A comparison of muscle activations during traditional and abbreviated tennis serves

The abbreviated tennis serve is a relatively novel modification of the traditional serve that has been reported to provide performance advantages over the traditional technique. However, there are limited objective data regarding the benefits and biomechanics of the abbreviated serve; no data exist that describe shoulder muscle activations during the abbreviated serve. The purpose of this study was to compare muscle activations between the traditional and abbreviated serves. Electromyographic data were collected for the anterior and posterior deltoid, infraspinatus, middle trapezius, latissimus dorsi, serratus anterior, and pectoralis major. When muscle activations were compared during each serve phase, no significant differences were observed between the traditional and abbreviated tennis serve techniques, indicating that the traditional and abbreviated serves are similar regarding shoulder muscle activations. These results could have implications for performance of and injury related to the abbreviated versus traditional serve technique. Although the abbreviated serve has anecdotally been described as advantageous, the present data do not indicate any significant advantages or disadvantages in performing the abbreviated serve technique versus the traditional serve.     

Biomechanical analysis of the “waiter’s serve” on upper limb loads in young elite tennis players

Waiter’s serve (WS) is a specific tennis serve posture frequently observed in young players, and commonly considered as a technical error by tennis coaches. However, biomechanical impact of WS is unknown. The aims of this study were to identify the potential consequences of WS in young elite players relating to performance and injury risk, and to explain the kinematic causes of WS. Serve of 18 male junior elite players (Top 10 national French ranking, aged 12–15 years) was captured with a 20 camera, 200?Hz VICON MX motion analysis system. Depending on their serve technique, the players were divided into two groups (WS versus Normal Serve [NS]) by experienced coaches. Injury data were collected for each player during a 12-month-period following the motion capture. Normalized peak kinetic values of the dominant arm were calculated using inverse dynamics. In order to explain WS posture, upper limb kinematics were calculated during the cocking and the acceleration phases of the serve. Shoulder internal rotation torque, wrist proximal and anterior forces (P?P?P?相似文献   

Tennis

This study investigated the effect of the larger diameter (Type 3) tennis ball on performance and muscle activation in the serve. Sixteen male advanced tennis players performed serves using regular size and Type 3 tennis balls. Ball speed, surface electromyography, and serve accuracy were measured. There were no significant differences in mean initial serve speeds between balls, but accuracy was significantly greater (19.3%) with the Type 3 ball than with the regular ball. A consistent temporal sequence of muscle activation and significant differences in mean activation of different muscles were observed. However, ball type had no effect on mean arm muscle activation. These data, combined with a previous study, suggest that play with the larger ball is not likely to increase the risk of overuse injury, but serving accuracy may increase compared to play with the regular ball.     

Effect of type 3 (oversize) tennis ball on serve performance and upper extremity muscle activity

This study investigated the effect of the larger diameter (Type 3) tennis ball on performance and muscle activation in the serve. Sixteen male advanced tennis players performed serves using regular size and Type 3 tennis balls. Ball speed, surface electromyography, and serve accuracy were measured. There were no significant differences in mean initial serve speeds between balls, but accuracy was significantly greater (19.3%) with the Type 3 ball than with the regular ball. A consistent temporal sequence of muscle activation and significant differences in mean activation of different muscles were observed. However, ball type had no effect on mean arm muscle activation. These data, combined with a previous study, suggest that play with the larger ball is not likely to increase the risk of overuse injury, but serving accuracy may increase compared to play with the regular ball.     

Electromyography activities for shoulder muscles over various movements on different torque changes

Abstract

The aim of the present study was to investigate the patterns of shoulder muscle activation and joint torques during maximal effort eccentric contractions with shoulder extension, abduction, and diagonal movements on the isokinetic device. Participants in this investigation were nine men and four women with no history of shoulder injury or disorders. They all participated in overhead sports at least three days a week, and volunteered to participate in this study for shoulder isokinetic muscle strength testing. They performed eccentric muscle action with shoulder flexion, abduction, and diagonal movements at velocities of 60 rad·s^?1 and 180 rad· s^?1, which was followed alternately by passive shoulder flexion, abduction and diagonal movement at a velocity of 30 rad· s^?1, and total range of motion was standardised to 90°. Electromyography (EMG) and torque values were calculated to every 10°, except for the start and end 5° during each task. During each test, the isokinetic force output and muscle activation were synchronised. EMG data were normalised by percentage of maximum voluntary isometric contraction (%MVIC). EMG signals were recorded by surface EMG from the anterior deltoid (AD), middle deltoid (MD), posterior deltoid (PD), upper trapezius (UT), middle trapezius (MT), and biceps brachii (BB) muscles during this test. All of the muscle patterns were significantly decreased at the last compared with the initial part during eccentric shoulder flexion movement, except for the BB muscle (P < 0.05). AD and BB muscles played a similar role when peak torque was generated under load during eccentric muscle action with varying shoulder movements. PD and UT muscle activities were significantly lower than the other muscle activities during eccentric contraction with shoulder flexion and abduction movements, and the PD and UT muscles played a significant role in conjunction with MD and MT muscles in varying degrees during eccentric contraction with shoulder diagonal movements at 180 rad·s^?1 (P < 0.05). Our study demonstrated that MT muscle activity was greatly influenced when torque values showed a peak moment under load during maximum effort, eccentric contraction with shoulder abduction and diagonal movements. However, the MD, PD, UT, and MT muscle activities had no great influence when peak torque was generated under load during eccentric muscle action with shoulder diagonal movement at high velocity. The present study suggested that varying eccentric muscle activity patterns may be needed to investigate proper training and functional contributions of upper extremity muscles to stabilisation of the shoulder joint when peak torque was generated under load.     

Changes in joint kinetics during learning the longswing on high bar

Biomechanics helps us understand the association between technique changes and performance improvement during learning. The aim of this research was to investigate joint kinetic characteristics of technique during learning of the longswing on the high bar. Twelve male, novice participants took part in the learning study. During swing attempts in 8 weekly testing sessions, kinematic data were collected. Inverse dynamics analysis was performed from known zero forces at the toes to quantify joint moments and power at the hips and shoulders. Key biomechanical constraints that limited performance outcome were identified based on changes in joint kinetics during learning. These constraints were the ability to perform a large shoulder power and to overcome passive kinetics acting during the downswing. Constraints to action at the level of joint kinetics differentially challenge learners and therefore could underpin more individual, specific learning interventions. Functional phases, defined by maximum hyperextension to flexion of the hips and maximum flexion to extension of the shoulders, did not describe the key joint kinetics of the hip and shoulder for novices. The functional phases may serve however to identify novices that were unable to overcome the passive kinetic constraint.     

Muscle recruitment patterns of the subscapularis,serratus anterior and other shoulder girdle muscles during isokinetic internal and external rotations

The aims of this study were to investigate the differences in peak muscle activity and recruitment patterns during high- and low-velocity, concentric and eccentric, internal and external isokinetic shoulder rotations. Electromyographic activity of the rotator cuff and eight superficial muscles of the shoulder girdle was recorded on 25 healthy adults during isokinetic internal and external shoulder rotation at 60°/s and 240°/s. Peak muscle activity, electromyographic envelopes and peak isokinetic moments were analyzed using three-factor ANOVA and statistical parametric mapping. The subscapularis and serratus anterior showed moderate to high peak activity levels during each conditions, while the middle and posterior deltoids, upper, middle and lower trapezius, infraspinatus and supraspinatus showed higher peak activity levels during external rotations (+36.5% of maximum voluntary activation (MVA)). The pectoralis major and latissimus dorsi were more active during internal rotations (+40% of MVA). Only middle trapezius and pectoralis major electromyographic activity decreased with increasing velocity. Peak muscle activity was similar or lower during eccentric contractions, although the peak isokinetic moment increased by 35% on average. The subscapularis and serratus anterior appear to be important stabilizers of the glenohumeral joint and scapula. Isokinetic eccentric training at high velocities may allow for faster recruitment of the shoulder girdle muscles, which could improve joint stability during shoulder internal and external rotations.     

周红发球技术特征的解析

通过对周红发球时身体主要关节声、（肩、肘、腕）运动轨迹解析，找出击球时鞭打动作的特征及其球速快的缘由．特征是以腰为轴，以肩、肘、腕三节鞭打的动作，使手腕获得较大的加速度、其他队员多是以肩为轴的肘、腕二节鞭打动作．     

运动员创伤性肩关节前不稳定表面肌电的特征

以临床疾病创伤性肩关节前方不稳（Traumatic Anterior Shoulder Instability,TASI）者为研究对象,通过研究患肩周围肌肉表面肌电活动与正常肩关节在不同功能性动作中比较来探寻TASI肩周肌肉活动募集的大致特征,为TASI患者选择治疗方案提供理论依据。方法：选取东方医院运动医学科就诊的TASI运动员患者和正常运动员肩关节（CON）对照。肌肉活动采用德国Biovision 16导联肌电图仪进行表面肌电信号采集,执行肩胛平面外展、前屈、后伸,0°和45°外展时内外旋,评价肌肉活动特征。结果：TASI和CON相比,TASI肩周肌肉具有以下特征,胸大肌在中立位内旋活动下降明显,三角肌前束在肩胛平面外展的后半部分范围和前屈的前半部分范围中明显下降,三角肌中束活动在前屈的中间范围活动下降,冈上肌活动在外展起始范围有增加的趋势,其余大多数运动范围均呈现下降趋势。肱二头肌活动在前屈和外旋运动中增加。冈下肌活动性在外旋时下降。前锯肌活动在前屈的后范围活动、内外旋运动中是下降的。结论：（1）增加了TASI发病机制的理解,补充了TASI康复训练和治疗选择依据的基本数据库。（2）TASI肩外展肌群、外旋肌群的工作能力下降,内外旋肌群存在失衡现象,外旋肌群的工作能力下降较明显。（3）TASI肩非手术治疗时可适当考虑前方动力性稳定结构,应加强冈上肌、前锯肌以及外旋肌肉的活动性训练,适当加强三角肌前、中束和内旋肌群的训练。     

Determinants of countermovement jump performance: a kinetic and kinematic analysis

Abstract

This study aimed to investigate the contributions of kinetic and kinematic parameters to inter-individual variation in countermovement jump (CMJ) performance. Two-dimensional kinematic data and ground reaction forces during a CMJ were recorded for 18 males of varying jumping experience. Ten kinetic and eight kinematic parameters were determined for each performance, describing peak lower-limb joint torques and powers, concentric knee extension rate of torque development and CMJ technique. Participants also completed a series of isometric knee extensions to measure the rate of torque development and peak torque. CMJ height ranged from 0.38 to 0.73 m (mean 0.55 ± 0.09 m). CMJ peak knee power, peak ankle power and take-off shoulder angle explained 74% of this observed variation. CMJ kinematic (58%) and CMJ kinetic (57%) parameters explained a much larger proportion of the jump height variation than the isometric parameters (18%), suggesting that coachable technique factors and the joint kinetics during the jump are important determinants of CMJ performance. Technique, specifically greater ankle plantar-flexion and shoulder flexion at take-off (together explaining 58% of the CMJ height variation), likely influences the extent to which maximal muscle capabilities can be utilised during the jump.     

Ground reaction forces, kinematics, and muscle activations during the windmill softball pitch

The aims of the present study were to examine quantitatively ground reaction forces, kinematics, and muscle activations during the windmill softball pitch, and to determine relationships between knee valgus and muscle activations, ball velocity and muscle activation as well as ball velocity and ground reaction forces. It was hypothesized that there would be an inverse relationship between degree of knee valgus and muscle activation, a direct relationship between ground reaction forces and ball velocity, and non-stride leg muscle activations and ball velocity. Ten female windmill softball pitchers (age 17.6 ± 3.47 years, stature 1.67 ± 0.07 m, weight 67.4 ± 12.2 kg) participated. Dependent variables were ball velocity, surface electromyographic (sEMG), kinematic, and kinetic data while the participant was the independent variable. Stride foot contact reported peak vertical forces of 179% body weight. There were positive relationships between ball velocity and ground reaction force (r = 0.758, n = 10, P = 0.029) as well as ball velocity and non-stride leg gluteus maximus (r = 0.851, n = 10, P = 0.007) and medius (r = 0.760, n = 10, P = 0.029) muscle activity, while there was no notable relationship between knee valgus and muscle activation. As the windmill softball pitcher increased ball velocity, her vertical ground reaction forces also increased. Proper conditioning of the lumbopelvic-hip complex, including the gluteals, is essential for injury prevention. From the data presented, it is evident that bilateral strength and conditioning of the gluteal muscle group is salient in the windmill softball pitch as an attempt to decrease incidence of injury.     

Principal components analysis to characterise fatigue-related changes in technique: Application to double under jump rope

The upper extremities play an important role in managing the rope-turning technique required to perform continuous double unders. However, acute adaptions in this technique may occur as a jumper fatigues. The purpose of this study was to examine how turning technique is adapted with fatigue. Three-dimensional kinematic data of the upper extremity were collected from 10 trained athletes as they performed consecutive double unders to volitional fatigue. Time series wrist, elbow and shoulder joint angles were calculated where joint angle waveforms representing 10 unique trials from the beginning (“fresh”) and end (“fatigued”) of the continuous jumping protocol for all participants were analysed using principal component analysis. Participants reported stopping due to cardiovascular and shoulder muscular fatigue. From a kinematics perspective, with fatigue athletes used a more internally rotated range of motion at the shoulder, which we believe prompted a series of more distal adaptions in order to maintain rope turning, preserving consecutive double under performance. The presence of a maladaptive adaptation at the shoulder may increase the risk of developing shoulder injuries. Coaches should consider helping jumpers develop appropriate shoulder muscle endurance such that they can continue to maximise their training and proficiency, while protecting against potential fatigue-related maladaptation.     

不同落点网球侧上旋发球技术的运动学对比分析

目的:探索不同落点(T内角、Body追身和Wide外角)网球侧上旋发球技术动作的运动学规律。方法:采用2台三维高速摄像机拍摄10名网球运动员侧上旋发球技术动作,使用北京体育大学视讯解析系统采集运动学参数,对原始数据进行平滑和归一化处理等(Fc=10)。结果:1)抛球引拍阶段:抛球时左肩水平投影角呈显著性差异,左肩、右肩和左膝关节角速度变量呈显著性相关(R=0.82),站位方式无显著性差异;2)"挠背"阶段:不同落点发球时发力顺序协调一致,由下至上逐步将力量传递至击球点;3)挥拍击球阶段:击球时刻不同落点间分速度和击球角度差异性显著,外角侧旋>追身侧旋>内角侧旋,内角上旋>追身上旋>外角上旋,外角Angle>追身Angle>内角Angle。击球点高度与身高的倍数为外角(1.32)、追身(1.25)和内角(1.21),击球点由内至外逐渐向右偏移;4)随挥阶段:击球后重心位移和速度分量未出现显著性差异,膝关节角度变化均值39.7±1.8°。结论:我国高校网球二级运动员亟需储备发球隐蔽性、击球点空间位置、挥拍轨迹和击球速度分量等方面的意识体系。应当继续以运动生物力学为手段加强网球各类型发球技术动作、各环节运动特征和发球所致损伤因素等进行系统化和精细化研究。     

The associations of selected technical parameters with discus throwing performance: A cross-sectional study

The aim of this study was to identify associations between discus throwing performance and the technical parameters of: hip–shoulder and shoulder–arm separation, trunk forward–backward tilt, and throwing-arm elevation angles. Video data of male and female discus throwers' competitive performances were captured during major competitions. Real-life three-dimensional coordinates of 21 body landmarks, and the discus's centre, were obtained for 94 trials using the direct linear transformation procedure. Each technical parameter was reduced at six critical instants. The trend of each parameter across four standards of performance was analysed separately for both sexes. For the female throwers, hip–shoulder and shoulder–arm separations after the flight phase, as well as forward–backward trunk tilts at the beginning and end of the throwing procedure were associated with performance. For male throwers, only the hip–shoulder separation immediately before the flight phase was associated with performance. These findings suggest that the relationships between technical parameters and discus throwing performance are different for males and females. Our results suggest that elite female discus throwers are reliant on effective technique throughout the throwing procedure to achieve long distances, whereas male discus throwers may have a relatively homogeneous technique, and a dependence on physical strength to achieve their long throws.     

Muscle activity in sprinting: a review

The use of electromyography (EMG) is widely recognised as a valuable tool for enhancing the understanding of performance drivers and potential injury risk in sprinting. The timings of muscle activations relative to running gait cycle phases and the technology used to obtain muscle activation data during sprinting are of particular interest to scientists and coaches. This review examined the main muscles being analysed by surface EMG (sEMG), their activations and timing, and the technologies used to gather sEMG during sprinting. Electronic databases were searched using ‘Electromyography’ OR ‘EMG’ AND ‘running’ OR ‘sprinting’. Based on inclusion criteria, 18 articles were selected for review. While sEMG is widely used in biomechanics, relatively few studies have used sEMG in sprinting due to system constraints. The results demonstrated a focus on the leg muscles, with over 70% of the muscles analysed in the upper leg. This is consistent with the use of tethered and data logging EMG systems and many sprints being performed on treadmills. Through the recent advances in wireless EMG technology, an increase in the studies on high velocity movements such as sprinting is expected and this should allow practitioners to perform the analysis in an ecologically valid environment.     

Comparison of Muscle Patterning in the Overarm Throw and Tennis Serve

The muscular patterning of three skilled throwers who were less skilled servers, three skilled servers who were less skilled throwers, and three individuals skilled in both sport skills, was studied by means of electromyography and tri-plane cinematography during performances of the throw and serve. Surface electrodes were used to record electrical activity from two trunk, four shoulder girdle, and four shoulder joint muscles. Regardless of skill level, the nine female subjects used common joint and segment movements and employed, with minor exceptions, the same number of muscles during late preparatory and force production phases in the two skills. However, for the two skills, there were differences in the duration during which the muscles were active. The serve took longer to perform and involved a different sequential coordination of muscular activity than did the throw. Differences in muscle patterning between the two skills were greater during the force production phase in individuals judged to be skilled in both sport skills. The temporal differences between the two overarm skills suggested that, if performers can perceive time differences between 200 to 800 mseconds, then reference to or practice in the throw may not be a good method to gain expertise in the serve.     

Effect of skill decomposition on racket and ball kinematics of the elite junior tennis serve

Whole body kinematics of the tennis serve have been reported extensively in the literature, yet comparatively less information exists regarding the kinematic characteristics of the swing and toss. In attempting to develop consistency in placement of the toss and racket trajectory, coaches will often decompose the serve and practice it in separate parts. A 22-camera VICON MX motion analysis system, operating at 250 Hz, captured racket, ball and hand kinematics of the serves of five elite junior players under three conditions. The conditions were flat first serves (FS) directed to a 1 x 1 m target bordering the 'T' of the deuce service box, a ball toss (BT) in isolation and a free swing (SW) in isolation. Players were instructed to perform BT and SW as in the FS. Paired t-tests assessed within-group differences in hand, racket and ball kinematics between the discrete skill and the two decomposed conditions. Vertical displacement of the ball at its zenith increased significantly during BT compared with the FS and temporal associations between racket and ball motion during the FS (r = 0.861) were affected during task decomposition. This study questions the pervasive use of task decomposition in the development of the tennis serve.     

网球发球技术的生物力学分析

采用高速立体摄像和现场调研等方法,对我国男,女网球选手的发球技术进行了分析,从生物力学角度对抛球,击球动作技术冯及动作节奏问题的本质做了探讨,认为抛球高度落差过大是造成球爆发用力动作不连贯的主要根源;提高发球重点是要发挥躯干力量,就采用螺旋式向上用力技术,上技心地球折有最后加速功能,但更重要的是控制用力方向和球的落点;新、旧发球技术在用力节奏上有着本质性区别,新的发球动作节奏更符合动作作目的和人体     

Comparing the pre- and post-impact ball and racquet kinematics of elite tennis players' first and second serves: a preliminary study

The aim of this study was to compare the pre- and post-impact three-dimensional kinematics of the ball and racquet during first and second serves performed by elite tennis players. Data were collected from four male and four female right-handed professional players during competition using two high-speed cameras (200 Hz). For each player, one first serve and one second serve from the 'deuce' or right service court that landed within the specified target area were analysed. To test for significant differences between the first and second serves, Wilcoxon tests (P < or = 0.05) were performed on selected parameters. The results indicate that the ball travelled forward and to the left during the flight phase of the toss in all but one trial. The average pre-impact ball forward location for the first serve was significantly more in front and had a higher associated forward ball velocity than the corresponding values for the second serve. On average, the decrease in post-impact ball speed from the first to the second serve was 24.1%. No significant differences between the first and second serves were found in the pre-impact racquet head speed and orientation, which was represented as a unit vector perpendicular to the racquet face. The major adjustments made by the players when going from the first to second serve were a decrease in pre-impact ball forward location (P < or = 0.01) and an increase in the pre-impact racquet vertical and lateral velocities (both P < or = 0.05). This implies that the players tossed the ball closer to the body and imparted topspin and sidespin on the ball by changing the racquet vertical and lateral velocities when going from the first to the second serve.     

Effect of skill decomposition on racket and ball kinematics of the elite junior tennis serve

Whole body kinematics of the tennis serve have been reported extensively in the literature, yet comparatively less information exists regarding the kinematic characteristics of the swing and toss. In attempting to develop consistency in placement of the toss and racket trajectory, coaches will often decompose the serve and practice it in separate parts. A 22-camera VICON MX motion analysis system, operating at 250 Hz, captured racket, ball and hand kinematics of the serves of five elite junior players under three conditions. The conditions were flat first serves (FS) directed to a 1 × 1 m target bordering the ‘T’ of the deuce service box, a ball toss (BT) in isolation and a free swing (SW) in isolation. Players were instructed to perform BT and SW as in the FS. Paired t-tests assessed within-group differences in hand, racket and ball kinematics between the discrete skill and the two decomposed conditions. Vertical displacement of the ball at its zenith increased significantly during BT compared with the FS and temporal associations between racket and ball motion during the FS (r = 0.861) were affected during task decomposition. This study questions the pervasive use of task decomposition in the development of the tennis serve.