The secular trend: History and prospects

The origin of the term secular trend and the history of study of this phenomenon are analyzed. Throughout most of the 20th century, the direction of changes was the same in most countries: improvement of socioeconomic conditions was accompanied by an increase in the physical parameters of the human body, primarily, the indices of longitudinal growth. This trend has occurred in various populations, all age groups, and representatives of different sections of society. Nevertheless, although the direction of the changes has been the same, their rates have varied. During the last decades of the 20th century and in the early 21st century, opposite changes in the body sizes have been observed in some countries. The patterns and causes of these processes are discussed.