Abstract: To analyze the genetic and environmental factors influences on the development of body ircumference and breadth in school-age twins, six body measurements including stature, chest circumference, waist circumference, hip circumference, shoulder breadth and crista breadth were measured and the related indices were calculated in 351 twin pairs aged from 6 to 12 years old. Mx software was used to fit the best structural equation model to calculate the heritability of each index and analyze the effect of age and gender. The results indicated that the best fitting model of each index was ACES. The age variance (S) of each body measurement (0.21~0.76) was obviously higher than that of derivative indices except for the waist-hip ratio (female 0.15, male 0.05). The common environmental variance (C) of each index (0.00~0.53) varied largely. The special environmental variance (E) of derivative indices (0.09~0.25) was generally higher than that of body measurements (0.01~0.09). After adjusting age, the heritability of each index was as follows: Stature (female 63%, male 59%), chest circumference (female 84%, male 88%), stature-chest circumference index (female 87%, male 55%), waist circumference (female 46%, male 64%), hip circumference (female 61%, male 61%), waist-hip ratio (female 44%, male 44%), shoulder breadth (female 78%, male 78%), crista iliaca breadth (female 62%, male 62%), statureshoulder breadth index (female 40%, male 40%), stature-crista iliaca index (female 35%, male 48%) and acromio-cristal index (female 24%, male 24%). The above-mentioned results showed that the stature, waist circumference, stature-chest circumference index, hip circumference, shoulder breadth and crista iliaca breadth of school-age children were mainly influenced by the genetic factors, while the other indexes were mainly impacted by the environmental factors. Meanwhile, there were gender differences in genetic effect to some extent for stature-chest circumference index and waist circumference, and the age effect on the related indices of body circumference and breadth was not obvious in this study.

Key words: School-age children; Twins; Circumference development; Breadth development