This study aimed to demonstrate the difference between the anthropometric and physical characteristics of forward (FW) and back (BK) collegiate rugby players, with respect to which the relationships between agility and physical characteristics were examined. The study recruited 28 collegiate rugby players, including FW (N=16) and BK (N=12), with average height of 1.76±0.07 m and body weight of 89.03±14.16 kg. All of the participants conducted the following, with their results recorded for analysis: squat 1 repetition maximum (RM), counter movement jump (CMJ) height, 20 m sprint time including split times at 5 m and 10 m, and reactive agility test (RAT) time. Pearson’s product-moment correlation and unpaired t-test were used at p = 0.05. FW players were significantly heavier than their BK counterparts (p < 0.01). Meanwhile, BK athletes achieved significantly higher measurements in CMJ height (p < 0.01), 10 m (p < 0.05) and 20 m (p < 0.01) sprint times, and RAT time (p < 0.05) compared with their FW peers. Although RAT time significantly correlated with the 10 m (r = 0.659) and 20 m (r = 0.696) sprint times and CMJ height (r = -0.619) in FW players, it did not correlate with any physical characteristics in BK players. Therefore, improvement in physical characteristics can contribute to enhanced agility in FW players. Meanwhile, BK players must improve in not only their physical characteristics but also other factors, such as perceptual and decision-making capabilities. These results inform coaches the necessity to assign the appropriate agility training depending on player positions.

It is well known that energy intake can delay fatigue and maintain performance in soccer players. Many studies showed the effect of energy intake on performance using soccer-match simulation protocols. However, the simulation protocols include no physical contacts among players which cause certainly fatigue in players. Therefore, we consider that the effect of energy intake on performance is overestimated. In this study, we evaluated the practical effect of energy intake on performance in soccer players using a designed game-style exercise. Sixteen male collegiate soccer players (age: 20.7 ± 0.7 years; height: 171.5 ± 5.4 cm; body mass: 66.8 ± 7.0 kg; percent body fat: 11.4 ± 2.5%) performed soccer game. Test foods, the mixture of carbohydrate and amino acids (180 kcal), or control foods (19 kcal) were ingested before 1^st and 2^nd half of soccer game. Subsequently, Yo-Yo intermittent recovery test (Level 2) was conducted as performance test. As a result, the subjects ingested test foods showed significantly higher scores in the Yo-Yo test compared to those ingested control foods (870 ± 55 m vs. 760 ± 59 m, respectively, p < 0.05). The result demonstrates the practical effect of energy intake on the performance in soccer game.

The aim of the present study was to compare physical and technical performances during 11-a-side matches (11M) and 6-a-side small-sided games (SGs) with various pitch sizes in trained young soccer players. Ten outfield players (age = 16.2 ± 0.6 years) performed 11M (area per player = 325 m²) and SGs with three different pitch sizes (area per player = 325 (SGL), 165 (SGM) and 81 (SGS) m²). A Global Positioning System (15 Hz) and video recording were employed to analyse physical and technical performances, respectively. Total distance covered was significantly longer during 11M than SGM and SGS, and high speed running distance was significantly greater during 11M than SGS (P < 0.05 for all). A greater acceleration frequency (1-2 and 2-3 m·s^-2) was observed during SGS compared to 11M (P < 0.05). A significantly less number of shots was attempted during 11M than SGM and SGS, and the number of tackles, touches and passes, and ball involvement were significantly less during 11M than SGS (P < 0.05 for all). Therefore, SGs can provide similar physical and technical stimulus to 11M as long as area per player is similar. Whereas, a reduction in area per player of SGs in comparison with 11M results in less running distances, and greater acceleration frequency and technical demands during SGs compared to 11M.

The purpose of this study was to analyze the items and characteristics of a criterion-referenced self-administered test utilizing video images for the development of a computerized adaptive test of tactical skills in soccer (TSS-CAT). In total 141 male soccer players in a University club, age (20.2±0.99 years), athletic career (11.9±2.16 years) participated in the study. The structure and the test items of tactical skills in soccer were constructed using qualitative analysis. The test items regarding tactical skills in soccer were analyzed based upon item response theory (IRT) with the 2-parameter logistic model (2PLM). The test items of tactical skills in soccer consisted of 4 domains of individual and group attacking tactical skills, and individual and group defensive tactical skills. The item uni-dimensionality, goodness-of-fit to the item characteristic curve (ICC), invariance of estimated parameters and ability score, the test reliability, validity and goodness-of-fit to the ICC were examined using IRT with 2PLM. The results confirmed the item characteristics of estimated parameters and ability score applying to TSS-CAT.

The purpose of this study was to analyze test characteristics of computerized adaptive test (CAT) of soccer tactical skill with movie image questions for constructing criterion-referenced measurement test of soccer specific tactical skill based upon item response theory (IRT) and CAT techniques. Samples for statistical analysis were 141 male college soccer players, age (20.2±0.99 yr), athletic career (11.9±2.16 yr) whose positions were divided into goal keeper (GK), central defenders (CDF), side defenders (SD), defensive midfielders (DMF), attacking and side midfielders (AMF), forward and attackers (FW). The attacking tactical skill score was high in attacking positions of AMF and FW, and the defensive tactical skill score was high in defensive positions of CDF, SDF and DMF. The criterion-related validity of CAT of soccer tactical skill to criterion-referenced measurement test consisted of 82 items, and the test-retest reliability of CAT of soccer tactical skill were high and significant statistically. It is concluded that CAT of soccer tactical skill have testability, reliability and validity.

Are there few junior soccer players (Aged 12 or Younger) competing at middle level who were born between January and March? When does the RAE (Relative Age Effects) start in school year at middle level soccer players? "Middle level" means they are the second highestlevel players with techniques and skills after junior players of Japan Professional Football League. This research was to clarify whether or not the RAE about the month of birth could be realized in middle competition level, and when the RAE could be started in school year. There were few junior soccer players in the 3rd, 5th and 6th grade in school year competing at middle level who were born between January and March. Furthermore, there were many junior soccer players the 6th grade in school year competing at middle level who were born between April and June. The results suggest that the RAE started in the 3rd grade in school year (9 years old) and became the maximum effect in the 6th grade in school year (12 years old). It has also been shown that the circumstance that makes players stop (give up) playing soccer occurs in the third grade of the elementary school.

Time motion analysis has shown that high-intensity running (HIR) during soccer games is one of the important actions for achieving high performance. However, it is unclear whether HIR is needed and how much the player should perform HIR for achieving score-box possessions which is defined as successful team possessions. This study aimed to quantify the distance covered at HIR with relation to classification of team possession. Eighteen collegiate male soccer players performed five official soccer games. During the games, x- and y- coordinates were determined by using a global positioning system. Total distance (D_SUM) and the distance covered over 5.0 m/s (D_HIR) were calculated from the two coordinates. Team possessions during games was classified from the films obtained by camera, score-box possession (SBP) vs. no score-box possession (NSBP), and counter attack vs. elaborate attack, and state of the opponent defenders (balanced vs. imbalanced). D_HIR in counter attack was longer in SBP than NSBP, regardless of opponent defender’s state. D_HIR in elaborate attack with balanced was greater in SBP than in NSBP. The current results demonstrate that D_HIR in score-box possession is superior to that in no score-box possession, indicating that D_HIR is one of the determinants for achieving score-box possession during soccer games.