Purpose: The aim of this study was to investigate genetic and environmental influences on different aspects of physical activity in young adult twins.
Methods: We studied 1274 Finnish twins with a mean age of 22.4 yr, from the population-based FinnTwin12 study. Physical activity was assessed with the Baecke Questionnaire, yielding four indexes: the sport index, leisure time activity index, work index, and total score. Quantitative genetic analyses based on linear structural equations were used to estimate the contribution of genetic and environmental factors on these physical activity traits.
Results: The overall heritability estimates were 64% (95% confidence interval (CI) = 0.56%-0.70%) for sports activity, 41% (95% CI = 0.31%-0.51%) for leisure time activity excluding sports, 56% (95% CI = 0.48%-0.63%) for physical activity at work, and 54% (95% CI = 0.45%-0.62%) for total physical activity. Unique environmental factors accounted for the rest of the trait variances. We did not find evidence for common environmental or dominant genetic influences. The heritability estimates did not differ between men and women, and no sex-specific genetic factors were found. Sports activity and leisure time activity excluding sports were associated (r = 0.27), and additive genetic factors explained 57% of their association.
Conclusions: Our results suggest that genetic factors contribute significantly to physical activity levels in young adults and that sports activity is under stronger genetic influence than leisure time physical activity excluding sports. We also concluded that physical activity at work does not seem to be associated with sports activities or other leisure time physical activity at this age.