Purpose: A twin design was used to assess the relative contribution of genetic and environmental influences on the variation in sports participation of Dutch male and female twins between the ages of 13 and 20 yr.
Methods: Survey data from 2628 complete twin pairs were available (443 male and 652 female monozygotic twin pairs, 377 male and 434 female dizygotic twin pairs, and 722 opposite-sex twin pairs). Subjects were classified as participating in sports if they engaged in competitive or noncompetitive leisure-time sports activities with a minimal intensity of 4 METs for at least 60 min·wk-1.
Results: An overall main effect of age and sex was found on the sports participation dichotomy. Younger twins participated more in sports than older twins, and for each age group males participated more often than females. Genetic analyses of twin resemblance showed a shift in the factors contributing to sports participation from adolescence to adulthood. Between the ages of 13 and 16 yr, environmental factors shared by children from the same family largely account for individual differences in sports participation (78-84%), whereas genes are of no importance. At the age of 17-18 yr, genetic influences start to appear (36%), and the role of common environment decreases (47%). After the age of 18 yr, genes largely explain individual differences in sports participation (85%), and common environmental factors no longer contribute.
Conclusions: Environmental factors shared by family members determine sports participation in young adolescence but cease to be of importance in adulthood when individual differences in sports participation are largely due to genetic variation.