Genetic influences on physical activity and sedentary time differ by sex in 9-year-old children, with the largest sex difference found for vigorous physical activity where genetic contribution was substantially larger in boys than girls.
In the total cohort, heritability was highest for vigorous physical activity and moderate for other activity types and sedentary time.
Genetic contribution to vigorous physical activity was significantly larger in boys than in girls.
Genetic contribution to light physical activity was larger in girls than in boys.
Shared environment showed the opposite pattern to genetic contributions across sexes.
The study used a twin framework with structural equation modelling to examine quantitative sex differences in genetic and environmental contributions to physical activity.
This research suggests that genes play a different role in shaping physical activity patterns in 9-year-old boys versus girls. By studying over 2,000 pairs of twins in Sweden and comparing identical twins (who share nearly all their genes) with fraternal twins (who share about half), researchers could estimate how much of the variation in activity levels is due to genetics versus the environment children share (like their home or school) versus individual experiences unique to each child. Overall, genes explained about half to two-thirds of the differences in how active children were, with vigorous activity being the most heritable. The most striking finding was a large sex difference in vigorous physical activity specifically. For boys, genes explained about 57% of the variation in vigorous activity, while for girls genes explained only about 15% — a statistically significant difference. For girls, genes played a somewhat larger role in light physical activity compared to boys. Wherever genetic contributions were higher, shared environmental contributions (like family or school influences) tended to be lower, suggesting these factors compensate for each other. This research suggests that the biological mechanisms driving how active children are — particularly at higher intensities — may differ fundamentally between boys and girls. This could help explain why girls are often observed to be less active and more sedentary than boys. The findings imply that interventions aimed at increasing physical activity in children, especially vigorous activity, might need to be tailored differently for boys and girls, as the underlying drivers of activity behavior appear to differ by sex.
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Upload Your LabsHelgadóttir B, Wang R, Kuja-Halkola R, Wiklund C, Ekblom &, Ekblom M. (2026). Genetic influences on accelerometer-measured physical activity and sedentary time in children: sex-specific patterns from a Swedish twin study.. Scientific reports. https://doi.org/10.1038/s41598-026-55559-w