Are children's activity levels determined by their genes or environment? A systematic review of twin studies

• Genetic influences may be expressed when children have brief opportunities for autonomous activity.
• Activity levels in daily-life are predominantly explained by environmental factors.
• Future research should aim to identify key environmental drivers of childhood activity.

ContextThe importance of physical activity to paediatric health warrants investigation into its determinants. Objective measurement allows a robust examination of genetic and environmental influences on physical activity.ObjectiveTo systematically review the evidence on the extent of genetic and environmental influence on children's objectively-measured activity levels from twin studies.Data sources and search termsMedline, EMBASE, PsycINFO, Health and Psychosocial Instruments and all Ovid Databases. Search terms: “accelerometer” OR “actometer” OR “motion sensor” OR “heart rate monitor” OR “physical activity energy expenditure” AND “twin”. Limited to Human, English language and children (0–18 years).ResultsSeven sets of analyses were included in the review. Six analyses examined children's daily-life activity and found that the shared environment had a strong influence on activity levels (weighted mean 60%), with a smaller contribution from genetic factors (weighted mean 21%). Two analyses examined short-term, self-directed activity in a standard environment and found a smaller shared environment effect (weighted mean 25%) and a larger genetic estimate (weighted mean 45%).ConclusionsAlthough genetic influences may be expressed when children have brief opportunities for autonomous activity, activity levels in daily-life are predominantly explained by environmental factors. Future research should aim to identify key environmental drivers of childhood activity.