Abstract
Using X-ray CT images, body composition of the cross-sectional area at the level of the 4 th lumber vertebra was studied in 46 humans (26 males and 20 females) who are in the same period of development. The total cross-sectional area of the subcutaneous fat, abdominal cavity, vertebra and muscles (rectus abdominis, abdominis lateralis, quadratus lumborum, psoas major, dorsi proprii) were measured and compared for sex and age. The result were as follows : 1) The increase in the total cross-sectional area was significant in males aged between 10 and 14, although in females the increase was also significant between 15 and 17. 2) The increase in the subcutaneous fat continued untill age 10-14 in males and age 15-17 in females, and this increase was significant in the latter. The muscles and vertebrae increased until 1517 in both sexes, although the increase in the muscle was more significant in males than in females. 3) The abdominal cavity increased in this period of development in both sexes, although the ratio of the total cross sectional areas decreased. 4) Comparison of body composition by age yielded : In males up to ages 10-14, the relative order of size was ; abdominal cavity, muscles, subcutaneous fat and vertebra. In those aged 15-17, the relative order was muscles, abdominal cavity, subcutaneous fat and vertebra. By contrast, in females up to ages 10-14, the relative order was the same as that for males, but in ages 15-17, the subcutaneous fat ratio was largest, followed muscles and vertebra by abdominal cavity. 5) The increase in the muscles during the period of development was continuous in both sexes for every muscle. It was presumed that significant increase occurs in all muscles except the rectus abdominis in males, and only in the dorsi proprii in females during adulthood. 6) The area sizes at all ages, in both sexes were in the order of abdominis lateralis, dorsi proprii, psoas major, rectus abdominis and quadratus lumborum.
