The accelerated increase in lean body mass of pre-pubescent Japanese boys at 10 to 11 years of age.

The present study investigated changes in body composition in relation to growth to evaluate at what age Japanese children begin their pre-pubescent growth spurt. Children aged 9 were followed to age 10 (The age 9 group), and those aged 10 were followed to age 11 (The age 10 group). The increase in lean body mass per one-year increment of body height (Δ LBM/ ΔBH) in the age 10 boys group was significantly higher than that in the age 9 boys group. In both the age 9 and 10 boys groups, the high Body Mass Index (BMI) boys showed greater mean ΔLBM/ ΔBH than that for the normal BMI boys. Our results of accelerated Δ LBM/ ΔBH from age 10 to 11 in Japanese boys hypothesize that an increase in LBM demonstrates pre-pubescent growth.