The secular trend in body proportion changes among Japanese adolescents using a body proportion chart method

Abstract

A number of studies have reported increased body size of Japanese adolescents after World War II. However, in recent decades, to the best of our knowledge, there has been no secular change in height due to exhaustion of the genetic potential for change. The present study aims to clarify secular changes in body size in Japanese adolescents aged 17 years using data from the Statistical Report of the School Health Survey and applying a body proportion chart method. This method simultaneously examined secular changes in height, sitting height, leg length and upper-lower length ratio, and revealed that the linear proportions of contemporary adolescents are changing with a trend toward increasing sitting height and decreasing leg length relative to sitting height, though overall height increase has stopped. This secular change in sitting height can be attributed to an increase in the population with a high sitting height as an inherited trait. If the delivery rate of women with a long torso is higher owing to their morphological advantage, the average sitting height of the next generation will increase. Considering that the linear proportions of Japanese adolescents are still changing, the annual measurement of sitting height as part of the school health survey should be maintained.