The purpose of this study was to investigate the relationship between lower limb explosive power, sprint and change of direction according to jumping type in male college soccer players. This study recruited 97 college soccer players including High level (n=50) and Low level (n=47). Participants who have been selected for the national team were classified as Top level (n=6). All of the participants conducted the following, with their results recorded for analysis: 30m sprint (30mS), Pro-agility test (PA), counter movement jump (CMJ) and rebound jump (RJ). All of the participants were classified into two types: CMJ type (relatively greater in CMJ), RJ type (relatively greater in RJ-index). The relationships between CMJ, RJ, 30mS and PA were analyzed in each type. The results indicated that CMJ showed significant negative correlation between 30mS and PA in CMJ type and RJ type respectively. On the other hand, RJ-index showed a significant negative correlation between 30mS and PA only in CMJ type, but no relationship was found in RJ type. It was also revealed that the number of RJ type was particularly large at the high level, and the CMJ type was large at the low level. Participants at Top level were significantly superior to those at High level in RJ-index and CMJ. On the basis of these findings, this study has shown that the importance of relatively high RJ ability and possible availability of training program according to jumping type.

The current investigation aimed to examine the cardiorespiratory responses to recreational walking soccer (WS) in middle-aged to older adults with mild metabolic disorders. Twenty volunteers (aged 54-73 yr) played recreational WS that consists of five field players without a goalkeeper in one team, with movement limited to walking for 10 minutes of total playing time in an indoor standardized basketball court. The heart rate (HR) was 127 ± 20 beats/min (bpm; 82 ± 14% of the age-predicted maximum HR) in the 10-min game of WS, and it was significantly associated with the number of plays with a ball after adjusting for age (p < 0.05). The estimated metabolic cost was 8.0 ± 1.6 metabolic equivalents, showing a significant correlation with the maximal oxygen uptake, number of plays with a ball, and stepping rate (p < 0.05). These results indicated that the cardiorespiratory responses to a 10-min, 5 vs. 5 recreational WS would probably be above the desirable levels of the exercise prescribed in middle to old-aged adults with mild metabolic disorders. However, the chronic adaptability and health benefits of the recreational WS remain unclear.

The purpose of this study is to clarify the characteristics of the game aspect depending on the number of players in rugby. We studied the world's top-level matches of 7, 10, and 15-a-side rugby games in recent years. The main results were as follows. 1) The greater the number of players, the longer the in-play time and out-of-play time per play, and the less frequent the number of plays. 2) The smaller the number of players, the higher the rate of try scoring, and also the higher the rate of tap-kick selection and the rate of source of tries from tap-kick. 3) The greater the number of players, the greater the number of the origin of tries from the opponent area, and the smaller the number of players, the smaller the number of phase attacks build up to tries. In addition, these results suggested that the 10- a-side players were required a high level of various skills and tactics, since the game has a high frequency of various play activities, including off-load passes, and ball retention and continuation skills in set play and phase play are also important.

The purpose of this study was to construct criterion-referenced measurement items for soccer defensive tactical play from soccer game tracking data. Scaling procedure included qualitative analysis of the causal structure of soccer defensive tactical play using the Delphi method and a causal-effect analysis, processing items to measure soccer defensive tactical play from tracking data, an analysis of construct validity of soccer defensive tactical play by structural equation modelling, an analysis of success criteria of defensive plays by decision tree analysis, an analysis of test and item characteristics of the scale of soccer defensive tactical play by using item response theory (IRT), and an analysis of validity of the criterion-referenced measurement test. Qualitative analysis revealed that soccer defensive tactical play consisted of the press defense and block defense. Twenty-five soccer defensive tactical play items were created from the tracking data. Seventeen soccer defensive tactical play items showed construct validity. The success criterion of the soccer defensive tactical play items was revealed by decision tree analysis. Test and item characteristics, which consisted of fourteen items, were shown by IRT. In conclusion, it was statistically valid to construct the criterion-referenced measurement items for soccer defensive tactical play from soccer game tracking data.

Management of sleep and diurnal rhythm is important for professional athletes to maintain a competitive condition, especially for soccer players, who have a mixed schedule of morning practice and afternoon or evening games. This study aimed to identify differences in circadian phenotypes, sleep hygiene, and diurnal rhythms in soccer players according to stage (J1 or J2) and performance in the top Japanese league, the J League. We administered a questionnaire survey to 89 J League (J1 and J2) players younger than 26 years old (22.4 ± 2.1) utilizing scale of index on diurnal rhythm disturbance, which covers sleeping habits, breakfast time, and diet. Players were divided into four groups according to their ranking as of the July 2016 season—Group 1: 11 players from teams that ranked in the upper half of the J1 league; Group 2: 17 players from teams in the lower half of the J1 league; Group 3: 48 players from teams in the upper half of the J2 league; Group 4: 13 players from teams in the lower half of the J2 league. In a multiple comparison analysis, levels of sleep quality in Group 1 were higher than those in Group 2. Group 3 players showed significantly lower levels of disturbance of diurnal rhythm relative to those in Group 2. Well-regulated lifestyle habits that result in good quality sleep and less disruption in diurnal rhythms may increase competitiveness in professional soccer players.

During the last 10 minutes of the Group H final match of the 2018 FIFA World Cup, Japan was one goal behind Poland. At the same time, Senegal was also one goal behind its opponent. If both teams were defeated by one goal, Japan would qualify to move forward based on fair play points. However, a second goal by Poland would eliminate Japan in the group stage. Therefore, for these 10 minutes, Japan kept rolling the ball between their defense and midfield. In this study, we analyze this incident from the standpoint of game theory to quantitatively evaluate the quality of Japan’s tactical decision to keep rolling the ball. We model this situation by estimating the scoring rate based on the number of goals scored in the group stage, and calculate the probability of qualifying. We assume that Japan and Poland can choose their tactics, “attack” or “keep rolling the ball,” and compare their expected results. According to our calculation, the scoring rate was estimated to be 0.0307 goals per minute. If Japan chose to “attack,” the probability of qualifying would be 0.676. However, if Japan chose to “keep rolling the ball,” the probability would increase. Therefore, Japan’s choice to “keep rolling the ball” during the last 10 minutes appeared to increase their probability of qualifying; thus, Japan made a rational decision in this situation.

The purpose of this study was to develop offence and defence tactical play items for a deep learning model of tactical play analysis. The procedures used in this study included the following three steps. First, features of offence and defence tactical play items were developed. Then, long short-term memory (LSTM) was architected. Finally, tactical plays were predicted by the model. The ball touch data and the tracking data from two official soccer games in the J-League 2016 season were used. The ball touch data, recorded player actions in text such as passes and shots with time-series order, and the tracking data of players, were used to construct thirty-one tactical play items. For the deep learning model, LSTM was used. LSTM allows the analysis of time-series text data. 6,444 sequential plays were used. The highly accurate tactical play predicted from LSTM was the feed after tactical play which started at low press defence and finished at GK ball catch (8 correct predictions of 8 frequencies in the data). In conclusion, all 31 items measuring offence and defence tactical play in soccer games constructed from the ball touch data and the tracking data are the feature items used to analyse tactical plays using LSTM.

The aim of this study was to categorize rugby players by performance characteristics irrespective of positions using principal component analysis (PCA) and cluster analysis (CA). Data were drawn from the Japan Rugby Top League 2015–2016 season; a sample of 231 players and 16 items were used in the analysis. We used PCA to identify the players’ ability and CA to categorize players’ performance characteristics, regardless of position. PCA reduced the 16 items to four principal components: penetration, defense and competition, ball handling and kicking, and turnovers. We categorized players into six clusters based on the four component scores: playmaker, ball carrier, tackler and supporter, competitor, passer and kicker, and spoiler. Although player categorization by CA was achieved regardless of position, the players’ performance characteristics also influenced categorization, and specific positions have performance characteristics. Unique players were identified for some positions. In addition, we clarified a difference in performance characteristics between Japanese and foreign players in the league. Since the categorization of players by performance characteristics irrespective of position enables teams to find necessary players, this study may be advantageous for team management and may contribute to more useful analysis of players and clarifying performance characteristics.

This study examined the relationships between training load, body composition and physical fitness in collegiate male soccer players during preseason. Eight soccer players completed regular training and informal games with a global positioning system sensor and a telemetry heart rate (HR) monitor for 79 days from the middle of January to the end of March. As indices of external load, total distance and the distance covered over 18 km/h (D_HIR) were measured. As indices of internal load, HR during training sessions was normalized to the maximal HR obtained from the Yo-Yo intermittent recovery test level 2 (YYIR2), and expressed to relative value (%HRmax). Training impulse (TRIMP) was calculated from Edward’s equation. Before (Pre) and after (Post) the preseason, whole body fat mass (FM) and fat-free soft tissue mass (FFSTM) were measured with a whole-body dual-energy X-ray absorptiometry scanner. The velocity of a 30-m sprint test and pro-agility test was determined by a photo cell. Height of vertical jump was calculated from the flight time. There was no significant change in physical fitness during the preseason. The %Δ in FFSTM was largely related to D_HIR (r = 0.76). The %Δ in the score of YYIR2 was positively related to TRIMP (r = 0.81) and %HRmax (r = 0.83). These findings indicate that the intra-individual variation in FFSTM may partially depend on external load, and that aerobic fitness may be affected by internal load in collegiate male soccer players.

The purpose of this study was to determine the intrinsic risk factors for ankle sprain in female soccer players. Twenty-four female soccer players from one team in Japan Women’s Football League participated in this study. Medical screenings before and during the season were conducted and ankle sprains sustained during one playing season were recorded. The medical screenings included foot alignment, toe flexor strength, joint laxity and range of motion, star excursion balance test, body mass index, body fat percentage, osteo-sono assessment index, and estimated hemoglobin concentration. Players who sustained ankle sprain had significantly increased joint laxity, especially of the ankle joint, reduced performance in the Star Excursion Balance test and weak toe flexor strength. Joint laxity and impaired dynamic balance ability are risk factors for ankle sprain in female soccer players.