490.

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