The Effect of FIFA 11+ on the Isometric Strength and Running Ability of Young Soccer Players

is the world's game, and keeping athletes healthy while playing the game has often been a focus of study. There is a high occurrence of musculoskeletal injuries reported in soccer. FIFA 11+ was developed as an intervention to help prevent such injuries. FIFA 11+ has previously been studied for its ef cacy as an injury prevention program, but not for its effect on sports performance in an adolescent population. The

the game has often been a focus of study. There is a high occurrence of musculoskeletal injuries reported in soccer. FIFA 11+ was developed as an intervention to help prevent such injuries. FIFA 11+ has previously been studied for its ef cacy as an injury prevention program, but not for its effect on sports performance in an adolescent population. The purpose of this study was to look at the effect of implementing the FIFA 11+ intervention on strength, speed, and agility. Twenty youth soccer players were randomly divided into an intervention group (INT) and a control group (CON). The intervention lasted for eight weeks and performance assessments were completed pre- and post-intervention. Post-test INT knee exor strength was signi cantly higher than pre-test scores (p< 0.05). INT also demonstrated signi cantly higher hamstring to quadriceps strength ratio (H/Q) after the intervention (p< 0.05), while the CON H/Q did not change signi cantly. 30-m sprint performance of both groups improved from pre- to post-test (p< 0.05). Shuttle run performance was signi cantly improved in post-test scores for INT players (p< 0.05), but did not change signi cantly for the CON players. It is suggested that implementing FIFA 11+ before training in young soccer players can lead to performance bene ts as well as injury prevention bene ts. Keywords:FIFA 11+; youth soccer; H/Q; performance; injury prevention 1. Introduction Soccer is the most popular sport in the world among people in different countries [1], but it often presents a high risk of injuries for musculoskeletal damage [2]. A statistical analysis of sport injuries over a 10 year period recorded 19,530 total injuries in 17,937 recreationally active participants [3]. 35% of those occurred during participation in soccer, making it the activity with the most injuries [3]. Elite soccer players suffer between 1.5 and 7.6 injuries per 1000 h of training and between 12 and 35 injuries per 1000 h of matches [4]. In youth soccer, the incidence of injuries during matches has been shown to increase with age from 1 to 5 injuries per 1000 match hours for players aged 13–15 years, to 15

injuries [3]. Elite soccer players suffer between 1.5 and 7.6 injuries per 1000 h of training and between 12 and 35 injuries per 1000 h of matches [4]. In youth soccer, the incidence of injuries during matches has been shown to increase with age from 1 to 5 injuries per 1000 match hours for players aged 13–15 years, to 15 to 20 injuries in the same period for players aged over 15 years [5]. These injuries can often cause loss of playing time for athletes, and loss of economic resources for clubs [6]. In response to high injury rates, the FIFA Medical Assessment and Research Center (F-MARC) developed FIFA 11+, a comprehensive warm-up program designed to prevent musculoskeletal injury. FIFA 11+ is broken down into three sections: low to moderate intensity running for eight minutes; strength, plyometric, and balance exercises for ten minutes; and high intensity Int. J. Environ. Res. Public Health2022,19, 13186.

Int. J. Environ. Res. Public Health2022,19, 13186 2 of 9 running exercises for two minutes. The purpose of this intervention is to induce bene cial neuromuscular effects by improving conscious control over running, sudden cutting, jumping, and landing [7]. Previous research has supported that the FIFA 11+ intervention reduces incidence of injuries for players at all levels [7]. For soccer players, strength is not only an important part of physical tness, but also a factor related to injury risks [8]. The relationship between isometric strength and injury occurrences has been widely discussed, and is often used to predict and monitor injuries of athletes [9]. High-level soccer players sprint 11% of the time in a game [10]. Previous research has proved that athletes with higher running velocities have a relatively lower risk of injuries [11]. Thus, sprint abilities not only can be used to determine the outcome of a soccer game but also can be regarded as a regulatory factor of injury risk as well. Researchers often associate and quantify injury risk with the ratio of concentric hamstring strength to concentric quadriceps strength [12]. The ability of the hamstring to stabilize the knee joint during dynamic movement reduces injury risk, which indicates that a larger hamstring-to-quadriceps-strength ratio can be bene cial for injury prevention [12]. Compared with elite players, unbalanced knee joint strength is more common in adoles- cent players who have relatively low muscular strength when in a stage of growth and development [13]. The relative weakness and immature movement patterns put adolescent athletes at a higher risk of injuries [13]. FIFA 11+ has also demonstrated performance bene ts when the intervention has been proven to improve speed and agility in soccer players [14]. The study which reported signi cant improvements in vertical jump height and sprint speed only investigated the effectiveness of the intervention program on adults [14]. Further research is still needed to determine the ef cacy of FIFA 11+ on sports performance on a youth population. The purpose of this study therefore was to evaluate the effectiveness of the FIFA 11+ intervention on performance components in adolescent

improvements in vertical jump height and sprint speed only investigated the effectiveness of the intervention program on adults [14]. Further research is still needed to determine the ef cacy of FIFA 11+ on sports performance on a youth population. The purpose of this study therefore was to evaluate the effectiveness of the FIFA 11+ intervention on performance components in adolescent soccer players compared to a typical warm-up. Performance components of interest included isometric knee strength, speed, and agility. Research has shown performance bene ts in adult participants and it was expected that similar bene ts would appear in adolescent participants [12,15,16]. It was hypothesized that the FIFA 11+ program would help improve knee muscular strength, as well as speed and agility. 2. Methods 2.1. Participants Twenty male soccer players in the U14 age group were selected to participate in this study. The participants regularly trained ve times a week for about 120 min each session, including three general training sessions, one video analysis session, and one team match per week. All participants had been in regular training for the last three years. Participants were all healthy with normal development and had no muscular injuries that would affect training performance. Only eld players were included in the study. 2.2. Experimental Procedures The 20 subjects were randomly divided into two groups by a random number table, the FIFA 11+ intervention group (INT) and the control group (CON), with 10 subjects in each. During the course of the experiment, the INT players completed the FIFA 11+ exercises, while CON players completed their regular warm-up before training. Each warm-up lasted 20 min. The study lasted eight weeks and interventions were conducted three times per week, prior to their regularly scheduled general training sessions. All of the players maintained normal routine, training, learning, and playing throughout the study. Players did not perform additional strength training outside of normal training time. The team members were responsible for recording the attendance of each player and using GPS (Catapult Open Field) to monitor the running distance and duration of each training session.

of the players maintained normal routine, training, learning, and playing throughout the study. Players did not perform additional strength training outside of normal training time. The team members were responsible for recording the attendance of each player and using GPS (Catapult Open Field) to monitor the running distance and duration of each training session.

Int. J. Environ. Res. Public Health2022,19, 13186 3 of 9 2.3. FIFA 11+ Intervention Plan The FIFA 11+ warm-up consisted of three parts. The rst part included low to moder- ate intensity running and dynamic stretching for approximately eight minutes. The second part then consisted of exercises aimed at developing strength, balance, muscular control, and core stability for 10 min. The last part was a combination of higher intensity running and soccer speci c drills for two minutes [17]. 2.4. Control Warm-Up Program The control group players completed typical warm-up activities that they were previ- ously accustomed to performing before training sessions. Running at the pace of about 6 min/km for 3 min. Stretching for 4 min in total, half kneeling hamstring stretch; side to side lunge with reach; dynamic squat stretch; standing calf and hamstring stretch, with each stretching action lasting for 20 s each time for 3 times. Running for 3 min, which includes a sprint of 30 m for 1 min, 10 m of change of direction speed training for 2 min. 10 min of ball practice: ball passing for 5 min, ball dribbling alternately for 5 min (20 m distance). The control warm-up was completed during the same 20-min time span as the intervention warm-up. 2.5. Muscular Strength Test Method Strength tests were all performed by the same therapist with two years of experience using a handheld dynamometer (MicroFET3, Hoggan, Salt Lake City, UT, USA). Testing locations were performed consistently according to dynamometer manufacturer instruction. Before the test, all participants performed a ve-minute warm-up, including jogging and dynamic stretching. Testing protocols were demonstrated to the players, and main points and precautions were explained prior to testing. A warm-up trial was conducted to familiarize the subjects with the test involving a 50% effort held for ve seconds. Each muscle group was then tested three times, with a rest period of one minute between trials. The average for the trials was calculated. Muscle groups tested included knee exors, and knee extensors. For knee extensor testing, the participants sat in a chair with hips and knees at 90 degrees.

the test involving a 50% effort held for ve seconds. Each muscle group was then tested three times, with a rest period of one minute between trials. The average for the trials was calculated. Muscle groups tested included knee exors, and knee extensors. For knee extensor testing, the participants sat in a chair with hips and knees at 90 degrees. The handheld dynamometer was applied to the anterior lower leg just proximal to the ankle joint. For the knee exor testing, the participants sat in the same position except the dynamometer was applied posterior lower leg, just superior to the calcaneus. Participants were instructed to push or pull against the dynamometer with maximum effort without moving their upper leg. Absolute strength was represented as maximum voluntary contraction under isometric conditions (MVC). Relative strength was calculated by dividing MVC by the subject's body weight (BW) and used for comparisons between subjects. Knee strength balance was also quanti ed by dividing hamstring strength by quadriceps strength (H/Q). 2.6. 30 m Sprint Test Method The players performed three separate 30 m sprint tests with 4-min intervals [18]. The segmented timing system was used to record the time (Smart speed, Australia, Fusion Sport) and the fastest time record was used as the nal result. 2.7. Shuttle Runs Test Method 5 training cones were placed on the soccer eld at the distance of 5, 10, 15, 20, and 25 m respectively. In the beginning of the test, players would run and knock down the 5 m training cone, and then run back to the starting point to knock down the training cone at the starting line (the training cone at the starting point is required to be put back every time it is knocked down). The players proceeded to knock down the 10 m training cone, and the cycle would continue until all the training cones were down at the end of the test [19]. The test would be performed once by the players due to potential fatigue caused by the drills. The split timing system was used to record the time (Smart speed, Australia,

The players proceeded to knock down the 10 m training cone, and the cycle would continue until all the training cones were down at the end of the test [19]. The test would be performed once by the players due to potential fatigue caused by the drills. The split timing system was used to record the time (Smart speed, Australia, Fusion Sport).

Int. J. Environ. Res. Public Health2022,19, 13186 4 of 9 2.8. Statistical Analysis Data and statistics in the study were analyzed by SPSS20.0. For continuous vari- ables that conformed to normal distribution, comparison of results between groups was conducted using Independent Samplest-test. Comparison of data before and after within- group tests were conducted using Paired-Samplest-test. The results were expressed as mean standard deviation ( s). Strength was normalized by dividing MVC by BW. Ratio of hamstring to quadriceps strength (H/Q) was also calculated as a measure of relative knee strength balance. 3. Results All 20 participants completed testing. There was no signi cant difference in height, weight, age, body mass index (BMI), or body fat percentage between the two groups before or after the experiment (Table). There was no signi cant difference in low-speed running, high-speed running, maximum speed, and training load between the two groups throughout the eight-week intervention (Table). Table 1.Baseline data. Baseline Data INT ( n= 10) CON ( n= 10) Age (years) 12.8 1.9 13.3 0.17 Body mass (kg) 51.08 8.36 54.33 7.55 BMI (kg/m 2 ) 18.02 1.36 19.03 1.34 Height (cm) 167.8 9.9 168.85 5.31 Body fat percentage (%) 5.37 2.35 7.63 4.93 Distance run per training (m) 6898.75 1889.23 6720.42 1384.18 Duration per training (min) 125.51 19.83 125.81 21.74 Low speed running (11–14 km/h) (m) 801.70 133.9 729.06 143.57 High speed running (>21 km/h) (m) 148.54 41.46 133.46 41.46 Maximum speed (km/h) 22.66 1.13 23.17 1.46 Training load (per minute) 6.65 0.40 6.66 0.71 3.1. Muscular Strength Testing in Knee Joint After eight weeks of FIFA 11+ there was a signi cant difference in knee exor strength in INT players, with greater strength observed post-intervention (p< 0.05). The change in the CON players was not signi cantly different from pre- to post-tests. Knee extensor strength of the INT players was slightly reduced after FIFA 11+ (p< 0.05), but did not change signi cantly for the CON players (Table). As a result, the H/Q of maximum strength was signi cantly higher in post-testing for the INT players compared to CON players (p< 0.05) (Figure).

was not signi cantly different from pre- to post-tests. Knee extensor strength of the INT players was slightly reduced after FIFA 11+ (p< 0.05), but did not change signi cantly for the CON players (Table). As a result, the H/Q of maximum strength was signi cantly higher in post-testing for the INT players compared to CON players (p< 0.05) (Figure). Table 2.Relative Lower Extremity Strength (MVC/BW). Muscles Intervention Group (n= 10) Control Group ( n= 10) Pre-Intervention Post-Intervention Pre-Control Post-Control Knee Flexors 0.39 0.05 0.42 0.04 *, & 0.34 0.09 0.33 0.07 Knee Extensors 0.56 0.10 0.50 0.05 * 0.50 0.11 0.50 0.10 Note: Comparison before and after the intervention within the group: * =p< 0.05; Comparison between the control group and the intervention group during the same period: & =p< 0.05. 3.2. Running and Agility Tests The 30-m sprint times of the INT players and the CON players were signi cantly better in post-testing than pre-testing (p< 0.05). The results of the inter-group comparison illustrated that the post-test 30-m sprint times of INT players were signi cantly better than those of the CON players (p< 0.05) (Table). The 5 25-m shuttle run time for the INT

Int. J. Environ. Res. Public Health2022,19, 13186 5 of 9 players was signi cantly better post-intervention than pre-intervention (p< 0.05), while the CON players had no signi cant change.Int. J. Environ. Res. Public Health 2022, 19, x FOR PEER REVIEW 5 of 9 Table 2. Relative Lower Extremity Strength (MVC/BW). Muscles Intervention Group (n = 10) Control Group (n = 10) Pre- Intervention Post- Intervention Pre- Control Post- Control Knee Flexors 0.39 ± 0.05 0.42 ± 0.04 *, & 0.34 ± 0.09 0.33 ± 0.07 Knee Extensors 0.56 ± 0.10 0.50 ± 0.05 * 0.50 ± 0.11 0.50 ± 0.10 Note: Comparison before and after the intervention within the group: * = p < 0.05; Comparison be- tween the control group and the intervention group during the same period: & = p < 0.05. Figure 1. Knee Strength Ratio (H/Q). Note: Comparison between the control group and the inter- vention group during the same period: & = p < 0.05. 3.2. Running and Agility Tests The 30-m sprint times of the INT players and the CON players were significantly better in post-testing than pre-testing (p < 0.05). The results of the inter-group comparison illustrated that the post-test 30-m sprint times of INT players were significantly better than those of the CON players (p < 0.05) (Table 3). The 5 × 25-m shuttle run time for the INT players was significantly better post-intervention than pre-intervention (p < 0.05), while the CON players had no significant change. Table 3. Changes in running ability. INT ( n = 10) CON ( n = 10) 30 m-sprint (seconds) pre-intervention 4.81 ± 0.26 5.11 ± 0.20 post-intervention 4.39 ± 0.26 *, & 4.60 ± 0.17 * 5 × 25 shuttle run (seconds) pre-intervention 36.01 ± 2.52 36.69 ± 2.16 post-intervention 33.51 ± 1.55 * 35.25 ± 2.55 Note: Comparison before and after the intervention within the group: * p < 0.05. Comparison be- tween the control group and the intervention group during the same period: & = p < 0.05. 4. Discussion This study illustrated the impact of FIFA 11+ on muscular strength and running

FIFA 11+ significantly enhances isometric strength and running ability in adolescent soccer players.