This study was designed to find out about the body composition of ordinary Japanese adults, and to clarify how gender and age have effects on it. The subjects were volunteers living in the northern, central and western parts of Japan. They consisted of 154 males and 142 females aged 20 to 59 years. Their body height and weight did not differ by more than 1 S. D. from the mean of the given age category cited in the Japanese Ministry of Education Annual Report. Body composition was estimated from densitometry using an underwater weighing method and pulmonary residual volume measurement. Within each age group, there were significant differences in body height, weight, body density, percentage body fat, lean body weight, fat per 1 m of body height and lean body weight per 1 m of body height, but there was no significant difference in fat between males and females. Percentage body fat and fat increased significantly with age in both genders. The rate of increases of fat were calculated to be 14.2% for males and 10.7% for females per decade. Lean body weight decreased significantly with age in males, decreasing at a rate of 3.3%. However, the lean body weight of females stayed constant over the given ages of this study. These results show that the difference in body weight between males and females is caused by lean body mass, not by fat.

Structural and mechanical adaptations of the femur and tibia to jump and run training were investigated in female Fischer 344 rats. Rats aged 4 weeks were trained for 8 weeks after 1 week of stabilization. In experiment A, the forced run-trained (speed : 30 m/min, duration: 1 h/day) group was compared with the control group. In experiment B, voluntary run and jump-trained (height : 40 cm, 100 times/day) groups were compared with the control group. The limb bones of the jump-trained group had greater cross-sectional areas and greater maximum load in a fracture test than the limb bones of the control group, but there was no significant difference in bone length between the jump-trained group and the controls. The bone adaptations to forced running and voluntary running were similar. The limb bones of both run groups were longer than those of each control group. The cross-sectional areas and the maximum load in the run-trained groups were greater than those in each control group but less than those in the jump-trained group. The present results indicate that bone adaptations to jump training and run training differ and that jump training is more effective for building stronger bones.

This study was designed to determine prediction equations of body density (BD) for athletes using anthropometric variables and to examine validity of the prediction equations. The subjects were 211 male and 198 female athletes aged 18 to 22 years. The subjects were measured for standing height, body weight, skinfold thickness, girth as well as body composition. Body composition was estimated from densitometry using underwater weighing method and pulmonary residual volume measurement. Skinfold thickness was measured at 9 sites on the right side of the body with an Eiken-type ski nfold caliper and 7 measures of girth were taken using a cloth tape. All measurements were done three times from April to October : pre-, mid- and post-competitive season, in order to find out a suitable site reflecting body composition change. Using multiple regression analysis, equations to estimate BD were obtained from standing height, body weight, skinfold thicknesses and girths. The effective prediction equations for BD were as follows : For Males
ED=1.11104-0.00053 (sum of chest, abdomen and quadriceps skinfold thicknesses in mm) -0.00027 (waist girth in cm) .
R=0.851, SEE=0.0051.
For Females
BD=1.11861-0.00054 (sum of abdomen, triceps and subscapula skinfold thicknesses in mm) -0.00054 (waist girth in cm) .
R=0.826, SEE=0.0062.
A cross-validation analysis of these prediction equations for BD correlated highly with hydrodensitometrically determined BD (r=0.832, SEE=0.0053 for males and r=0.812, SEE= 0.0062 for females) . Thus the prediction equations developed in the present study will be applicable to athletes.