A computational method for analysis of underwater dolphin kick hydrodynamics in human swimming

We present a new method that combines the use of laser body scans, underwater video footage, software-based animation, and a fully unsteady computational fluid dynamics technique to simulate and examine the hydrodynamics of the dolphin kick. The focus of the current work is to model this particular stroke in all its complexity with minimal ad-hoc assumptions or simplifications. Simulations of one female and one male swimmer (both at about 1.7 m beneath the water surface) at velocities of 0.95 and 1.31 m/s and Strouhal numbers of 1.21 and 1.06 respectively are presented. Vorticity and fluid velocity profiles in the wake are examined in detail for both swimmers. A three-dimensional vortex ring is clearly identified in the wake for one of the cases and a two-dimensional slice through the ring corroborates previous experiments of Miwa et al. (2006). We also find that most of the thrust is produced by the feet and in both cases the down-kick produces much larger thrust than the up-kick.     

竞赛速度条件下游泳体位与打腿技术的变化趋势与评价

应用阻力与速度的平方成正比定律[1][2],审视在竞赛速度条件下游泳体位与打腿配合技术。认为身体水中姿态与打腿技术的合理性与否在于通过技术动作所产生的推进阻力纯值的大小来给予评价。以此为依据,提出在竞赛条件下,游泳体位姿态与打腿配合技术相关的两种新技术观点:对水中人体姿态流线型的新诠释;快频率、小幅度打腿技术在竞赛速度条件下对水中游泳体位的影响。     

The effect of leg kick on sprint front crawl swimming

Abstract

The aim of this study was to examine the influence of leg kick on the pattern, the orientation and the propulsive forces produced by the hand, the efficiency of the arm stroke, the trunk inclination, the inter-arm coordination and the intra-cyclic horizontal velocity variation of the hip in sprint front crawl swimming. Nine female swimmers swam two maximal trials of 25 m front crawl, with and without leg kick. Four camcorders were used to record the underwater movements. Using the legs, the mean swimming velocity increased significantly. On the contrary, the velocity and the orientation of the hand, the magnitude and the direction of the propulsive forces, as well as the Froude efficiency of the arm stroke were not modified. The hip intra-cyclic horizontal velocity variation was also not changed, while the index of coordination decreased significantly. A significant decrease (13%) was also observed in the inclination of the trunk. Thus, the positive effect of leg kick on the swimming speed, besides the obvious direct generation of propulsive forces from the legs, could probably be attributed to the reduction of the body’s inclination, while the generation of the propulsive forces and the efficiency of the arm stroke seem not to be significantly affected.     

Determination of a quantitative parameter to evaluate swimming technique based on the maximal tethered swimming test

The aim of this study was to propose a new force parameter, associated with swimmers’ technique and performance. Twelve swimmers performed five repetitions of 25 m sprint crawl and a tethered swimming test with maximal effort. The parameters calculated were: the mean swimming velocity for crawl sprint, the mean propulsive force of the tethered swimming test as well as an oscillation parameter calculated from force fluctuation. The oscillation parameter evaluates the force variation around the mean force during the tethered test as a measure of swimming technique. Two parameters showed significant correlations with swimming velocity: the mean force during the tethered swimming (r = 0.85) and the product of the mean force square root and the oscillation (r = 0.86). However, the intercept coefficient was significantly different from zero only for the mean force, suggesting that although the correlation coefficient of the parameters was similar, part of the mean velocity magnitude that was not associated with the mean force was associated with the product of the mean force square root and the oscillation. Thus, force fluctuation during tethered swimming can be used as a quantitative index of swimmers’ technique.     

Wearable inertial sensors in swimming motion analysis: a systematic review

The use of contemporary technology is widely recognised as a key tool for enhancing competitive performance in swimming. Video analysis is traditionally used by coaches to acquire reliable biomechanical data about swimming performance; however, this approach requires a huge computational effort, thus introducing a delay in providing quantitative information. Inertial and magnetic sensors, including accelerometers, gyroscopes and magnetometers, have been recently introduced to assess the biomechanics of swimming performance. Research in this field has attracted a great deal of interest in the last decade due to the gradual improvement of the performance of sensors and the decreasing cost of miniaturised wearable devices. With the aim of describing the state of the art of current developments in this area, a systematic review of the existing methods was performed using the following databases: PubMed, ISI Web of Knowledge, IEEE Xplore, Google Scholar, Scopus and Science Direct. Twenty-seven articles published in indexed journals and conference proceedings, focusing on the biomechanical analysis of swimming by means of inertial sensors were reviewed. The articles were categorised according to sensor’s specification, anatomical sites where the sensors were attached, experimental design and applications for the analysis of swimming performance. Results indicate that inertial sensors are reliable tools for swimming biomechanical analyses.     

跆拳道横踢动作的运动学分析

探讨了横踢动作的力学原理，就如何提高檄竭速度进行了分析。结论是：各关节速度曲线中，髋关节速度较小并且变化不大；膝关节、踝关节和脚尖的速度曲线变化明显；膝关节较早达到速度峰值，然后3dL速，接着在场中目标瞬间踝和脚尖几乎同时达到速度最大住。     

Measurement of three-dimensional hand kinematics during swimming with a motion capture system: a feasibility study

Current trends in swimming biomechanics are focused on accurate measurements. Nowadays, reliable calibration methods have been proposed to reach an accuracy of about 1 mm on rigid structure. But the question remains about the final accuracy for three-dimensional hand kinematics measurement during the underwater phase of front crawl swimming. Furthermore, most research is based on manual tracking with two or more cameras. In this paper we propose a protocol to acquire three-dimensional hand kinematics when swimming in a specific pool with a motion analysis system behind windows. Results highlight the benefits of using such a system in terms of accuracy and feasibility: the time allowed for post-processing is ten times lower and the quantified improved accuracy is better than with manual tracking.     

跆拳道跳踢动作中起跳技术运动学研究

起跳技术是跆拳道运动员获得腾空高度的关键。利用运动学方法对起跳技术的下蹲和蹬离两个阶段的技术动作以及起跳技术的影响因素进行运动力学分析;对起跳技术的运动学参数进行了解析,结果显示：体重、蹬离角、蹬离垂直起跳时间、地面垂直作用力和髋、膝、踝三关节的控制和柔韧性等因素对跆拳道起跳技术有显著影响。最后,给出了提高跆拳道运动员起跳技术质量的几点建议。     

花样游泳自由自选技术编排的发展趋势

对近4年花样游泳国际三大赛事中,集体和双人前6名自由自选项目的技术编排情况进行了研究。结果显示：配合类技术的难度、推进技术和上肢动作配合技术发展是当前集体自由自选技术编排最显著的趋势;花样动作技术难度在集体自由自选技术编排中有下降现象,单纯依赖高难度花样动作表现技术能力不是当前集体自由自选技术编排的主流;双人项目的推进、移动技术和上肢动作配合技术成为难度发展的重点方向,花样技术内容多样性及难度技术的采用情况双人较集体自由自选要好。     

A theoretical and experimental analysis of diver technique in underwater fin swimming

This research was theoretical and experimental, with an objective of a better understanding of the physics of fin swimming. The theoretical work followed Lighthill’s slender body theory (1960). Video measurements were made on underwater fin swimmers swimming in an annular pool (58.6 m in circumference). This study considers only SCUBA divers. Five male swimmers swam at five speeds between 0.4 m/s-0.8 m/s. Skilled divers consumed less oxygen and had lower kick frequencies at each speed. The skilled divers adhered to the requirements of the theory, but not the unskilled. Specifically, the fin’s trailing edge (TE) lateral velocity was greater than the relative velocity of the water at the TE (requirement 1); which is the most forgiving. The second requirement is more stringent, and requires the TE lateral velocity and the relative velocity of the water at the TE to be of the same sign. Violating the first requirement sometimes causes a change in the instantaneous thrust’s direction. Violating the second requirement almost always produced instantaneous thrust in the opposite direction than the diver’s desired swimming direction. This study found that the Lighthill model can be used to describe diver fin swimming, which was optimised when the diver met the two requirements required for efficient thrust.     

世界花样游泳集体自由自选造型变化趋势

为了探索世界花样游泳造型变化的趋势,对2007年十二届世锦赛,2006年第六届世界杯,2005年十一届世锦赛和2004年第28届奥运会花样游泳比赛集体自由自选前六名队伍的造型变化进行统计分析。结果显示：造型数量增加,变化速度加快,密度难度加大;托举的类型增加、层次增多,出水的人数增多,出水位置高,成型时间短,动作惊险、多变。中国队托举与立体造型进步明显,而密集编队、盲点编队、倒立移动编队等体现编队难度的指标与世界前三名队伍相比有一定的差距。     

舞蹈式柔韧训练对提升青少年花样游泳运动员动作表现的影响研究

研究目的:运动员青少年时期的柔韧素质发展是成年后提高运动成绩的关键因素之一。本文通过舞蹈式柔韧训练对提高动作表现影响的实验研究,为花样游泳的陆上训练提供实践方法和理论依据。研究方法:选取广州市花样游泳队20名9-12岁运动员,分实验组10人、对照组10人。实验组进行为期4个月的舞蹈式柔初训练干预,对照组开展一般柔初训练。干预前后分别对两组的四个动作指标进行测试评价,数据采用SPSS分析系统进行T检验,组内纵向比较,组间横向比较。研究结果:实验组经过舞蹈式柔初训练干预后,指标数据呈明显变化趋势,显著性优于对照组(P<0.01)。在竖高叉、横高叉、前腿踢搬、紫金冠四个动作的表现中,实验组比对照组的动作提升幅度大。研究结论:经过舞蹈式柔軔训练教学干预后,柔韧动作干预的实验组各指标显著高于对照组。训练能够显著提升运动员的比赛动作表现能力。广州市花样游泳队夺得2016年鄂尔多斯全国青少年花样游泳锦标赛陆上柔初操项目第一名,优异的成绩与4个月的舞蹈式柔初训练有着紧密联系。     

游泳抓台式出发技术的运动学特征研究

采用高速摄影方法,对12名男性大学生游泳运动员的游泳抓台式出发技术进行了运动学分析,揭示了抓台式出发技术的预备姿势、离台技术、重心移动以及入水技术的运动特征,为今后游泳抓台式出发技术的训练提供了有关参数。     

Kinematic analysis of the double side kick in pointfighting,kickboxing

The double side kick is a frequently used technique in pointfighting on which most offensive kicking techniques are based on. The aim of the study was to identify parameters, e.g., trunk and leg positions, durations and velocities that affect successful technique execution.

44 fighters, male and female, including European and World champions, participated in the research. The participants performed double side kicks to a punching bag with the target at chest level. 10 international experts scored (1–10 points; interrater correlation ICC (3,1): 0.952) videos of the best individual trial for quality of technique execution. Based on the average of the scores participants were categorised into 2 equally sized groups. For kinematic data acquisition, a Vicon 3D-motion capturing system was used. The normalised knee height of the kick leg (KHK), normalised absolute distance to the frontal shoulder (DKS) at the end of both chambering phases, the horizontal velocity during both chambering phases (KEV), the durations of all 6 functional phases and total duration, were analysed.

KHK1, KHK2, DKS1 and DKS2, total duration as well as 4 out of 6 phase durations and KEV1 showed significant differences between groups in two-sided t-test or Mann–Whitney U-test for not normally distributed variables.     

Motion analysis of front crawl swimming applying CAST technique by means of automatic tracking

Abstract

Kinematic analysis of swimming is of interest to improve swimming performances. Although the video recordings of underwater swimmers are commonly used, the available methodologies are rarely precise enough to adequately estimate the three dimensional (3D) joint kinematics. This is mainly due to difficulties in obtaining the required kinematic parameters (anatomical landmarks, joint centres and reference frames) in the swimming environment. In this paper we propose a procedure to investigate the right upper limb’s 3D kinematics during front crawl swimming in terms of all elbow and shoulder degrees of freedom (three rotations of the shoulder, two of the elbow). The method is based upon the Calibrated Anatomical Systems Technique (CAST), a technique widely used in clinics, which allows estimation of anatomical landmarks of interest even when they are not directly visible. An automatic tracking technique was adopted. The intra-operator repeatability of the manual tracking was also assessed. The root mean squared difference of three anatomical landmarks, processed five times, is always lower than 8 mm. The mean of the root mean squared difference between trajectories obtained with the different methodologies was found to be lower than 20 mm. Results showed that complete 3D kinematics of at least twice as many frames than without CAST can be reconstructed faster and more precisely.     

Development of a markerless optical motion capture system for daily use of training in swimming

The main objective of this research was to develop a markerless optical motion capture system that can be used for daily use in swimming training. The butterfly stroke was targeted since it is considered bilaterally symmetric in motion. The system consisted of a segmentation process to obtain the participant’s silhouettes and a matching process to estimate the pose of the participant. A variable thresholding method was used to extract the silhouettes to solve non-uniform illumination in the recorded swimming video. Prior to the matching process, the human body was modeled as a series of nine segments to help the matching process. The model was then mapped so that it aligned with the silhouettes, which were investigated by similarity of intensity value. To minimize the degree of freedom in image matching, the available joint motion in the swimming human simulation model was used as a priori information for kinematics data of the swimming motion. As a result, the rotation angle’s correlation coefficients between the references and result of the matching process were around 0.95 for trunk, thigh, shank, upper arm, forearm, hand and 0.78 for head, hip and foot. The rotation angle and the velocity of the center of mass were put into the swimming human simulation model for a dynamics analysis. The simulation results show that the velocity obtained in the experiment corresponded to the fluid force exerted on the lower and upper limbs. Consequently, the proposed system of obtaining the joint motion of the butterfly stroke is suitable for daily training and coaching.     

The effect of vibration on active and passive range of motion in elite female synchronized swimmers

Abstract

The purpose of this study was to assess the acute effects of vibration and stretching on passive and active forward split range of motion in elite adult female synchronized swimmers. Eleven athletes performed a passive forward split test measuring the height of the anterior superior iliac spine on both sides and an active split test on both sides by adopting an inverted split position. Then athletes were assigned randomly by right or left leg to receive vibration on one leg while stretching. The contralateral leg was stretched but did not receive vibration and served as the control. The treatment involved a 40-s exposure to vibration of the forward leg in a split and 40 s of vibration to the rear leg in a split. The athletes were then post-tested using the same protocols. The results indicated that the vibration had a statistically significant influence on passive forward split flexibility, but not active split flexibility. The results of this study confirm earlier work and further demonstrate the efficacy of vibration in enhancing range of motion in a passive split position. Given that it is often difficult to achieve large changes in range of motion with already highly trained elite athletes, this methodology shows considerable promise. Vibration may not be powerful enough to evoke changes in active range of motion in spite of the changes in passive range of motion.     

Assessment of planarity of the golf swing based on the functional swing plane of the clubhead and motion planes of the body points

The purposes of this study were (1) to determine the functional swing plane (FSP) of the clubhead and the motion planes (MPs) of the shoulder/arm points and (2) to assess planarity of the golf swing based on the FSP and the MPs. The swing motions of 14 male skilled golfers (mean handicap = -0.5 +/- 2.0) using three different clubs (driver, 5-iron, and pitching wedge) were captured by an optical motion capture system (250Hz). The FSP and MPs along with their slope/relative inclination and direction/direction of inclination were obtained using a new trajectory-plane fitting method. The slope and direction of the FSP revealed a significant club effect (p < 0.001). The relative inclination and direction of inclination of the MP showed significant point (p < 0.001) and club (p < 0.001) effects and interaction (p < 0.001). Maximum deviations of the points from the FSP revealed a significant point effect (p < 0.001) and point-club interaction (p < 0.001). It was concluded that skilled golfers exhibited well-defined and consistent FSP and MPs, and the shoulder/arm points moved on vastly different MPs and exhibited large deviations from the FSP. Skilled golfers in general exhibited semi-planar downswings with two distinct phases: a transition phase and a planar execution phase.     

宁波大学游泳教学的现状调查与分析

游泳教学是体育教学的重要组成部分,是提高身体素质的一个有效手段。通过对我校98 级学生的问卷调查与分析,发现:由于种种原因学生掌握游泳技术的合格率极低,难以完成学校提出的任务。对此,从影响掌握游泳技术的因素着手,分析原因,提出措施与对策。     

对高校速度滑冰弯道滑行技术教学要点的探讨

速度滑冰是北方高等院校冬季教学的重点项目，弯道教学是速度滑冰教学的难点。通过观察、理论分析和实验得出弯道教学的8个技术教学要点，旨在为高等院校冬季教学突破弯道教学难点提供理论依据。