The main purpose of the present study was to assess if the intervention of the Video Assistant Referee (VAR) had effects in the playing time and in the technical-tactical and physical performances of the teams in the Spanish LaLiga during 2018-19 season. A total of 375 matches were grouped according the number of VAR interventions: none (VAR0), one (VAR1) and two or three (VAR2). The variables recorded were: total (TPT) and effective (EPT) playing time, passes, dribbles, crosses, shots, goals, corners, fouls, width, length, height, distance from the goalkeeper to their defence, and total (TD) and above 21 km/h distance covered. The results were: I) there was a slight increase in the TPT in VAR2 compared to VAR1 and VAR0 (99.1 vs. 96.0 vs. 95.1, respectively); II) there was a decrease in the EPT between VAR0 and VAR1 (52.5 vs. 51.5); III) there was an increase in the number of goals (1.2 vs. 1.5 vs. 1.7, in VAR0, VAR1 and VAR2); and, IV) there was a slight decrease in the TD (108,916 vs. 107,916 vs. 106,977, in VAR0, VAR1 and VAR2). In conclusion, the findings of the study suggest that the VAR hardly changes the game in elite soccer.

The aim of this study was to analyze the influence of different large-sided games on the physical and physiological variables in under-13 soccer players. The effects on heart rate (HR) and physical demands of different number of players (NP) (7, 9, and 11) together with the relative pitch area (RPA) (100, 200, and 300 m) during two 12-minute repetitions were analyzed in this study. The variables analyzed were mean, maximum and different intensity zones of HR; total distance (TD); work:rest ratio (W:R); player load (PL); 5 absolute and 3 relative speed categories. The results support the hypothesis that a change in pitch dimensions affects locomotor activity more than the NP does but also refute the hypothesis that the change in the NP has a greater effect on HR. To be more specific, an increase in the RPA per player (300/200/100 m2) was associated with higher values of the following variables: TD (2,250-2,314/2,003-2,148/1,766-1,845 m), W:R (0.5-0.6/0.4-0.5/0.3 arbitrary unit [AU]), PL (271-306/246-285/229-267 AU), %HRmean (85-88/85-89/81-83%), %HRmax (95-100/97-100/95-98%), and affected the percentage of time spent in both absolute (above 8 km·h(-1)) and relative speed (above 40% Vmax) categories (p ≤ 0.05, effect size: 0.31-0.85). These results may help youth soccer coaches to plan the progressive introduction of large-sided games so that task demands are adapted to the physiological and physical development of participants.

This study’s main objective is to analyse the relationship between network-based centrality measures and physical demands in elite football players. Thirty-six matches from La Liga, the Spanish league, were analysed in the 2017/18 season. The analysis of networks formed by team players passing the ball included: degree-prestige (DP), degree-centrality (DC), betweenness-centrality (BC), page-rank (PRP) and closeness-centrality (IRCC). A video-based system was used for analysing total distance (TDpos) and distance run >21Km/h (TD21pos) when the team was in possession of the ball. A magnitude-based inference and correlation analysis were applied. There were different styles of play, team-A was characterized by greater ball circulation (e.g. higher values of DP, DC, BC and IRCC) while team-B used a more direct game (lower values in centrality-metrics except with PRP). Furthermore, TDpos was higher in team-A than in team-B, but those differences disappeared for TD21pos between teams with the exception of the forwards. Finally, the correlation among centrality measures and physical performance were higher in team-B. Coaches could identify the key opponents and players who are linked to them, allowing to adjust performance strategies. Furthermore, interaction patterns between teammates can be used to identify preferential paths of cooperation and to take decisions regarding these relations in order to optimize team performance.

The aim of the present study is to analyse the influence of different large-sided games (LSGs) on the physical and physiological variables in under-12s (U12) and -13s (U13) soccer players. The effects of the combination of different number of players per team, 7, 9, and 11 (P7, P9, and P11, respectively) with three relative pitch areas, 100, 200, and 300 m² (A100, A200, and A300, respectively), were analysed in this study. The variables analysed were: 1) global indicator such as total distance (TD); work:rest ratio (W:R); player-load (PL) and maximal speed (V_max); 2) heart rate (HR) mean and time spent in different intensity zones of HR (90%), and; 3) five absolute (16 Km h^-1) and three relative speed categories (60% V_max). The results support the theory that a change in format (player number and pitch dimensions) affects no similarly in the two players categories. Although it can seem that U13 players are more demanded in this kind of LSG, when the work load is assessed from a relative point of view, great pitch dimensions and/or high number of player per team are involved in the training task to the U12 players. The results of this study could alert to the coaches to avoid some types of LSGs for the U12 players such as: P11 played in A100, A200 or A300, P9 played in A200 or A300 and P7 played in A300 due to that U13>U12 in several physical and physiological variables (W:R, time spent in 84–90%HR_max, distance in 8–13 and 13–16 Km h^-1 and time spent in 40–60%V_max). These results may help youth soccer coaches to plan the progressive introduction of LSGs so that task demands are adapted to the physiological and physical development of participants.

The aim of the study was to assess the relationship of external and internal training load (TL) indicators with the objective and subjective fatigue experienced by fifteen semi-professional football players, over 8 complete weeks of the competition period in the 2015-2016 season, which covered microcycles from 34th to 41st. The maximum heart rate (HRmax) and maximum speed (Vmax) of all the players were previously measured in specific tests. The TL was monitored via questionnaires on perceived exertion (RPE), pulsometers and GPS devices, registering the variables: total distance (TD), player load 2D (PL2D), TD at >80% of the Vmax (TD80), TD in deceleration at 2 m·seg-2 (TDA>2), Edwards (ED), time spent at between 50-80% (50-80%HRmax), 80-90% (80-90%HRmax) and >90% of the HRmax (>90%HRmax), and RPE both respiratory/thoracic (RPEres) and leg/muscular (RPEmus). All the variables were analysed taking into account both the absolute values accumulated over the week and the normalised values in relation to individual mean competition values. Neuromuscular fatigue was measured objectively using the countermovement jump test (CMJ) and subjectively via the Total Quality Recovery (TQR) scale questionnaire. Analytical correlation techniques were later applied within the general linear model. There is a correlation between the fatigue experienced by the player, assessed objectively and subjectively, and the load accumulated over the week, this being assessed in absolute and relative terms. Specifically, the load relative to competition correlated with the physical variables TD (-0.279), PL2D (-0.272), TDD2 (-0.309) and sRPEmus (-0.287). The variables related to heart rate produced a higher correlation with TQR. There is a correlation between objectively and subjectively assessed fatigue and the accumulated TL of a player over the week, with a higher sensitivity being shown when compared to the values related to the demands of competition. Monitoring load and assessing fatigue, we are closer to knowing what the prescription of an adequate dose of training should be in order for a player to be as fresh as possible and in top condition for a match. Normalizing training demands with respect to competition could be an appropriate strategy for individualizing playerTL.

Tactical behavior could be affected by changes in small-sided game (SSG) formats. The aim of the present study was to analyze the influence of different pitch lengths during 7-a-side SSGs played by young football players. Fourteen male soccer players in each age group (13 and 14 years old, U13 and U14 teams) were divided in two teams of seven players who played four SSGs of 7 minutes, interspersed with 4 minutes of passive recovery. The only modification to the SSG format was pitch length: 60 m (SSG60), 50 m (SSG50), 40 m (SSG40), and 30 m (SSG30), while the width of the field was kept constant at 40 m. The variables used to characterize collective behavior were grouped in a) intra-team variables, namely, team length (L), team width (W), effective area of team play or convex hull (CH), and stretch index (SI); and b) inter-team variables, namely distance between centroids (DC), length of both teams (L2), width of both teams (W2), convex hull of both teams (CH2), and stretch index of both teams (SI2). Our results revealed different intra and inter-team behaviors according to SSG format and player age. L, CH, SI, DC, L2, CH2, and SI2 all increased with increasing pitch length, while W and W2 showed only minimal changes. The differences were greater in the U13 group, suggesting that younger players were more likely to vary their collective behavior in response to changes to pitch length, inter-task, particularly in the longer pitches (SSG50 and SSG60). Conversely, using the analysis of the entropy, greater unpredictability of tactical behavior was observed in the U14 group, intra-task, compared with the U13 group. Overall, the findings suggest that responses to task constraints, such as modifications to pitch length and accordingly relative area of play, are dependent on age (experience, skill) and this is something coaches should consider when designing SSGs to develop team tactics.