The objectives of this study were 1) to quantify the differences in body densities and percent body fat using various methods for evaluating body composition (e.g., underwater weighing (UWW), air displacement plethysmography (ADP), skinfold caliper (SKF) measurement, ultrasound (US), bioelectrical impedance analysis (BIA), and dual-energy x-ray absorptiometry (DXA)), and 2) to examine the relationship between trends of the differences in body density and percent body fat obtained by these methods and characteristics of morphology and body composition. To this end, the body compositions of 73 healthy male adults were measured using UWW, ADP, SKF, US, and BIA. Twenty-seven of these 73 subjects underwent further measurement using DXA. Differences in body densities determined with ADP, SKF, and US were compared with those measured using UWW as a reference, and the differences in percent body fat estimated with UWW, ADP, SKF, US and BIA were compared with those measured by DXA as a reference. The results of this study indicate that 1) ADP is useful as a method for evaluating body density, as the results differed insignificantly from the reference method and showed no systematic errors due to differences in morphological characteristics and body composition, and 2) UWW measurements exhibited the smallest difference in percent body fat from the reference method, however, more than in any other method, there were systematic errors due to differences in morphological characteristics and body composition, specifically, trunk composition.

The purpose of this study was to investigate the cross-sectional development characteristics of body composition, lower-leg multi-joint power output and sprint running in non-elite junior and youth soccer players. The leg extension power, counter-movement vertical jump(CMJ), and 30m-sprint time for eighty male soccer players aged 13.8-18.1 yrs were measured. Junior and youth soccer players were compared with sedentary normal identical aged boys. Statistical analysis was used by one-way ANOVA and multiple comparisons of variance were performed on the basis of the Tukey-Kramer HSD test. Statistical significance was accepted at level of p < 0.05. Relative increases from 14 yrs to 18 yrs players were significantly (p < 0.05) indicated; body height (7.7%), leg extension power (87.8%), CMJ (35.3%), 30m-sprint (8.7%). 10m-sprint time was negatively correlated with both leg extension power (r = -0.52) and CMJ (r = -0.60). Comparison of relative values of increase from 14 to 18 yrs in junior and youth soccer players to those in sedentary normal boys were as follows; 2.3 (body height), 2.5 (leg extension power), 3.0 (CMJ), 2.1 (sprint ability). It might be suggested that consistent regular soccer training from junior and youth aged might prompt developmental gains not only largely for lower-leg multi-joint power but also not a little for sprint ability.

The purpose of this study was to investigate the characteristics of running on self-driven treadmill equipped with curve-shaped bed (TM) from kinematics and kinetics variables by comparing with those obtained on overground running (OG). Eight healthy male subjects run on TM and OG under constant speed condition of 3m/s. Thirty five reflective anatomical landmarkers were attached on the subject according to Plug-in-gait model. Kinematics and kinetics data were recorded during stance phase using VICON MX (200fps) motion capture system and Kistler force plate (1kHz). Running spatio-temporal parameters such as stride length /stride frequency, lower limb joint kinematics and ground reaction force were compared between TM and OG conditions. Significant high stride frequency on TM running was indicated compare with OG condition (P<0.05). Contact time were almost same between TM and OG, whereas in vertical ground reaction force, non-first impact force as well as lower average loading rate were indicated in TM compared to OG (P<0.05). Lower joint kinematics were significantly different between TM and OG running during first 20% stance phase of normalized stance time. Hip and knee flexion angular velocities were larger in OG than TM (P<0.05). These results suggest that TM running causes lowed intensity for lower limb joints during stance phase, which might be applicable for prevention of running injury.