A comparative study of body composition of urban and rural Japanese boys 12 to 14 years old.

Whole body counting of potassium-40 and anthropometric measurements were done on 88 urban and rural Japanese boys 12 to 14 years of age. The log-normal distribution provided a good fit to the observed data of potassium content in both groups. The urban and rural boys did not differ significantly in age, weight, body and sitting height, chest and abdomen circumferences, antero-posterior diameter of chest and abdomen, and grip strength. On the other hand, the mean potassium content, K/body weight, K/fat-free mass and estimated upper-arm muscle circumference were significantly greater in rural boys. Skinfold thickness and percentage fat were significantly greater in urban boys. In a regression analysis estimating whole body potassium from anthropometric variables, body weight and skinfold thickness were the most significant variables, accounting for 85.2% of the total variation. Estimation errors were smaller in the rural than in the urban group. Factor analysis was used to identify the factors which could explain the items measuring body composition and strength. Factor 1, in which potassium content and grip strength are the most important items, was designated as the 'Muscular Factor', and Factor 2, in which skinfold thickness and upper-arm circumference are the most significant items, was designated as the 'Fatness Factor'. The factor scores of rural subjects were scattered in a considerably narrower range than those of urban subjects.