Effects of free play or artificial rules on young soccer players' individual tactical behaviour: a one-by-one analysis.

This study assessed the effects of playing freely and introducing artificial rules on individual tactical behaviour during the team-possession game phase in two youth soccer categories. Thirty-two developmental players from U-14 and U-16 teams participated in the study, which consisted of four identical training sessions and two test sessions performed before and after the intervention. Each team was divided into two balanced groups, free-play and conditioned, that faced each other during three eight-a-side games (Gk + 7 vs 7 + Gk) in all training sessions. The free-play groups played freely, while the conditioned ones did so constrained by artificial rules. Individual tactical behaviour was assessed during a non-constrained eight-a-side match by the distance to centroid, spatial exploration index, their entropy measures, and the regularity of each player's displacement on the length and width of the pitch using a local positioning system. In addition to the average outcomes of all the players all together, the one-by-one analysis considered the mean values of each player to appraise individual responses. While the average outcomes of all the players in both groups and categories barely changed (Cohen's d ≤ small), with a very high inter-player variability, the one-by-one analysis revealed that the training intervention affected each player's tactical behaviour differently. Introducing artificial rules decreased and raised considerably (Cohen's d ≥ moderate) in-width and exploratory regularities of most U-14 and U-16 players, respectively. Therefore, assessing the training effects of game-based interventions from the individual to the whole team may provide unique and meaningful insight regarding the tactical competence of each player.

Comparing Sampling Frequencies to Measure Collective Tactical Variables During Soccer Training.

ABSTRACT: Rico-González, M, Pino-Ortega, J, Rojas-Valverde, D, and Arcos, AL. Comparing sampling frequencies to measure collective tactical variables during soccer training. J Strength Cond Res 36(10): 2862-2867, 2022-The sampling frequency of microsensors that measure the position of the players in team sports is a variable that could affect the accuracy of the measurement. The aim of this study was to assess the impact of the sampling frequency on the outcomes of tactical behavior variables during soccer training. Sixteen U16 male soccer players participated in the study. Three tactical variables (change in the geometrical center position [cGCp], mean distance between players [mean-DbP], and total area [TA]) were measured at 4 different sampling frequencies (i.e., 10, 4, 2, and 1 Hz) during a 7+goalkeeper-a-side soccer match by a time motion tracking system using inertial measurement units (IMU; WIMU PRO, RealTrack Systems, Almeria, Spain). Significant (p < 0.01) and substantial (ES = moderate-large) differences were found in the cGCp values across all sampling frequencies. Several significant (p < 0.05) and substantial (ES = small-moderate) differences were found in the mean-DbP values between 10 data per second and the rest of the sampling frequencies. There were no significant (p > 0.05) and substantial (ES = trivial) differences in the TA values across all sampling frequencies. The sampling frequency affects the outcomes of cGCp and mean-DbP but does not affect the values of TA. The outcomes of the studies that assess collective tactical behavior should be compared with caution if GC-related and distance variables were measured using different sampling frequencies. In addition, it seems that a smaller amount of data could be sufficient to measure area variables with greater magnitudes.

Guidelines for performing systematic reviews in sports science.

Most of the reviews carried out in sports science have used the general items suggested by Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA). Due to the specific requirements of each knowledge area, several modifications of the PRISMA are necessary to optimize the process of the systematic reviews and, in consequence, the quality of the conclusions provided in this type of study. Therefore, this work aimed to adapt PRISMA to provide specific guidelines to carry out systematic reviews in sports science. The methodology criteria (search strategy, databases, and eligibility) and the results section (flow diagrams and study contents) were adapted based on previous studies, and several new considerations were added to design the new guidelines. We compiled 28 items suggested by sports science researchers and included two new items: (i) population/problem (i.e., age, level, and country) and (ii) the entire training process, which is monitored and compared between groups (e.g., total training load). To maximize the benefit of this document, we encourage people to read it in conjunction with the PRISMA statement. The main differences between PRISMA and the PRISMA adapted to sports science were related to registration, search strategy, flow diagrams, and results. Application of the new guidelines could improve the information provided to readers and make it easier to generalize and compare the results in sports science.

Identification, Computational Examination, Critical Assessment and Future Considerations of Spatial Tactical Variables to Assess the Use of Space in Team Sports by Positional Data: A Systematic Review.

The aim of the review was to identify the spatial tactical variables used to assess the use of space in team sports using positional data. In addition, we examined computational methods, performed a critical assessment and suggested future considerations. We considered four electronic databases. A total of 3973 documents were initially retrieved and only 15 articles suggested original spatial variables or different computation methods. Spatial team sport tactical variables can be classified into 3 principal types: occupied space, total field coverage by several players; exploration space, the mean location (±standard deviations in X- and Y-directions) of the player/team during the entire game; and dominant/influence space, the region the players can reach before any other players. Most of the studies, i.e., 55%, did not include goalkeepers (GKs) and total playing space to assess occupied space, however, several proposed new variables that considered that all playing space could be "played" (i.e. effective free-space, normalized surface area). Only a collective exploration space variable has been suggested: the major range of the geometrical centre (GC). This suggestion could be applied to assess collective exploration space variables at a sub-system level. The measurement of the dominant/influence space has been based on the Voronoi region (i.e. distance d criteria), but several studies also based their computation on the time (t). In addition, several weighted dominant areas have been suggested. In conclusion, the use of spatial collective tactical variables considering the principal structural traits of each team sport (e.g. players of both teams, the location of the space with respect to the goal, and the total playing space) is recommended.

A systematic review of collective tactical behaviour in futsal using positional data.

Although many studies on collective tactical behaviour have been published in the last decade, no study has revised and summarized the findings provided for futsal. The main aim of this systematic review was to identify and discuss the geometrical centre (GC), distance and area tactical variables used to assess team behaviour in futsal. In addition, it summarizes the findings on the tactical response during futsal competition and training. A systematic review of the relevant articles provided on futsal was carried out using seven electronic databases (SPORTDiscus, ProQuest, Cochrane Plus, Scopus, Google Scholar, PubMed and Web of Science) until September 25, 2019. From a total of 1,209 studies initially found, 12 were included in the qualitative synthesis. There were some trends in the analysis of positional data in futsal with the most relevant situations analysed being 1 vs 1 and 5 vs 4+Goalkeeper. The distances and angles between two points were the most assessed tactical variables. Five types of distance variables were used to assess collective tactical behaviour in futsal: GC-GC, GC-player, player-player, player-ball and player-space. Pressure (GC-GC) was greater in shots on goal than in tackles during professional futsal matches. Area variables were reduced to occupied space, exploration space and dominant area. Occupied space was measured only during competition while the dominant area was measured only during training sessions. The surface area and dominant regions were greater when players were attacking in comparison to when they were defending. In addition, two non-linear techniques (i.e. relative phase and entropy) were applied to analyse synchronisation and complexity and regularity or predictability. Defenders were highly synchronous, while attackers tried to break this coordination to achieve possibilities for action. Task constraints are suitable to induce different regularity patterns. This review is an opportunity to develop studies aimed at bridging the gap in collective tactical behaviour in futsal.

The Influence of Antenna Height on the Measurement of Collective Variables Using an Ultra-Wide Band Based Local Positioning System in Team Sports.

Ultra-wide band (UWB) based local positioning systems (LPS) are based on devices and a portable antenna set. The optimal installation height of the antennae is crucial to ensure data accuracy. Collective variables are metrics that consider at least two pairs of coordinates, which may lead to lower precision than an individual one. Therefore, the aim of this study was to compare the influence of antenna height with collective metrics using a UWB (i.e., IMU; WIMU PRO™, RealTrack Systems, Almeria, Spain) based LPS. Data acquisition was carried out in a basketball court measuring 28 × 15 m. Five devices were used; one of which was carried by a healthy and well-trained athlete (age: 38 years, mass: 76.34 kg, height 1.70 m), while each of the remaining four was positioned on a tripod in one of the four corners of the court. Four kinds of variables were extracted: (1) static distances, (2) dynamic distances, (3) static areas and (4) dynamic areas in all antenna installation modes of 0.15, 1.30 and 2.00 m. The results showed that the antenna of 1.30 m provided better accuracy for all measures (% difference range from -0.94 to 1.17%) followed by the antenna of 2.00 m (% difference range from -2.50 to 2.15%), with the antenna of 0.15 m providing the worst accuracy level (% difference range from -1.05 to 3.28%). Overall, the measurements of distance metrics showed greater accuracy than area metrics (distance % difference range from -0.85 to 2.81% and area % difference range from -2.50 to 3.28). In conclusion, the height of the antennae in basketball courts should be similar to the height at which the devices are attached to a player's upper back. However, as the precision is sensitive to the magnitude of the measure, further studies should assess the effects of the relative height of antennae in team sports with greater playing spaces.

Assessing Change of Direction Ability in a Spanish Elite Soccer Academy.

The aims of the study were: a) to analyze the reproducibility of the Modified Agility Test (MAT) according to two types of displacement (i.e. constrained [MATtop] vs. free [MATfree]), b) to examine the explanatory capacity of anthropometric characteristics and neuromuscular performance on the ability to change the direction (CODA), c) to look into the practical consequences of the types of displacement from the perspective of an elite soccer academy. 118 male soccer players (age: 16 (13-25) years old) from the same elite Spanish soccer academy (U13 to senior) were tested twice on two versions of the MAT (MATtop and MATfree), with 48 hours between testing sessions. Moreover, they were tested on linear-sprint performance, over 5 m (S5m) and 15 m (S15m), and the vertical jump (VJ) (countermovement jump with [ACMJ] and without an arm swing [CMJ]). The main findings were: a) the type of displacement did not affect the reliability of the CODA test; b) weight, S15m, ACMJ and CMJ variables explained close to 60% of CODA performance; c) MATtop (i.e. constrained displacement) and MATfree (i.e. free-displacement) CODA tests could show different profiles of development along the age groups; and d) the impact of the task's constraints was relatively higher in U16 and U17 groups. CODA seems to have a variable meaning depending on the characteristics of the test and the age of the participants.

Spanish Elite Soccer Reserve Team Configuration and the Impact of Physical Fitness Performance.

The aim of this study was threefold: 1) to assess the configuration of an elite reserve soccer team, 2) to compare physical fitness performance of promoted and new players according to the playing position, and 3) to analyze the level of competitive participation attained by these players. We considered physical fitness tests (5 m and 15 m sprint, countermovement jump [CMJ] and aerobic endurance) performed by 192 players (age = 20.2 ± 2.3 years) enrolled in the reserve team of a Spanish La Liga club from 1994 to 2013. The players were classified according to the previous club criterion (promoted from the soccer academy and new players signed from other clubs), b) their playing position, and c) the competitive level attained until the 2016/2017 season (Spanish 1st and 2nd Divisions and the remaining competition levels). The proportion of promoted and new players was similar (p = 0.47). Overall, no substantial differences (unclear-small) were found in physical fitness performance between promoted and new players. Considering the playing position, promoted lateral defenders (LDs) showed better sprinting (ES = moderate) and CMJ (ES = moderate) performance than new LDs. In addition, promoted central midfielders (CMs) demonstrated better performance in the 5 m sprint and the CMJ (ES = moderate) than new CMs. The percentage of players who later competed in the Spanish 1st and 2nd Divisions was greater in promoted players compared to new players (p = 0.006). Physical fitness performance did not determine the selection of new players in a soccer elite reserve team. We may conclude that soccer academies should prioritize the selection and the training process of youth soccer players.

Effects of different agility training programs among first-grade elementary school students.

The aim of the study was to determine which agility training program (low, moderate or high contextual interference) was more effective in first-grade primary school students to provide reliable information to physical education teachers for designing more effective agility programs. A total of 57 first-grade elementary school students participated in the present study. They were randomized into three groups to compare the effects of three different agility training programs based on contextual interference: low contextual interference (N = 19), moderate contextual interference (N = 19), and high contextual interference (N = 19). Contextual interference refers to the relative amount of interference created when integrating two or more tasks into a particular aspect of a training session. Significant improvements in agility were found in the low (p < 0.01, ES = 1.79) and moderate (p < 0.05, ES = 0.61) contextual interference groups after a 4-week training period. These improvements were higher in the low contextual interference group. The high contextual interference group showed no improvements (p > 0.05, ES = 0.28) after the intervention program. Our results suggested that the low contextual interference program is still more effective than the moderate contextual interference program in this group of primary school students.

Negative Associations between Perceived Training Load, Volume and Changes in Physical Fitness in Professional Soccer Players.

The purpose of this study was to examine the usefulness of the rating of perceived exertion training load for monitoring changes in several aerobic fitness and neuromuscular performance variables during 9 weeks of soccer training in young professional players. Nineteen male soccer players (20.2 ± 1.9 years) belonging to the same reserve team of a Spanish La Liga Club participated in this study. Countermovement jump (CMJ), CMJ arm swing, single leg CMJ, a sprint running test (i.e., 5 m and 15 m times) and an aerobic fitness running test were performed at the start of the pre-season (Test 1) and 9 weeks later (Test 2). During 9 weeks, after each training session and match, players reported their rating of perceived exertion (RPE) separately for respiratory (RPEres) and leg musculature (RPEmus) effort. The training load (TL) was calculated by multiplying the RPE value by the duration in minutes of each training session or match. Accumulated RPEmus, and associated TL, as well as accumulated training volume were negatively correlated with the changes in most physical fitness attributes after 9 weeks of training (r = -0.51 to -0.64). Present results suggest that a high perception of leg muscular effort associated with training sessions and matches, as well as an excessive accumulation of training volume (time), can impair the improvement in several physical fitness variables believed to be relevant for on-field soccer performance. Therefore, the independent assessment of leg muscular effort to quantify TL can be an interesting additional monitoring measure in soccer training. Key pointsThe purpose of this study was to examine the usefulness of the perceived exertion-derived TL for monitoring changes in several aerobic fitness and neuromuscular parameters during 9 weeks of soccer training in young professional players.A high perception of leg muscular effort associated with training and matches, as well as an excessive accumulation of training volume (time), can impair several physical fitness factors believed to be relevant for on-field soccer performance.The independent assessment of muscular effort to quantify TL can be an interesting additional monitoring measure in soccer training.

Rating of muscular and respiratory perceived exertion in professional soccer players.

This study investigated, in male professional players: (a) fluctuations in rating of local-muscular (sRPEmus) and central-respiratory (sRPEres) perceived exertion measured after the completion of each training and competitive session, over a 9-week competitive period and (b) the influence of quantitative assessment of different training and competition modes on changes in physical performance. sRPEres, sRPEmus, and heart rate were measured in 21 players in 847 individual training and competitive sessions. Training load was calculated by multiplying sRPEmus or sRPEres by the duration of the training or competition sessions. A test battery (vertical jump, sprint, and endurance running) was performed before and after the studied period. At the end of official matches, average sRPEmus was higher (7.4 ± 0.6; p ≤ 0.05) than sRPEres (6.4 ± 1.3). Significant negative correlations were observed between the values of total training and competition time (r = -0.62; p < 0.01) or total added sRPEmus (r = -0.59; p ≤ 0.05), and vertical jump or sprint running velocity changes, respectively. This suggests that sRPEmus should be considered the main fatigue rating during a soccer match. Training and competition volume may have negative effects on the muscle power performance gains of the legs.

Effects of eccentric exercise on optimum length of the knee flexors and extensors during the preseason in professional soccer players.

OBJECTIVE: To assess the effects of eccentric exercise on optimum lengths of the knee flexors and extensors during the preseason in professional soccer. DESIGN: Twenty-eight athletes from a professional Spanish soccer team (Division II) were randomly assigned to an eccentric exercise intervention group (EG) or a control group (CG). Over the four-week period two athletes from the control group suffered RF injuries and two athletes were contracted by other clubs. After these exclusions, both groups (EG, n=13; and CG, n=11) performed regular soccer training during the four-week preseason period. RESULTS: After the four weeks, the optimum lengths of the knee flexors were significantly (P<0.05) increased by 2.3 degrees in the CG and by 4.0 degrees in the EG. The change in the EG was significantly (P<0.05) greater than that of the CG. The optimum lengths of the knee extensors were significantly increased only in the EG by 6.5 degrees . Peak torque levels and ratios of quadriceps to hamstring (Q/H ratios) were not significantly altered throughout the study for either group. CONCLUSION: Eccentric exercise can increase the optimum lengths of both the knee extensors and knee extensors flexors during the preseason in professional soccer.