Secular Changes in Body Proportions and Composition

Abstract

The manifestations of the secular trend in size are seen as increases in most body dimensions; however, little attention has been given to the question of possible concomitant secular changes in body proportions or composition. The notion of altering body proportions or composition implies tissues of the body respond differentially to whatever factors are responsible for secular changes. Hence, bone may respond more or less to secular factors than does muscle or fat; such modification through time may be seen as changes in body composition or body proportions. An intertissue allometric response also may vary according to particular body site. So, for example, the growth of bone, such as the elongation of the trunk or arms, may not be proportionate to that of the elongation of the legs; thus, body proportions may be altered. The interpretation of secular changes in proportions and composition may be rather straightforward, as in the previous examples, or may be quite complex, such as possible shape changes of the head or face. This chapter reviews selected indices of body proportions and composition in populations that have evidenced secular changes in overall body size.