The present study examined characteristics of the body composition of elementary and junior high school students (1,323 boys, 455 girls) who were between 6 and 15 years old. The participants’ body fat mass (BFM) and lean body mass (LBM) were measured by the electrical impedance method; the thickness of their muscle and subcutaneous fat was measured by B mode ultrasonography. The partial correlation coefficients between LBM and a muscle mass index (MMI: muscle thickness(cm) x body height(m)) were statistically significant (boys, 0.782; girls, 0.766), as were the correlation coefficients between BFM and subcutaneous fat mass index (SFMI: fat thickness(cm) x body height(m)), (boys, 0.936; girls, 0.914). The MMI increased with body height, most notably in the boys over 151.7 cm and the girls over 144.7 cm in height.

This study investigated the effects of the verbal instructions on lifting motion after holding an object with the hip and knee flexion in healthy men. The instructions consisted of the following four conditions; no instruction, instruction on the upper body posture (UB), instruction on the distance between the object and the body, and instruction on the direction of gaze. The results suggest that the UB condition prevented greater knee extension and trunk tilting forward at the beginning of the lift compared to the other three conditions. Therefore, instructions such as ʻhold the object by lowering the hips (squatting) and lift by keeping the trunk (or back) straightʼ may be effective in preventing back-straining work, whereas lifting without instructions could put strain on the lower back.