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Participants
The study involved two grassroots soccer teams from the exact first division club in Argentina, made up of an under-23 team with 23 professional players (age: 20.61 ± 1.57and experience: 11.58 ± 2.27years) and an under-21 team with 23 professional players (age: 19.21 ± 1.03 and experience: 9.16 ± 2.59years). The selection of the participating players was carried out through purposive selection sampling. The inclusion criteria were as follows: (i) players should be ≥ 18 years, (ii) playing in the national category and with a minimum experience of 6 years playing soccer. The exclusion criteria were:(i) players who have completed less than 80% of the sessions with the team, (ii) players who have participated in training sessions with the first team, and (iii) players who have participated in training with national teams. Some players from each team were excluded due to exclusion criteria, which can be seen in Fig. 1. Consequently, the final sample comprised 16 and 21 players from the U-23 and U-21 teams.
CONSORT diagram of study for each team
After coordinating with the team’s staff, all the players were presented with the advantages and disadvantages of the study. Then all players signed the consent form. The study followed the Declaration of Helsinki guidelines for human studies in all phases. Before starting the study, the ethics committee of the University of Extremadura approved this study (156/2021). ClinicalTrials.gov Protocol Registration and Results System (PRS) have registered in Release Date: June 15, 2023. All data were treated according to the privacy, ethics, and protection policies of the American Psychological Association.
Study design
This research conducted a quasi-experimental intervention design at a longitudinal level, the study used an uncontrolled two group pre-posttest design. The intervention program was based on analyzing and integrating tactical behaviors (game principles) and psychological aspects/variables associated with stress scenarios, coping with adverse situations and specific attention work. Then, different strategies to be used during specific soccer training tasks were established under a design used by the coach to mentally challenge the players [5]. There, the goal was associated with being able to challenge and stress players to develop psychological and mental aspects (e.g., attention and concentration, self-talk, arousal control) due to the manipulations included during the training tasks [20]. Fundamentally, the scenarios during the training tasks were associated with causing states of mental fatigue linked to tactical, technical performance [21], and fundamentally oriented to (i) Divide attention and maintain high levels of concentration concerning the ball, teammates, rival, playing space and change of rules during soccer training tasks; (ii) Establish objectives and physical, technical and tactical challenges during the tasks, promote confrontations in numerical inferiority, encourage stress and adversity scenarios through sanctions associated with the game (i.e. taking possession of the ball from a team), and favor actions of the game that promotes fighting and melee aggressiveness with the rival (i.e. duels).
In Table 1, it is possible to observe the explanations and relationships between tactical and psychological behaviors, seeking as an objective within the training tasks that both behaviors were united. After this, the study’s first author and the coaching staff of the different teams organized by consensus the moments of data collection and the introduction of the specific constraints 30 days before the beginning of the present research. The study employed two experienced observers who assessed each session, and both observers had several years of experience in soccer. The intervention program implemented consisted of three stages: (a) an introductory and theoretical stage, where all the information was presented: the objectives of the study, the tasks and dynamics to be developed, as well as the duration of the program; (b) the experimental stage, where the coaches received detailed training to develop the intervention program; (c) the intervention stage, where the specific program was developed by the coaches and implemented with the players of both teams. The first two phases were conducted in three 2-hour meetings [22], and the third phase lasted five weeks. There, the two teams trained under the same plan and task design five days a week, performing 25 training sessions. During this period, psychological strategies and constraints were incorporated into the technical-tactical training tasks. Specifically, before the intervention, technical-tactical behaviors and actions were analyzed during the first five games of both teams (from week 1 to 5 inclusive). During the following five weeks (weeks 6 to 10 inclusive), the strategies and constraints were used in the tasks established by the coaches, with no record of competitions during this period. Finally, the behaviors and technical-tactical actions of the following five weeks (from week 11 to 15 inclusive) were analyzed without intervention in the training tasks. The first measure, between competitions 1 and 5 inclusive, was used to determine the percentage of actions performed by both teams in the competitions without psychological conditioning during the training tasks. Subsequently, the coaches’ intervention in soccer-specific training tasks was performed between weeks 6 and 10 inclusive, using the integrated tactical and psychological constraints designed by the experts. Finally, measurements were performed during the post-intervention period to evaluate and know the effects of the intervention on the percentage of actions performed during competitions 11 to 15 inclusive (Table 1).
Instruments and measurements
Sony Vegas Pro 13 software was used to evaluate tactical behaviour competition, allowing quantitative and qualitative analysis of the images recorded. An observation and registration form designed by the experts mentioned above was used to quantify the players’ game actions related to each match’s tactical and psychological components. For the statistical analysis of the tactical behaviors, SPSS 25 software was used.
For this objective, the observation sheet was based on four tactical principles of the game to check if the players were developing the requested behavior. Based on these principles, four-game situations were established to be evaluated, which were to be carried out during the competitions played by the team (Table 2): 1.- Taking the ball out of those sectors where it is recovered; 2.- Marking in the attack: Faced with the loss of the ball, the defenders of our team had to be marking the closest rivals when they receive the ball; 3. – First option of forwarding pass: the player who has the ball under control and with an unmarked teammate in front of him, should try to play it to that teammate as the first option; 4.- Immediate pressure and recovery after a turnover: when the ball is lost, he or the closest players should react immediately, through movements and physical actions of high intensity.
In all cases, the game situations were evaluated through the category of “Performed (+)” and “Not Performed (-)” according to the objective of this research. That is to say, the total of game actions to be performed in the competitions was added and the percentage of the actions performed (+) was obtained. The objective was linked to the actions and behaviors that were intended to be developed beyond the effectiveness and the result of each action. It was evaluated whether the actions were performed (for example, taking the ball out of those sectors where it is recovered), regardless of the effectiveness or result obtained (whether a teammate in another sector received the ball).
The evaluations were conducted in two-time steps in the following order: (i) the first evaluation was conducted between games 1 to 5 as pre-intervention, (ii) the second evaluation was conducted between games 11 and 15 as post-intervention. The observation sheet of both teams was used to measure the players’ behavior during the competition. A baseline measurement (before the intervention, during competitions 1 to 5 inclusive), and a post-measurement (during competitions 11 to 15), after the intervention process carried out between competitions 6 and 10 inclusive.
In Table 3, it is possible to observe how the different stages and measures used during the intervention program were proposed. The first measure, between competitions 1 and 5 inclusive, was used to determine the percentage of actions performed by both teams in the competitions without psychological constraints during the training tasks. Subsequently, the coaches’ intervention was carried out in the soccer-specific training tasks between weeks 6 and 10 inclusive, using the tactical and psychological constraints integrated and designed by the experts. Finally, measurements were taken during the post-intervention period to evaluate and know the effects of the intervention on the percentage of actions performed during competitions 11 to 15 inclusive.
Data analysis
The SPSS 25.0 and GraphPad Prisma 9.4.1 software’s were used to handle and analyze the data. Prior to running the parametric tests that require normally distributed data, assessments of data normality were conducted. There, descriptive statistics were carried out for each team, and each game principle was represented in each competition. On all parameters, a factorial ANOVA with repeated measurements was conducted. In comparison, the between-group component considered groups (i.e., U 21 and U23), and the within-group factor considered time (i.e., pre- or post-test). It also has been calculated for the partial eta effect size (ηp2). If a significant time-group interaction was found, each group was subjected to a one-way repeated-measures ANOVA with a Bonferroni post hoc analysis. Then we made a comparison with Paired Samples T-Test to merge considering both groups with each other. We utilized an effect size of Hedge’s g type with a 95% confidence interval to calculate the magnitude of pairwise comparisons for the pre-and post-test. We classified it as trivial, < 0.2; small, ≥ 0.2; moderate ≥ 0.5, and large for more than 0.8. All significance levels were considered at p < 0.05.
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