Secular changes in relative leg length in post-war Japan.

Longitudinal secular changes of height and estimated leg length (ELL) or subischial leg length 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. A significant trend towards greater relative leg length (long-leggedness) among Japanese children and youth has occurred during the period of about four decades covered by this study. After showing a strikingly consistent trend at all age levels between 6 and 17 years and a dramatic trend during the birth-year age period 1943-1963, the relative growth in leg length has been rapidly slowing or has stopped in both sexes. The relative growth of ELL seemed to be fixed after 11 years in boys and 9 years in girls. Maximum increment ages (MIA), both in height and ELL, were used as estimates of the timing of maximum growth during the adolescent spurt. Regression analysis was used to demonstrate the overall trend patterns of MIA in height and ELL. After removing autocorrelation effects, MIA for height is accelerated by 0.03 year in both sexes, while the MIA in ELL is accelerated by 0.03 year in boys and 0.01 year in girls. Thus, MIA in ELL in girls is occurring earlier but to a smaller extent than in boys. The average maturity difference between boys and girls is 2.07 years in height, but 2.83 years in lower extremity length. Am. J. Hum. Biol. 12:405-416, 2000. Copyright 2000 Wiley-Liss, Inc.