Biomechanical determinants of high ball speed during instep soccer kick by prepubescent male athletes: The importance of muscle elasticity

Biomechanical determinants of high ball speed during instep soccer kick by prepubescent male athletes: The importance of muscle elasticity | 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 Research Article Biomechanical determinants of high ball speed during instep soccer kick by prepubescent male athletes: The importance of muscle elasticity Volkan Deniz, Abdullah Kilci This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5412234/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 Background This study aimed to investigate the effects of kinetic–kinematic parameters and muscle viscoelastic properties on high ball speed during instep soccer kick by prepubescent male athletes. Methods This study included 34 male soccer players with an average age of 11.2 ± 0.5 years. Maximal ball speed during the instep kick was measured using a radar gun. The activation of the rectus abdominis (RA) and rectus femoris (RF), as well as the thigh's three-dimensional rotational velocity and acceleration, were evaluated using surface electromyography and an inertial measurement unit. Mechanical properties such as tone, elasticity, and stiffness of the superficial abdomen and leg muscles were measured at rest using myotonometry. Results Significant positive correlations existed between maximum ball speed and RA–RF activation (r = 0.505 and 0.575), maximum thigh velocity in the sagittal plane (r = 0.599), and maximum thigh acceleration in the sagittal (r = 0.423) and horizontal (r = 0.387) planes (power > 0.95; p 0.95; p < 0.05 for all). The multiple linear regression analysis demonstrated that important factors for maximum ball velocity were HM (B = 0.432) and GM (B = 0.771) elasticity (adjusted R 2 = 0.60, delta R 2 = 0.40). Conclusions GM and HM elasticity were the prominent factors affecting ball speed during instep kick. To increase ball speed during instep kick, training methods that focus on improving the elasticity of the GM and HL muscles, as well as activating the core and RF, should be prioritized for prepubescent male soccer players. Trial registration: Not applicable Instep kick ball speed muscle activation leg angular velocity muscle elasticity Figures Figure 1 Introduction Soccer organizations invest significant financial and logistical resources in the identification and development of talented young athletes [ 1 ]. As outlined in the Elite Player Performance Plan, the yearly investment for a category one academy in England is £2.3 to £4.9 million [ 2 ]. The next generation of potential stars can be expected to emerge from these academy programs and eventually progress to become top-level professional players [ 3 ]. The rise in soccer’s popularity, increased competition, and the implementation of new codes of conduct have all played a role in shaping a fresh scientific methodology for nurturing academy players. This is implemented by multidisciplinary teams who are dedicated to refining training strategies for optimal performance [ 4 ]. This approach underscores the necessity for athletes to undergo comprehensive preparation encompassing physical, psychological, and technical facets to excel in their performance. The training progression in many academies typically commences with individual technical training and development for younger athletes, advancing to elite academy soccer teams for older athletes [ 5 ]. Kicking is a foundational motor skill that holds significant importance across various sports such as soccer, rugby, American Football, and Australian Rules Football. In such sports, the kicking motion is employed to score goals or points, requiring the generation of high ball-releasing velocity [ 6 ]. Biomechanically, a kicking motion can be likened to a throw-like movement, where the distal segments trail behind the proximal segments as they propel forward. Furthermore, kicking can be viewed as a culmination of forces, with the foot serving as the final and swiftest segment in the open kinetic chain [ 7 ]. Consequently, the velocity of the foot at the moment of impact is closely linked to the velocity of the ball [ 8 , 9 ]. Various kicking techniques can be employed in offensive and defensive situations to facilitate passing, maintaining possession, and scoring goals. The instep kick stands out as the predominant kicking method in soccer, executed by striking the ball with the top part of the foot while the foot is pointed downward [ 10 ]. The effectiveness of soccer kicking is determined by both the velocity and accuracy of the ball [ 11 ]. Although accuracy is significant, assessments of soccer kicking performance have primarily focused on maximizing ball speed. Provided that the kick is precise, a higher ball speed enhances the likelihood of scoring by reducing the time for the goalkeeper to react [ 12 ]. Numerous studies have examined the function of ball speed in soccer by determining the elements that influence the maximum kicking velocity. These factors encompass various aspects such as limb dominance [ 13 ], technique [ 11 ], approach speed and angle [ 14 ], skill level [ 15 ], lower extremity muscle strength and power [ 16 ], and leg muscle activity [ 17 ]. These researches have focused on highlighting the influence of the lower limbs on kicking performance. Given the growing body of recent studies on kicking biomechanics, the need for incorporating upper-body muscle activity into the analysis should be reassessed, particularly in studies on academy soccer players. The stretching–shortening cycle of the leg muscles in the backward and forward phases of the instep kick may be a considerable biomechanical factor affecting ball speed. In this cycle, the ability of the anterior muscles to stretch with controlled eccentric contraction in the stretching phase affects the concentric contraction of the anterior leg muscles in the shortening phase. Likewise, the ability of the posterior muscles to stretch with optimal eccentric contraction during the forward phase of the kick may be a determinant of the ball speed [ 18 ]. Therefore, viscoelastic properties of muscles such as tone, elasticity, and stiffness, which determine the ability to stretch, may be key parameters determining leg angular velocity and thus maximum ball speed. This study examined the relationships between maximum ball speed; abdominal and thigh muscle activity; and the sagittal, horizontal, and frontal plane maximum velocities and accelerations of the kicking leg during instep kick by prepubescent soccer players. It also investigated the effects of the viscoelastic properties of the superficial abdominal and leg muscles on the maximum ball speed. The hypotheses of the present study were as follows: (i) RA-RF activation and leg angular velocity/acceleration and (ii) viscoelastic properties of lower extremity muscles are the determinants of the maximum ball speed during instep soccer kick by prepubescent male athletes. Methods Participants and instep kicks This observational, cross-sectional study was conducted at XXXX Sports Club (XXXX, XXXX). Thirty-four prepubescent male soccer players with official licenses issued by the Turkish Football Federation were recruited. All participants were injury-free and were preparing for competition at the time of data collection. This study was approved by the Clinical Research Ethics Committee of XXXX University (Decision no.: 143/75, Approval date: 5 April 2024). All athletes were informed about the study protocol, and written consent was obtained from the participants and their legal representatives. All testing was completed in a soccer training field to represent competition performance and provide athletes with maximum freedom of movement. On the days the data were collected (23–25 April 2024), the weather was clear, the highest temperature was 36 ºC, the highest wind speed was 4 km/h, and the mean humidity was 37%. The task performed was an instep kick at maximum speed on a stationary ball. The standard-sized (Lotto FB1000 4, Italy) and standard-inflated (11 psi) ball was kick 11 m toward a 2 x 2 m goal. To minimize movement in the frontal plane, players were limited to a 1-m straight-line approach from a position directly ahead. Before the task, the players performed a standardized warm-up consisting of 10-minute submaximal running and several whole-body stretching exercises. They then performed five submaximal soccer kicks. Following this warm-up, the athletes were asked to perform an instep kick with maximum ball speed, and they were required to try to hit the target area. Each player kick three times with his preferred leg, and the muscle activation and thigh angular velocity during the highest-ball speed were analyzed [ 14 , 19 ]. Maximal ball speed was measured using a radar gun (Bushnell Velocity Speed Gun, USA), which can measure speed in the range of 16–177 km/h from a distance of 14 m and has an accuracy of ± 2 km/h. This radar gun has high reliability [intraclass correlation coefficient (ICC) = 0.91] for measuring ball speed [ 20 ]. It was positioned by an observer 1.5 m behind the goal and at a height of 1.5 m (Fig. 1 ). Two-dimensional motion analysis A high-resolution video camera (Galaxy-S22, Samsung, Korea) was positioned on a tripod at a height of approximately 1.5 m, located approximately 6 m directly perpendicular to the athlete’s sagittal plane [ 21 ]. It recorded the instep kick at a rate of 240 frames per second (fps). The camera and electromyography (EMG) data acquisition program (EMG Works® version 4.8.0, Delsys Inc., USA) were synchronized using an LED system. The synchronization of the EMG with the LED was achieved with an Android application. An ESP32 microcontroller was used to control the LED, and App Inventor was used to prepare the Android application. The recording of the kick was separated into the backswing and acceleration phases, in which the highest kinematic and kinetic values were expected [ 22 ], using Kinovea (version 0.8.15, Kinovea Open Source Project) software that permitted single-frame viewing. The backswing phase demonstrates the temporal window between the toe off of the kicking leg and the maximum hip extension, and the acceleration phase shows the temporal window between the maximum knee flexion and the ball strike [ 22 ]. The start and end times of each phase were marked on the video records. The EMG and inertial measurement unit (IMU) data for these periods were collected. EMG and IMU acquisition A wireless-mobile (Android application) EMG system (TRIGNO, Delsys Inc., USA, input impedance < 10 ohms, baseline noise < 750nV root mean square (RMS), effective EMG signal gain 909 V/V ± 5%) was used to obtain raw EMG data for the rectus abdominis (RA) and rectus femoris (RF). EMG signals were sampled at 2,000 Hz and a bandwidth of 20–450 Hz, full-wave rectified and smoothed with a second-order Butterworth low-pass filter. The distance between the metal surfaces of the wireless electrode was 1 cm. The Surface Electromyography for the Non-Invasive Assessment of Muscles recommendations were considered in the preparation of the skin and placement of the wireless electrodes [ 23 ]. For RA the electrode was placed 3 cm above and 2 cm lateral to the umbilicus, over the muscle belly and parallel to the muscle fibers [ 24 ]. For RF the electrode was placed at the midpoint of the line from the anterior spina iliaca superior to the superior part of the patella, parallel to the muscle fibers [ 23 ]. The RF—the superficial muscle showing the highest activation along with the iliopsoas muscle [ 22 ]—and the RA—one of the core muscles that may affect the thigh angular velocity during instep kick, with a possible force transfer from trunk to leg, along with the anterior superficial fascia [ 25 ]—were preferred for EMG analysis. The mean RMS collected from the muscles during the backswing and acceleration phases were normalized according to the maximum activation obtained during the instep kick [%maximum activation = muscle activity (RMS)/maximum activation of the muscle × 100]. To reduce the possibility of obtaining normalized EMG levels of greater than 100%, we used this normalization method, which has high reliability (ICC > 0.80; [ 26 – 28 ]. Trigno Avanti sensor-IMU Technology® (Delsys, Boston, MA, USA) was used to evaluate the thigh angular velocity and acceleration during the instep kick. The sensor was placed on the midpoint of the femur and fixed with adhesive tape. The IMU sensor measured the angular velocity [degree per second (deg/s)] and acceleration (g force) of the thigh along the kick in three planes (frontal, sagittal, and horizontal) [ 21 ]. The peak angular velocity and acceleration values in three planes were considered for the data analysis. Myotonometry Myotonometry provides objective data on the viscoelasticity of muscles, such as tone, elasticity, and stiffness. Tone characterizes the intrinsic tension of biological soft tissues on the cellular level. Stiffness characterizes the resistance of biological soft tissues to a force of elongation or deformation. Elasticity is the biomechanical property of soft tissues that characterizes the ability of elongation and to recover its initial shape from being deformed [ 29 ]. It uses a smartphone-sized, handheld device for myotonometric measurement (MyotonPro®, Myoton AS, Tallinn, Estonia). Myotonometry has shown good to excellent reliability (ICC ranging from 0.69 to 0.98) in evaluating the viscoelastic properties of muscles in young athletes [ 29 ]. The MyotonPro® device determines the tone, elasticity, and stiffness values of the muscles by analyzing the characteristics of the oscillation wave formed in response to five short (0.15 ms) stimuli applied by the probe to the tissue with a force of 0.56 N and a frequency of 1 Hz [ 21 , 30 ] Myotonometric assessment was performed of the major superficial muscles in the abdomen and lower extremity: the RA, RF, gluteus medius, adductor magnus, hamstring medialis (HM), tibialis anterior, and gastrocnemius medialis (GM). The measurement was performed when the athletes arrived at the sports facility, before the warm-up and kicking. During the measurement, the athlete was lying down and stationary. The device probe was placed perpendicular to the midpoint of the muscle. The device was sufficiently pressed to the muscle, and short stimulations were applied to the tissue. The tone [oscillation frequency (Hz)], elasticity [logarithmic decrement (arb)], and stiffness [dynamic stiffness (N/m)] values appearing on the screen were noted. Three measurements were performed for each muscle and averaged. Higher values indicate higher muscle tone and stiffness and lower elasticity [ 21 , 30 ]. Data analysis Statistical analyses were carried out using SPSS (version 22.0; SPSS, Chicago, IL, USA). The distribution of data was determined by visual (histograms and probability plots) and analytical (Shapiro–Wilk test) methods. Pearson’s correlation test was used to determine the potential relationship between the biomechanical parameters and the maximum ball speed. Variables that were significant at the p < 0.05 level in the univariate analysis were included in the multiple linear regression analysis. Stepwise multiple linear regression analysis was used to examine the potential effects of confounders on the dependent variable (maximum ball speed). Alpha values of < 0.05 were considered statistically significant. Results A total of 37 players were enrolled in the study, and the data of 34 who met the inclusion criteria were collected and analyzed. The baseline characteristics of the athletes are shown in Table 1. Table 1. Baseline characteristics of the players. Mean ± SD Minimum-maximum Age, (year) 11.2±0.5 11.0-12.0 Height, (cm) 143.8±10.6 129.0-168.0 Weight, (kg) 36.8±7.9 26.1-58.2 Body mass index (kg/m 2 ) 17.6±1.8 14.8-21.8 Number of months played soccer 28.7±11.1 18.0-60.0 Abbreviation: SD: Standard deviation All potential confounders had no significant effect on the maximum ball speed (p>0.05). The mean value of the maximum ball speed was 62.1±8.2 km/h. Tables 2 and Table 3 was shown the results of the correlation analysis between the maximum ball speed and the biomechanical parameters. Significant positive correlations (Pearson’s r ranging from 0.377 to 0.599) were found between the maximum ball speed and the maximum thigh acceleration in the sagittal plane during the backswing phase and RA–RF activation, the maximum thigh velocity in the sagittal plane, and the maximum thigh acceleration in the sagittal and horizontal planes during the acceleration phase. Furthermore, significant negative associations existed between maximum ball speed and HM and GM elasticity (Pearson’s r=-0.592 and -0.771; power>0.95; p<0.05 for all). Table 2. Correlation of maksimum ball speed with muscle activity and thigh velocity/acceleration Backswing phase Acceleration phase Mean ± SD r p Mean ± SD r p EMG, (%) Rectus abdominis 54.01±19.75 0,198 0.295 63.88 ±22.35 0.505 0.004 Rectus femoris 51.02±20.94 0.116 0.540 69.08 ±18.51 0.575 0.001 Velocity MAX, (deg/s) Frontal plane 618.23±233.93 0.178 0.363 854.93 ±311.22 0.178 0.363 Sagittal plane 743.50±385.89 0.101 0.610 979.21 ±411.06 0.599 0.001 Horizontal plane 417.70 ±258.21 0.100 0.620 681.28 ±301.65 0.100 0.620 Acceleration MAX, (g) Frontal plane 7.30 ±3.17 0.309 0.110 10.53 ±4.20 0.309 0.110 Sagittal plane 8.02 ±4.00 0.377 0.048 12.71 ±4.04 0.413 0.020 Horizontal plane 7.35 ±3.58 0.330 0.086 12.24 ±4.37 0.387 0.028 Abbreviations: SD: Standard deviation, EMG: Electromyography, Max: Maximum, deg/s: Degree per second, g: acceleration of gravity. Significant associations (p < 0.05) are highlighted in bold. Table 3. Correlation of maksimum ball speed with muscle tone, elasticity, and stiffness Tone [Oscillation frequency (Hz)] Elasticity [Logarithmic decrement (arb)] Stiffness [Dynamic stiffness(N/m)] Muscle Mean±SD r p Mean±SD r p Mean±SD r p RA 14.32±1.88 0.390 0.265 0.76±0.22 -0.015 0.967 228.20±57.53 0.294 0.410 GMed 15.20±1.11 0.160 0.659 1.00±0.15 -0.232 0.519 250.70±37.84 0.221 0.539 RF 12.94±0.96 0.366 0.299 0.98±0.15 -0.259 0.471 185.60±25.92 0.091 0.804 AMag 14.37±1.03 0.019 0.958 1.00±0.18 -0.322 0.364 234.00±24.81 -0.081 0.824 HM 18.11±1.77 -0.029 0.936 0.85±0.09 -0.592 0.041 345.50±53.61 -0.062 0.864 TA 14.66±1.66 0.254 0.479 1.06±0.24 -0.401 0.250 238.90±27.95 0.290 0.417 GM 13.03±1.95 0.316 0.373 1.13±0.27 -0.771 0.009 192.70±63.10 0.329 0.353 Abbreviations: Arb: Relative arbitrary unit, SD: Standard deviation, RA: Rectus abdominis, GMed: Gluteus medius, RF: Rectus femoris, Amag: Adductor magnus, HM: Hamstring medialis, TA: Tibialis anterior, GM: Gastriconemius medialis. Significant associations (p < 0.05) are highlighted in bold. Biomechanical parameters were significantly associated with the maximum ball speed in the univariate correlation analysis and thus included in multiple linear regression analysis with two models. However, since the EMG, rotational velocity, and elasticity parameters met 100% of the regression model, some of the acceleration parameters were removed from the model 2 by the software. The multiple linear regression analysis demonstrated that important factors for maximum kick velocity were HM (B=0.432) and GM (B=0.771) elasticity (adjusted R 2 =0.60, Delta R 2 =0.40; Table 4). Table 4. Multiple lineer regression analysis for the association between biomechanical parameters and maksimum ball speed Model 1 B(SE) ß p GM-Elasticity -14.77 (4.31) 0.771 0.009 Model 2 GM-Elasticity -14.78 (2.68) 0.771 0.001 HM-Elasticity -25.35 (7.60) 0.432 0.044 RA-EMG Acc 0.12 (0.05) 0.476 0.117 RF-EMG Acc 0.11 (0.05) 0.460 0.102 Velocity-Saggittal Acc 0.01(0.00) 0.230 0.158 Acceleration-Saggittal Acc 0.15 (0.23) 0.100 0.558 Note R 2 =0.60 for model 1, ΔR 2 = 0.40 for model 2 Constant=43.85 for model 1, Constant= 16.13 for model 2 Abbreviations: GM: Gastriconemius medialis, HM: Hamstring medialis, RA-EMG Acc : Rectus abdominus activation in acceleration phase, RF-EMG Acc : Rectus femoris activation in acceleration phase, Acc: Acceleration phase, B: unstandardized coefficients, SE: standard error, β: standardized coefficients, R 2 : adjusted R-squared Significant associations (p < 0.05) are highlighted in bold. Discussion This study explored the biomechanical factors in prepubescent male soccer players associated with the development of high ball speed. It revealed that HM and GM elasticity was the most important determinant parameter of instep kick velocity. RA and RF activity and thigh angular velocity and acceleration were also associated with the maximum ball speed. Many previous studies have aimed to determine the relationship between the activation patterns of lower extremity muscles and the instep kick velocity [9,17,19,22,31]. Considering the results of these studies, the significant positive relationship between RF muscle activation and the ball speed for a successful kick is not surprising. A high level of hip flexor and RF activation is required to generate excessive rotational torque during the acceleration phase [22,31]. Unlike previous studies the current study revealed that the RA, which generates force to stabilize the core during the instep kick, may also contribute to RF activity through force transmission along with the anterior superficial fascia [32,33]. Stabilization of the trunk and force transmission from proximal muscles to the leg seem to be key factors for a successful high-speed kick. The instep soccer kick is characterized by joint motions in multiple planes [9]. Previous studies have shown that the angular velocity of the combined movement pattern formed by flexion and external rotation of the thigh during the acceleration phase has an important effect on the ball speed [9,19,34]. Similarly, the current study revealed a relationship between the ball speed and the maximum angular velocity of the thigh in the sagittal plane. However, the result that must be emphasized is the significant association of the acceleration of the thigh in the sagittal and horizontal planes with the ball speed. The higher the leg acceleration before impact, the shorter the ball–foot contact and the higher the ball speed [9]. Therefore, the leg should reach its maximum rotational velocity in the shortest time to maximize the ball speed. On a biomechanical basis, the stretch–shorten cycle of agonist and antagonist muscles during the instep kick likely affects ball speed [35]. For the stretch–shorten cycle to be optimal, the contraction abilities of the muscles and their viscoelastic properties must be at appropriate levels [36]. Avrillon et al. [37] showed that hamstring elasticity is a key factor distinguishing specialized athletes from the general population. However, past studies investigating the determinants of ball speed have not focused on the viscoelastic properties of muscles [9,17,19,22,34]. In our study, multiple linear regression analysis revealed that HM and GM elasticity was the primary determinant of ball speed in prepubescent male soccer players. These muscles, located in the posterior thigh and leg, are connected by the posterior superficial fascia and control anterior movements of the hip, knee, and ankle. We propose that during the acceleration phase of the instep kick, the elasticity of the HM and GM muscles—due to their tendency to return to their original length—creates a passive opposing force, which counteracts the action of the muscles acting as agonists for the instep kick. Therefore, in athletes with high HM and GM elasticity, the torque generated by the torque generated by the hip flexors and other anterior muscles is more effectively transmitted to the ball through the foot, resulting in higher ball speeds. It is noteworthy, however, that despite a significant interaction between muscle elasticity and maximum ball speed, no interaction was observed between tonus and stiffness values. This result indicates that the muscle's tendency to return to its original length after elongation affects maximum ball speed more than baseline tonus or the ability to elongate. We believe that further researchs examining the effects of muscle elasticity, tonus, and stiffness on athletic performance will yield deeper insights. Limitations This study has some limitations. First, to ensure standardization, the athletes were asked to perform an instep kick limited to certain patterns. Since soccer players kick moving or stationary balls from various distances and with various approach angles during matches or training, the method followed in the study may not fully comply with the nature of the sport. The second limitation is that EMG analysis of the deep abdominal (core) muscles could not be performed. Therefore, the possible force transmission from the deep abdominal muscles to the anterior thigh muscles during the instep kick could not be determined. Conclusion GM and HM elasticity was the primary biomechanical parameter affecting the ball speed during instep kicks among prepubescent male soccer players. Additionally, RA and RF activity and the acceleration of the thigh in the sagittal and horizontal planes may be determinants of the ball speed. We recommend that to increase the ball speed during instep kick, training methods that improve the GM and HM elasticity, along with core and anterior thigh muscle activation, should be preferred in prepubescent male soccer players. Abbreviations EMG: Electromyography IMU: Inertial measurement unit RMS: Root mean square RA: Rectus abdominis RF: Rectus femoris HM: Hamstring medialis GM: Gastriconemius medialis Declarations Ethics approval and consent to participate This study followed the Declaration of Helsinki. Ethical Approval was obtained from the Local Ethics Committee of Cukurova University Faculty of Medicine (Decision no.: 143/75, Approval date: 5 April 2024). An informed consent form was signed by participants and their legal representatives before they participated in the study. Consent for publication Written informed consent was obtained from participants for publication of identifying information in an online open-access publication. Availability of data and materials The data that support the findings of this study are available from the corresponding author upon reasonable request. Competing interests The authors declare no competing interests. Funding None Authors' contributions VD contributed to the literature search, conceptual development, and study design. AK was responsible for data collection, analysis, manuscript drafting, and the preparation of tables and Figure 1. All authors have reviewed and approved the final version of the manuscript. Acknowledgements We extend our gratitude to all participants who voluntarily contributed to this study. Author information Faculty of Health Sciences, Department of Physiotherapy and Rehabilitation, Tarsus University, Mersin, Turkey. Volkan Deniz Cukurova University, Faculty of Sport Sciences, Adana-Türkiye Abdullah Kılcı Corresponding author Correspondence to Volkan Deniz References Baker J, Schorer J, Wattie N. Compromising talent: Issues in identifying and selecting talent in sport. Quest. 2018;70(1):48-63. https://doi.org/10.1080/00336297.2017.1333438 Larkin P, Reeves MJ. Junior-elite football: time to re-position talent identification? Soccer & Society. 2018;19(8):1183-92. https://doi.org/10.1080/14660970.2018.1432389 McCalman W, Crowley-McHattan ZJ, Fransen J, Bennett KJ. Skill assessments in youth soccer: A scoping review. Journal of sports sciences. 2022;40(6):667-95. https://doi.org/10.1080/02640414.2021.2013617 McBurnie AJ, Dos’ Santos T, Johnson D, Leng E. 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The Journal of Strength & Conditioning Research. 2003;17(3):475-83. https://doi.org/10.1519/1533- 4287(2003)017%3C0475:ecotua%3E2.0.co;2 Wilke J, Krause F, Vogt L, Banzer W. What is evidence-based about myofascial chains: a systematic review. Archives of physical medicine and rehabilitation. 2016;97(3):454-61. https://doi.org/10.1016/j.apmr.2015.07.023 Albertus-Kajee Y, Tucker R, Derman W, Lamberts RP, Lambert MI. Alternative methods of normalising EMG during running. Journal of Electromyography and Kinesiology. 2011;21(4):579-86. https://doi.org/10.1016/j.jelekin.2011.03.009 Halaki M, Ginn K. Normalization of EMG signals: to normalize or not to normalize and what to normalize to. Computational intelligence in electromyography analysis-a perspective on current applications and future challenges. 2012;10:49957. http://dx.doi.org/10.5772/49957 Meghdadi N, Yalfani A, Minoonejad H. Electromyographic analysis of shoulder girdle muscle activation while performing a forehand topspin in elite table tennis athletes with and without shoulder impingement syndrome. Journal of shoulder and elbow surgery. 2019;28(8):1537-45. https://doi.org/10.1016/j.jse.2019.01.021 Pruyn EC, Watsford ML, Murphy AJ. Validity and reliability of three methods of stiffness assessment. Journal of Sport and Health Science. 2016;5(4):476-83. https://doi.org/10.1016/j.jshs.2015.12.001 Chang C-H, Ho C-S, Li F, Chen C-Y, Yeh H-C, Ho C-A. Acute effects of muscle mechanical properties after 2000-m rowing in young male rowers. PeerJ. 2024;12:e16737. https://doi.org/10.7717/peerj.16737 Cerrah AO, Şimsek D, Soylu AR, Nunome H, Ertan H. Developmental differences of kinematic and muscular activation patterns in instep soccer kick. Sports Biomechanics. 2024;23(1):28-43. https://doi.org/10.1080/14763141.2020.1815827 Ajimsha M, Shenoy PD, Surendran PJ, Jacob P, Bilal MJ. Evidence of in-vivo myofascial force transfer in humans-a systematic scoping review. Journal of Bodywork and Movement Therapies. 2022;32:183-95. https://doi.org/10.1016/j.jbmt.2022.05.006 Lin H-T, Huang Y-C, Li Y-Y, Chang J-H. The effect of rectus abdominis fatigue on lower limb jumping performance and landing load for volleyball players. Applied Sciences. 2021;11(15):6697. https://doi.org/10.3390/app11156697. Nunome H, Lake M, Georgakis A, Stergioulas LK. Impact phase kinematics of instep kicking in soccer. Journal of sports Sciences. 2006;24(1):11-22. https://doi.org/10.1080/02640410400021450 Amiri-Khorasani M, MohammadKazemi R, Sarafrazi S, Riyahi-Malayeri S, Sotoodeh V. Kinematics analyses related to stretch-shortening cycle during soccer instep kicking after different acute stretching. The Journal of Strength & Conditioning Research. 2012;26(11):3010-7. https://doi.org/10.1519/jsc.0b013e3182443442 Taylor DC, Dalton JR JD, Seaber AV, Garrett JR WE. Viscoelastic properties of muscle-tendon units: the biomechanical effects of stretching. The American journal of sports medicine. 1990;18(3):300-9. https://doi.org/10.1177/036354659001800314 Avrillon S, Lacourpaille L, Hug F, Le Sant G, Frey A, Nordez A, et al. Hamstring muscle elasticity differs in specialized high‐performance athletes. Scandinavian journal of medicine & science in sports. 2020;30(1):83-91. http://dx.doi.org/10.1111/sms.13564 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. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5412234","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":380034430,"identity":"9a1fa3d1-5cb8-46d5-b723-d0e4c0c64914","order_by":0,"name":"Volkan Deniz","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA70lEQVRIiWNgGAWjYFAC5mYQIcfGzJD4AMji4SOshRGsxZifneGxAUgLG7FaEmf2Mz6TAPEJajE43ths8HOHNeOGw8xplV9z7GTYGJgfPrqBT8uZg82JvWfSmQ0Os6Xdlt2WDHQYm7FxDh4tkjMSmw/wth1mMzjMk3ZbchszUAsPmzQhLQf/th3mMTjM/61Ycls9YS38EonNyUBbJCSbGdIYP247TIQWnoPNxrJt6Qb8zAzJ0ozbjvOwMRPwCxt782HJt23W9W38BxI//txWbc/P3vzwMT4tKICZB0wSqxwEGH+QonoUjIJRMApGDAAAbx1EUm4iI0kAAAAASUVORK5CYII=","orcid":"","institution":"Tarsus University","correspondingAuthor":true,"prefix":"","firstName":"Volkan","middleName":"","lastName":"Deniz","suffix":""},{"id":380034431,"identity":"90d10042-9742-42e9-9439-bf5ffd2d17cc","order_by":1,"name":"Abdullah Kilci","email":"","orcid":"","institution":"Cukurova University","correspondingAuthor":false,"prefix":"","firstName":"Abdullah","middleName":"","lastName":"Kilci","suffix":""}],"badges":[],"createdAt":"2024-11-07 20:38:09","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5412234/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5412234/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":70033775,"identity":"9f38e0b7-2d1f-4a77-bf6e-4cf6cf896d96","added_by":"auto","created_at":"2024-11-27 16:55:29","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":69321,"visible":true,"origin":"","legend":"\u003cp\u003eSet up of instep kicking motion and devices.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5412234/v1/320234580685a05bf9c383d5.png"},{"id":78428484,"identity":"44074c0f-5fad-4e5d-99d1-3ef8969f3800","added_by":"auto","created_at":"2025-03-13 06:53:39","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":873891,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5412234/v1/513c321c-d5df-4f42-8146-9a9c671630b2.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Biomechanical determinants of high ball speed during instep soccer kick by prepubescent male athletes: The importance of muscle elasticity","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSoccer organizations invest significant financial and logistical resources in the identification and development of talented young athletes [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. As outlined in the Elite Player Performance Plan, the yearly investment for a category one academy in England is \u0026pound;2.3 to \u0026pound;4.9\u0026nbsp;million [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. The next generation of potential stars can be expected to emerge from these academy programs and eventually progress to become top-level professional players [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. The rise in soccer\u0026rsquo;s popularity, increased competition, and the implementation of new codes of conduct have all played a role in shaping a fresh scientific methodology for nurturing academy players. This is implemented by multidisciplinary teams who are dedicated to refining training strategies for optimal performance [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. This approach underscores the necessity for athletes to undergo comprehensive preparation encompassing physical, psychological, and technical facets to excel in their performance. The training progression in many academies typically commences with individual technical training and development for younger athletes, advancing to elite academy soccer teams for older athletes [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eKicking is a foundational motor skill that holds significant importance across various sports such as soccer, rugby, American Football, and Australian Rules Football. In such sports, the kicking motion is employed to score goals or points, requiring the generation of high ball-releasing velocity [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Biomechanically, a kicking motion can be likened to a throw-like movement, where the distal segments trail behind the proximal segments as they propel forward. Furthermore, kicking can be viewed as a culmination of forces, with the foot serving as the final and swiftest segment in the open kinetic chain [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Consequently, the velocity of the foot at the moment of impact is closely linked to the velocity of the ball [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Various kicking techniques can be employed in offensive and defensive situations to facilitate passing, maintaining possession, and scoring goals. The instep kick stands out as the predominant kicking method in soccer, executed by striking the ball with the top part of the foot while the foot is pointed downward [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe effectiveness of soccer kicking is determined by both the velocity and accuracy of the ball [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Although accuracy is significant, assessments of soccer kicking performance have primarily focused on maximizing ball speed. Provided that the kick is precise, a higher ball speed enhances the likelihood of scoring by reducing the time for the goalkeeper to react [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Numerous studies have examined the function of ball speed in soccer by determining the elements that influence the maximum kicking velocity. These factors encompass various aspects such as limb dominance [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], technique [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], approach speed and angle [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], skill level [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], lower extremity muscle strength and power [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e], and leg muscle activity [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. These researches have focused on highlighting the influence of the lower limbs on kicking performance. Given the growing body of recent studies on kicking biomechanics, the need for incorporating upper-body muscle activity into the analysis should be reassessed, particularly in studies on academy soccer players.\u003c/p\u003e \u003cp\u003eThe stretching\u0026ndash;shortening cycle of the leg muscles in the backward and forward phases of the instep kick may be a considerable biomechanical factor affecting ball speed. In this cycle, the ability of the anterior muscles to stretch with controlled eccentric contraction in the stretching phase affects the concentric contraction of the anterior leg muscles in the shortening phase. Likewise, the ability of the posterior muscles to stretch with optimal eccentric contraction during the forward phase of the kick may be a determinant of the ball speed [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Therefore, viscoelastic properties of muscles such as tone, elasticity, and stiffness, which determine the ability to stretch, may be key parameters determining leg angular velocity and thus maximum ball speed.\u003c/p\u003e \u003cp\u003eThis study examined the relationships between maximum ball speed; abdominal and thigh muscle activity; and the sagittal, horizontal, and frontal plane maximum velocities and accelerations of the kicking leg during instep kick by prepubescent soccer players. It also investigated the effects of the viscoelastic properties of the superficial abdominal and leg muscles on the maximum ball speed. The hypotheses of the present study were as follows: (i) RA-RF activation and leg angular velocity/acceleration and (ii) viscoelastic properties of lower extremity muscles are the determinants of the maximum ball speed during instep soccer kick by prepubescent male athletes.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eParticipants and instep kicks\u003c/h2\u003e \u003cp\u003eThis observational, cross-sectional study was conducted at XXXX Sports Club (XXXX, XXXX). Thirty-four prepubescent male soccer players with official licenses issued by the Turkish Football Federation were recruited. All participants were injury-free and were preparing for competition at the time of data collection. This study was approved by the Clinical Research Ethics Committee of XXXX University (Decision no.: 143/75, Approval date: 5 April 2024). All athletes were informed about the study protocol, and written consent was obtained from the participants and their legal representatives.\u003c/p\u003e \u003cp\u003eAll testing was completed in a soccer training field to represent competition performance and provide athletes with maximum freedom of movement. On the days the data were collected (23\u0026ndash;25 April 2024), the weather was clear, the highest temperature was 36 \u0026ordm;C, the highest wind speed was 4 km/h, and the mean humidity was 37%. The task performed was an instep kick at maximum speed on a stationary ball. The standard-sized (Lotto FB1000 4, Italy) and standard-inflated (11 psi) ball was kick 11 m toward a 2 x 2 m goal. To minimize movement in the frontal plane, players were limited to a 1-m straight-line approach from a position directly ahead. Before the task, the players performed a standardized warm-up consisting of 10-minute submaximal running and several whole-body stretching exercises. They then performed five submaximal soccer kicks. Following this warm-up, the athletes were asked to perform an instep kick with maximum ball speed, and they were required to try to hit the target area. Each player kick three times with his preferred leg, and the muscle activation and thigh angular velocity during the highest-ball speed were analyzed [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eMaximal ball speed was measured using a radar gun (Bushnell Velocity Speed Gun, USA), which can measure speed in the range of 16\u0026ndash;177 km/h from a distance of 14 m and has an accuracy of \u0026plusmn;\u0026thinsp;2 km/h. This radar gun has high reliability [intraclass correlation coefficient (ICC)\u0026thinsp;=\u0026thinsp;0.91] for measuring ball speed [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. It was positioned by an observer 1.5 m behind the goal and at a height of 1.5 m (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eTwo-dimensional motion analysis\u003c/h3\u003e\n\u003cp\u003eA high-resolution video camera (Galaxy-S22, Samsung, Korea) was positioned on a tripod at a height of approximately 1.5 m, located approximately 6 m directly perpendicular to the athlete\u0026rsquo;s sagittal plane [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. It recorded the instep kick at a rate of 240 frames per second (fps). The camera and electromyography (EMG) data acquisition program (EMG Works\u0026reg; version 4.8.0, Delsys Inc., USA) were synchronized using an LED system. The synchronization of the EMG with the LED was achieved with an Android application. An ESP32 microcontroller was used to control the LED, and App Inventor was used to prepare the Android application.\u003c/p\u003e \u003cp\u003eThe recording of the kick was separated into the backswing and acceleration phases, in which the highest kinematic and kinetic values were expected [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e], using Kinovea (version 0.8.15, Kinovea Open Source Project) software that permitted single-frame viewing. The backswing phase demonstrates the temporal window between the toe off of the kicking leg and the maximum hip extension, and the acceleration phase shows the temporal window between the maximum knee flexion and the ball strike [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. The start and end times of each phase were marked on the video records. The EMG and inertial measurement unit (IMU) data for these periods were collected.\u003c/p\u003e\n\u003ch3\u003eEMG and IMU acquisition\u003c/h3\u003e\n\u003cp\u003eA wireless-mobile (Android application) EMG system (TRIGNO, Delsys Inc., USA, input impedance\u0026thinsp;\u003cem\u003e\u0026lt;\u003c/em\u003e\u0026thinsp;10 ohms, baseline noise\u0026thinsp;\u003cem\u003e\u0026lt;\u003c/em\u003e\u0026thinsp;750nV root mean square (RMS), effective EMG signal gain 909 V/V\u0026thinsp;\u0026plusmn;\u0026thinsp;5%) was used to obtain raw EMG data for the rectus abdominis (RA) and rectus femoris (RF). EMG signals were sampled at 2,000 Hz and a bandwidth of 20\u0026ndash;450 Hz, full-wave rectified and smoothed with a second-order Butterworth low-pass filter. The distance between the metal surfaces of the wireless electrode was 1 cm. The Surface Electromyography for the Non-Invasive Assessment of Muscles recommendations were considered in the preparation of the skin and placement of the wireless electrodes [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. For RA the electrode was placed 3 cm above and 2 cm lateral to the umbilicus, over the muscle belly and parallel to the muscle fibers [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. For RF the electrode was placed at the midpoint of the line from the anterior spina iliaca superior to the superior part of the patella, parallel to the muscle fibers [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The RF\u0026mdash;the superficial muscle showing the highest activation along with the iliopsoas muscle [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]\u0026mdash;and the RA\u0026mdash;one of the core muscles that may affect the thigh angular velocity during instep kick, with a possible force transfer from trunk to leg, along with the anterior superficial fascia [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u0026mdash;were preferred for EMG analysis.\u003c/p\u003e \u003cp\u003eThe mean RMS collected from the muscles during the backswing and acceleration phases were normalized according to the maximum activation obtained during the instep kick [%maximum activation\u0026thinsp;=\u0026thinsp;muscle activity (RMS)/maximum activation of the muscle \u0026times; 100]. To reduce the possibility of obtaining normalized EMG levels of greater than 100%, we used this normalization method, which has high reliability (ICC\u0026thinsp;\u0026gt;\u0026thinsp;0.80; [\u003cspan additionalcitationids=\"CR27\" citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTrigno Avanti sensor-IMU Technology\u0026reg; (Delsys, Boston, MA, USA) was used to evaluate the thigh angular velocity and acceleration during the instep kick. The sensor was placed on the midpoint of the femur and fixed with adhesive tape. The IMU sensor measured the angular velocity [degree per second (deg/s)] and acceleration (g force) of the thigh along the kick in three planes (frontal, sagittal, and horizontal) [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. The peak angular velocity and acceleration values in three planes were considered for the data analysis.\u003c/p\u003e\n\u003ch3\u003eMyotonometry\u003c/h3\u003e\n\u003cp\u003eMyotonometry provides objective data on the viscoelasticity of muscles, such as tone, elasticity, and stiffness. Tone characterizes the intrinsic tension of biological soft tissues on the cellular level. Stiffness characterizes the resistance of biological soft tissues to a force of elongation or deformation. Elasticity is the biomechanical property of soft tissues that characterizes the ability of elongation and to recover its initial shape from being deformed [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. It uses a smartphone-sized, handheld device for myotonometric measurement (MyotonPro\u0026reg;, Myoton AS, Tallinn, Estonia). Myotonometry has shown good to excellent reliability (ICC ranging from 0.69 to 0.98) in evaluating the viscoelastic properties of muscles in young athletes [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. The MyotonPro\u0026reg; device determines the tone, elasticity, and stiffness values of the muscles by analyzing the characteristics of the oscillation wave formed in response to five short (0.15 ms) stimuli applied by the probe to the tissue with a force of 0.56 N and a frequency of 1 Hz [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]\u003c/p\u003e \u003cp\u003eMyotonometric assessment was performed of the major superficial muscles in the abdomen and lower extremity: the RA, RF, gluteus medius, adductor magnus, hamstring medialis (HM), tibialis anterior, and gastrocnemius medialis (GM). The measurement was performed when the athletes arrived at the sports facility, before the warm-up and kicking. During the measurement, the athlete was lying down and stationary. The device probe was placed perpendicular to the midpoint of the muscle. The device was sufficiently pressed to the muscle, and short stimulations were applied to the tissue. The tone [oscillation frequency (Hz)], elasticity [logarithmic decrement (arb)], and stiffness [dynamic stiffness (N/m)] values appearing on the screen were noted. Three measurements were performed for each muscle and averaged. Higher values indicate higher muscle tone and stiffness and lower elasticity [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eData analysis\u003c/h2\u003e \u003cp\u003eStatistical analyses were carried out using SPSS (version 22.0; SPSS, Chicago, IL, USA). The distribution of data was determined by visual (histograms and probability plots) and analytical (Shapiro\u0026ndash;Wilk test) methods. Pearson\u0026rsquo;s correlation test was used to determine the potential relationship between the biomechanical parameters and the maximum ball speed. Variables that were significant at the p\u0026thinsp;\u0026lt;\u0026thinsp;0.05 level in the univariate analysis were included in the multiple linear regression analysis. Stepwise multiple linear regression analysis was used to examine the potential effects of confounders on the dependent variable (maximum ball speed). Alpha values of \u0026lt;\u0026thinsp;0.05 were considered statistically significant.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eA total of 37 players were enrolled in the study, and the data of 34 who met the inclusion criteria were collected and analyzed. The baseline characteristics of the athletes are shown in Table 1.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1.\u003c/strong\u003e Baseline characteristics of the players.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 35.9272%;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 34.4371%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMean \u0026plusmn; SD\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29.6358%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMinimum-maximum\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 35.9272%;\"\u003e\n \u003cp\u003eAge, (year)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 34.4371%;\"\u003e\n \u003cp\u003e11.2\u0026plusmn;0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29.6358%;\"\u003e\n \u003cp\u003e11.0-12.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 35.9272%;\"\u003e\n \u003cp\u003eHeight, (cm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 34.4371%;\"\u003e\n \u003cp\u003e143.8\u0026plusmn;10.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29.6358%;\"\u003e\n \u003cp\u003e129.0-168.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 35.9272%;\"\u003e\n \u003cp\u003eWeight, (kg)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 34.4371%;\"\u003e\n \u003cp\u003e36.8\u0026plusmn;7.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29.6358%;\"\u003e\n \u003cp\u003e26.1-58.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 35.9272%;\"\u003e\n \u003cp\u003eBody mass index (kg/m\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 34.4371%;\"\u003e\n \u003cp\u003e17.6\u0026plusmn;1.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29.6358%;\"\u003e\n \u003cp\u003e14.8-21.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 35.9272%;\"\u003e\n \u003cp\u003eNumber of months played soccer\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 34.4371%;\"\u003e\n \u003cp\u003e28.7\u0026plusmn;11.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29.6358%;\"\u003e\n \u003cp\u003e18.0-60.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eAbbreviation: SD: Standard deviation\u003c/p\u003e\n\u003cp\u003eAll potential confounders had no significant effect on the maximum ball speed (p\u0026gt;0.05). The mean value of the maximum ball speed was 62.1\u0026plusmn;8.2 km/h. Tables 2 and Table 3 was shown the results of the correlation analysis between the maximum ball speed and the biomechanical parameters. Significant positive correlations (Pearson\u0026rsquo;s r ranging from 0.377 to 0.599) were found between the maximum ball speed and the maximum thigh acceleration in the sagittal plane during the backswing phase and RA\u0026ndash;RF activation, the maximum thigh velocity in the sagittal plane, and the maximum thigh acceleration in the sagittal and horizontal planes during the acceleration phase. Furthermore, significant negative associations existed between maximum ball speed and HM and GM elasticity (Pearson\u0026rsquo;s r=-0.592 and -0.771; power\u0026gt;0.95; p\u0026lt;0.05 for all).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2.\u003c/strong\u003e Correlation of maksimum ball speed with muscle activity and thigh velocity/acceleration\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 141px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" valign=\"top\" style=\"width: 227px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Backswing phase\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" valign=\"top\" style=\"width: 236px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Acceleration phase\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 141px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003eMean \u0026plusmn; SD\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003er\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003ep\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003eMean \u0026plusmn; SD\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003er\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003ep\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 141px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eEMG, (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 141px;\"\u003e\n \u003cp\u003eRectus abdominis\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e54.01\u0026plusmn;19.75\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e0,198\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e0.295\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e63.88\u0026nbsp;\u0026plusmn;22.35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.505\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.004\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 141px;\"\u003e\n \u003cp\u003eRectus femoris\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e51.02\u0026plusmn;20.94\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e0.116\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e0.540\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e69.08\u0026nbsp;\u0026plusmn;18.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.575\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.001\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 141px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eVelocity\u003csub\u003eMAX,\u0026nbsp;\u003c/sub\u003e (deg/s)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 141px;\"\u003e\n \u003cp\u003eFrontal plane\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e618.23\u0026plusmn;233.93\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e0.178\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e0.363\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e854.93\u0026nbsp;\u0026plusmn;311.22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.178\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e0.363\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 141px;\"\u003e\n \u003cp\u003eSagittal plane\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e743.50\u0026plusmn;385.89\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e0.101\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e0.610\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e979.21\u0026nbsp;\u0026plusmn;411.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.599\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.001\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 141px;\"\u003e\n \u003cp\u003eHorizontal plane\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e417.70\u0026nbsp;\u0026plusmn;258.21\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e0.100\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e0.620\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e681.28\u0026nbsp;\u0026plusmn;301.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.100\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e0.620\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 141px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAcceleration\u003csub\u003eMAX,\u0026nbsp;\u003c/sub\u003e(g)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 141px;\"\u003e\n \u003cp\u003eFrontal plane\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e7.30\u0026nbsp;\u0026plusmn;3.17\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e0.309\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e0.110\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e10.53\u0026nbsp;\u0026plusmn;4.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.309\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e0.110\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 141px;\"\u003e\n \u003cp\u003eSagittal plane\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e8.02\u0026nbsp;\u0026plusmn;4.00\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e0.377\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.048\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e12.71\u0026nbsp;\u0026plusmn;4.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.413\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.020\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 141px;\"\u003e\n \u003cp\u003eHorizontal plane\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e7.35\u0026nbsp;\u0026plusmn;3.58\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e0.330\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e0.086\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e12.24\u0026nbsp;\u0026plusmn;4.37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.387\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.028\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eAbbreviations: SD: Standard deviation, EMG: Electromyography, Max: Maximum, deg/s: Degree per second, g: acceleration of gravity.\u003c/p\u003e\n\u003cp\u003eSignificant associations (p \u0026lt; 0.05) are highlighted in bold.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 3.\u003c/strong\u003e Correlation of maksimum ball speed with muscle tone, elasticity, and stiffness\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 60px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" valign=\"top\" style=\"width: 178px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTone\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e[Oscillation frequency (Hz)]\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" valign=\"top\" style=\"width: 177px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eElasticity\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e[Logarithmic decrement (arb)]\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" valign=\"top\" style=\"width: 189px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eStiffness\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e[Dynamic stiffness(N/m)]\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 60px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMuscle\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 78px;\"\u003e\n \u003cp\u003eMean\u0026plusmn;SD\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 53px;\"\u003e\n \u003cp\u003er\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 47px;\"\u003e\n \u003cp\u003ep\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 69px;\"\u003e\n \u003cp\u003eMean\u0026plusmn;SD\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003er\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 52px;\"\u003e\n \u003cp\u003ep\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003eMean\u0026plusmn;SD\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 53px;\"\u003e\n \u003cp\u003er\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 47px;\"\u003e\n \u003cp\u003ep\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 60px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eRA\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 78px;\"\u003e\n \u003cp\u003e14.32\u0026plusmn;1.88\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 53px;\"\u003e\n \u003cp\u003e0.390\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 47px;\"\u003e\n \u003cp\u003e0.265\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 69px;\"\u003e\n \u003cp\u003e0.76\u0026plusmn;0.22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e-0.015\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 52px;\"\u003e\n \u003cp\u003e0.967\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003e228.20\u0026plusmn;57.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 53px;\"\u003e\n \u003cp\u003e0.294\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 47px;\"\u003e\n \u003cp\u003e0.410\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 60px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eGMed\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 78px;\"\u003e\n \u003cp\u003e15.20\u0026plusmn;1.11\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 53px;\"\u003e\n \u003cp\u003e0.160\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 47px;\"\u003e\n \u003cp\u003e0.659\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 69px;\"\u003e\n \u003cp\u003e1.00\u0026plusmn;0.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e-0.232\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 52px;\"\u003e\n \u003cp\u003e0.519\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003e250.70\u0026plusmn;37.84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 53px;\"\u003e\n \u003cp\u003e0.221\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 47px;\"\u003e\n \u003cp\u003e0.539\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 60px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eRF\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 78px;\"\u003e\n \u003cp\u003e12.94\u0026plusmn;0.96\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 53px;\"\u003e\n \u003cp\u003e0.366\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 47px;\"\u003e\n \u003cp\u003e0.299\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 69px;\"\u003e\n \u003cp\u003e0.98\u0026plusmn;0.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e-0.259\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 52px;\"\u003e\n \u003cp\u003e0.471\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003e185.60\u0026plusmn;25.92\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 53px;\"\u003e\n \u003cp\u003e0.091\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 47px;\"\u003e\n \u003cp\u003e0.804\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 60px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAMag\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 78px;\"\u003e\n \u003cp\u003e14.37\u0026plusmn;1.03\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 53px;\"\u003e\n \u003cp\u003e0.019\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 47px;\"\u003e\n \u003cp\u003e0.958\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 69px;\"\u003e\n \u003cp\u003e1.00\u0026plusmn;0.18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e-0.322\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 52px;\"\u003e\n \u003cp\u003e0.364\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003e234.00\u0026plusmn;24.81\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 53px;\"\u003e\n \u003cp\u003e-0.081\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 47px;\"\u003e\n \u003cp\u003e0.824\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 60px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eHM\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 78px;\"\u003e\n \u003cp\u003e18.11\u0026plusmn;1.77\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 53px;\"\u003e\n \u003cp\u003e-0.029\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 47px;\"\u003e\n \u003cp\u003e0.936\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 69px;\"\u003e\n \u003cp\u003e0.85\u0026plusmn;0.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e-0.592\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 52px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.041\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003e345.50\u0026plusmn;53.61\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 53px;\"\u003e\n \u003cp\u003e-0.062\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 47px;\"\u003e\n \u003cp\u003e0.864\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 60px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTA\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 78px;\"\u003e\n \u003cp\u003e14.66\u0026plusmn;1.66\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 53px;\"\u003e\n \u003cp\u003e0.254\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 47px;\"\u003e\n \u003cp\u003e0.479\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 69px;\"\u003e\n \u003cp\u003e1.06\u0026plusmn;0.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e-0.401\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 52px;\"\u003e\n \u003cp\u003e0.250\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003e238.90\u0026plusmn;27.95\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 53px;\"\u003e\n \u003cp\u003e0.290\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 47px;\"\u003e\n \u003cp\u003e0.417\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 60px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eGM\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 78px;\"\u003e\n \u003cp\u003e13.03\u0026plusmn;1.95\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 53px;\"\u003e\n \u003cp\u003e0.316\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 47px;\"\u003e\n \u003cp\u003e0.373\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 69px;\"\u003e\n \u003cp\u003e1.13\u0026plusmn;0.27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e-0.771\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 52px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.009\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003e192.70\u0026plusmn;63.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 53px;\"\u003e\n \u003cp\u003e0.329\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 47px;\"\u003e\n \u003cp\u003e0.353\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eAbbreviations: Arb: Relative arbitrary unit, SD: Standard deviation, RA: Rectus abdominis, GMed: Gluteus medius, RF: Rectus femoris, Amag: Adductor magnus, HM: Hamstring medialis, TA: Tibialis anterior, GM: Gastriconemius medialis.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eSignificant associations (p \u0026lt; 0.05) are highlighted in bold.\u003c/p\u003e\n\u003cp\u003eBiomechanical parameters were significantly associated with the maximum ball speed in the univariate correlation analysis and thus included in multiple linear regression analysis with two models. However, since the EMG, rotational velocity, and elasticity parameters met 100% of the regression model, some of the acceleration parameters were removed from the model 2 by the software. The multiple linear regression analysis demonstrated that important factors for maximum kick velocity were HM (B=0.432) and GM (B=0.771) elasticity (adjusted R\u003csup\u003e2\u003c/sup\u003e=0.60, Delta R\u003csup\u003e2\u003c/sup\u003e=0.40; Table 4).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;4.\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eMultiple\u0026nbsp;lineer\u0026nbsp;regression analysis\u0026nbsp;for the association between biomechanical parameters and\u0026nbsp;maksimum\u0026nbsp;ball speed\u003c/p\u003e\n\u003cdiv align=\"center\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 103px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eModel 1\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 104px;\"\u003e\n \u003cp\u003eB(SE)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e\u0026szlig;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 125px;\"\u003e\n \u003cp\u003ep\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 103px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003eGM-Elasticity\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 104px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e-14.77 (4.31)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e0.771\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 125px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e0.009\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"4\" valign=\"top\" style=\"width: 414px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;Model 2\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 103px;\"\u003e\n \u003cp\u003eGM-Elasticity\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 104px;\"\u003e\n \u003cp\u003e-14.78 (2.68)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e0.771\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 125px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.001\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 103px;\"\u003e\n \u003cp\u003eHM-Elasticity\u003c/p\u003e\n \u003cp\u003e\u003csub\u003e\u0026nbsp;\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 104px;\"\u003e\n \u003cp\u003e-25.35 (7.60)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e0.432\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 125px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.044\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 103px;\"\u003e\n \u003cp\u003eRA-EMG\u003csub\u003eAcc\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 104px;\"\u003e\n \u003cp\u003e0.12 (0.05)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e0.476\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 125px;\"\u003e\n \u003cp\u003e0.117\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 103px;\"\u003e\n \u003cp\u003eRF-EMG\u003csub\u003eAcc\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 104px;\"\u003e\n \u003cp\u003e0.11 (0.05)\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e0.460\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 125px;\"\u003e\n \u003cp\u003e0.102\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 103px;\"\u003e\n \u003cp\u003eVelocity-Saggittal\u003csub\u003eAcc\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 104px;\"\u003e\n \u003cp\u003e0.01(0.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e0.230\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 125px;\"\u003e\n \u003cp\u003e0.158\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 103px;\"\u003e\n \u003cp\u003eAcceleration-Saggittal\u003csub\u003eAcc\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 104px;\"\u003e\n \u003cp\u003e0.15 (0.23)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 83px;\"\u003e\n \u003cp\u003e0.100\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 125px;\"\u003e\n \u003cp\u003e0.558\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 103px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003eNote\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" valign=\"top\" style=\"width: 311px;\"\u003e\n \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e=0.60 for model 1, \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u0026Delta;R\u003csup\u003e2\u003c/sup\u003e= 0.40 for model 2 \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/p\u003e\n \u003cp\u003eConstant=43.85 for model 1, \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;Constant= 16.13 for model 2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u0026nbsp;Abbreviations: GM: Gastriconemius medialis, HM: Hamstring medialis, RA-EMG\u003csub\u003eAcc\u003c/sub\u003e: Rectus abdominus activation in acceleration phase, RF-EMG\u003csub\u003eAcc\u003c/sub\u003e: Rectus femoris activation in acceleration phase, Acc: Acceleration phase,\u0026nbsp;B: unstandardized coefficients, SE: standard error, \u0026beta;: standardized coefficients, R\u003csup\u003e2\u003c/sup\u003e: adjusted R-squared Significant associations (p \u0026lt; 0.05) are highlighted in bold.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThis study explored the biomechanical factors in prepubescent male soccer players associated with the development of high ball speed. It revealed that HM and GM elasticity was the most important determinant parameter of instep kick velocity. RA and RF activity and thigh angular velocity and acceleration were also associated with the maximum ball speed.\u003c/p\u003e\n\u003cp\u003eMany previous studies have aimed to determine the relationship between the activation patterns of lower extremity muscles and the instep kick velocity [9,17,19,22,31].\u0026nbsp;Considering the results of these studies, the significant positive relationship between RF muscle activation and the ball speed for a successful kick is not surprising. A high level of hip flexor and RF activation is required to generate excessive rotational torque during the acceleration phase [22,31]. Unlike previous studies the current study revealed that the RA, which generates force to stabilize the core during the instep kick, may also contribute to RF activity through force transmission along with the anterior superficial fascia [32,33].\u0026nbsp;Stabilization of the trunk and force transmission from proximal muscles to the leg seem to be key factors for a successful high-speed kick.\u003c/p\u003e\n\u003cp\u003eThe instep soccer kick is characterized by joint motions in multiple planes\u0026nbsp;[9]. Previous studies have shown that the angular velocity of the combined movement pattern formed by flexion and external rotation of the thigh during the acceleration phase has an important effect on the ball speed\u0026nbsp;[9,19,34]. Similarly, the current study revealed a relationship between the ball speed and the maximum angular velocity of the thigh in the sagittal plane. However, the result that must be emphasized is the significant association of the acceleration of the thigh in the sagittal and horizontal planes with the ball speed. The higher the leg acceleration before impact, the shorter the ball–foot contact and the higher the ball speed\u0026nbsp;[9]. Therefore, the leg should reach its maximum rotational velocity in the shortest time to maximize the ball speed.\u003c/p\u003e\n\u003cp\u003eOn a biomechanical basis, the stretch–shorten cycle of agonist and antagonist muscles during the instep kick likely affects ball speed\u0026nbsp;[35].\u0026nbsp;For the stretch–shorten cycle to be optimal, the contraction abilities of the muscles and their viscoelastic properties must be at appropriate levels\u0026nbsp;[36]. Avrillon et al.\u0026nbsp;[37]\u0026nbsp;showed that hamstring elasticity is a key factor distinguishing specialized athletes from the general population. However, past studies investigating the determinants of ball speed have not focused on the viscoelastic properties of muscles\u0026nbsp;[9,17,19,22,34].\u0026nbsp;\u0026nbsp;In our study, multiple linear regression analysis revealed that HM and GM elasticity was the primary determinant of ball speed in prepubescent male soccer players. These muscles, located in the posterior thigh and leg, are connected by the posterior superficial fascia and control anterior movements of the hip, knee, and ankle. We propose that during the acceleration phase of the instep kick, the elasticity of the HM and GM muscles—due to their tendency to return to their original length—creates a passive opposing force, which counteracts the action of the muscles acting as agonists for the instep kick. Therefore, in athletes with high HM and GM elasticity, the torque generated by the torque generated by the hip flexors and other anterior muscles is more effectively transmitted to the ball through the foot, resulting in higher ball speeds. It is noteworthy, however, that despite a significant interaction between muscle elasticity and maximum ball speed, no interaction was observed between tonus and stiffness values. This result indicates that the muscle's tendency to return to its original length after elongation affects maximum ball speed more than baseline tonus or the ability to elongate. We believe that further researchs examining the effects of muscle elasticity, tonus, and stiffness on athletic performance will yield deeper insights.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eLimitations\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study has some limitations. First, to ensure standardization, the athletes were asked to perform an instep kick limited to certain patterns. Since soccer players kick moving or stationary balls from various distances and with various approach angles during matches or training, the method followed in the study may not fully comply with the nature of the sport. The second limitation is that EMG analysis of the deep abdominal (core) muscles could not be performed. Therefore, the possible force transmission from the deep abdominal muscles to the anterior thigh muscles during the instep kick could not be determined.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eGM and HM elasticity was the primary biomechanical parameter affecting the ball speed during instep kicks among prepubescent male soccer players. Additionally, RA and RF activity and the acceleration of the thigh in the sagittal and horizontal planes may be determinants of the ball speed. We recommend that to increase the ball speed during instep kick, training methods that improve the GM and HM elasticity, along with core and anterior thigh muscle activation, should be preferred in prepubescent male soccer players.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003e\u003cstrong\u003eEMG:\u0026nbsp;\u003c/strong\u003eElectromyography\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIMU:\u0026nbsp;\u003c/strong\u003eInertial measurement unit\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eRMS:\u003c/strong\u003e Root mean square\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eRA:\u003c/strong\u003e Rectus abdominis\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eRF:\u003c/strong\u003e Rectus femoris\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eHM:\u003c/strong\u003e Hamstring medialis\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eGM:\u003c/strong\u003e Gastriconemius medialis\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study followed the Declaration of Helsinki. Ethical Approval was obtained from the Local Ethics Committee of Cukurova University Faculty of Medicine (Decision no.: 143/75, Approval date: 5 April 2024). An informed consent form was signed by participants and their legal\u0026nbsp;representatives before they participated in the study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWritten informed consent was obtained from participants for publication of identifying information in an online open-access publication.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study are available from the corresponding author upon reasonable request.\u0026nbsp;\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\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNone\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors' contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eVD contributed to the literature search, conceptual development, and study design. AK was responsible for data collection, analysis, manuscript drafting, and the preparation of tables and Figure 1. All authors have reviewed and approved the final version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe extend our gratitude to all participants who voluntarily contributed to this study.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFaculty of Health Sciences, Department of Physiotherapy and Rehabilitation, Tarsus University, Mersin, Turkey.\u003c/p\u003e\n\u003cp\u003eVolkan Deniz\u003c/p\u003e\n\u003cp\u003eCukurova University, Faculty of Sport Sciences, Adana-Türkiye\u003c/p\u003e\n\u003cp\u003eAbdullah Kılcı\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorresponding author\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCorrespondence to Volkan Deniz\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eBaker J, Schorer J, Wattie N. 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Journal of sports Sciences. 2006;24(1):11-22. https://doi.org/10.1080/02640410400021450\u003c/li\u003e\n \u003cli\u003eAmiri-Khorasani M, MohammadKazemi R, Sarafrazi S, Riyahi-Malayeri S, Sotoodeh V. Kinematics analyses related to stretch-shortening cycle during soccer instep kicking after different acute stretching. The Journal of Strength \u0026amp; Conditioning Research. 2012;26(11):3010-7. https://doi.org/10.1519/jsc.0b013e3182443442\u003c/li\u003e\n \u003cli\u003eTaylor DC, Dalton JR JD, Seaber AV, Garrett JR WE. Viscoelastic properties of muscle-tendon units: the biomechanical effects of stretching. The American journal of sports medicine. 1990;18(3):300-9. https://doi.org/10.1177/036354659001800314\u003c/li\u003e\n \u003cli\u003eAvrillon S, Lacourpaille L, Hug F, Le Sant G, Frey A, Nordez A, et al. Hamstring muscle elasticity differs in specialized high‐performance athletes. Scandinavian journal of medicine \u0026amp; science in sports. 2020;30(1):83-91. http://dx.doi.org/10.1111/sms.13564\u003c/li\u003e\n\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":"Instep kick, ball speed, muscle activation, leg angular velocity, muscle elasticity ","lastPublishedDoi":"10.21203/rs.3.rs-5412234/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5412234/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cb\u003eBackground\u003c/b\u003e\u003c/p\u003e \u003cp\u003eThis study aimed to investigate the effects of kinetic\u0026ndash;kinematic parameters and muscle viscoelastic properties on high ball speed during instep soccer kick by prepubescent male athletes.\u003c/p\u003e\u003cp\u003e\u003cb\u003eMethods\u003c/b\u003e\u003c/p\u003e \u003cp\u003eThis study included 34 male soccer players with an average age of 11.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5 years. Maximal ball speed during the instep kick was measured using a radar gun. The activation of the rectus abdominis (RA) and rectus femoris (RF), as well as the thigh's three-dimensional rotational velocity and acceleration, were evaluated using surface electromyography and an inertial measurement unit. Mechanical properties such as tone, elasticity, and stiffness of the superficial abdomen and leg muscles were measured at rest using myotonometry.\u003c/p\u003e\u003cp\u003e\u003cb\u003eResults\u003c/b\u003e\u003c/p\u003e \u003cp\u003eSignificant positive correlations existed between maximum ball speed and RA\u0026ndash;RF activation (r\u0026thinsp;=\u0026thinsp;0.505 and 0.575), maximum thigh velocity in the sagittal plane (r\u0026thinsp;=\u0026thinsp;0.599), and maximum thigh acceleration in the sagittal (r\u0026thinsp;=\u0026thinsp;0.423) and horizontal (r\u0026thinsp;=\u0026thinsp;0.387) planes (power\u0026thinsp;\u0026gt;\u0026thinsp;0.95; p\u0026thinsp;\u0026lt;\u0026thinsp;0.05 for all). Significant negative correlations were found between the maximum ball speed and the hamstring medialis (HM) and gastrocnemius medialis (GM) elasticity (r=-0.592 and \u0026minus;\u0026thinsp;0.771; power\u0026thinsp;\u0026gt;\u0026thinsp;0.95; p\u0026thinsp;\u0026lt;\u0026thinsp;0.05 for all). The multiple linear regression analysis demonstrated that important factors for maximum ball velocity were HM (B\u0026thinsp;=\u0026thinsp;0.432) and GM (B\u0026thinsp;=\u0026thinsp;0.771) elasticity (adjusted R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.60, delta R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.40).\u003c/p\u003e\u003cp\u003e\u003cb\u003eConclusions\u003c/b\u003e\u003c/p\u003e \u003cp\u003eGM and HM elasticity were the prominent factors affecting ball speed during instep kick. To increase ball speed during instep kick, training methods that focus on improving the elasticity of the GM and HL muscles, as well as activating the core and RF, should be prioritized for prepubescent male soccer players.\u003c/p\u003e\u003cp\u003e\u003cb\u003eTrial registration:\u003c/b\u003e\u003c/p\u003e \u003cp\u003eNot applicable\u003c/p\u003e","manuscriptTitle":"Biomechanical determinants of high ball speed during instep soccer kick by prepubescent male athletes: The importance of muscle elasticity","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-11-27 16:55:25","doi":"10.21203/rs.3.rs-5412234/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":"04e76309-4541-4563-8c95-5ac42d25e5cb","owner":[],"postedDate":"November 27th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-03-13T06:53:17+00:00","versionOfRecord":[],"versionCreatedAt":"2024-11-27 16:55:25","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5412234","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5412234","identity":"rs-5412234","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}