A Mesh Meta-Analysis of the Effectiveness of Different Warm-Up Exercises to Prevent Knee Injuries in Young Child Soccer Players

Objective: A mesh Meta-analysis was used to evaluate the effectiveness of four warm-up exercises to prevent knee injuries in juvenile soccer players. Method: They are a randomized controlled trial (RCT) on FIFA 11+ integrated warm-up, FIFA 11+ Kids integrated warm-up, and neuromuscular training (NMT) warm-up for the prevention of knee joint in juvenile soccer players by a computer search of CNKI, CBMdisc, WanFangdata, Pubmed, Web of science, and SPORTDicus database. The search period was from the establishment of each database to February 2022. Two investigators screened the literature, extracted data, and assessed risk bias for the included studies according to the pre-defined inclusion and exclusion criteria, and finally analyzed the data using Stata 14.0 software and OpenBUGS software. Results: A total of 10 RCT studies with 17,143 subjects, spanning the age range of 7 to 19 years, were included. The results of the reticulated Meta-analysis showed that all three warm-up modalities were effective in reducing the incidence of knee injuries in junior soccer players compared to conventional warm-up, with the optimality in descending order of FIFA 11+ Kids comprehensive warm-up (SUCRA = 85.3), neuromuscular training warm-up (SUCRA = 66.7), and FIFA 11+ combined warm-up (SUCRA = 44). Conclusion: The FIFA 11+ Kids comprehensive warm-up is the most effective warm-up exercise for the prevention of knee injuries in junior and child soccer players, but the above findings need further validation due to the quantity and quality of the literature and the quality of the evidence.


Introduction
Soccer is one of the most played sports in the world, and the popularity of the sport continues to grow, especially among children and teenagers [1]. The sport has a potentially beneficial effect on the health of children and adolescents, however, due to the highly combative nature of soccer, participation in the sport can be accompanied by a large number of sports injuries, and Leppänen's research shows that the knee area is the most frequently injured in soccer players aged 9 -14 [2]. Injuries to the knee area not only reduce a sportsperson's current and future opportunities to participate in sports but also result in significant medical and social costs [3] [4]. However, it is widely believed that the benefits of participation in soccer for the social development, leadership development, and overall physical and mental health of children and youth outweigh the risk of injury [5] [6]. Therefore, effective warm-up activities to avoid injuries are crucial for the development of soccer in children and youth.
At present, the warm-up activities for young children's soccer mainly include FIFA 11+ integrated warm-up, FIFA 11+ Kids integrated warm-up, neuromuscular training warm-up (NMT), and regular warm-up. FIFA 11+ integrated warm-up has been adopted by a large number of professional and amateur soccer players since it was launched by FIFA in 2006 and has an improvement effect in reducing the incidence of knee injuries [7] [8]. FIFA 11+ Kids Comprehensive Warm-up is an injury prevention exercise developed by the F-MARC International Expert Panel for children aged 7 -13 years old, which can effectively reduce sports injuries and the social costs brought about by injuries [9] [10]. Neuromuscular warm-up programs are primarily a combination of multi-modal exercise activities, such as balance exercises, strength exercises, and core stability exercises, that are equally effective in reducing sports injuries and improving athletic performance. The effectiveness of these warm-up activities in preventing sports injuries has been demonstrated by numerous RCT studies and Meta-analyses, but the relative effectiveness of various warm-up activities in preventing knee injuries has yet to be verified. Therefore, this study used a reticulated Meta-analysis to indirectly compare a variety of warm-up activities to rank the relative effectiveness of different warm-up activities for preventing knee injuries in children and youth soccer players to provide a theoretical reference for training applications.

Participants (P)
Children and youth soccer players.

Intervention (I)
The experimental groups were FIFA 11+ integrated warm-up, FIFA 11+ Kids integrated warm-up, and neuromuscular training warm-up. The specific warm-up exercises were as follows (Table 1). This includes aerobic exercises, dynamic stretching exercises, and soccer-specific exercises.

Comparative Factors (C)
Control group was one of the regular warm-ups, FIFA 11+ combined warm-ups, FIFA 11+ Kids comprehensive warm-up, and neuromuscular training warm-up.

Outcome Indicator (O)
Effectiveness in preventing knee injuries.

Study Design (S)
The included study designs were all randomized controlled trials (RCTs).

Exclusion Criteria
1) The full text could not be downloaded; 2) The literature was in a language other than Chinese or English; 3) The data were incomplete; 4) The study was conducted on college students.

Literature Screening and Data Extraction
Two researchers conducted literature screening and data extraction in strict accordance with the inclusion and exclusion criteria, respectively, and cross-checked after completion, and discussed and resolved any divergent literature and data, and in case of disputes, through third-party discussions, and contacted the au-

Evaluation of the Risk of Biased Chairs in the Literature
The risk of bias in the included studies was evaluated comprehensively by two researchers according to the Cochrane Handbook, and in case of disagreement between the two evaluations, an agreement was reached through discussion with a third author.

Statistical Analysis
Statistical analysis of the included data was performed using Stata 14.0 software, OpenBUGS. Since the outcome indicators were dichotomous variables, the effect size was evaluated using the ratio of ratios (OR) and 95% confidence intervals, and the effectiveness of each intervention was ranked for comparison using SUCRA values, with higher SCURA values indicating better effectiveness of the interventions and vice versa. Since this study was a comparison of each intervention with a conventional warm-up, and there was no closed structure, then no consistency test was required [14]. Published bias chairs are inspected using calibration funnel charts.

Literature Search Process and Screening Results
According to the pre-defined search strategy, Chinese and foreign language databases were searched, and a total of 489 kinds of literature were retrieved, and 8 literature were retrieved through other means. According to the inclusion and exclusion criteria, the literature that was not relevant to this study was excluded in EndNote X9 software, and a total of 10 studies were finally included.

Basic Characteristics of the Included Studies
A total of 10 English-language publications were included, all of which were randomized controlled trials containing four types of warm-up: FIFA 11+ Kids integrated warm-up, neuromuscular training warm-up, FIFA 11+ integrated warm-up, and conventional warm-up, with a total of 17,143 subjects, spanning the age range of 7 -19 years, mainly concentrated in Switzerland, the Netherlands, Germany, and the Czech Republic, and the United States; the intervention time was mostly concentrated in 15 -25 min, the training frequency was mainly focused on 2 times per week, and the intervention period was 1.5 -9 months; the main index was a knee injury. The specific characteristics are shown in Table 2.

Methodological Quality of the Included Studies
The quality of the included RCT studies was evaluated according to the Cochrane Handbook, and a total of six studies used the random number method or computer-automated randomized group generation for the grouping of experiments, which were not influenced by human intervention and evaluated as low risk; the blinding of the included studies was not described in detail, and other sources of bias could not be determined. The risk of bias for the included literature is shown in Table 3.

Evidence Network Diagram and Consistency Analysis of the Included Studies
The

Mesh Meta-Analysis Ranking
A total of 10 RCT studies reported knee injury indicators, containing 17,143 subjects, and the results of the reticulated Meta-analysis are shown in Table 4 and      (Table 4 and Table 5).

Published Bias Chair Test
Comparison-corrected funnel plots were used to identify small sample effects and publication bias in the included studies, and comparison-corrected funnel plots plotted with a knee injury as the effect indicator showed that the symmetry of the included studies was fair, indicating a possible small sample effect ( Figure  2).

The Relative Effectiveness of the Comprehensive Warm-Up of FIFA 11+ Kids
A total of 10 RCT studies involving four types of warm-up exercises were included in this study, and the results of the mesh Meta-analysis showed that the Currently available for soccer players between the ages of 7 -14, the FIFA 11+ Kids comprehensive warm-up is an exercise that prevents injury and improves performance by increasing stability in the legs and core area as well as im-

Advantages of Various Warm-Up Exercises
The three warm-up exercises have different advantages for reducing knee injuries in children and youth soccer players. The FIFA 11+ Kids comprehensive warm-up takes into account the developmental characteristics and injury types of soccer players at lower ages, focusing on improving spatial perception, body stability, and proper movement techniques at different ages [21]. The FIFA 11+ comprehensive warm-up mainly includes 10 movements to improve the core stability, balance, and other qualities of soccer players as well as the concept of fair play, applied to professional and amateur soccer players over 13 years old, with the main objective of reducing the occurrence of sports injuries while improving athletic ability. In neuromuscular warm-up exercises (NMT), athletes change the wrong movement patterns through strength training, core stability training, explosive power training, and other ways to enhance their perceptual ability of space, thus achieving a training method to prevent injuries and improve athletic ability, which is also effective for preventing sports injuries in volleyball and basketball for middle school students [22].

Shortcomings of the Study and Outlook
Although the current study showed that the effectiveness of FIFA 11+ Kids inte-

Conclusion
Compared to the other three warm-up exercises, the FIFA 11+ Kids comprehensive warm-up exercise was the most effective warm-up for preventing knee injuries in junior and child soccer players, but the results of this study need further in-depth validation due to the quantity and quality of the literature.