Total body water (TBW) measured by isotope dilution techniques can be used to assess body composition safely and accurately in children. Unfortunately, this method is not readily available for most research projects, particularly when working with large groups of people, because the equipment is complicated and highly specialized. Bioelectrical impedance (BI) method is a simple, quick, and inexpensive method for the assessment of total body water (TBW). In Japanese child population, however, a lack of prediction equations is a problem to determine TBW. The purpose of this study was to determine the prediction equation for TBW determination in Japanese children using the isotope dilution technique as the reference method. Seventy Japanese children (39 boys, 31 girls) with ages ranging between 3 and 6 years participated in this study. They were randomly divided into the validation group (26 boys, 20 girls) and cross-validation group (13 boys, 11 girls). In a forward stepwise regression analysis, 96% of the variability in TBW measured by deuterium oxide (D₂O) dilution could be predicted by the following equation: TBW(kg)=0.149×Resistance Index (Stature²/resistance, cm²/Ω)+0.244×Weight(kg)+0.460×Age(y)+0.501×Sex (boy=1, girl=0)+1.628, with a root mean square error (RMSE) of 0.440 kg in the validation group. This equation predicted TBW in the cross-validation group with R²=0.946 and a pure error (PE)=0.400 kg TBW. Hence, this equation should be applicable for predicting TBW in Japanese children aged 3–6 y.

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The purposes of this study were to clarify the kinetics of muscle oxygenation (Oxy-Hb, Deoxy-Hb) by near infrared spectroscopy (NIR) in the decreasing force phase, especially the pre- and post-phases of the inflection point, in sustained maximal static gripping (SSG), and to examine the relationship between kinetics of muscle oxygenation and force-decreasing parameters. The experiment was conducted on 20 male subjects aged 15–18 years. The time at the lowest Oxy-Hb value (20.5±5.5 s) significantly correlated with the decreasing times of forces of 40, 60 and 80% of maximal voluntary contraction (MVC), and the rate of decreasing force for 0–1 min (r=.60, .53, .49, and −.63 respectively). These parameters reflect the decreasing force based on the oxygenation deficiency into the muscle with the obstruction of the blood flow. The time of reaching the highest Deoxy-Hb value (46.8±15.0 s) and the regression coefficient in the Deoxy-Hb decreasing phase correlated significantly with the decrement for 1–2 min. This parameter evaluates the phase where resumption of the blood flow began, and Deoxy-Hb in the tissue was eliminated. The inflection point of the gripping force is related to the time at the highest Deoxy-Hb, and reflects the beginning and the resumption of the blood flow. The decrement for 2–3 min and the regression coefficient of post-inflection point evaluate the steady state phase of force decreasing, in which oxygen is sufficiently supplied to active muscles.

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We investigated the relation between the vitamin D receptor (VDR) genotype and bone mass including the effect of exercise history as a measure of physical activity. BUA (broadband ultrasound attenuation), SOS (speed of sound) and Stiffness index of the calcaneus were measured using an ultrasound bone densitometer in 105 Japanese young adult women (age: mean±SD 20.4±4.1 years, ranged 18–37) by the calcaneal ultra sound measurement to assess bone mass. Physical activity was measured using a questionnaire about exercise and was calculated as exercise hours per week during prepuberty (elementary school), puberty (junior and senior high school) and a current period (from >18 years old). VDR genotype was determined by the BsmI restriction site of the VDR gene. Significant differences were observed in age-adjusted and menarche age-adjusted SOS and Stiffness between BsmI VDR genotypes. We also examined the interaction between VDR genotype and the amount of exercise. The association between ultrasound parameters and exercise hours per week was evaluated with simple regression analysis according to VDR genotype. There was a significant difference in the slope between VDR genotypes in regression analysis of exercise hours per week during senior high school for SOS (P<0.05). Furthermore, we conducted multiple regression analysis to examine the contribution of each factor to ultrasound parameters. VDR genotype was a significant independent variable for SOS (P<0.05). Exercise hours each week during senior high school was a significant independent variable for all ultrasound parameters (all: P<0.001). In conclusion, there was a partial significant relation between VDR genotype and ultrasound parameters, but the exercise hours each week during senior high school was the strongest independent factor for bone mass in young adult Japanese women.

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