Variation in physical activity lies with the child, not his environment: evidence for an 'activitystat' in young children (EarlyBird 16).

OBJECTIVE: There is currently wide interest in the physical activity of children, but little understanding of its control. Here, we use accelerometers to test the hypothesis that habitual activity in young children is centrally, rather than environmentally, regulated. By central regulation we mean a classic biological feedback loop, with a set-point individual to the child, which controls his/her activity independently of external factors.
DESIGN: Non-intervention, observational and population-based, set in the home and at school.
RESULTS: Girls were systematically less active than boys, and both weekday/weekend day and year-on-year activities were correlated (r=0.43-0.56). A fivefold variation in timetabled PE explained less than 1% of the total variation in physical activity. The activity cost of transport to school was only 2% of total activity, but over 90% of it was recovered elsewhere in the day. The weekly activity recorded by children in Plymouth was the same (to within <0.3%) as that recorded independently in Glasgow, 800 km away. Total daily activity was unrelated to time reportedly spent watching TV.
INTERPRETATION: The correlations within groups and the similarities between them suggest that physical activity in children is under central biological regulation. There are implications both for public health planners and for the potentially novel signalling pathways involved.