Inertial characteristics of children and their application to growth study.

The water displacement method was used in this study to obtain volume distribution data on limb segments. A mathematical method was then applied to those data to calculate the values for centre of gravity, radius of gyration, principal moment of inertia, and volume. The results showed the water displacement method is not sensitive to random error, while giving a good estimation of inertial properties. Centre of gravity, expressed as percentage of segment length, has a very small variance; the variance of radius of gyration was even smaller. These two variables show sex-related differences, the former also displaying differences relating to age, especially for multi-segment units such as the forearm with hand. The principal moment of inertia and volume were highly correlated with anthropometric variables. Volume ratios had significant sex and age differences, absent for the absolute value for volumes. Since the results demonstrated characteristics absent from conventional anthropometric investigation, the inertial properties may find an application as new indicators of children's growth. It has also noted that the results from previous studies had different results for some inertial characteristics, indicating a need for further studies of the inertial properties of the human body.