Adolescent growth events in eight decades of Japanese cohort data: sex differences

The presence of secular trends in sex differences for the onset or takeoff of the adolescent growth spurt and subsequent (adolescent) growth of Japanese boys and girls were investigated using data published in "The Statistical Report of the School Health Survey" of the Ministry of Education, Science, Sports and Culture, Japan. An optimum kernel regression method was used to derive the biological parameters of the adolescent growth curve. The six parameters derived from the regression analysis were age at takeoff (ATO), height at takeoff (HTO), velocity at takeoff (VTO), peak height velocity (PHV), age at PHV (APHV), and height at PHV (HPHV). The sex difference in age at PHV is about 2.1 years. The sex difference in age at takeoff was about 2.1 years starting with the birth year of 1943, but has become almost insignificant with the birth year of 1980. After 1960, the sex difference in mean HPHV varied within 12-13 cm, but the difference in HTO showed a decreasing trend. After the birth year of 1911, the rate of growth at HTO for girls has become markedly greater than for boys. In contrast, the rate of growth at HPHV for girls has become significantly smaller than for boys (P < 0.05). Sex differences in ATO, HTO and VTO were significantly and negatively correlated with differences in APHV and HPHV, but positively correlated with the difference in PHV. The sex difference in PHV had no relationship with the differences in APHV and HPHV.