To evaluate quantitatively the development of equilibrium function in children, the author investigated head movement (H. M.) and movement of the body's center of gravity (M. C. G.) in six agegroups of children and adults, using a cephalograph to record H. M., a straingauge-platform to record M. C. G., and a technical computer. One hundred twenty-six healthy subjects aged 4 to 28 years were instructed to stand with feet close together on the platform with eyes open and with eyes closed for 60 seconds each.
1. The area and total length of H. M. and M. C. G. decreased with age. They were significantly larger in children younger than 12 years of age than in adults. Changes in the swaying velocities of H. M. and M. C. G. in 8 directions paralleled the area and total length of sway.
2. The averaged divisional frequencies of H. M. and M. C. G. decreased with age both in the lateral component and in the anteroposterior component. They were significantly larger in children younger than 9 years of age than in adults.
3. In all six agegroups the total length, swaying velocities and averaged divisional frequencies of H. M. were smaller than those of M. C. G.
4. The ratio of the anteroposterior component to the lateral component in H. M. did not differ among the agegroups. On the other hand this ratio in M. C. G. was significantly larger in children younger than 9 years of age than in adults.
5. The ratio of the total length of H. M. to that of M. C. G. was significantly larger in children younger than 9 years of age than in adults.
6. The ratio of the area and total length of H. M. and M. C. G. with eyes closed to those with eyes open did not differ among the agegroups.
These results suggest that the body sway of children is not only larger than that of adults, but also different from it in nature. It appears that the ratio of H. M. to M. C. G. is larger in children than in adults, and that the ratio of the anteroposterior component to the lateral component in M. C. G. is also larger in children than in adults.