The present study analyzed how task constraints affect the pass skills in young soccer players. The tasks were three-vs-one (3v1) ball possession in three different area sizes (8m× 8m, 10m×10m and 12m×12m square). The sizes were the task constraints in the study. The characteristic of the pass skill which is accomplished at the play area under each constraint appeared to be the following: 1. In the 12m area players had enough time and space to play. Therefore the ratio of 2-touch plays was higher. Also movement time was longer than others. 2. In the 10m area and the 8m area, there was no difference of ratio of 2-touch plays and ratio of pass success. 3. In the 8m area, the movement time of 2-touch plays was shortest. From these findings it was clear that size of the play area produced an effect on the pass skill which is shown with the respective environment. Coaches should make the purpose of practice clear in order to make passing an optimum task for players. To achieve that purpose, coaches should manipulate play area sizes.

This study investigated head-trunk motion and muscle activity during soccer-ball heading for the frontal and lateral directions. Subjects were six soccer players who each had a soccer playing career of more than 10 years. Kinematic data were collected by three high-speed-video cameras. Head-rotation and trunk-twisting angles in the back-swing, forward-swing and follow-through phases were calculated. The electromyographic (EMG) activities of four muscles (the sternocleidomastoid, trapezius, external oblique abdominal and erector spinae muscle) were recorded bilaterally. The peak-time-lag, the lag between the greatest activation point of the right side and left side muscles, was calculated to evaluate the qualitative features of muscle activation. The volume of variation of head rotation angle in the backswing showed a significant difference between the two conditions (P<0.01). In the trapezius and external oblique abdominal muscles, the peak-time lag revealed a significant difference between the two conditions (P<0.01). From the results of this study, when skilled players headed the ball for the lateral direction, in the backswing, the head was rotated and the trunk was bent laterally to the opposite direction of the target. In the forward swing, the head was kept in position to see the target and ball in the same field of vision and the trunk was bent laterally toward the direction of target to impact the ball. The muscles surrounding the neck were activated to prepare for ball impact. Finally, in the follow through, back muscles were used to prevent the body from falling forward. We concluded that in the heading motion for the lateral direction, subjects move their trunk laterally while rotating their heads, and that in the heading motion for the frontal direction, subjects move their heads and trunks backward and forward. These results from this study are useful in coaching activities.

The aim of this study was to examine effectiveness of FIFA/Coca-Cola World Ranking (FIFA Ranking) in the prediction of the results of FIFA World Cup^TM (World Cup) finals. All results of World Cup USA 94, France 98, Korea/Japan 2002, and Germany 2006 and FIFA Rankings just prior to each World Cup were used as data. The analytical procedures were as follows: 1) establishing rules for winning and losing in the World Cup, and 2) confirming the prediction accuracy of results of World Cup Germany 2006 based on these rules. The probability that the top sixteen teams in FIFA Ranking would advance to the final tournament was 78.0%. The probability was statistically higher than the probability for teams lower than the top sixteen teams. The probability that high-ranked teams beat low-ranked teams in the preliminary round was 69.1% (p < 0.05). The probability that the top sixteen teams in Germany 2006 would participate in the final tournament was 68.8%. There was no significant difference between competitions (χ²(1) = 0.024, ns). In Germany 2006, the prediction accuracy of participation in the final tournament was 62.5%. FIFA Ranking and results of World Cup were moderately correlated (r = 0.40). These findings indicated that FIFA Ranking was effective as a prediction method for the results of World Cup finals.

Two types of curve kicks are seen in football (soccer). One is a kick in which the player attempts to rub the ball with the toe trying to keep in contact with the ball as long as possible (hereafter called the Usual Curve Kick). This is frequently described in common tutorial manuals. The second is a kick in which the ball is spun by the angle of attack which is made by the swing direction of the kicking foot and the direction of the impact surface (hereafter called the Angle Curve Kick). No studies have examined the difference between these two types of kicking. The purpose of this study was to clarify these two types of curve kicks using kinematic and electromyographic analysis. Kick movements confined to the vicinity of impact were examined. The subjects were six male college football players. In order to observe the kicks from below, a platform with two plates of hardened glass on top was fabricated. Kicking movements were shot with a high speed camera (250 Hz). The subjects tried to kick a ball at their full strength five times for each type of kick, namely the Usual Curve Kick, the Angle Curve Kick and the Inside Kick which was included for the sake of comparison. The direction of the kicking foot, the swing direction, the initial ball velocity and the number of ball rotations were obtained using the images. Results indicate that there was no great difference in performance between the Usual Curve Kick and the Angle Curve Kick, though muscle discharge of the adductor muscle group showed greater values in the Usual Curve Kick. The impact point of the kick was nearest to the toe in the Usual Curve Kick. In the Usual Curve Kick, the direction of the kicking foot changed toward the right at the target suggesting that the hip joint could externally rotate. These findings led to the conclusion that in a comparison between the Usual Curve Kick and the Angle Curve Kick, the Angle Curve Kick was considered to impose less strain on the adductor muscle group in the case of similar performance level.

The purpose of this study was to defi ne a biomechanical profile of the soccer goalkeeper. We tested whether the skill level of 6 goalkeepers correlated with a number of biomechanical tests. The skill level of each goalkeeper was defi ned as the league he played in. The biomechanical tests were designed as standardized measurements of typical goalkeeper actions; they comprised various jumps, a short sprint and a leg strength measurement. The results showed no correlation between the goalkeepers’ skill level and their score in any of the tests. Thus, with reservation for the limited number of subjects, we conclude that the measured biomechanical parameters are of minor importance for assessment of the goalkeeper’s skill level. We suggest that other skills as for example tactical understanding, positioning, perception and anticipation might be more important for the goalkeeper.

The coefficient of restitution (COR) was determined for toe and instep soccer kicks. Furthermore, experiments were performed with a pendulum that modeled the different impact areas in toe and instep kicking. Six sub-elite soccer players performed 20 toe and 20 instep kicks with no run-up at a range of velocities. The path of the foot and ball were recorded using a high-speed video camera (240 Hz) and manually digitized. The velocity of the pendulum and the velocity of the ball were determined using an opto-electrical system (500 Hz). The COR is the ratio between the foot/pendulum and ball velocity before and after impact. In the pendulum experiments the COR was larger for the small area (Toe) at all velocities, whereas this only was found at the lower velocities (< ~15 m s^-1) in the human experiments. In both experiments the COR dropped with increased impact velocity. The different impact areas in the two types of kicks might explain why it is advantageous to perform a toe kick if aiming at producing the highest possible ball velocity. However, this advantage is lost at higher velocities, possibly because, in toe kicks, it is not possible to keep the foot aligned.

The present study is aimed at determining the concentration of heavy metals leached from various types of infills on artificial turfs by using acid solutions as a representative of acid rain. Acid solutions with pH values of 3.0, 3.5, 4.0, and 4.5 were prepared from 0.1 mol/ℓ sulfuric acid and distilled water. Leaching was carried out according to the standard method prescribed by the Ministry of Environment in Japan. The concentrations of heavy metals such as zinc leached in the acid solutions were determined by inductively coupled plasma spectrometry (ICP-MS). The concentrations of heavy metals in the infills were analyzed using an ICP analyzer after the infills were burnt to ashes and dissolved with aqua regia. Zinc (Zn), Iron (Fe), Barium (Ba), and Manganese (Mn) in styrene-butadiene rubber (SBR) infills were leached in acid solutions. Their concentrations increased with increasing acidity of the leaching solutions. In the case of the SBR infill, the concentrations of Zn exceeded the effl uent standard (2 mg/ℓ) in Japan, but decreased with aging time, and were less than the effluent standard for aging time greater than 1.25 years. The concentrations of Zn leached from SBR coated with polyurethane (PU-SBR), ethylene-propylene rubber (EPDM), Eco-fill, and the bark of a cedar tree were less than the effluent standard of Zn in Japan, and were approximately proportional to the Zn contents (%) in all these infills except for the cedar bark.