The Short-Term Effects of Complex Training on Dribbling Agility and Shooting Efficiency of U9 Football Players

The Short-Term Effects of Complex Training on Dribbling Agility and Shooting Efficiency of U9 Football Players | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article The Short-Term Effects of Complex Training on Dribbling Agility and Shooting Efficiency of U9 Football Players Lei Yang, Syahrul Ridhwan Morazuki, Wei Chen, Jianjun Li This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7872999/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract This study examined the effects of an 8-week complex training program on dribbling agility and shooting efficiency of U9 male football players. Twenty-seven participants were randomly assigned to a complex training group, a traditional resistance training group, or a control group. The complex training group performed combined high-resistance strength and low-resistance plyometric exercises, the traditional group followed conventional strength training, and the control group received no additional training. Vertical jump height and T-test performance were assessed before and after the intervention. Data were analyzed using GraphPad Prism 10. Results showed that the complex training group significantly improved both vertical jump and T-test performance (P < 0.01), with a strong correlation observed between explosive power and change-of-direction ability (P < 0.01). Although the traditional training group showed some improvement (P < 0.05), the gains were less pronounced than in the complex training group. The control group exhibited no significant changes. These findings suggest that complex training is more effective than traditional resistance training in enhancing lower limb power, agility, and directional movement in young football players, supporting its application in youth football development programs. Health sciences/Health care Biological sciences/Physiology Complex training U9 football players Football training Dribbling agility Shooting efficiency Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction Football is a type of field confrontation sport that requires athletes to have excellent physical movement abilities 1 . In traditional physical training, isolated training movements such as squats and bench presses are primarily adopted, which only require the participation of one muscle group or joint 2 . However, in football, most movements require the coordinated effort of multiple muscle groups or more than two joints to complete, such as compound training movements like shooting and jumping 3 . Some scholars believe that compared with isolated training, complex training is more specific to the sport and can transfer the training effects to actual game performance more effectively 4 . Complex training (CT) usually consists of a set of high-resistance strength training (RT) and low-resistance plyometric training 5 . This form of training typically involves two biomechanically similar exercises. Firstly, a high-load resistance exercise is performed (e.g., squatting at 90% of one-repetition maximum (1RM)), followed by a low-load power exercise (e.g., squat jumps) 6 . This sequence of movements stimulates the post-activation potentiation effect, it enhances the potential of the muscle tissue used in a given movement to exert force by stimulating the recruitment of motor units 7 . In modern football, the combination of technique and physical fitness is a key factor in improving the overall performance of athletes 8 . Especially at the youth stage, the skill development of football players is closely related to the improvement of their physical fitness 9 . Complex Training (CT), as an effective training method, by combining high-resistance strength training (RT) and low-resistance plyometric training, has been widely used in various sports to enhance the explosive power and agility of athletes 10 . For football players in the U9 age group, shooting and dribbling abilities are the core skills that determine their performance in the game 9 . Shooting requires athletes to have good strength, accuracy, and coordination, while dribbling requires athletes to maintain the ability to control the ball and flexibility during rapid movement 11 . Therefore, training methods to improve these two skills are particularly important. Previous studies have shown that complex training can effectively enhance the strength and speed of young athletes, thereby improving their performance in the game 12 . Currently, there are few studies on the shooting and dribbling abilities of football players 13 . This study aims to explore the impact of complex training on the shooting and dribbling abilities of U9 football players 14 . By comparing the effects of complex training and traditional resistance training methods, as well as examining the relationship between lower limb explosive power and change-of-direction ability and shooting and dribbling abilities, it is hoped to provide a scientific basis for youth football training and help coaches formulate more effective training plans to promote the all-round development of athletes. The research results will provide important theoretical support for understanding the role of complex training in the skill improvement of young athletes and offer guidance for future training practices. Material and Methods Experimental Approach to the Problem This study adopted a repeated measures design, aiming to explore the effects of complex training (CT) on the lower limb explosive power, change-of-direction ability, and shooting and dribbling efficiency of adolescent football players. The participants were randomly divided into three groups, the complex training group (high-resistance strength training and low-resistance plyometric training, n = 9), the traditional resistance training group (n = 9), and the control group (no training intervention, n = 9). In addition to undergoing the 8-week complex training (CT) program or traditional resistance training, all groups conducted football training in the conventional manner. Two evaluations, one before and one after the test, included indicators such as vertical jump, T-test, shooting efficiency, and dribbling efficiency. The first evaluation was conducted before the complex training (CT) program or traditional resistance training (RT), the second evaluation was conducted after the 8-week intervention. Through this short-term study, it hopes to gain a more comprehensive understanding of the effects of different types of exercises on the physical fitness of adolescent football players and provide a basis for formulating more scientific and reasonable training plans. Participants This study randomly divided 27 male adolescent football players into three groups. One group underwent complex training (CT) every week (n = 9), one group underwent traditional resistant training every week (n = 9), the control group did not undergo strength training (n = 9). A blank control group was set up to eliminate the additional effects of growth and development and regular football training in adolescents. Before the start of the experiment, we informed the participants and their guardians in detail about the protocol and experimental risks and asked them to sign the informed consent form. Ethical Approval and Consent to Participate This study was approved by the UTM Research Ethics Committee(UTMREC) (Approval No.:UTMREC-2025-165). All procedures involving human participants were performed in accordance with the ethical standards of the institutional and national research committees and with the 1964 Helsinki Declaration and its later amendments. Prior to participation, written informed consent was obtained from all children’s legal guardians. The study purpose, procedures, and potential risks were fully explained to participants and their guardians before obtaining consent. The experimental protocols were reviewed and approved by the UTM Research Ethics Committee(UTMREC). All methods were carried out in accordance with relevant guidelines and regulations. Load scheme According to the research of Connolly et al. 15 , the phased theory of strength training suggests adopting a linear periodization for strength training load arrangement. Under this training mode, there are 2 strength training sessions per week in the first stage, while in the second stage, it increases to 3 times per week. Traditional resistance training focuses on structural exercises of large muscle groups, such as squats, deadlifts, lunges, and single-leg deadlifts. In contrast, complex training, based on traditional resistance s training, adds plyometric exercises within the training sets, such as box jumps and scissor jumps, to enhance the diversity and effectiveness of the training. To optimize the training effect, a double complex pair exercise mode is adopted, that is, two training methods with similar movement patterns are combined together. A short interval of 0–30 seconds is arranged between traditional resiatance training and plyometric training. For example, after completing the deadlift exercise, 12 rapid box jump exercises are immediately carried out. During the complex training period, as the athlete's strength level improves, the difficulty of plyometric training will also increase accordingly. For example, in the second stage, upper limb plyometric training may choose to use 5kg dumbbells for practice. All exercises are performed in 4 sets for each movement, with an interval of 30 seconds within the set and 2 minutes between sets. The specific training cycle and load design are detailed in Table 1 . In addition to strength training, athletes also need to maintain at least 2 sessions of low-to-moderate intensity aerobic exercise per week, as well as conduct sports injury prevention training and football skills practice to comprehensively improve physical fitness and sports performance. Table 1 Period Strength Training Programmer Phase Cycle Traditional strength training Complex training Phase 1 1–4 week Pull-ups 2.5kg dumbbells×10×2 Push-up with lunge 2.5kg dumbbell×8×2 Pull-ups 2.5kg dumbbells×10×2 Jumping box (45CM)×12×2 Push-up with lunge 2.5kg dumbbell×8×2 Phase 2 5–8 week Squat 5kg dumbbell×10×3 Single-leg deadlift (2.5kg dumbbell)×8×3 Squat 5kg dumbbell×10×3 Split jump×12×3 Single-leg deadlift (2.5kg dumbbell)×8×3 Procedures In the early stage of the experiment, a two-week basic movement adaptation training program was arranged, after which the formal experiment commenced. The pre-test was conducted one week before the intervention, and the post-test was conducted in the 9th week following the intervention. The warm-up content included jogging five laps (high knee lift, small step run, backward kick, lateral slide step, body rotation exercise, crossover step) and dynamic stretching exercises (knee-hugging heel raise, quadriceps stretch, baby-style knee hug, cross-legged squat, lunge rotation, side lunge, lateral rotation + sprint run). Complex training should be carried out on the premise of having basic strength, adopting the mode of "one set of strength training + 0 to 30 seconds of rest + one set of low-resistance plyometric training" to utilize the neural stimulation triggered by strength training to enhance the training effect. In the training session, both strength and low-resistance plyometric training should be considered, ensuring high intensity and low load. The training frequency in the first stage is twice a week, with a recovery interval of 48 to 96 hours for the same muscle group to avoid excessive fatigue and ensure the training effect. In the second stage, three high-intensity and low-load complex training sessions are arranged weekly. Traditional resistance training only involves strength training; the control group undergoes regular football training without any additional training. In the 9th week after the intervention, all participants will be re-evaluated. Physical fitness test The requirements for the venue of the physical fitness evaluation index of vertical jump are as follows. The take-off ground should be flat and have good friction. The reach board should be undamaged, and the scale on the dial should be accurate to 1 cm. First, set the height and position of the colored plastic dial on the reach board reasonably; it should neither be too high nor too low. Next, the tester should bend over, flex the knees and hips, and swing the arms backward, taking off directly without any redundant preparatory actions. During the vertical take-off process, try to slap the dial with the dominant hand coated with chalk while moving upward. Finally, land with natural cushioning. The evaluation index of physical fitness in the T-test requires participants to get ready in the starting position at bucket A with the right hand touching the bucket. Upon hearing the command "go", they should immediately sprint to bucket B, touch it with the right hand, then shuffle to the left to bucket C, touch it with the left hand, immediately shuffle to the right to bucket D and touch it with the right hand. Finally, complete the backward running and touch bucket A with the left hand, and the test is over. Note that athletes must touch the markers (lines or buckets), indicate to the athletes with 3, 2, 1, Go, the timing is accurate to 0.01 seconds; if an athlete fouls, the fouls include not using the prescribed steps, not always facing forward, not touching the markers with the hand, etc., the test should be stopped immediately. Football-specific skills test The requirements for the test site of the football special skill evaluation index - shooting ability. A flat natural grass football field is required, and a 30-meter × 5-meter area is demarcated. The distance from the starting point to the first pole is 4 meters, and the distance between the other poles is 2 meters. The size of the goal is 3.32 meters × 2 meters, and the distance from the starting point to the goal line is 20 meters. After hearing the command, the participants start dribbling from the starting line in a standing start position, bypass the five marker poles spaced 2 meters apart in sequence, and then complete the shot to end. The test site requirements for the evaluation index of football-specific dribbling ability are a flat natural grass football field with an area of 22 meters × 5 meters. The distance between the start and end points is 20 meters. The width spacing of the marker poles is 4 meters, and the length spacing is 8 meters. After the participants hear the command, they start dribbling from the starting line, bypass the outside of the marker poles respectively, and rush across the finish line. The stopwatch starts when dribbling begins and stops when the participant crosses the finish line. Statistical Analyses In this study, Excel 2019 was used to edit function formulas to calculate the mean ± standard deviation (M ± SD) of each group of data, and GraphPad Prism 10 was used for statistical analysis of the experimental data. First, one-way analysis of variance (ANOVA) was used for inter-group comparisons to test the overall differences among the three training groups (control group, traditional resistance group, and complex training group). If the ANOVA result shows a significant P value (usually P < 0.05), it indicates that there are significant differences among at least two groups, and further post hoc tests are required. Repeated measures ANOVA was used for time variation analysis to compare within-group and between-group differences at different time points before and after training (such as pre-training and post-training). If the ANOVA result is significant, the Tukey HSD (Honest Significant Difference) test is used for multiple comparisons. The Tukey HSD test is used to further compare the mean differences between the following groups after ANOVA shows significant differences between groups, control group vs. traditional resistance training group, control group vs. complex training group, traditional resistance training group vs. complex training group. The mean difference (Mean Difference, MD), 95% confidence interval (CI), and adjusted P value were calculated among each group to control the type I error rate (false positive) caused by multiple comparisons. Measurements The influence of complex training on the physical fitness of players’ Vertical jump height (cm). In the control group, the pre-test was (31.91 ± 3.59 cm), and the post-test was (32.12 ± 3.46 cm), with an increase of 0.21 cm, which was not significant. This indicates that without specific training intervention, vertical jump ability was hardly improved. In the traditional resistance training group, the pre-test was (34.21 ± 3.30 cm), and the post-test was (35.74 ± 3.41 cm), with an increase of 1.53 cm, showing some progress. This suggests that traditional resistance training has a certain promoting effect on vertical jump ability. In the complex training group, the pre-test was (33.66 ± 3.71 cm), and the post-test was (39.62 ± 3.04 cm), with an increase of 5.96 cm, the largest increase among the three groups. This indicates that complex training has the most significant effect on improving vertical jump ability. The pre-test of the T-test control group was (13.51 ± 0.75 s), and the post-test was (14.22 ± 0.74 s), with an increase of 0.71 s, indicating a decline in performance. This suggests that without training intervention, agility may decline. The pre-test of the traditional resistance training group was (13.56 ± 0.49 s), and the post-test was (13.14 ± 0.54 s), with a reduction of 0.42 s, indicating an improvement in performance. This indicates that traditional resistance training has a certain enhancing effect on agility. The pre-test of the complex training group was (13.49 ± 0.62 s), and the post-test was (11.86 ± 0.59 s), with a reduction of 1.63 s, which is the most significant improvement. This suggests that complex training has the most significant enhancing effect on agility. Table 2 Physical fitness and football skills change of players Control group Resistance training Complex training R² Pre Post Δ Pre Post Δ Pre Post Δ Vertical Jump /CM 31.91 ± 3.59 32.12 ± 3.46 0.21 34.21 ± 3.30 35.74 ± 3.41 1.53 33.66 ± 3.71 39.62 ± 3.04 5.96 0.64 T-test/s 13.51 ± 0.75 14.22 ± 0.74 0.71 13.56 ± 0.49 13.14 ± 0.54 -0.42 13.49 ± 0.62 11.86 ± 0.59 -1.63 0.18 Shooting/s 10.6 ± 0.75 10.56 ± 0.77 -0.04 10.58 ± 0.76 10.56 ± 0.77 -0.02 10.57 ± 0.74 9.65 ± 0.58 -0.92 0.14 Dribbling/s 12.8 ± 1.29 12.79 ± 1.29 -0.01 12.79 ± 1.3 12.23 ± 0.96 -0.56 12.87 ± 1.32 11.14 ± 0.80 -1.73 0.55 The pre-test of the shooting test control group was (10.6 ± 0.75s), and the post-test was (10.56 ± 0.77s), with a reduction of 0.04s, the change was not significant. This indicates that without training intervention, shooting efficiency did not improve markedly. The pre-test of the traditional resistance training group was (10.58 ± 0.76s), and the post-test was (10.56 ± 0.77s), with a reduction of 0.02s, the change was also not significant. This suggests that the effect of traditional resistance training on improving shooting efficiency is limited. The pre-test of the complex training group was (10.57 ± 0.74s), and the post-test was (9.65 ± 0.58s), with a reduction of 0.92s; the improvement was substantial. This demonstrates that complex training has the most significant impact on enhancing shooting efficiency. Dribbling test of the control group: pre-test (12.8 ± 1.29s), post-test (12.79 ± 1.29s), with a change of -0.01s, indicating no significant improvement. This suggests that without training intervention, there is no noticeable improvement in dribbling agility. For the traditional resistance training group, pre-test (12.79 ± 1.3s), post-test (12.23 ± 0.96s), showing a reduction of 0.56s and some improvement. This indicates that traditional resistance training has a certain enhancing effect on dribbling agility. For the complex training group: pre-test (12.87 ± 1.32s), post-test (11.14 ± 0.80s), showing a reduction of 1.73s, which is the most significant improvement. This suggests that complex training has the most significant enhancing effect on dribbling agility. Discussion This study explored the short-term effects of an 8-week complex training intervention on the dribbling agility and shooting efficiency of U9 football players. The research results indicated that the complex training had significant effects in improving the lower limb explosive power, change-of-direction ability, shooting efficiency, and dribbling agility of U9 football players, and its effects were superior to those of traditional strength training and the blank control group. After 8 weeks of complex training, the vertical jump and reach performance of the experimental group improved significantly (P < 0.01), with an increase of 5.96 cm, which was significantly higher than that of the traditional training group (1.53 cm) and the blank control group (0.21 cm). This indicates that complex training has significant advantages in improving lower limb explosive power. Complex training combines high-resistance strength training and low-resistance plyometric training, which can effectively activate more motor units, especially the recruitment of fast-twitch muscle fibers, thereby improving the contraction speed and power output of the muscles 16 . This promotes the development of the high-speed region, enabling athletes to generate greater explosive power in a short period of time 17 . Research indicates that in complex training (CT), combining resistance training (RT) and power training (PT) may lead to the superimposition of the cellular and structural adaptation effects induced by RT and PT. In fact, an increase in the volume of leg muscles was indeed observed in football players after complex training (CT) 18 . Although an increase in muscle volume is typically achieved through resistance training (RT) intervention 19 , recent studies have shown that power training (PT) may also cause significant hypertrophy effects 20 . Additionally, such structural adaptations following resistance training (RT) and power training (PT) do not seem to interfere with neuromechanical adaptations 21 . In fact, complex training (CT) may facilitate energy transfer between concentric and eccentric muscle actions, provide better coordination and synchronization of active muscle groups, thereby improving and enhancing motor skills 21 . These improvements may include enhancements in sprinting, vertical jumping, and change-of-direction sprinting performance, as well as improvements in other motor skills such as kicking ability 22 . Overall, complex training (CT) is an effective training strategy for improving sprinting, jumping, and change-of-direction sprinting abilities 23 . Thapa et al. found that in the complex training (CT) group, significant moderate to large improvements were observed compared with the control group [sprint: standardized mean difference (SMD) = 0.92–1.91, jump: SMD = 0.96–1.58, change of direction: SMD = 0.97–1.49] 24 . In the T test, the performance of the complex training group improved significantly (P < 0.01), and the theoretical consistency of the shortening-velocity curve was observed. Complex training not only enhanced adaptability in the high-intensity zone, reducing times by 1.63 seconds, while the traditional training group only reduced times by 0.42 seconds, and the blank control group showed a decline 25 . The improvements in linear sprint, vertical jump, and change of direction sprint performance after complex training (CT) may be similar to the adaptation mechanisms caused by separate resistance training (RT) and power training (PT), including maximum strength, hormonal environment, structure, and neuromechanical adaptations, which may be strengthened by the cumulative post-activation potentiation effect induced by complex training (CT) 24 . Compared with other studies, complex training has a significant advantage in improving athletes' change of direction ability 26 . Through the combination of resistance training and plyometric training, complex training can effectively improve athletes' muscle reaction speed and coordination during rapid changes of direction 27 . Especially in football matches, the ability for rapid changes of direction is one of the key factors for athletes to maintain an advantage in confrontation 28 . Complex training enhances athletes' muscle contraction efficiency during the change of direction process through post-activation potentiation (PAP) and stretch-shortening cycle (SSC) mechanisms, thereby improving change of direction ability 29 . In the shooting test, the shooting efficiency of the complex training group improved significantly (P < 0.01), reducing the time by 0.92 seconds, while the improvements in the traditional training group and the blank control group were relatively small. This indicates that complex training has a significant advantage in improving shooting efficiency 30 . The shooting action requires athletes to have good strength, coordination, and accuracy 31 . Complex training enhances the explosive power of the lower limbs and the rapid contraction ability of the muscles, enabling athletes to complete the action more quickly and maintain high accuracy when shooting 32 . Additionally, the plyometric exercises in complex training can improve muscle coordination during the shooting process, thereby enhancing shooting efficiency. In the dribbling test, the dribbling agility of the complex training group improved significantly (P < 0.01), reducing the time by 1.73 seconds, while the traditional training group only reduced the time by 0.56 seconds, and there was no significant change in the blank control group. This indicates that complex training has a significant advantage in improving dribbling agility. Dribbling agility requires athletes to maintain ball control during rapid movement. Complex training improves the explosive power of the lower limbs and the ability to change direction, enabling athletes to complete direction changes and accelerations more quickly during dribbling, thereby enhancing dribbling agility 33 . The cumulative post-activation performance enhancement effect induced by complex training may help explain the improvement in performance 34 . Moreover, since complex training (CT) combines higher loads (i.e., RT) and lower loads (i.e., PT), this may optimize the force-velocity curve of football players by ensuring that the prescribed training covers two broad components of the continuum 35 . Considering the correlation of force-velocity spectrum parameters among football players 36 , the optimization of the force-velocity spectrum may help explain the improvement in performance after complex training (CT) 36 . During complex training (CT), the combination of high-load low-velocity and low-load high-velocity exercises may be beneficial for the recruitment of fast muscle fibers 37 , which is particularly important in maximum strength and short-duration actions (such as vertical jumps) 38 . The advantage of complex training lies in its full utilization of the post-activation potentiation (PAP) and stretch-shortening cycle (SSC) mechanisms 39 . PAP activates more motor units through high-load resistance training, increasing the sensitivity of muscle contraction and thereby enhancing the power output of subsequent plyometric exercises 40 . SSC enhances an athlete's performance in rapid direction changes and explosive movements by improving the muscles' ability to rapidly transform between eccentric and concentric contractions 39 . These physiological mechanisms give complex training significant advantages in improving the explosive power, agility, and technical skills of football players 41 . Compared with traditional strength training, complex training has significant advantages in improving various physical qualities and technical abilities in U9 football players. While traditional strength training can improve lower limb explosive power, its effect on improving directional change quality, shooting efficiency, and dribbling agility is limited 42 . However, complex training, by combining resistance training and plyometric training, can comprehensively enhance the physical and technical abilities of athletes, especially in rapid direction changes and explosive movements 43 . Research limitations Although this study has achieved remarkable research results, there are still some limitations. Firstly, the sample size of the study is small, including only 27 U9 football players. Future studies can expand the sample size to verify the universality of the results. Secondly, the study period is short, lasting only 8 weeks. Future studies can extend the study period to explore the long-term effects of complex training. Finally, this study only focused on the impact of complex training on U9 football players. Future studies can explore the impact of complex training on other age groups or different sports events. Conclusion complex training has significant advantages in improving the lower limb explosive power, change-of-direction ability, shooting efficiency, and dribbling agility of U9 football players. Complex training, by combining resistance training and plyometric training, makes full use of the post-activation potentiation effect and the stretch-shortening cycle mechanism, enabling athletes to generate greater explosive power and faster reaction speeds in a short period of time. The research results provide a scientific basis for youth football training, and it is recommended that coaches introduce complex training into their programs to comprehensively improve the physical fitness and technical abilities of athletes. Declarations Acknowledgements: The author extends heartfelt gratitude to the supervisor at Universiti Teknologi Malaysia for their unwavering guidance, insightful feedback, and steady encouragement throughout every stage of this study. Sincere thanks are further extended to the journal’s editor and anonymous reviewers for their thoughtful critiques and constructive suggestions, which substantially improved the clarity, coherence, and scientific rigour of the manuscript. A uthor contributions Yang Lei: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Data curation, Visualization. Jianjun Li : Writing – original draft. Resources, Investigation, Writing – review & editing. Chen Wei: Data curation, Software, Formal analysis. Syahrul Ridhwan Morazuki : Supervision, Conceptualization, Methodology, Writing – review & editing, Project administration. Competing interests The authors declare no competing interests. Ethics declarations The authors declare that they have no conflict of interest. Additional information Correspondence and requests for materials should be addressed to JJ.L Consent for publication: Not applicable. Availability of data and materials: All results are available in the text of the manuscript, figures and Tables. The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation. The authors can be contacted by e-mail upon request. Correspondence: [email protected] . Competing interests: The authors declare no conflicts of interest. Funding: This research received no external funding. References Bujnovsky, D. et al. 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Haghighi, A. H., Hosseini, S. B., Askari, R., Shahrabadi, H. & Ramirez-Campillo, R. Effects of plyometric compared to high-intensity interval training on youth female basketball player’s athletic performance. Sport Sci. Health . 20 (1), 211–220. 10.1007/s11332-023-01096-2 (2024). Flórez Gil, E., Vaquera, A., Ramírez-Campillo, R., Sanchez-Sanchez, J. & Rodríguez Fernández, A. Can complex training improve acute and long-lasting performance in basketball players? A systematic review. Appl. Sci. 14 (15), 6839 (2024). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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08:12:20","extension":"html","order_by":18,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":123543,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7872999/v1/38de6a40a8501771e384b166.html"},{"id":97124741,"identity":"68e596fd-f163-405a-8ac6-9221286076fb","added_by":"auto","created_at":"2025-12-01 08:12:20","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":91320,"visible":true,"origin":"","legend":"\u003cp\u003eExperimental Design\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7872999/v1/7e9a8b8773b541db7ecbc975.png"},{"id":97142083,"identity":"5c3c2e23-c5c9-4855-95f5-1053af714186","added_by":"auto","created_at":"2025-12-01 10:07:19","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":13668,"visible":true,"origin":"","legend":"\u003cp\u003eIllustration of the vertical jump test procedure. The vertical jump test measures lower-body explosive power by comparing standing reach height and jump reach height.\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7872999/v1/9409b6080f7cca7863ddb18a.jpeg"},{"id":97142376,"identity":"a4844ce5-d496-4025-8c07-21e21e61a3ae","added_by":"auto","created_at":"2025-12-01 10:07:33","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":28351,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of the T-test for agility assessment\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7872999/v1/aa510ba879b66ac560f54c31.jpeg"},{"id":97142411,"identity":"41b11031-1e24-4e84-8f73-dc9787edf048","added_by":"auto","created_at":"2025-12-01 10:07:36","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":15449,"visible":true,"origin":"","legend":"\u003cp\u003eDiagram of the Dribbling and Shooting Ability Test\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-7872999/v1/047ceabd540f979327516b24.png"},{"id":97140693,"identity":"70583205-0f67-43eb-9fdf-fdc10335afb3","added_by":"auto","created_at":"2025-12-01 10:05:36","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":61386,"visible":true,"origin":"","legend":"\u003cp\u003eDiagram of the Dribbling Agility Training Drill\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-7872999/v1/157da6765948c52f6f643529.png"},{"id":97141460,"identity":"33dec1de-97f5-46e1-a220-02c04a727ecb","added_by":"auto","created_at":"2025-12-01 10:06:43","extension":"jpeg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":303347,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of 8-week complex training on vertical jump and agility performance in U9 soccer players. *Values are presented as mean ± SD. Control = no training intervention, RT = resistance training, CT = complex training. Significant differences between groups are indicated as **p \u0026lt; 0.01, ***p \u0026lt; 0.001, ***p \u0026lt; 0.0001.\u003c/p\u003e","description":"","filename":"floatimage6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7872999/v1/a926582fbb87d971aa2ba10a.jpeg"},{"id":97124745,"identity":"56895653-5353-4118-ab93-c21050df3769","added_by":"auto","created_at":"2025-12-01 08:12:20","extension":"jpeg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":318958,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of 8-week complex training on shooting and dribbling performance in U9 soccer players. *Values are presented as mean ± SD. Control = no training intervention, RT = resistance training, CT = complex training. Significant differences between groups are indicated as *p \u0026lt; 0.05, p \u0026lt; 0.01.\u003c/p\u003e","description":"","filename":"floatimage7.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7872999/v1/0160138d4baa995de03d4def.jpeg"},{"id":97145081,"identity":"7662b3ea-463f-4d45-b2a5-981c91ea665c","added_by":"auto","created_at":"2025-12-01 10:13:00","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1568075,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7872999/v1/eeb5830e-5a24-455d-812e-ed7342a9e5c3.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"The Short-Term Effects of Complex Training on Dribbling Agility and Shooting Efficiency of U9 Football Players","fulltext":[{"header":"Introduction","content":"\u003cp\u003eFootball is a type of field confrontation sport that requires athletes to have excellent physical movement abilities\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. In traditional physical training, isolated training movements such as squats and bench presses are primarily adopted, which only require the participation of one muscle group or joint\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. However, in football, most movements require the coordinated effort of multiple muscle groups or more than two joints to complete, such as compound training movements like shooting and jumping\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. Some scholars believe that compared with isolated training, complex training is more specific to the sport and can transfer the training effects to actual game performance more effectively\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eComplex training (CT) usually consists of a set of high-resistance strength training (RT) and low-resistance plyometric training\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. This form of training typically involves two biomechanically similar exercises. Firstly, a high-load resistance exercise is performed (e.g., squatting at 90% of one-repetition maximum (1RM)), followed by a low-load power exercise (e.g., squat jumps)\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. This sequence of movements stimulates the post-activation potentiation effect, it enhances the potential of the muscle tissue used in a given movement to exert force by stimulating the recruitment of motor units\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eIn modern football, the combination of technique and physical fitness is a key factor in improving the overall performance of athletes\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. Especially at the youth stage, the skill development of football players is closely related to the improvement of their physical fitness\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. Complex Training (CT), as an effective training method, by combining high-resistance strength training (RT) and low-resistance plyometric training, has been widely used in various sports to enhance the explosive power and agility of athletes\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. For football players in the U9 age group, shooting and dribbling abilities are the core skills that determine their performance in the game\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. Shooting requires athletes to have good strength, accuracy, and coordination, while dribbling requires athletes to maintain the ability to control the ball and flexibility during rapid movement\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. Therefore, training methods to improve these two skills are particularly important. Previous studies have shown that complex training can effectively enhance the strength and speed of young athletes, thereby improving their performance in the game\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. Currently, there are few studies on the shooting and dribbling abilities of football players\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. This study aims to explore the impact of complex training on the shooting and dribbling abilities of U9 football players\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. By comparing the effects of complex training and traditional resistance training methods, as well as examining the relationship between lower limb explosive power and change-of-direction ability and shooting and dribbling abilities, it is hoped to provide a scientific basis for youth football training and help coaches formulate more effective training plans to promote the all-round development of athletes. The research results will provide important theoretical support for understanding the role of complex training in the skill improvement of young athletes and offer guidance for future training practices.\u003c/p\u003e"},{"header":"Material and Methods","content":"\u003cp\u003eExperimental Approach to the Problem\u003c/p\u003e\u003cp\u003eThis study adopted a repeated measures design, aiming to explore the effects of complex training (CT) on the lower limb explosive power, change-of-direction ability, and shooting and dribbling efficiency of adolescent football players. The participants were randomly divided into three groups, the complex training group (high-resistance strength training and low-resistance plyometric training, n\u0026thinsp;=\u0026thinsp;9), the traditional resistance training group (n\u0026thinsp;=\u0026thinsp;9), and the control group (no training intervention, n\u0026thinsp;=\u0026thinsp;9). In addition to undergoing the 8-week complex training (CT) program or traditional resistance training, all groups conducted football training in the conventional manner. Two evaluations, one before and one after the test, included indicators such as vertical jump, T-test, shooting efficiency, and dribbling efficiency. The first evaluation was conducted before the complex training (CT) program or traditional resistance training (RT), the second evaluation was conducted after the 8-week intervention. Through this short-term study, it hopes to gain a more comprehensive understanding of the effects of different types of exercises on the physical fitness of adolescent football players and provide a basis for formulating more scientific and reasonable training plans.\u003c/p\u003e\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eParticipants\u003c/h2\u003e\u003cp\u003eThis study randomly divided 27 male adolescent football players into three groups. One group underwent complex training (CT) every week (n\u0026thinsp;=\u0026thinsp;9), one group underwent traditional resistant training every week (n\u0026thinsp;=\u0026thinsp;9), the control group did not undergo strength training (n\u0026thinsp;=\u0026thinsp;9). A blank control group was set up to eliminate the additional effects of growth and development and regular football training in adolescents. Before the start of the experiment, we informed the participants and their guardians in detail about the protocol and experimental risks and asked them to sign the informed consent form.\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eEthical Approval and Consent to Participate\u003c/strong\u003e\u003cp\u003e This study was approved by the UTM Research Ethics Committee(UTMREC) (Approval No.:UTMREC-2025-165). All procedures involving human participants were performed in accordance with the ethical standards of the institutional and national research committees and with the 1964 Helsinki Declaration and its later amendments.\u003c/p\u003e\u003c/p\u003e\u003cp\u003e Prior to participation, written informed consent was obtained from all children\u0026rsquo;s legal guardians. The study purpose, procedures, and potential risks were fully explained to participants and their guardians before obtaining consent.\u003c/p\u003e\u003cp\u003e The experimental protocols were reviewed and approved by the UTM Research Ethics Committee(UTMREC). All methods were carried out in accordance with relevant guidelines and regulations.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eLoad scheme\u003c/h3\u003e\n\u003cp\u003eAccording to the research of Connolly et al. \u003csup\u003e15\u003c/sup\u003e, the phased theory of strength training suggests adopting a linear periodization for strength training load arrangement. Under this training mode, there are 2 strength training sessions per week in the first stage, while in the second stage, it increases to 3 times per week. Traditional resistance training focuses on structural exercises of large muscle groups, such as squats, deadlifts, lunges, and single-leg deadlifts. In contrast, complex training, based on traditional resistance s training, adds plyometric exercises within the training sets, such as box jumps and scissor jumps, to enhance the diversity and effectiveness of the training. To optimize the training effect, a double complex pair exercise mode is adopted, that is, two training methods with similar movement patterns are combined together. A short interval of 0\u0026ndash;30 seconds is arranged between traditional resiatance training and plyometric training. For example, after completing the deadlift exercise, 12 rapid box jump exercises are immediately carried out. During the complex training period, as the athlete's strength level improves, the difficulty of plyometric training will also increase accordingly. For example, in the second stage, upper limb plyometric training may choose to use 5kg dumbbells for practice. All exercises are performed in 4 sets for each movement, with an interval of 30 seconds within the set and 2 minutes between sets. The specific training cycle and load design are detailed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. In addition to strength training, athletes also need to maintain at least 2 sessions of low-to-moderate intensity aerobic exercise per week, as well as conduct sports injury prevention training and football skills practice to comprehensively improve physical fitness and sports performance.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003ePeriod Strength Training Programmer\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePhase\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCycle\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eTraditional strength training\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eComplex training\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePhase 1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u0026ndash;4 week\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePull-ups\u003c/p\u003e\u003cp\u003e2.5kg dumbbells\u0026times;10\u0026times;2\u003c/p\u003e\u003cp\u003ePush-up with lunge\u003c/p\u003e\u003cp\u003e2.5kg dumbbell\u0026times;8\u0026times;2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003ePull-ups\u003c/p\u003e\u003cp\u003e2.5kg dumbbells\u0026times;10\u0026times;2\u003c/p\u003e\u003cp\u003eJumping box (45CM)\u0026times;12\u0026times;2\u003c/p\u003e\u003cp\u003ePush-up with lunge\u003c/p\u003e\u003cp\u003e2.5kg dumbbell\u0026times;8\u0026times;2\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePhase 2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e5\u0026ndash;8 week\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eSquat\u003c/p\u003e\u003cp\u003e5kg dumbbell\u0026times;10\u0026times;3\u003c/p\u003e\u003cp\u003eSingle-leg deadlift\u003c/p\u003e\u003cp\u003e(2.5kg dumbbell)\u0026times;8\u0026times;3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eSquat\u003c/p\u003e\u003cp\u003e5kg dumbbell\u0026times;10\u0026times;3\u003c/p\u003e\u003cp\u003eSplit jump\u0026times;12\u0026times;3\u003c/p\u003e\u003cp\u003eSingle-leg deadlift\u003c/p\u003e\u003cp\u003e(2.5kg dumbbell)\u0026times;8\u0026times;3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\n\u003ch3\u003eProcedures\u003c/h3\u003e\n\u003cp\u003eIn the early stage of the experiment, a two-week basic movement adaptation training program was arranged, after which the formal experiment commenced. The pre-test was conducted one week before the intervention, and the post-test was conducted in the 9th week following the intervention. The warm-up content included jogging five laps (high knee lift, small step run, backward kick, lateral slide step, body rotation exercise, crossover step) and dynamic stretching exercises (knee-hugging heel raise, quadriceps stretch, baby-style knee hug, cross-legged squat, lunge rotation, side lunge, lateral rotation\u0026thinsp;+\u0026thinsp;sprint run). Complex training should be carried out on the premise of having basic strength, adopting the mode of \"one set of strength training\u0026thinsp;+\u0026thinsp;0 to 30 seconds of rest\u0026thinsp;+\u0026thinsp;one set of low-resistance plyometric training\" to utilize the neural stimulation triggered by strength training to enhance the training effect. In the training session, both strength and low-resistance plyometric training should be considered, ensuring high intensity and low load. The training frequency in the first stage is twice a week, with a recovery interval of 48 to 96 hours for the same muscle group to avoid excessive fatigue and ensure the training effect. In the second stage, three high-intensity and low-load complex training sessions are arranged weekly. Traditional resistance training only involves strength training; the control group undergoes regular football training without any additional training. In the 9th week after the intervention, all participants will be re-evaluated.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\n\u003ch3\u003ePhysical fitness test\u003c/h3\u003e\n\u003cp\u003eThe requirements for the venue of the physical fitness evaluation index of vertical jump are as follows. The take-off ground should be flat and have good friction. The reach board should be undamaged, and the scale on the dial should be accurate to 1 cm. First, set the height and position of the colored plastic dial on the reach board reasonably; it should neither be too high nor too low. Next, the tester should bend over, flex the knees and hips, and swing the arms backward, taking off directly without any redundant preparatory actions. During the vertical take-off process, try to slap the dial with the dominant hand coated with chalk while moving upward. Finally, land with natural cushioning.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe evaluation index of physical fitness in the T-test requires participants to get ready in the starting position at bucket A with the right hand touching the bucket. Upon hearing the command \"go\", they should immediately sprint to bucket B, touch it with the right hand, then shuffle to the left to bucket C, touch it with the left hand, immediately shuffle to the right to bucket D and touch it with the right hand. Finally, complete the backward running and touch bucket A with the left hand, and the test is over. Note that athletes must touch the markers (lines or buckets), indicate to the athletes with 3, 2, 1, Go, the timing is accurate to 0.01 seconds; if an athlete fouls, the fouls include not using the prescribed steps, not always facing forward, not touching the markers with the hand, etc., the test should be stopped immediately.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\n\u003ch3\u003eFootball-specific skills test\u003c/h3\u003e\n\u003cp\u003eThe requirements for the test site of the football special skill evaluation index - shooting ability. A flat natural grass football field is required, and a 30-meter \u0026times; 5-meter area is demarcated. The distance from the starting point to the first pole is 4 meters, and the distance between the other poles is 2 meters. The size of the goal is 3.32 meters \u0026times; 2 meters, and the distance from the starting point to the goal line is 20 meters. After hearing the command, the participants start dribbling from the starting line in a standing start position, bypass the five marker poles spaced 2 meters apart in sequence, and then complete the shot to end.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe test site requirements for the evaluation index of football-specific dribbling ability are a flat natural grass football field with an area of 22 meters \u0026times; 5 meters. The distance between the start and end points is 20 meters. The width spacing of the marker poles is 4 meters, and the length spacing is 8 meters. After the participants hear the command, they start dribbling from the starting line, bypass the outside of the marker poles respectively, and rush across the finish line. The stopwatch starts when dribbling begins and stops when the participant crosses the finish line.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003eStatistical Analyses\u003c/h2\u003e\u003cp\u003eIn this study, Excel 2019 was used to edit function formulas to calculate the mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation (M\u0026thinsp;\u0026plusmn;\u0026thinsp;SD) of each group of data, and GraphPad Prism 10 was used for statistical analysis of the experimental data. First, one-way analysis of variance (ANOVA) was used for inter-group comparisons to test the overall differences among the three training groups (control group, traditional resistance group, and complex training group). If the ANOVA result shows a significant P value (usually P\u0026thinsp;\u0026lt;\u0026thinsp;0.05), it indicates that there are significant differences among at least two groups, and further post hoc tests are required. Repeated measures ANOVA was used for time variation analysis to compare within-group and between-group differences at different time points before and after training (such as pre-training and post-training). If the ANOVA result is significant, the Tukey HSD (Honest Significant Difference) test is used for multiple comparisons. The Tukey HSD test is used to further compare the mean differences between the following groups after ANOVA shows significant differences between groups, control group vs. traditional resistance training group, control group vs. complex training group, traditional resistance training group vs. complex training group. The mean difference (Mean Difference, MD), 95% confidence interval (CI), and adjusted P value were calculated among each group to control the type I error rate (false positive) caused by multiple comparisons.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eMeasurements\u003c/h3\u003e\n\u003cp\u003eThe influence of complex training on the physical fitness of players\u0026rsquo; Vertical jump height (cm). In the control group, the pre-test was (31.91\u0026thinsp;\u0026plusmn;\u0026thinsp;3.59 cm), and the post-test was (32.12\u0026thinsp;\u0026plusmn;\u0026thinsp;3.46 cm), with an increase of 0.21 cm, which was not significant. This indicates that without specific training intervention, vertical jump ability was hardly improved. In the traditional resistance training group, the pre-test was (34.21\u0026thinsp;\u0026plusmn;\u0026thinsp;3.30 cm), and the post-test was (35.74\u0026thinsp;\u0026plusmn;\u0026thinsp;3.41 cm), with an increase of 1.53 cm, showing some progress. This suggests that traditional resistance training has a certain promoting effect on vertical jump ability. In the complex training group, the pre-test was (33.66\u0026thinsp;\u0026plusmn;\u0026thinsp;3.71 cm), and the post-test was (39.62\u0026thinsp;\u0026plusmn;\u0026thinsp;3.04 cm), with an increase of 5.96 cm, the largest increase among the three groups. This indicates that complex training has the most significant effect on improving vertical jump ability.\u003c/p\u003e\u003cp\u003eThe pre-test of the T-test control group was (13.51\u0026thinsp;\u0026plusmn;\u0026thinsp;0.75 s), and the post-test was (14.22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.74 s), with an increase of 0.71 s, indicating a decline in performance. This suggests that without training intervention, agility may decline. The pre-test of the traditional resistance training group was (13.56\u0026thinsp;\u0026plusmn;\u0026thinsp;0.49 s), and the post-test was (13.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.54 s), with a reduction of 0.42 s, indicating an improvement in performance. This indicates that traditional resistance training has a certain enhancing effect on agility. The pre-test of the complex training group was (13.49\u0026thinsp;\u0026plusmn;\u0026thinsp;0.62 s), and the post-test was (11.86\u0026thinsp;\u0026plusmn;\u0026thinsp;0.59 s), with a reduction of 1.63 s, which is the most significant improvement. This suggests that complex training has the most significant enhancing effect on agility.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003ePhysical fitness and football skills change of players\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"11\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e\u003cp\u003eControl group\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e\u003cp\u003eResistance training\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"3\" nameend=\"c10\" namest=\"c8\"\u003e\u003cp\u003eComplex training\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c11\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eR\u0026sup2;\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePre\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePost\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eΔ\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003ePre\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003ePost\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eΔ\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003ePre\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\"\u003e\u003cp\u003ePost\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c10\"\u003e\u003cp\u003eΔ\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eVertical Jump /CM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e31.91\u003c/p\u003e\u003cp\u003e\u0026plusmn;\u0026thinsp;3.59\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e32.12\u003c/p\u003e\u003cp\u003e\u0026plusmn;\u0026thinsp;3.46\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.21\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e34.21\u003c/p\u003e\u003cp\u003e\u0026plusmn;\u0026thinsp;3.30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e35.74\u003c/p\u003e\u003cp\u003e\u0026plusmn;\u0026thinsp;3.41\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e1.53\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e33.66\u003c/p\u003e\u003cp\u003e\u0026plusmn;\u0026thinsp;3.71\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e39.62\u003c/p\u003e\u003cp\u003e\u0026plusmn;\u0026thinsp;3.04\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e5.96\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0.64\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eT-test/s\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e13.51\u003c/p\u003e\u003cp\u003e\u0026plusmn;\u0026thinsp;0.75\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e14.22\u003c/p\u003e\u003cp\u003e\u0026plusmn;\u0026thinsp;0.74\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.71\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e13.56\u003c/p\u003e\u003cp\u003e\u0026plusmn;\u0026thinsp;0.49\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e13.14\u003c/p\u003e\u003cp\u003e\u0026plusmn;\u0026thinsp;0.54\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e-0.42\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e13.49\u003c/p\u003e\u003cp\u003e\u0026plusmn;\u0026thinsp;0.62\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e11.86\u003c/p\u003e\u003cp\u003e\u0026plusmn;\u0026thinsp;0.59\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e-1.63\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0.18\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eShooting/s\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e10.6\u003c/p\u003e\u003cp\u003e\u0026plusmn;\u0026thinsp;0.75\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e10.56\u003c/p\u003e\u003cp\u003e\u0026plusmn;\u0026thinsp;0.77\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-0.04\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e10.58\u003c/p\u003e\u003cp\u003e\u0026plusmn;\u0026thinsp;0.76\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e10.56\u003c/p\u003e\u003cp\u003e\u0026plusmn;\u0026thinsp;0.77\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e-0.02\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e10.57\u003c/p\u003e\u003cp\u003e\u0026plusmn;\u0026thinsp;0.74\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e9.65\u003c/p\u003e\u003cp\u003e\u0026plusmn;\u0026thinsp;0.58\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e-0.92\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0.14\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDribbling/s\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e12.8\u003c/p\u003e\u003cp\u003e\u0026plusmn;\u0026thinsp;1.29\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e12.79\u003c/p\u003e\u003cp\u003e\u0026plusmn;\u0026thinsp;1.29\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-0.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e12.79\u003c/p\u003e\u003cp\u003e\u0026plusmn;\u0026thinsp;1.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e12.23\u003c/p\u003e\u003cp\u003e\u0026plusmn;\u0026thinsp;0.96\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e-0.56\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e12.87\u003c/p\u003e\u003cp\u003e\u0026plusmn;\u0026thinsp;1.32\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e11.14\u003c/p\u003e\u003cp\u003e\u0026plusmn;\u0026thinsp;0.80\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e-1.73\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e0.55\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe pre-test of the shooting test control group was (10.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.75s), and the post-test was (10.56\u0026thinsp;\u0026plusmn;\u0026thinsp;0.77s), with a reduction of 0.04s, the change was not significant. This indicates that without training intervention, shooting efficiency did not improve markedly. The pre-test of the traditional resistance training group was (10.58\u0026thinsp;\u0026plusmn;\u0026thinsp;0.76s), and the post-test was (10.56\u0026thinsp;\u0026plusmn;\u0026thinsp;0.77s), with a reduction of 0.02s, the change was also not significant. This suggests that the effect of traditional resistance training on improving shooting efficiency is limited. The pre-test of the complex training group was (10.57\u0026thinsp;\u0026plusmn;\u0026thinsp;0.74s), and the post-test was (9.65\u0026thinsp;\u0026plusmn;\u0026thinsp;0.58s), with a reduction of 0.92s; the improvement was substantial. This demonstrates that complex training has the most significant impact on enhancing shooting efficiency.\u003c/p\u003e\u003cp\u003eDribbling test of the control group: pre-test (12.8\u0026thinsp;\u0026plusmn;\u0026thinsp;1.29s), post-test (12.79\u0026thinsp;\u0026plusmn;\u0026thinsp;1.29s), with a change of -0.01s, indicating no significant improvement. This suggests that without training intervention, there is no noticeable improvement in dribbling agility. For the traditional resistance training group, pre-test (12.79\u0026thinsp;\u0026plusmn;\u0026thinsp;1.3s), post-test (12.23\u0026thinsp;\u0026plusmn;\u0026thinsp;0.96s), showing a reduction of 0.56s and some improvement. This indicates that traditional resistance training has a certain enhancing effect on dribbling agility. For the complex training group: pre-test (12.87\u0026thinsp;\u0026plusmn;\u0026thinsp;1.32s), post-test (11.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.80s), showing a reduction of 1.73s, which is the most significant improvement. This suggests that complex training has the most significant enhancing effect on dribbling agility.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThis study explored the short-term effects of an 8-week complex training intervention on the dribbling agility and shooting efficiency of U9 football players. The research results indicated that the complex training had significant effects in improving the lower limb explosive power, change-of-direction ability, shooting efficiency, and dribbling agility of U9 football players, and its effects were superior to those of traditional strength training and the blank control group.\u003c/p\u003e\u003cp\u003eAfter 8 weeks of complex training, the vertical jump and reach performance of the experimental group improved significantly (P\u0026thinsp;\u0026lt;\u0026thinsp;0.01), with an increase of 5.96 cm, which was significantly higher than that of the traditional training group (1.53 cm) and the blank control group (0.21 cm). This indicates that complex training has significant advantages in improving lower limb explosive power. Complex training combines high-resistance strength training and low-resistance plyometric training, which can effectively activate more motor units, especially the recruitment of fast-twitch muscle fibers, thereby improving the contraction speed and power output of the muscles\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. This promotes the development of the high-speed region, enabling athletes to generate greater explosive power in a short period of time\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. Research indicates that in complex training (CT), combining resistance training (RT) and power training (PT) may lead to the superimposition of the cellular and structural adaptation effects induced by RT and PT. In fact, an increase in the volume of leg muscles was indeed observed in football players after complex training (CT)\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. Although an increase in muscle volume is typically achieved through resistance training (RT) intervention\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e, recent studies have shown that power training (PT) may also cause significant hypertrophy effects\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. Additionally, such structural adaptations following resistance training (RT) and power training (PT) do not seem to interfere with neuromechanical adaptations\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. In fact, complex training (CT) may facilitate energy transfer between concentric and eccentric muscle actions, provide better coordination and synchronization of active muscle groups, thereby improving and enhancing motor skills\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. These improvements may include enhancements in sprinting, vertical jumping, and change-of-direction sprinting performance, as well as improvements in other motor skills such as kicking ability\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e. Overall, complex training (CT) is an effective training strategy for improving sprinting, jumping, and change-of-direction sprinting abilities\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eThapa et al. found that in the complex training (CT) group, significant moderate to large improvements were observed compared with the control group [sprint: standardized mean difference (SMD)\u0026thinsp;=\u0026thinsp;0.92\u0026ndash;1.91, jump: SMD\u0026thinsp;=\u0026thinsp;0.96\u0026ndash;1.58, change of direction: SMD\u0026thinsp;=\u0026thinsp;0.97\u0026ndash;1.49]\u003csup\u003e24\u003c/sup\u003e. In the T test, the performance of the complex training group improved significantly (P\u0026thinsp;\u0026lt;\u0026thinsp;0.01), and the theoretical consistency of the shortening-velocity curve was observed. Complex training not only enhanced adaptability in the high-intensity zone, reducing times by 1.63 seconds, while the traditional training group only reduced times by 0.42 seconds, and the blank control group showed a decline\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e. The improvements in linear sprint, vertical jump, and change of direction sprint performance after complex training (CT) may be similar to the adaptation mechanisms caused by separate resistance training (RT) and power training (PT), including maximum strength, hormonal environment, structure, and neuromechanical adaptations, which may be strengthened by the cumulative post-activation potentiation effect induced by complex training (CT)\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e. Compared with other studies, complex training has a significant advantage in improving athletes' change of direction ability\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e. Through the combination of resistance training and plyometric training, complex training can effectively improve athletes' muscle reaction speed and coordination during rapid changes of direction\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. Especially in football matches, the ability for rapid changes of direction is one of the key factors for athletes to maintain an advantage in confrontation\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. Complex training enhances athletes' muscle contraction efficiency during the change of direction process through post-activation potentiation (PAP) and stretch-shortening cycle (SSC) mechanisms, thereby improving change of direction ability\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eIn the shooting test, the shooting efficiency of the complex training group improved significantly (P\u0026thinsp;\u0026lt;\u0026thinsp;0.01), reducing the time by 0.92 seconds, while the improvements in the traditional training group and the blank control group were relatively small. This indicates that complex training has a significant advantage in improving shooting efficiency\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e. The shooting action requires athletes to have good strength, coordination, and accuracy\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. Complex training enhances the explosive power of the lower limbs and the rapid contraction ability of the muscles, enabling athletes to complete the action more quickly and maintain high accuracy when shooting\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eAdditionally, the plyometric exercises in complex training can improve muscle coordination during the shooting process, thereby enhancing shooting efficiency. In the dribbling test, the dribbling agility of the complex training group improved significantly (P\u0026thinsp;\u0026lt;\u0026thinsp;0.01), reducing the time by 1.73 seconds, while the traditional training group only reduced the time by 0.56 seconds, and there was no significant change in the blank control group. This indicates that complex training has a significant advantage in improving dribbling agility. Dribbling agility requires athletes to maintain ball control during rapid movement. Complex training improves the explosive power of the lower limbs and the ability to change direction, enabling athletes to complete direction changes and accelerations more quickly during dribbling, thereby enhancing dribbling agility\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eThe cumulative post-activation performance enhancement effect induced by complex training may help explain the improvement in performance\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e. Moreover, since complex training (CT) combines higher loads (i.e., RT) and lower loads (i.e., PT), this may optimize the force-velocity curve of football players by ensuring that the prescribed training covers two broad components of the continuum\u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e. Considering the correlation of force-velocity spectrum parameters among football players\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e, the optimization of the force-velocity spectrum may help explain the improvement in performance after complex training (CT)\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e. During complex training (CT), the combination of high-load low-velocity and low-load high-velocity exercises may be beneficial for the recruitment of fast muscle fibers\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e, which is particularly important in maximum strength and short-duration actions (such as vertical jumps)\u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eThe advantage of complex training lies in its full utilization of the post-activation potentiation (PAP) and stretch-shortening cycle (SSC) mechanisms\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e. PAP activates more motor units through high-load resistance training, increasing the sensitivity of muscle contraction and thereby enhancing the power output of subsequent plyometric exercises\u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e. SSC enhances an athlete's performance in rapid direction changes and explosive movements by improving the muscles' ability to rapidly transform between eccentric and concentric contractions\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e. These physiological mechanisms give complex training significant advantages in improving the explosive power, agility, and technical skills of football players\u003csup\u003e\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/sup\u003e. Compared with traditional strength training, complex training has significant advantages in improving various physical qualities and technical abilities in U9 football players. While traditional strength training can improve lower limb explosive power, its effect on improving directional change quality, shooting efficiency, and dribbling agility is limited\u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e. However, complex training, by combining resistance training and plyometric training, can comprehensively enhance the physical and technical abilities of athletes, especially in rapid direction changes and explosive movements\u003csup\u003e\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003eResearch limitations\u003c/h2\u003e\u003cp\u003eAlthough this study has achieved remarkable research results, there are still some limitations. Firstly, the sample size of the study is small, including only 27 U9 football players. Future studies can expand the sample size to verify the universality of the results. Secondly, the study period is short, lasting only 8 weeks. Future studies can extend the study period to explore the long-term effects of complex training. Finally, this study only focused on the impact of complex training on U9 football players. Future studies can explore the impact of complex training on other age groups or different sports events.\u003c/p\u003e\u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003ecomplex training has significant advantages in improving the lower limb explosive power, change-of-direction ability, shooting efficiency, and dribbling agility of U9 football players. Complex training, by combining resistance training and plyometric training, makes full use of the post-activation potentiation effect and the stretch-shortening cycle mechanism, enabling athletes to generate greater explosive power and faster reaction speeds in a short period of time. The research results provide a scientific basis for youth football training, and it is recommended that coaches introduce complex training into their programs to comprehensively improve the physical fitness and technical abilities of athletes.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements:\u003c/strong\u003e The author extends heartfelt gratitude to the supervisor at Universiti Teknologi Malaysia for their unwavering guidance, insightful feedback, and steady encouragement throughout every stage of this study. Sincere thanks are further extended to the journal\u0026rsquo;s editor and anonymous reviewers for their thoughtful critiques and constructive suggestions, which substantially improved the clarity, coherence, and scientific rigour of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eA\u003c/strong\u003e\u003cstrong\u003euthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eYang Lei:\u0026nbsp;\u003c/strong\u003eConceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Data curation, Visualization.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eJianjun Li :\u003c/strong\u003e Writing \u0026ndash; original draft. Resources, Investigation, Writing \u0026ndash; review \u0026amp; editing.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eChen Wei:\u0026nbsp;\u003c/strong\u003eData curation, Software, Formal analysis.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSyahrul Ridhwan Morazuki\u003c/strong\u003e\u003cstrong\u003e:\u003c/strong\u003e Supervision, Conceptualization, Methodology, Writing \u0026ndash; review \u0026amp; editing, Project administration.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics declarations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAdditional information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCorrespondence and requests for materials should be addressed to JJ.L\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication:\u003c/strong\u003e Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials:\u003c/strong\u003e All results are available in the text of the manuscript, figures and Tables. The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation. The authors can be contacted by e-mail upon request. Correspondence: [email protected].\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests:\u003c/strong\u003e The authors declare no conflicts of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u003c/strong\u003e This research received no external funding.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBujnovsky, D. et al. Physical fitness characteristics of high-level youth football players: Influence of playing position. \u003cem\u003eSports\u003c/em\u003e \u003cb\u003e7\u003c/b\u003e (2), 46 (2019).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAndroulakis Korakakis, P. et al. Optimizing resistance training technique to maximize muscle hypertrophy: A narrative review. \u003cem\u003eJ. Funct. 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Sci.\u003c/em\u003e \u003cb\u003e14\u003c/b\u003e (15), 6839 (2024).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Complex training, U9 football players, Football training, Dribbling agility, Shooting efficiency","lastPublishedDoi":"10.21203/rs.3.rs-7872999/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7872999/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study examined the effects of an 8-week complex training program on dribbling agility and shooting efficiency of U9 male football players. Twenty-seven participants were randomly assigned to a complex training group, a traditional resistance training group, or a control group. The complex training group performed combined high-resistance strength and low-resistance plyometric exercises, the traditional group followed conventional strength training, and the control group received no additional training. Vertical jump height and T-test performance were assessed before and after the intervention. Data were analyzed using GraphPad Prism 10. Results showed that the complex training group significantly improved both vertical jump and T-test performance (P\u0026thinsp;\u0026lt;\u0026thinsp;0.01), with a strong correlation observed between explosive power and change-of-direction ability (P\u0026thinsp;\u0026lt;\u0026thinsp;0.01). Although the traditional training group showed some improvement (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05), the gains were less pronounced than in the complex training group. The control group exhibited no significant changes. These findings suggest that complex training is more effective than traditional resistance training in enhancing lower limb power, agility, and directional movement in young football players, supporting its application in youth football development programs.\u003c/p\u003e","manuscriptTitle":"The Short-Term Effects of Complex Training on Dribbling Agility and Shooting Efficiency of U9 Football Players","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-01 08:12:15","doi":"10.21203/rs.3.rs-7872999/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"37f4d1f1-1566-47e1-b1a9-8025cfa70f69","owner":[],"postedDate":"December 1st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":58653669,"name":"Health sciences/Health care"},{"id":58653670,"name":"Biological sciences/Physiology"}],"tags":[],"updatedAt":"2025-12-01T08:12:17+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-01 08:12:15","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7872999","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7872999","identity":"rs-7872999","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}