Small-sided games (SSGs) are typically designed to target multiple objectives in youth soccer players, encompassing physical, physiological, technical, and tactical aspects (Hill-Haas et al., 2011; Halouani et al., 2014; Ferreira-Ruiz et al., 2022). Various task conditions are employed to achieve these objectives, including changes in the format of play, pitch dimensions and shape, and other rules such as scoring methods, feedback provision, and action limitations (Bujalance-Moreno et al., 2019; Praca et al., 2022). For instance, altering the dimensions of the pitch can significantly impact the acute demands of the drill on players, including external and internal load demands (Praca et al., 2022). It is well-established that elongated and larger pitch dimensions tend to encourage more high-intensity running actions and contribute to a greater accumulation of distance covered in high-speed running or sprinting compared to smaller pitch dimensions (Riboli et al., 2020; 2022). Moreover, the shape of the pitch can also influence player performance (Casamichana et al., 2018). Even when the total area of the pitch remains constant, different shapes can affect gameplay differently. For instance, pitches with a greater length-to-width ratio may favor more linear and curvilinear speed running actions, while those with a more balanced ratio (equally balancing length and width) might encourage more exploration of the wings and frequency of accelerations and decelerations (Fradua et al., 2013; Casamichana et al., 2018).

The utilization of SSGs as a training intervention has been progressively gaining traction in the realm of sports science (Clemente et al., 2021a). The evidence consistently supports the positive impact of SSGs on enhancing aerobic fitness, analogous to other methods such as high-intensity interval training (Moran et al., 2019; Clemente et al., 2024). However, the effects of SSGs on certain aspects of training interventions, particularly acceleration and sprinting, remain inconsistent (Faude et al., 2014; Jastrzebski et al., 2014; Arslan et al., 2020). Available evidence fails to conclusively support the effectiveness of SSGs in enhancing acceleration and sprinting, suggesting that they are less effective compared to high-intensity interval training (Faude et al., 2014; Jastrzebski et al., 2014; Arslan et al., 2020). One methodological gap in utilizing SSGs as training interventions is the lack of exploration into the acute demands of various task constraints and their influence on structured programs (Praca et al., 2022). For instance, studies focusing on sprint adaptations through SSG often neglect to compare different SSG approaches (e.g., bigger vs. smaller pitch sizes; longer vs narrow) (Faude et al., 2014; Jastrzebski et al., 2014; Arslan et al., 2020).

Given the scarcity of studies considering task constraints as independent variables influencing training interventions (Clemente et al., 2021b), understanding how to manage these constraints - specifically, pitch dimensions and shape (length per width ratio) - becomes crucial for innovative approaches and practical applications aimed at tailoring SSG training interventions to enhance potential positive adaptations across multiple levels. Therefore, employing different pitch dimensions not just for evaluating acute effects (as commonly done in existing literature) but also for investigating the impact of repeated exposure on physical fitness adaptation is innovative. Thus far, only one experimental study has been reported (Faga et al., 2022), comparing small (75m²) versus large (300m²) pitch sizes on the maximal aerobic speed and anaerobic speed reserve of male soccer players. However, further research is needed, particularly in other crucial outcomes such as sprinting. Such research can offer practical insights for coaches striving to understand the genuine influence of these constraints while designing training programs to foster enhancements in vital physical attributes.

Therefore, the present study aims to compare the effects of two additional SSG-based training interventions (one with a length per width ratio of 2.0 and another with a ratio of 1.0, both utilizing the same pitch area) on the aerobic fitness, acceleration, and linear sprint performance of youth male soccer players, in comparison to a control group participating only in in-field sessions. We hypothesize that the more elongated pitch will significantly promote positive adaptations in sprinting compared to the less elongated SSG experimental group (Castagna et al., 2017). Additionally, we anticipate that both experimental groups based on SSG will induce effective positive adaptations in aerobic fitness and acceleration (Faga et al., 2022).

This study adhered to the CONSORT guidelines for reporting experimental studies (Turner et al., 2012).

This study employed a randomized controlled design. Two male soccer teams voluntarily participated, and their players were randomly assigned to one of three groups: (i) additional SSGs training intervention using a length per width ratio of 2.0 (SSGlw2); (ii) additional SSGs training intervention using a length per width ratio of 1.0 (SSGlw1); and (iii) a control group that only participated in regular in-field training sessions. Randomization occurred before the initial evaluation to ensure allocation concealment. The randomization method involved using opaque envelopes with an equal probability for each group. Each team had an equal number of participants in the three groups. Researchers conducting evaluations were blinded to the groups to minimize bias.

The a priori sample size was estimated using a power of 0.85, considering three groups and two evaluation moments, a p-value of 0.05, and an effect size of 0.25. Utilizing G*power (version 3.1.9.6., Universität Düsseldorf, Germany) to execute the F test for within-between factors, it recommended a sample size of 48 participants. The eligibility criteria defined for this study included: (i) outfield players only; (ii) players who participated in both pre and post-intervention assessments; (iii) players free from injury and/or illness; and (iv) players who attended at least 90% of the training interventions.

Convenience sampling was utilized to select the two teams participating in the study. The teams granted permission for their players to participate, and the players were informed about the study design and agreed to participate voluntarily, with the option to withdraw at any time without penalty. From a potential sample of 53 players, five were excluded for serving as goalkeepers, leaving 48 male soccer players who participated in the study (Figure 1).

Participants had an average age of 16.4 ± 0.6 years, weight of 62.4 ± 1.9 kg, height of 173.5 ± 2.5 cm, and 4.7 ± 0.7 years of experience. Since two teams participated in the study, the randomization of participants was conducted to ensure that each team had a similar number of players in each of the three groups. Consequently, each team had 8 players in SSGlw2 group, 8 in SSGlw1 group, and 8 players in the control group.

The youth players competed at a trained/developmental level, participating in the same regional competitive competition. Furthermore, both teams engaged in three to four training sessions per week, each session lasting between 80 and 100 minutes, in addition to one match. As a result, they were very similar in terms of the type and structure of their training process.

Participants and their legal guardians were briefed on the study design and protocol. Following verbal explanation, they read and signed a voluntary informed consent form. The study protocol was approved by the Institutional Ethical Review Board of XXX Institute of Physical Education under reference code 2023#145. The study adhered to the principles outlined in the Declaration of Helsinki.

The SSG interventions served as a supplement to the regular in-field training sessions. The control group solely engaged in the regular in-field sessions, while players assigned to the experimental groups received additional two weekly SSG intervention sessions, spaced 48 hours apart. The intervention spanned eight consecutive weeks. These interventions took place immediately before the regular in-field sessions and were conducted on synthetic turf.

The players assigned to SSGlw2 completed three sets of 4-minute bouts in a 4v4 format, with 3 minutes of rest between each set. The pitch dimensions were 40 20 m, providing a relative area per player of 100m², with a length-to-width ratio of 2:1. Players in SSGlw1 also participated in three sets of 4-minute bouts in a 4v4 format, with 3 minutes of rest between each set, although the pitch dimensions were 28, 28 m, with a relative area per player of 98m², and a length-to-width ratio of 1:1. The objective of the task was to score in a small goal (2, 1 m) centered on the endline, while the rules of the game mirrored the official ones, except for the non-application of the offside rule and the omission of cards. It is worth noting that throughout the games, no instances of unethical or aggressive behavior were observed. The ball was manually repositioned when it crossed the boundaries.

Players were assigned to the teams for the 4v4 formats based on a balanced distribution of one defender, two midfielders, and one forward. This assignment was made by the coach, taking into account perceptual analysis to ensure competitive balance during the games. However, exploratory analysis was conducted to examine differences in fitness levels within the teams, aiming to ensure balance. It was observed that variations in sprint performance among teams were approximately 1.6%, while variations in aerobic performance were around 1.9%. This indicates that fitness levels were similar across team members. Players remained on the same team throughout the intervention. The coach did not provide instructions regarding tactical or strategic approaches. Additionally, no verbal encouragement was given during the games. Balls were positioned closer to the pitches to ensure quicker ball repositioning. Throughout the generated reports, none of the observed matches during the experiment exhibited a difference in score greater than two goals over the duration of the games. It was noted that draws between teams occurred in 38% of the instances following the conclusion of the games.

The physical fitness evaluations were conducted one week before the start of the intervention and again in the week following the intervention's conclusion. These evaluations occurred on the same day of the week to ensure a 24-hour rest period following the previous training session. They took place in the afternoon on a synthetic field, approximately two hours after the participants' last meal. The average temperature during the assessments was 19.2 ± 1.3ºC and relative humidity of 47.5 ± 3.1%.

The evaluations began with the collection of demographic information, followed by anthropometric measurements. A standardized warm-up protocol was then implemented, comprising 10 minutes of jogging, 8 minutes of dynamic stretching, and 5 minutes of neuromuscular activation exercises such as reactive jumps and accelerations.

The order of the tests was consistent for all players. After five minutes of the end of warm-up, the players completed the 30-meter sprint test three times, with three minutes of rest between each sprint. Following the final sprint trial, the players rested for five minutes. The five-minute period was allowed to maximize recovery. Previous studies on neuromuscular efforts recommend a five-minute recovery instead of a shorter one to ensure maintaining a high volume of effort without compromising muscular ability (Willardson and Burkett, 2005). Finally, they undertook the Yo-Yo intermittent recovery test level 1 (YYIRT).

The 30-m linear sprint test was utilized to evaluate sprint performance. Consistently noted as valid and reliable for evaluating sprint performance in soccer players (Altmann et al., 2019), this test used two pairs of photocells (SmartSpeed, Fusion Sport, Queensland, Australia): one at the starting line, and the second pair at the endline (30 meters). Participants assumed a split position, leading with their preferred leg, which remained consistent throughout the trials. They began their sprint 30 centimeters before the first pair of photocells and were instructed to sprint at maximum speed, decelerating only after passing the last pair of photocells. The photocells height was adjusted to align with the participants' hips. Each player completed three trials with three-minute intervals between each. The fastest time recorded in seconds was then selected for further data analysis.

The research utilized the YYIRT level 1 as a test to evaluate the aerobic capacity of the participants. Taking place on the synthetic turf, this assessment comprised repetitive 20-meter shuttle runs governed by auditory cues signaling incremental speed adjustments. Players engaged in a shuttle run pattern between two designated lines positioned 20 meters distant from each other, with brief active recovery interspersed between each 40-m shuttle. The test commenced at a velocity of 10 km/h and progressively intensified in pace as per the auditory prompts (Krustrup et al., 2003).

Participants were instructed to maintain the pace dictated by the audio signals for as long as possible, ensuring they reached the end line before the next signal. If a participant failed to reach the line before the signal, they were given a warning. After two consecutive failures to reach the line in time, the test was terminated, and the total distance covered (in meters) was recorded as the test score.

Descriptive statistics, comprising mean and standard deviation, were presented. The Kolmogorov-Smirnov test (p > 0.05) was employed to assess normality, while Levene’s test (p > 0.05) was utilized to evaluate homogeneity. Upon confirmation of both normality and homogeneity assumptions, a mixed ANOVA test (time*group) was executed to compare pre- and post-intervention outcomes across various groups. The effect size was quantified using partial eta squared. Post-hoc pairwise comparisons were conducted using the Bonferroni test, with Cohen's standardized effect size utilized to measure the magnitude of inter-group differences. Effect sizes were categorized as small (d = 0.2 to 0.5), medium (d = 0.5 to 0.8), or large (d ≥ 0.8) (Cohen, 1988). All statistical analyses were performed utilizing SPSS (version 28.0.0.0, IBM, USA), with significance threshold set at p < 0.05.

Baseline comparisons revealed no significant differences between groups on YYIRT (F = 0.030; p = 0.971; η² = 0.001) and 30-m sprint time (F = 0.498; p = 0.611; η² = 0.022). Descriptive statistics of physical fitness outcomes pre and post-intervention can be observed in Table 1.

Significant interactions time group were observed in regards YYIRT (F = 15.857; p < 0.001; = 0.413). Between-group differences were found in post-intervention (F = 13.969; p < 0.001; = 0.383), on which SSGlw2 (+328.8 m; p < 0.001) and SSGlw1 (+280.0 m; p < 0.001) were significantly greater in comparison to control group. No significant differences were found between both experimental groups (48.8 m; p > 0.999). Within-group analysis revealed significant improvements on SSGlw2 (+333.8 m; p < 0.001) and SSGlw1 (+308.8 m; p < 0.001), while no significant differences was found on control group (+10 m; p = 0.826). Figure 2 illustrates the mean differences observed within each group, taking into account the within-player variations.

Significant interactions time x group were observed in regards 30-m sprint test (F = 43.965; p < 0.001; = 0.661). Between-group differences were found in post-intervention (F = 25.425; p < 0.001; = 0.531), on which SSGlw2 was significantly better than SSGlw1 (-0.073s; p < 0.001) and control group (-0.095s; p < 0.001). No significant differences were found between SSGlw1 and control groups (0.022s; p = 0.363). Within-group analysis revealed significant improvements on SSGlw2 (-0.092s; p < 0.001) and SSGlw1 (-0.017s; p = 0.022), while no significant differences was found on control group (-0.006s; p = 0.440).

This study is one of the few to investigate how differences in pitch shape during SSG can influence physical fitness adaptation. Our findings revealed that the more elongated pitch (SSGlw2) significantly outperformed the other intervention group (SSGlw1) and the control group in eliciting positive adaptations in sprinting performance. Moreover, both experimental groups exhibited significantly superior improvements in enhancing aerobic capacity compared to the control group, although there was no significant difference between the two experimental groups. This evidence suggests that incorporating SSG promotes positive adaptations at such levels. However, further comparisons in future research are needed to understand whether the primary factor contributing to improvements is the training method itself (SSG) or the supplementation of exercise by adding extra training volume.

Research on acute demands induced by SSGs often highlights their limited ability to facilitate stable and significant distances covered at high-speed running and sprinting (Dello Iacono et al., 2023). However, investigations comparing larger pitches, particularly those elongated from goal-to-goal, have provided evidence that this modification significantly increases running speed actions (Castagna et al., 2017). Specifically, players achieve more actions and cover greater distances at faster speeds on larger pitches (Casamichana et al., 2018; Castagna et al., 2019). Building upon these findings, the current study innovated by examining whether this critical modification could enhance the typical adaptations induced by SSGs, which, thus far, have only marginally surpassed control groups in terms of sprint performance adaptations (Clemente et al., 2021b).

Interestingly, and in line with our hypothesis, the more elongated condition implemented in the SSGlw2 group significantly improved sprinting performance, surpassing the adaptations induced by both SSGlw1 and control groups. Despite SSGlw1 and SSGlw2 having the same relative area per player, the elongated nature of SSGlw2 likely facilitated more continuous running periods, leading to greater speeds (Casamichana et al., 2018). This contrasts with games played in smaller spaces, where running demands are more associated with frequent changes of direction, acceleration, and deceleration, typically linked to possession-oriented tactics and circulation along the wings (Fradua et al., 2013; Casamichana et al., 2018).

The specific tactical behavior observed in SSGs on elongated pitches emphasizes mobility actions, transitions, and exploitation of the longitudinal axis (Silva et al., 2014). By allowing players to explore this axis more frequently, they are exposed to intense running actions, particularly in counter-attacks (Fradua et al., 2013), which may benefit the adaptations observed in this research. Notably, the SSGlw1 group also demonstrated improved sprint performance in within-group analysis, although not significantly surpassing the control group, which only participated in regular in-field sessions.

Considering the effects of both SSG training interventions on aerobic capacity, our findings revealed that both significantly promote capacity enhancement, surpassing the control group. The 4v4 format of play, commonly associated with a more metabolic stimulus, effectively targets aerobic and anaerobic metabolisms, favoring aerobic power training (Lacome et al., 2018). Regardless of pitch shape, our results demonstrated that both interventions were equally effective in significantly enhancing aerobic capacity. These findings are consistent with existing literature on SSG interventions, which show comparable adaptations in aerobic capacity to other intense and intermittent methods such as high-intensity interval training (Moran et al., 2019; Clemente et al., 2024). On the other hand, our results contradict a study (Faga et al., 2022) that examined the effects of small (75 m²) and large (300 m²) pitches on maximal aerobic speed. In that study (Faga et al., 2022), it was found that only the largest pitch led to significant improvements in this capacity.

The intermittent nature of SSGs, characterized by repeated bursts of high-intensity activity interspersed with brief rests, closely mirrors the demands of aerobic interval training, known for its efficient improvement of cardiovascular fitness (Clemente et al., 2021c). Additionally, the high intensity and varied movement patterns inherent in SSGs, including intense accelerations, decelerations, and changes of direction, engage a larger muscle mass, resulting in greater energy expenditure and cardiovascular demand (Gaudino et al., 2014) compared to traditional continuous exercise. Moreover, the social and competitive aspects of these games often enhance motivation and enjoyment (Selmi et al., 2020; Farhani et al., 2022), further facilitating physiological adaptations associated with improved aerobic capacity.

Despite implementing innovative and adhering to recommended practices for randomized experimental studies, our research is not without limitations. One such limitation is the absence of progression in task challenges throughout the study weeks. It would be advisable to explore the potential benefits of incorporating progressive periodization in SSGs, as this may lead to varied adaptations in players. Furthermore, due to methodological limitations, we did not have access to microelectromechanical systems that could aid in monitoring the acute locomotor and mechanical impact during the use of SSGs, nor did we have heart rate sensors to provide information about the players' physiological responses to the games. This lack of instrumentation hindered our ability to gain a comprehensive understanding of the mechanisms contributing to the observed adaptations. Additionally, our study overlooked other physical fitness variables that could be influenced by modifications in pitch size, such as change of direction ability or jumping performance. Furthermore, we chose to conduct in-field tests rather than examining competitive performance measures. While competitive performance is undoubtedly important, some match running performance measures are highly dependent on the context of the game, rather than solely representing specific physical qualities (Buchheit and Simpson, 2017). This led us to focus on a capacity that is not contingent upon the playing dynamics. However, we acknowledge that future studies should also consider employing tests that evaluate performance in matches, while controlling for the influence of game dynamics on these outcomes. Moreover, we only examined a single format of play, neglecting the potential impact of different training formats on the interaction with pitch size. Finally, the experimental groups received an additional 24 minutes of training per week compared to the control group. Therefore, future research should explore alternative training approaches for control groups to match the same training volume. This would ensure that improvements are not solely due to the additional training volume but also to the specific training method employed. Future research should also aim to establish dose-response relationships between accumulated external load demands during games and the resulting adaptations in physical fitness.

Despite these limitations, our study is, to the best of our knowledge, the first to investigate the hypothesis that different pitch shapes influence physical fitness adaptations during SSG interventions. Our findings suggest that, from a practical standpoint, coaches should consider employing more elongated games to create conditions conducive to improving sprint performance over time. Merely reducing pitch size along the longitudinal axis may not guarantee to achieve significant improvements in this regard.

Our study findings indicate that employing more elongated pitch sizes during SSG training interventions significantly enhances sprint performance compared to less elongated pitches and control groups. However, regardless of the pitch shapes utilized in this study, coaches can effectively utilize SSG training interventions to significantly improve aerobic capacity in youth male soccer players, as both approaches outperformed the control group. Coaches are advised to prioritize the use of more elongated pitch sizes to promote adaptations in sprint performance, while still acknowledging that aerobic capacity improvements remain significant compared to other pitch shapes.