Speed and Agility Training in Female Soccer Players - A Systematic Review

Female soccer players performs between 1350-1650 activity changes, along with jumping, accelerating and deceler-ating. The ability to repeat these actions identically in competition are essential for success in female soccer. Hence, the study aim was to summarize relevant literature on the effects of speed and agility training in female soccer players. Literature identification were conducted according to the PRISMA guidelines and in multiple databases (Google Scholar, PubMed, Scopus, Cochrane Library, ProQuest, EBSCOhost and Science Direct). Based on the pre-defined inclusion criteria (year of publication (2003-2022), full-text study published in English, the experimental study that had included healthy and injury-free female soccer players as participant sample) database search have identified 23502 potential studies. In the end, a total of seven full-text studies were included, with a total of 165 female participants. There were a variety of experimental programs, such as resisted, assisted and traditional sprint training, high-speed treadmill, speed and agility trainings, and repeated agility and strength group, along with their comparison with strength training group. Likewise, different types of duration, intensity and frequency were observed and resulted overall speed and agility improvements in female soccer players. Authors can conclude that only with well prepared and organized program, especially in pre-season, female soccer players should be able to improve important and specific factors, in order to achieve desired aim and result in terms of speed and agility.


Introduction
Women's soccer has advanced significantly in terms of play, finance and media in recent years and as a result, the demands for women's soccer as team sport have risen sharply (Peeters & Elling, 2005).Nevertheless, it's growing popularity, female athletes are subjected to higher training volumes and competition demands than ever before, necessitating a better understanding of female athletes' performance changes in order to design effective training programs (Datson et al., 2004).Changes in the movement mechanism of the arms or legs can influence linear action such as acceleration and velocity.Thus, the ability to develop speed quickly (acceleration) is an important component for supporting performance in a variety of sporting activities (Azmi & Kusnanik, 2018).Speed, agility, along with the quickness (SAQ) exercises covers the entire training intensity spectrum and it is a very small percentage that can be improved due to heredity (Szabo, Neagu, & Sopa, 2020).What is more, acceleration and sprint performance is associated with maturity status (Murtagh et al., 2020).
According to the match statistics, female soccer players covers 9-12km during the game (Mohr, Krustrup, Andersson, Kirkendal, & Bangsbo, 2008), with as much as 8-12% of that being high-intensity running or sprinting (Rampinini et al., 2007).The average sprint duration is between 2-4sec.and occurs during crucial moments of the soccer game, with the vast majority of sprint displacements being less than 20m (Andrašić et al., 2021).Furthermore, fe-male soccer players performs between 1350-1650 activities changes, including dribbling passing and tackling (Munro & Herrington, 2011).Jumping, accelerating, decelerating, different sprints with changes of direction and the ability to repeat these actions identically in competition are essential for success in team sports like soccer (Stankovic et al., 2022).Moreover, mentioned explosive actions, like tackling, jumping, changing directions (COD) and sprinting, have a direct impact on the outcome of the result (Loturco et al., 2022).Therefore, explosive strength of the lower extremities is one of the most important motor characteristics (Prvulović, Martinović, Kostić, & Katanić).
There are numerous studies that compare the level of speed between competition levels, age categories, as well as the relationship between reactive speed, COD speed and individual movement speed (Ates, 2018;Andrašić et al., 2021;Stankovic et al., 2022).Despite the research mentioned above, there is currently little scientific evidence to shows effects of speed and agility training in female soccer players (Paradis, 2003;Upton, 2011;Shalfawi et al., 2013a;Shalfawi et al., 2013b;Mathisen & Danielsen, 2014;Mathisen & Svein, 2015;Page et al., 2021).Paradis et al. (2003) reported that the SAQ program improved power, speed and agility, but not strength in young soccer players.In addition, Shalfawi et al. (2013a) reported significant improvements in repeated agility training and repeated sprint training in elite female soccer players, with no significant differences between groups in any of the measured variables.Furthermore, two studies (Mathisen & Danielsen, 2014;Mathisen & Svein, 2015) found that short sprint bouts at maximum effort had a significant effect on agility performance in adolescent female soccer players.On the other hand, Shalfawi et al. (2013b), reported that agility and repeated sprint training had no significant effects in well-trained elite female soccer players.
To the authors' knowledge, there are a few studies that have analyzed the effects of speed and agility training in female soccer players.However, no study has been conducted that summarizes the literature in women's soccer.As a result, the purpose of this study is to summarize relevant literature on the effects of speed and agility training in female soccer players.

Literature Identification
PRISMA guidelines (Page et al., 2021;Rethlefsen et al., 2021) were used for the search and analysis of the studies.Furthermore, a multiple database identification was carried out, such as Google Scholar, PubMed, Scopus, Cochrane Library, ProQuest, EBSCOhost and Science Direct.
For study identification in mentioned databases, the multiple keywords (combination are separately) were used: ("speed enhancement "OR "quickness "OR "soccer speed "OR "agility enhancement "OR "аgility" OR "soccer agility" OR "SAQ" OR "mechanical stress" OR "physical stress") AND ("soccer" OR "football" OR "female soccer" OR "female football" "team sport" OR "collective sport" OR "female team sport").The study identification and data extraction were examined separately, by a total of two authors (M.S. and D.Dj.).Then, each author had to cross-examine the identified studies, and considered if the study is eligible for further analysis or not.Furthermore, a descriptive method was used for obtained data examination, whereas all titles, abstracts and full-text articles were reviewed for eventual study inclusion in the systematic review.After detailed identification process, studies were considered to be relevant and included, only if they met the pre-defined inclusion criteria.

Exclusion Criteria
The studies were not included if they have realized before 2003, published studies in other language than English, studies with male or mixed gender participants, studies where full-text possibility was unable, the studies that have included supplements usage and studies where experimental program was influenced on other parameters beside physical performance.

Bias Risk Assessment
The study quality and the potential risk of bias was assessed and determined by the PEDro scale (de Morton, 2009).Assessment were carried out by two authors, separately.The author's concordance was calculated using k-statistics data to examine the complete text, to determine relativity and bias risk.In case of disagreement, the provided data was evaluated and finalized by a third reviewer, independently.The concordance between reviewers was k=0.93.

Data Extraction
The necessary information was extracted from the studies, using Cochrane Consumer and Communication Review Group's.The main study characteristics were: first author and year of publication, age, sample size, experimental intervention program (type, duration, frequency and training duration), measured outcomes and study results.

Study Quality
According to Maher et al. (2003), a PEDro scale points has to be awarded in order to identify the study quality.Further, if the study has gained between 0-3 points, the study will be classified with poor quality, 4-5 points with fair quality, 6-8 points with good quality and 9-10 points with excellent quality.Same authors have also stated that 8-11 points are optimal.In studies that have included in the final analysis, three studies have classified with fair quality, while rest of three studies with good quality.Table 1 presents PEDro scale total results.

Selection and Characteristics of Studies
Based on the database study identification, a total of 23502 were identified.At the main beginning, 522 duplicate studies were excluded, whereas a total of 22980 studies were further taken into consideration.According to the pre-defined inclusion criteria, 78 were excluded by review-ers and 22879 were excluded by automation tools, whereas 23 studies were assessed for eligibility.Additional 16 studies were excluded based on in-deeper check, non-relevant outcomes, editorials and executive summaries.In the end, seven studies were included in the systematic review (Figure 1.).
Table 2 presents studies that have included in the systematic review based on pre-defined criteria.
There were a variety of experimental programs, such as resisted, assisted and traditional sprint training (Upton, 2011), high-speed treadmill (Johnson et al., 2013), speed and agility trainings (Paradis et al., 2003), repeated agility and strength group (Shalfawi et al., 2013a), along with their comparison with strength training group (Shalfawi et al., 2013b).

Discussion
The study aim was to summarize relevant literature on the effects of speed and agility training in female soccer players.The main study findings are seven studies that have presented various types of speed and agility training, with different types of duration, intensity and frequency that have resulted overall speed and agility improvements in female soccer players.
Increased step frequency and reduced ground contact time have a positive effect on maximum speed as well as the result of reduced acceleration time (Mero et al., 1992;Paradis, 2003).Kyröläinen, Avela and Komi (2005) have found that during the acceleration phase of sprinting, maximal integrated electromyographic (EMG) activity is greater than during the constant velocity period, indicating that this is the moment when the sprinter's neural activation is greatest.A significant increase in muscle force development in initial acceleration in the AST group occurred in the first 5yd (4.6m) of the sprint, while the RST group had the greatest increase in speed during the 15 to 25yd (13.7 to 22.9m), and as it was hypothesized acceleration increased significantly (p<0.001) over a 4 week period (Upton, 2011).Repeated linear sprint training improves intermittent running ability more than agility training, while repeated agility training improves specific agility improvement and both groups on the RSA test (10x40m) with 95% maximum running speed finished with 97% in the post-test (Shalfawi et al., 2013a).In that regard, similar results were also presented elsewhere (Tønnessen et al., 2011).Above mentioned indicates the ability to achieve repeated sprints close to maximal intensity.
Since it was observed only moderate improvements (d=0.8) in the RAG/RSG group, as well as trivial to negative in agility performance in the STG group (Shalfawi et al., 2013b), these results are not in accordance with Dupont et al. (2004), who have observed improvements in RSA.These soccer players have performing one repeated sprint session and one aerobic training session each week, in addition to one game and 8-10 normal soccer training sessions during the season.As a result, a physical conditioning program must be carefully balanced with regular soccer training (Morgans, Orme, Anderson, & Drust 2004).A carefully constructed training program for one set of skills may impede the development of other vital attributes and vice versa (Jalilvand, 2015).It is also recognized that the constant stress, along with the strength and conditioning program, can create a "chronic catabolic environment" for the neuromuscular system.Because these studies were done in-season, this setting may result in modest or no changes in other physical characteristics (Kraemer et al., 2004).Hence, an additional physical fitness program must be well planned and balanced together with regular soccer training, especially during in-season period.
According to Yap and Brown (2000), female training regimens are identical to males training protocols, as women's training programs have improved significantly over the years.Mathisen & Danielsen (2014) have resulted a significant increase (6.2%) in agility performance in a 8 week LIN and COD program, which is consistent with findings Pettersen and Mathisen (2012).Although initial acceleration and short sprint are reported to be more difficult to improve than maximal speed (Meilan & Malatesta, 2009), this study also shows a significant improvement in the acceleration phase (5.1%) in the 10m sprint and (3.5%) in 20m sprint.Furthermore, results from other study (Mathisen et al., 2015), with a bit older participants have revealed 10m straight sprint (4.1%), 20m straight sprint (3.2%) and agility performance (5.2%) improvement.Since growth and maturation could increase sprint performance (Vescovi et al., 2011), maturity status has a crucial role in modulating the response to speed exercises (Malina et al., 2004).
Likewise, women go through a biological process during the menstrual cycle, where hormone levels rise and fall (Keay et al., 2021).Julian et al. (2017) have highlighted that there could be a performance decreases during the mid-luteal phase where hormones were contrasted in the peak phase of the menstrual cycle and this decreases was not found in jumping or sprint performance.Hence, in order to examine and analyze how the phases of the menstrual cycle affect physical performance, it is necessary to take into consideration the specificity of sport (Mkumbuzi et al., 2021).But further investigation is needed.
The strength of this study lies in the fact that it is the only systematic review on the topic of speed and agility training in women's soccer.This is especially significant given that the majority of soccer training research focuses on men.Additionally, the paper has provided valuable guidelines for the training of female soccer players.Thus, the practical implications would involve the implementation of various training programs that have shown positive effects on speed and agility qualities in female soccer players.
As far as the study limitations, there is some.First, they have taken into consideration studies that have dealt with regular speed and agility, but not reactive.Second, they did not take into consideration the anterior cruciate ligaments (ACL) condition in the participants' sample, which can be an important factor for both speed and agility.Hence, future studies can include the mentioned medical state for both future experimental studies and systematic reviews.

Conclusion
Since the speed is about 95% congenital, the same can be relatively enhanced.On the other hand, agility is not congenital as speed, but it can be more influenced.Hence, only with well prepared and organized program, especially in pre-season, female soccer players should be able to improve these important and specific factors, in order to achieve desired aim and result.

FIGURE 1 .
FIGURE 1. PRISMA flow chart of study identification

Table 1 .
PEDro scale for cross-sectional studies