Verification Regarding Secular Trend of Height Growth and The Maximum Peak Velocity during Adolescence

Judging from annual trends in physical growth and development, human physiques are becoming larger and growth is occurring earlier worldwide. However, in conventional analysis methods growth distance curves are analyzed in nearly all cases, and analysis of velocity curves is done by analyzing the difference in the amount of annual growth. This method may show that young people are becoming taller, but there is no guarantee that it objectively demonstrates early maturation. The present study applied the wavelet interpolation method and specified the age of maximum peak velocity (MPV) in growth during puberty from the described physical growth velocity curve. Then, from an investigation of annual changes in age at MPV and the MPV, it was demonstrated that annual trends in physical growth are accompanied by earlier ages at MPV. This study used height growth data for boys and girls from the 2004 School Health Statistical Survey Report. In the analysis of annual trends in particular, there is a need to treat data by the same year of birth. Therefore, height cohort data were established as data sets. The wavelet interpolation method was applied to these height cohort data, and the annual trends in growth in height were obtained. First, a triphasic pattern was taken for MPV age for boys, and quadratic, cubic and cubic least squares approximation polynomials were applied to each phase. quintic least squares approximation polynomials were applied to all years for girls. The tendency was for MPV age among boys to rapidly become earlier from 1925 to 1937, after which the most delayed convex point was seen in 1944. There was then another trend for rapidly earlier MPV age until 1953. Afterward, there was a gradual trend toward earlier MPV age until 1992. Among girls, the most delayed convex point for MPV age was in 1942, after which MPV age became earlier each year until 1971, remained steady until 1977, and then again tended to be earlier until 1992. A triphasic pattern was taken for the annual transition of MPV in both boys and girls, and age at MPV and annual changes in MPV were considered together. Among boys, age at MPV was the latest at the end of World War II (around 1945), whereas MPV was the maximum. MPV in girls reached a maximum earlier than in boys, but the tendency for MPV to reach a maximum in the period when MPV age was most delayed is assumed to have been a growth mechanism that resulted from the increasing MPV during puberty amid the poor living and health conditions during the war, so that people approached the adult height they would naturally reach genetically.