The purpose of this study was to investigate the influence of maturity category on the Yo-Yo intermittent recovery level 2 test (YYIR2) in pubescent soccer players. Twenty-six soccer players aged 12.7±0.2 yrs participated in the study and were divided into two groups (Under and Over) by maturity category according to their peak height velocity curves. Maximal oxygen consumption (VO₂max), onset of blood lactate accumulation (OBLA), running economy (RE), fat-free mass (FFM), thigh muscle cross-sectional area (MCSA) by magnetic resonance imaging and distance in the five-jump test (5J) were measured to monitor the development of aerobic capacity and muscle strength, and correlations with the YYIR2 were investigated. The YYIR2 for Under and Over were 255.0±48.2 m and 336.0±71.1 m, respectively, and significant difference was found between the groups. The YYIR2 was significantly correlated with 5J, and the correlations with FFM and MCSA were also significant regardless of whether the data were expressed in absolute or relative value to height. In contrast, no relation with the YYIR2 was found in VO₂max relative value to weight, OBLA and RE, it was suggested that the YYIR2 might not be a good indicator for aerobic development in pubescent soccer players. These results indicated that maturity category affected the YYIR2 of pubescent soccer players due to physique and the development of muscle strength.

Soccer is a competitive sport in which teams aim to score as much as possible and concede as few goals as possible. Soccer players are therefore expected to have skill in intercepting their opponent’s shots by making aggressive sliding tackles. In this study, the effectiveness of sliding tackles on defense and their influence on game results were clarified through an analysis of the games played by the top teams of the respective groups of the first round of the 2006 FIFA World Cup Germany. To be more specific, the frequencies, areas, and success ratios of the sliding tackles made by the teams and their opponents were analyzed. Based on the analysis data, the effectiveness of these sliding tackles and their influence on the game results were evaluated. This study has revealed that the top teams of the respective groups of the first round of the 2006 World Cup utilized sliding tackles more effectively than their opponent teams did.

There are many cases of Osgood-Schlatter disease (OSD) in soccer players. It’s disturbs their activity in playing soccer. It is necessary to protect them from OSD. It’s known that quadriceps muscle tightness and hardness are increasing before OSD would occur. Because muscle fatigue makes it’s muscle harden. Measuring muscle hardness, we can detect the symptom of OSD. The purpose of this study was to investigate changes in muscle hardness and mean frequency (MNF) of surface electromyography (EMG) during 100 repetitions of maximal isokinetic knee extension. Nineteen healthy subjects performed 100 isokinetic knee extensions at 90°/s using a calibrated isokinetic device. Peak Torque (PT) was determined for each extension (90°-0°), and MNF were recorded from the vastus lateralis (VL), rectus femoris (RF) and vastus medialis (VM) of the right thigh at the same time. Quadriceps muscle hardness of the anterior thigh was measured with knee extended both before- and after-exercise. MNF of each muscle and PT decreased with increasing repetitions. MNF showed higher correlation coefficients with PT for RF than for VL or VM (r=0.59, p<0.01). Muscle hardness for each muscle was increased after exercise (VM, 49.6±3.9; RF, 54.9±3.6; VL, 62.6±5.4 ) compared with before exercise (VM, 47.1±4; RF, 47.1±4.2; VL, 56.7±5.4) (p<0.01 each). Reductions in MNF and PT showed the characteristics of muscle fatigue during repetitive maximal isokinetic knee extension exercise, and a correlation between these values was recognized in RF. Muscle hardness showed consistent increases after exercise in all muscles and can thus be used as a marker of muscle fatigue in the RF.

Soccer is played with the aims of scoring goals while preventing the opponent from scoring goals. Today’s soccer exhibits advanced techniques, speedy performances, and quick switches between attack and defense. In order to score goals, players are required not only to formulate systemic defense tactics but also to acquire sliding tackle skills. In the 2006 World Cup, the Italian team conceded only 2 goals throughout the tournament and won the title. These 2 goals resulted from an own goal and a PK, not from their failure in defense. Focusing on their defense capability, this study aimed to clarify the effect of Italy’s sliding tackle skills on their defense in the second round through the analysis of their games using the methodology employed by Sekine et al., (2008). The Italian team calmly judged the situation of their opponents and the run of the game and chose suitable areas and timing for attempting sliding tackles, and effective ways to put pressure on the key players of the opposing team. Not individually but as a unified team, they systematically formed a block against their opponents and performed steady risk management by making multiple players move simultaneously for the sake of covering. Immediately after making a sliding tackle, the player would move on to the next performance, which often resulted in making a pass (purposeful sliding tackle).Though sliding tackles are essential for strengthening defense, any failure of sliding tackles in the penalty area, the vital area, can result in allowing the opponent to make a penalty kick/ free kick and can involve a high risk of conceding a goal. It is important to acquire good sliding tackle skills and to carry out purposeful sliding tackles (aimed at making a shot or sending the ball to a dribble/ pass course).

Computational simulations of motions of rugby balls are presented. Fluid-structure interaction plays an important role in rugby ball motion. An incompressible Navier-Stokes equation is solved on a Cartesian coordinate system. The rugby ball motions are calculated simultaneously using Newton’s equation of motion for transitional motion and Euler’s equation of motion for rotation. Computational results for screw and high punt kick cases are compared with those obtained from experiments.

This study aimed to examine the ‘early-season bias’ in rugby union in Japan, and to describe the nature and severity of injuries in matches during the 2005 season at the collegiate level. Injury surveillance involved sixty-six rugby union players from one university club. The playing season was divided into three phases; pre-competition phase, specific preparation phase, and main competition phase. The difference of injury incidence among the three phases and the trend of injury incidence in the pre-competition phase and main competition phase were examined statistically. Overall injury incidence was 48.4 injuries/1000 player-hours in matches and there was a significant difference of injury incidence among the three phases (p<0.05). Injury incidence in the pre-competition phase indicated a significant decline (p<0.001), however, in the main competition phase, injury incidence significantly increased toward the end of the season (p<0.001). The current study showed less possibility of the association of ‘early-season bias’ with ground condition in Japan.