Kinematic differences of elite and high-performance tennis players in the cross court and down the line forehand     

Johannes Landlinger  Stefan Josef Lindinger  Thomas Stöggl  Herbert Wagner  Erich Müller 《Sports biomechanics / International Society of Biomechanics in Sports》2013,12(4):280-295

This study identified and compared the full body kinematics of different skill levels in the forehand groundstroke when balls were hit cross court and down the line. Forty-three three-dimensional retro-reflective marker trajectories of six elite and seven high-performance players were recorded using an eight-camera 400 Hz, Vicon motion analysis system. The six highest horizontal velocity forehands with reliable kinematics of all participants were analysed for each specific situation (a total of 156 analysed shots). Significant differences (p < 0.01) and large effect sizes were observed between elite and high-performance players in linear velocity of the shoulder (2.0 vs. 1.2 m/s), angular velocity of the pelvis (295 vs. 168 °/s), and angular velocity of the upper trunk (453 vs. 292 °/s) at impact. The elite group showed a tendency towards higher racquet velocities at impact (p < 0.05). No significant differences were found in angular displacement of the racquet, hip alignment, or shoulder alignment at the completion of the backswing; nor did angular displacement vary significantly at impact. Irrespective of the group, different shoulder, hip, and racquet angles were found at impact, depending on the situation. The results should assist coaches when striving to improve their players' forehand.  相似文献   

List of Reviewers     

Coral Falco  Javier Molina-García  Octavio Álvarez  Isaac Estevan 《Sports biomechanics / International Society of Biomechanics in Sports》2013,12(4):381-382

The aim of this study was to investigate the effects of target distance on temporal and impact force parameters that are important performance factors in taekwondo kicks. Forty-nine taekwondo athletes (age = 24.5 ± 5.9 years; mass = 79.9 ± 10.8 kg) were recruited: 13 male experts, 21 male novices, 8 female experts, and 6 female novices. Impact force, reaction time, and execution time were computed. Three-way repeated measure ANOVAs revealed significant ‘distance’ effect on impact force, reaction time, and execution time (p = 0.001). Comparisons between distance conditions revealed that taekwondo athletes kicked with higher impact force from short distance (17.6 ± 7.5 N/kg) than from long distance (13.1 ± 5.7 N/kg) (p < 0.001), had lower reaction time from short distance (498 ± 90 ms) and normal distance (521 ± 111 ms) than from long distance (602 ± 121 ms) (p < 0.001), and had lower execution time from short distance (261 ± 69 ms/m) than from normal distance (306 ± 105 ms/m) or from long distance (350 ± 106 ms/m) (p = 0.003 and p < 0.001, respectively). In conclusion, target distance affected the kick performance; as distance increases, impact force decreased and reaction time increased. Therefore, when reaction to a simple visual stimulus is needed, kicking from a long distance is not recommended, as longer time is required to respond.  相似文献   

Statistical modelling of knee valgus during a continuous jump test     

Y. Nagano  M. Sakagami  H. Ida  M. Akai  T. Fukubayashi 《Sports biomechanics / International Society of Biomechanics in Sports》2013,12(3):342-350

Landing with the knee in a valgus position is recognized as a risk factor for anterior cruciate ligament (ACL) injury. Using linear and non-linear regression analyses, the purpose of this study was to examine the correlation between two-dimensional (2D) knee valgus and three-dimensional (3D) knee kinematics measured during a jump landing task. Twenty-eight female collegiate athletes participated. All participants were required to perform a continuous jump test. The average maximum angles of abduction and internal tibial rotation during landing were measured using the Point Cluster Technique. Average peak knee valgus angle was measured using a 2D approach. Linear and non-linear regression analyses between 2D valgus and 3D knee abduction, and between 2D valgus and 3D internal tibial rotation, were performed. The R ² value between 2D valgus and 3D knee abduction was significantly different from zero and had a moderate correlation for all models, whereas the R ² value between 2D valgus and 3D internal tibial rotation was not significantly different from zero. The 2D approach could be used to screen a specific group of individuals for risk of ACL injury; however, using frontal plane 2D analysis of valgus motion to evaluate internal tibial rotation is not advised.  相似文献   

Biomechanics of the ski cross start indoors on a customised training ramp and outdoors on snow     

Niels Jensby Nedergaard  Frederik Heinen  Simon Sloth  Hans-Christer Holmberg 《Sports biomechanics / International Society of Biomechanics in Sports》2013,12(3):273-286

An effective start enhances an athlete's chances of success in ski cross competitions. Accordingly, this study was designed to investigate the biomechanics of start techniques used by elite athletes and assess the influence of different start environments. Seven elite ski cross athletes performed starts indoors on a custom-built ramp; six of these also performed starts on an outdoor slope. Horizontal and vertical forces were measured by force transducers located in the handles of the start gate and a 12-camera motion capture system allowed monitoring of the sagittal knee, hip, shoulder, and elbow kinematics. The starting movement involved Pre, Pull, and Push phases. Significant differences between body sides were observed for peak vertical and resultant forces, resultant impulse, and peak angular velocity of the shoulder joint. Significantly lower peak vertical forces (44 N), higher resultant impulse (0.114 Ns/kg), and knee joint range of motion (12°) were observed indoors. Although movement in the ski cross start is generally symmetrical, asymmetric patterns of force were observed among the athletes. Two different movement strategies, i.e. pronounced hip extension or more accentuated elbow flexion, were utilised in the Pull phase. The patterns of force and movement during the indoor and outdoor starts were similar.  相似文献   

Shoulder 3D range of motion and humerus rotation in two volleyball spike techniques: injury prevention and performance     

Elena Seminati  Alessandra Marzari  Oreste Vacondio  Alberto E. Minetti 《Sports biomechanics / International Society of Biomechanics in Sports》2013,12(2):216-231

Repetitive stresses and movements on the shoulder in the volleyball spike expose this joint to overuse injuries, bringing athletes to a career threatening injury. Assuming that specific spike techniques play an important role in injury risk, we compared the kinematic of the traditional (TT) and the alternative (AT) techniques in 21 elite athletes, evaluating their safety with respect to performance. Glenohumeral joint was set as the centre of an imaginary sphere, intersected by the distal end of the humerus at different angles. Shoulder range of motion and angular velocities were calculated and compared to the joint limits. Ball speed and jump height were also assessed. Results indicated the trajectory of the humerus to be different for the TT, with maximal flexion of the shoulder reduced by 10 degrees, and horizontal abduction 15 degrees higher. No difference was found for external rotation angles, while axial rotation velocities were significantly higher in AT, with a 5% higher ball speed. Results suggest AT as a potential preventive solution to shoulder chronic pathologies, reducing shoulder flexion during spiking. The proposed method allows visualisation of risks associated with different overhead manoeuvres, by depicting humerus angles and velocities with respect to joint limits in the same 3D space.  相似文献   

Effect of the coefficient of friction of a running surface on sprint time in a sled-towing exercise     

Nicholas P. Linthorne  James E. Cooper 《Sports biomechanics / International Society of Biomechanics in Sports》2013,12(2):175-185

This study investigated the effect of the coefficient of friction of a running surface on an athlete's sprint time in a sled-towing exercise. The coefficients of friction of four common sports surfaces (a synthetic athletics track, a natural grass rugby pitch, a 3G football pitch, and an artificial grass hockey pitch) were determined from the force required to tow a weighted sled across the surface. Timing gates were then used to measure the 30-m sprint time for six rugby players when towing a sled of varied weight across the surfaces. There were substantial differences between the coefficients of friction for the four surfaces (μ = 0.21–0.58), and in the sled-towing exercise the athlete's 30-m sprint time increased linearly with increasing sled weight. The hockey pitch (which had the lowest coefficient of friction) produced a substantially lower rate of increase in 30-m sprint time, but there were no significant differences between the other surfaces. The results indicate that although an athlete's sprint time in a sled-towing exercise is affected by the coefficient of friction of the surface, the relationship relationship between the athlete's rate of increase in 30-m sprint time and the coefficient of friction is more complex than expected.  相似文献   

中外男子掷标枪最后用力效果的对比分析     

沈小燕  郑志磊 《山西广播电视大学学报》2007,12(6):56-57

采用文献资料法、对比分析法,对影响中外优秀男子掷标枪运动员最后用力效果部分运动学技术指标——挥臂用力因子、左膝关节蹬伸因子和人体向前运动因子进行对比分析。希望我国教练员从中得到启发,促进我国男子标枪水平的提高。  相似文献   

差分粒子群算法在PUMA机器人逆运动学求解中的应用     

汪院林  袁锐波  袁安华 《教育技术导刊》2020,19(4):203-207

传统逆运动学求解主要从逆运动学方程出发,基于一定的数学理论推导,不能完全实现计算机程序化,且精度与计算效率较低;为改善这一缺陷,基于机器人正向运动学方程,借助MATLAB工具,使用蒙特卡洛法仿真分析出PUMA560机器人的工作空间,任取一点末端执行器位姿作为逆运动学求解的已知位姿矩阵T,结合差分粒子群仿生智能算法作为逆运动学求解的主要理论算法。将计算出的旋转关节变量[θ1~θ6]代入正运动学方程,得出末端位姿矩阵[T];通过计算分析T与[T]相关角度误差,两矩阵所对应的位置向量与姿态向量误差精度为0.001数量级,完全满足目前机器人定位要求。基于差分粒子群理论的机器人逆运动学求解方法计算收敛速度更快,能高度实现计算机程序化,误差精度高,提高计算效率。  相似文献   

Graphonomics,automaticity and handwriting assessment     

Oliver Tucha  Lara Tucha  Klaus W. Lange 《Literacy》2008,42(3):145-155

A recent review of handwriting research in Literacy concluded that current curricula of handwriting education focus too much on writing style and neatness and neglect the aspect of handwriting automaticity. This conclusion is supported by evidence in the field of graphonomic research, where a range of experiments have been used to investigate this issue from a movement perspective. The present article offers a brief introduction to a graphonomic approach to handwriting analysis and the findings of graphonomic research about handwriting automaticity. These findings indicate that attentional control to any characteristic of the writing process (e.g. direction, lexical status, movement, style) results in an impairment of handwriting automaticity. These findings support and add a new dimension to previous conclusions.  相似文献   

Shorter Method for Computing the Coefficient of Correlation     

《The Journal of educational research》2012,105(3):216-221

ABSTRACT

Handwriting is used throughout the school day and is important to demonstrate knowledge. This research evaluated how handwriting instructional practices and intrinsic and extrinsic factors in actual classroom settings impacted learning handwriting over the course of the school year. Findings indicated that extrinsic factors (educational instructional practices, spatial constraints) and intrinsic factors (task cognitive complexity) influenced handwriting performance, but not always in the same way for writing product and process measures. In addition, stronger relationships were found between writing process measures and handwriting fluency than legibility. Even though handwriting improved over the school year, some instructional practices resulted in a widening performance gap as the school year progressed. The impact of these findings for implementing and differentiating handwriting instruction and guiding future research is discussed.  相似文献