INTRODUCTION
Soccer is the most popular sport in the world; it requires players to perform for 45 min each in the first and second halves and demands the ability to maintain intense exercise during the matches. Players’ movement during soccer matches combines aerobic and anaerobic exercise that repeats instantaneous movements with a short rest period of 15 min between the two halves. Due to tactical changes in modern soccer, the quantity and quality of movements affect performance and require more high-intensity movements. Players need to maintain short distances with constant movements for high performance during the match, so they must repeatedly perform instantaneous and intermittent exercises (Pettersen and Brenn, 2019). Although the form of movement varies depending on the playing positions, all positions frequently require movements such as tackles, sprints, change of direction, and pressure (Stølen et al., 2005). Therefore, explosive movements during matches are essential in all positions.
In modern society, lack of physical activity among elementary school students due to studies, computer games, etc., can cause various physical and psychological problems. Indeed, lack of physical activity during childhood increases the incidence of obesity and reduces self-efficiency (Ha et al., 2016). Fundamentally, these problems can be solved by increasing physical activity through methods that spur interest in participating in sports and exercises. Previous studies reported that elementary school students’ physical activities were significantly related to academic achievements and physical fitness (Lambourne et al., 2013; Watson et al., 2017). Playing soccer can have positive psychological and physical effects, such as improving physical fitness for children and adolescents. Regular soccer playing can improve self-esteem, confidence (Quinn and Carr, 2006), and physical fitness (Zouhal et al., 2020). For these reasons, many young students enjoy playing soccer and other sports.
Although young soccer players are not fully developed physically, they perform similar forms of exercise, such as sprinting and changing direction during the match, as senior soccer players. Although the exercise forms are similar during the match, training for young soccer players should not be structured as that for senior players. The growth and development processes are essential to design desirable training for young soccer players. For example, training structured to improve muscle strength can cause injury in young soccer players as muscle growth has not been completed and training efficiency is low. Training for young soccer players should be organized as an effective way to improve their technique and skills. Regarding physical fitness, training for young players needs to mainly involve coordination and balance training to improve the dynamic postrural control ability (Cakir et al., 2020).
Proprioception is the sense of perception of the position and movement of skeletal muscles and joints. It contributes to joint stability during daily life or exercise by preventing muscles and tendons from being out of the normal range (Proske and Chen, 2021). Proprioception sense stimulation exercises positively affect injury prevention and exercise performance due to improved body balance and functional movement of the lower extremities (Han et al., 2015). Owing to these effects of the proprioceptive exercises, soccer players perform the exercise during general training and as postinjury rehabilitation training (Ambhore et al., 2021). Training to develop functional movements is essential, especially for childhood soccer players, compared to other periods of physical growth (Duncan et al., 2022). Improving the coordination ability between nerves and muscles could enhance functional movement.
Balance ability is essential for controlling the body’s movement and significantly correlates with exercise performance (Hrysomallis, 2011). Various exercise methods, including proprioceptive exercise, improve balance ability when performed optimally. In particular, proprioceptive exercise in childhood soccer players, which focuses on technical development, can improve exercise performance due to the enhanced balance ability. However, few studies have investigated the relationship between proprioceptive exercise and young soccer players’ performance. Therefore, this study aims to analyze the effect of proprioceptive exercise training on soccer skills and physical fitness in young soccer players.
MATERIALS AND METHODS
Participants
Soccer players in the 5th and 6th grades of elementary school who voluntarily expressed interest in participating in the study were recruited. Participants were divided into proprioceptive exercises training (PT) and control (Cont) groups; the purpose and methods of the study were explained to players, parents, and coaching staff through verbal description with an explanatory document to understand the purpose. Nineteen players (PT; n=10, 11.4± 0.5 year, career 1.8±0.9 year, Cont; n=9, 11.1±0.3 year, career 2.1±1 year) participated in the study. The study recruited soccer players with no injuries (fractures, sprain, etc.) and no restrictions on performing 8 weeks of exercise training. The exclusion criteria were participants with limited exercise capacity because they were on medications and those considered inappropriate by a doctor due to injury. The Ethics Committee of Kangwon National University approved this study (KWNUIRB-2023-02-006-001), which was conducted in accordance with the Declaration of Helsinki.
Study procedures
The PT group performed 30 min of proprioceptive sensory exercise 2 times weekly for 8 weeks after approximately 3 hr of team training. The control group was instructed to only participate in general team training during the experiment. Body composition (Inbody 370, InBody Co. Ltd., Seoul, Korea), dynamic balance ability, agility, quickness, and soccer skills (juggling, dribbling, short and long passes, shooting) were assessed a day before and after the training sessions. The players performed a 20-min warm-up exercise before the test, and a soccer skill test was conducted after the exercise performance test. After each test, a 10-min break was provided for the players to recover fully. Finally, players performed a cool-down exercise for 10 min after completing all tests. All tests were conducted on artificial turf, and players were allowed to drink water freely during the test.
Proprioceptive exercise training program
A proprioceptive training program for 8 weeks was applied by modifying the exercise program according to a previous study to suit young soccer players (Gidu et al., 2022). Table 1 shows the exercise program. Exercise was carried out in groups of two for 30 sec using the Both Sides Utilized (BOSU) balance trainer (Bosu Fitness, LLC, SanDiego, CA, USA), and 30 sec of rest was given after each exercise type. Each exercise was performed 4 times. Squats, lunges, swings, and jumps were performed without using the ball on the BOSU ball for the first 4 weeks and with the ball for the remaining 4 weeks. The exercise with the ball was performed by balancing on the BOSU ball and passing the ball thrown by the assistant.
Assessment of physical fitness
The physical fitness test assessed balance ability, agility, and power. Balance capacity was assessed using a balance measurement system (MFT challenge disc 2.0, TST-Trend Sport Trading, Großhöflein, Austria) consisting of a board with a diameter of 44 cm and a height of 7.5 cm. The method of moving to the center point of the target area on the computer screen while standing with a foot on the board was applied to evaluate the balance ability (Fig. 1). The arrowhead test was performed for agility. A measuring system (Speedlight, Swift performance, Brisbane, Australia) using a laser was applied, and the fastest time performed was recorded after measuring twice in each direction (Joo, 2016). Power was assessed with a standing long jump using the device (Trajković et al., 2020). The players performed jumping with recoil in the standing position, and the distance from the start line to the posterior part of the farthest point of landing was recorded. The longest distance was selected after jumping twice.
Soccer skill tests
The soccer skill performance test followed the methods used in previous study (Rosch et al., 2000). The juggling test recorded how many times the ball was kicked without dropping it on the ground, starting with dropping it with hands from chest-level height; it was performed on the left and right feet. The dribble test used a timing system (Speedlight, Swift performance, Brisbane, Australia) to assess how quickly to dribble past a cone with a 2-m distance between cones for 10 m, with three cones between the first and the last, and return to the starting point similarly. If the players touch the cones with a ball during the dribbling test, 2 sec were added to the dribbling time (Fig. 2).
The short-pass test was conducted on the left and right feet five consecutive times. The players passed the ball towards the goalpost 11 m ahead after dribbling 4 m. One, two, and three points were recorded for hitting the goalpost, hitting the crossbar, and scoring the goal directly, respectively (Fig. 3).
In the long-pass test, the players kicked the ball from 31 m away from the center of a circle with a radius of 2 m in a 10×10 m square, assigning 3 and 1 points when the ball arrived directly into the circle and the square, respectively. The sum of the scores for the left and right foot was assessed for five consecutive trials (Fig. 4).
Shooting was assessed based on a set score per goal area (Fig. 5). The players shot the ball 15 m away from the goal, divided into nine spaces. The scores for the left and right feet each were summed up after shooting 5 times.
Statistical analyses
All statistical analyses were performed using IBM SPSS Statistics ver. 26.0 (IBM Co., Armonk, NY, USA). All values were expressed as mean values±standard deviation. A two-way repeated-measures analysis of variance (ANOVA) was used to analyze the differences between the groups and periods. A paired t-test was used to identify differences between the periods within the groups. Partial eta-square (repeated ANOVA) and Hedges’g (t-test) were calculated to estimate the effect size (ES). Statistical significance was set at P<0.05.
RESULTS
Changes in body composition
The changes in body composition after 8 weeks of proprioceptive exercise training are shown in Table 2. There was no change in body composition according to the training period in the PT group (ES range of 0.02–0.19); however, height (ES=0.14) and muscle mass (ES=0.16) increased after the study period in the Cont group (P<0.05).
Physical fitness
Balance ability (ES=0.59) and power (ES=0.59) significantly improved in both groups after 8 weeks of training (P<0.05); however, there was no difference between groups after training. As for agility, the main effect of time (ES=0.39) and group (ES=0.38) and the interaction effect between time x groups (ES<0.01) were not significant (Table 3).
Skills performance
Dribble in the PT group was similar between pre- (17.01± 2.94 sec) and posttraining (16.53±1.79 sec) (ES=0.2), with a statistically significant difference in the Cont group (pre-; 16.96± 1.17 sec, post-; 15.52±1.08 sec) (ES=1.28) (P<0.05) (Fig. 6).
There were no significant differences within and between groups according to training in the left and right feet for juggling (left foot juggling pre- [PT; 23.66±13.09, Cont; 17.11±10.63] and posttraining [PT; 21.44±12.86, Cont; 24.11±15.12] and right foot jugging pre- [PT; 28±14.72, Cont; 30.66±15.83] and posttraining [PT; 23.22±11.3, Cont; 30.55±15.12]) (ES range of 0.02–0.17) (Fig. 7).
Pretraining, short passes for the PT and Cont groups were 13.11± 6.62 and 10.11±3.78, respectively. The PT and Cont groups did not differ significantly regarding short passes posttraining (9.88± 4.45 vs. 10.44±2) (ES=0.16). However, a significant improvement in long passes was observed in the PT group from 1.77±2.27 at pretraining to 6±4 at posttraining (ES=1.3) (P<0.05); there was no significant change in the Cont group (pre-; 2.33±2.06, post-; 3.66±3.27) (ES=0.49) (Fig. 8).
Shooting was no different between and within the groups (ES range of 0.01–0.14). It was 21.44±6.87 and 18.66±5.4 at pretraining and 20.11±4.85 and 19.33±4.44 at posttraining in PT and Cont groups, respectively (Fig. 9).
DISCUSSION
This study analyzed the effect of 8 weeks of proprioceptive exercise training on young soccer players’ physical fitness and skill performance. Principally, the study found that physical fitness tended to improve in both groups, and skill performance differed depending on the variable. Dribbling changed in the Cont group; however, long passes improved only in the PT group.
In this study, height and muscle mass significantly increased only in the Cont group, which could be related to the player’s career. Considering that the Cont group started their career earlier than the PT group, it can be guessed that repeated and regular exposure to more stimulation for height growth at a relatively young age accounted for this difference. Previous study also reported that regular exercise at young ages causes growth (Alves and Alves, 2019). In addition, the growth of young athletes may be influenced by genetic factors; unfortunately, we did not analyze genetic factors in the current study. Changes in growth hormones due to exercise and genetic factors could have further improved the height of the Cont group compared to the PT group. Increased muscle mass in the Cont group resulted from height growth due to regular exercise at an earlier age than in the PT group.
Analyzing the change in physical strength according to the 8-week training period, balance ability and power significantly improved in both groups. Powerful actions are required during exercise training due to the specificity of soccer, and repetitive exercise training can change the ability to express power. Indeed, exercise training for young soccer players improves the powerful movements (Michailidis et al., 2019). Interestingly, however, there was no difference in balance ability between groups after training, despite additional proprioceptive exercise after general team training in the PT group. This result may have been due to this study’s measurement method for balance ability. In other words, the balance ability was assessed by moving the center of the body along with a moving target on a computer monitor rather than by applying technical movements that can be performed during a soccer game. In the PT group, the exercise applied technical movements that should be performed in football game situations along with the ball; however, the balance ability during these movements could not be measured due to the limitations of equipment and measurement techniques the study employed. Therefore, in future studies, assessing the balance ability of soccer players more accurately and realistically will necessitate developing a method to measure the balance ability while performing soccer skills and apply it to analyze the effectiveness of proprioceptive training for elite soccer players.
Soccer skill evaluation can be an essential indicator to evaluate potentially talented players who can grow to a high level in the future. Dribbling is one of the critical skills in carrying and possessing a ball in soccer. The youth players with good dribbling ability had high stride frequency and reduced hip and knee flexion range of motion. Dribbling ability improved in both groups, but statistically significant differences were found only in the Cont group. It is thought that the change in body composition affects the improvement of dribbling records. The coordination ability, closely related to the balance ability, can affect the performance of the dribble skill (Daulay and Azmi, 2021). As mentioned earlier, even if the balance ability measurement method employed was inappropriate considering the characteristics of soccer skill performance, it improved in both groups. However, only the Cont group showed a statistically significant improvement, indicating that balance ability and other factors affected the young soccer players’ dribbling ability. This improvement in dribbling ability may have been positively affected by the degree of body growth, such as height and muscle mass changes. In line with the result, a previous study reported that youth players’ dribbling skills improved with age, especially among those aged 12–14 years (Huijgen et al., 2010).
Among soccer skills, passes can be influenced by various factors such as the balance of footsteps, the ability to touch the ball accurately, and the timing of impacting the ball. In particular, this ability can be more necessary in performing a long pass with a wider range of motion and requiring greater force than a short pass. In this study, long-pass performance improved with 8 weeks of proprioceptive exercise training. It is well-known that long-pass ability is generally strongly related to muscle strength (Cerrah et al., 2024). However, the training group showed a significantly lower increase in muscle mass than the Cont group in this study; improved long-pass performance results suggest that long-pass performance by young soccer players is more closely related to accurate movement performance, for example, by stability of the stepping up foot than muscle strength. This observation is supported by the lack of significant difference before and after training in both groups in short-pass ability that requires less force and sense of balance than long passes for accurate exercise performance.
There was no change in juggling and shooting in either group, primarily due to the short training period. In the case of juggling, it may be related to the level of cognitive function in addition to physical abilities such as ball touch and sense of balance. Indeed, cognitive functions, especially working memory capacity, were positively related to ball control and ball juggling in elite youth soccer players aged 11–13 years (Scharfen and Memmert, 2019). High-level players have higher shooting skills than low-level players and long-term strength and power training improve young players’ shooting skills (Keller et al., 2016; Wong et al., 2010). The 8-week proprioceptive exercise training conducted in this study is presumed to have resulted in no changes in juggling and shooting performance due to the lack of relevance to the composition of the exercise program to improve the cognitive function and muscle strength of young athletes and the short training period.
In conclusion, muscle mass and height were found to have grown in the Cont group than in the PT group, and balance and power ability had significant results in both groups. There was a significant difference in long passes only in the PT group and dribbles only in the Cont group. These inconsistent findings are thought to be due to the applied exercise method, training duration, and the specificity of the physical growth period of the young players. Therefore, it is necessary to increase the frequency and time of proprioceptive exercise training and apply factors for cognitive ability improvement to training programs for young soccer players in future studies. These studies could suggest appropriate training methods necessary to improve the performance of young soccer players.
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