Flight dynamics of the screw kick in rugby

This paper describes the aerodynamic forces and the flight trajectory for the screw (spiral) kick in rugby. The screw kick is defined as that which causes the ball to spin on its longitudinal axis. The aerodynamic forces acting on a rugby ball spinning on its longitudinal axis were measured in a wind tunnel using a six-component strut type balance. It was found that the drag, the lift and the pitching moment depend on the angle of attack, while the side force (Magnus force) depends on both the spin rate and the angle of attack in the range where the wind speed lies between 15 and 30 m s^-1 and the spin rate is between 1 and 10 revolutions per second. Moreover, the flight trajectory was obtained by integrating the full nonlinear six degrees of freedom equations of motion on the basis of aerodynamic data. In a simulation, a ball spinning on its longitudinal axis tended to hook toward or away from the touchline even if the velocity and angular velocity vectors were parallel to the touchline. The direction of the hook depends on the direction of the angular velocity vector. The initial direction of the hook depends on the relationship between the flight path angle and the pitch angle as well as the direction of the angular velocity vector.     

Assessing rugby place kick performance from initial ball flight kinematics: development,validation and application of a new measure

The appropriate determination of performance outcome is critical when appraising a performer’s technique. Previous studies of rugby place kicking technique have typically assessed performance based on ball velocity, but this is not the sole requirement. Therefore, a mathematical model of rugby place kick ball flight was developed to yield a single measure more representative of true performance. The model, which requires only initial ball flight kinematics, was calibrated and validated using empirical place kick data, and found to predict ball position with a mean error of 4.0% after 22 m of ball flight. The model was then applied to the performances of 33 place kickers. The predicted maximum distance, a single performance measure which accounted for initial ball velocity magnitude and direction, and spin, was determined using the model and was compared against ball velocity magnitude. A moderate association in the rank-order of the kicks between these two measures (ρ = 0.52) revealed that the relative success of the kicks would be assessed differently with each measure. The developed model provides a representative measure of place kick performance that is understandable for coaches, and can be used to predict changes in performance outcome under different ball launch or environmental conditions.     

Scaling the cricket pitch to fit junior players

ABSTRACT

Studies in several sports have shown the benefits of adapting the playing environment to fit junior players. Frequently the changes are pragmatic choices based on space constraints or existing line markings, or the result of simple scaling based on stature. In this study, a method of scaling the cricket pitch length is presented which is based on the age-specific size and performance of the bowlers and batters. The objective was a pitch length which enabled young bowlers to bowl good length deliveries while releasing the ball at a more downward angle, similar to elite bowlers. The steeper release angle has the benefit of reducing the sensitivity of the ball flight distance to the variability of ball release. Based on data from county standard under-10 and under-11 players a pitch length of 16.22 yards (14.83 m) was calculated, 19% shorter than previously recommended for under-11s in England. A shorter pitch also increases the temporal challenge for batters, encouraging a wider variety of shots and improved anticipation skills. Pitch lengths scaled in this way to fit the players’ abilities as they develop will enable a more consistent ball release by bowlers and more consistent temporal demand for batters.     

Ground reaction forces and kinematics of plant leg position during instep kicking in male and female collegiate soccer players

The players' ability to achieve the greatest distance in kicking is determined by their efficiency in transferring kinetic energy from the body to the ball. The purpose of this study was to compare the kinetics and kinematics of the plant leg position between male and female collegiate soccer players during instep kicking. Twenty-three soccer players (11 males and 12 females) were filmed in both the sagittal and posterior views while performing a maximal instep kick. Plant leg kinetic data were also collected using an AMTI 1000 force platform. There were no significant differences between the sexes in plant leg position, but females had significantly greater trunk lean, plant leg angle, and medial-lateral ground reaction force than the males. Males showed higher vertical ground reaction forces at ball contact, but there were no significant differences in ball speed at take-off between the sexes. Ball speed at take-off was inversely related to peak anterior-posterior ground reaction force (-0.65). The anatomical differences between the sexes were reflected in greater trunk lean and lower leg angle in the females.     

Ground reaction forces and kinematics of plant leg position during instep kicking in male and female collegiate soccer players

The players' ability to achieve the greatest distance in kicking is determined by their efficiency in transferring kinetic energy from the body to the ball. The purpose of this study was to compare the kinetics and kinematics of the plant leg position between male and female collegiate soccer players during instep kicking. Twenty-three soccer players (11 males and 12 females) were filmed in both the sagittal and posterior views while performing a maximal instep kick. Plant leg kinetic data were also collected using an AMTI 1000 force platform. There were no significant differences between the sexes in plant leg position, but females had significantly greater trunk lean, plant leg angle, and medial-lateral ground reaction force than the males. Males showed higher vertical ground reaction forces at ball contact, but there were no significant differences in ball speed at take-off between the sexes. Ball speed at take-off was inversely related to peak anterior–posterior ground reaction force ( ? 0.65). The anatomical differences between the sexes were reflected in greater trunk lean and lower leg angle in the females.     

Early visual cues associated with a directional place kick in soccer

The purpose of this paper was to establish postural cues in kicking that may be of use to goalkeepers. Eight male soccer players (age 20.5 +/- 1.1 yrs; height 1.78 +/- 0.053 m; mass 75.18 +/- 9.66 kg) performed three types of kick: a low side-foot kick to the left hand corner of the goal, a low side-foot kick straight ahead, and a low instep kick straight ahead. Kicks were recorded by an optoelectronic motion analysis system at 240 Hz. At kicking foot take-off (about 200 ms before ball contact) the variables which were significantly different and could act as cues were support foot progression angle, pelvis rotation, and kicking hip and ankle flexion. The support foot progression angle was considered to be the most valuable of these variables as its angle coincided with the direction of ball projection. The other variables were less clear in their interpretation and so less valuable for a goalkeeper to use for decision making. Cues appearing after support foot contact were thought unlikely to be of value to a goalkeeper in their decision making. These include kicking leg knee flexion angle, and support leg shank and thigh angles.     

标枪飞行轨迹的计算机仿真及实际应用

研究采用风洞实验和计算机仿真的方法，计算标枪在三维空间的飞行轨迹，对影响标枪飞行远度的各种因素，如出手速度、出手角度、初始攻角、初始俯仰角速度、初始偏航角等进行了定量分析，本文还根据标枪运动员投掷的实际情况提出了女子标枪运动员的最佳初始条件组合。     

Early visual cues associated with a directional place kick in soccer

The purpose of this paper was to establish postural cues in kicking that may be of use to goalkeepers. Eight male soccer players (age 20.5 ± 1.1 yrs; height 1.78 ± 0.053 m; mass 75.18 ± 9.66 kg) performed three types of kick: a low side-foot kick to the left hand corner of the goal, a low side-foot kick straight ahead, and a low instep kick straight ahead. Kicks were recorded by an optoelectronic motion analysis system at 240 Hz. At kicking foot take-off (about 200 ms before ball contact) the variables which were significantly different and could act as cues were support foot progression angle, pelvis rotation, and kicking hip and ankle flexion. The support foot progression angle was considered to be the most valuable of these variables as its angle coincided with the direction of ball projection. The other variables were less clear in their interpretation and so less valuable for a goalkeeper to use for decision making. Cues appearing after support foot contact were thought unlikely to be of value to a goalkeeper in their decision making. These include kicking leg knee flexion angle, and support leg shank and thigh angles.     

The influence of club-head kinematics on early ball flight characteristics in the golf drive

Despite many coaching and biomechanical texts describing how the kinematics of the club-head at impact lead to distance and accuracy of the ball flight, there is limited quantitative evidence supporting these assertions. The purpose of this study was to quantify the relationships between club-head kinematics and subsequent early ball flight characteristics during the golf drive. An opto-reflective system operating at 400 Hz was used to capture the swings of 21 male golfers using their own drivers. The 3D displacement data permitted the calculation of club-head kinematics at impact, as well as subsequent early ball flight characteristics. Using regression analyses, club-head kinematics at impact (velocity, orientation, path, and centeredness) were used to explain the variability in five dependent variables of early ball flight characteristics (resultant velocity, launch angle, side angle, back spin, and side spin). The results of the study indicated that club-head kinematics at impact explained a significant proportion of early ball flight characteristics (adjusted r ² = 0.71–0.82), even when generalized across individual clubs.     

Aerodynamic effects on the accuracy of an end-over-end kick of an American football

The effects of initial conditions on the flight of an American football kicked in an end-over-end manner were investigated using a dynamic simulation employing the quaternion method. The effects of initial tilt and spin about the longitudinal axis of the ball were considered. For the most accurate kick, our simulations show that the ball should be vertical leaving the kicker’s foot, and have no angular velocity about the longitudinal axis of the ball. A case study was performed for which experimental data were available, showing the trends of the flight of the ball captured in our simulations in actual game situations.     

艺术体操运动员脊柱曲度异常与躯干两侧活动度和力量对称性的关系

目的:描述艺术体操运动员在日常状况下和完成专项动作时脊柱异常的表现及左右对称性,探讨与之相关的因素。方法:以9名艺术体操运动员为研究对象,进行站立位脊柱X光片拍摄,获得脊柱额状面和矢状面的弯曲方向和角度;使用三维摄像方法定量评价运动员完成后搬腿动作和侧搬腿动作时的脊柱活动幅度;运用后伸肌群和双侧屈肌群测试系统对运动员的坐姿躯干后伸和双侧侧屈等长收缩力量进行测试。比较躯干活动幅度和躯干肌肉力量的左右对称性,比较不同脊柱侧凸方向间躯干活动差异。检验脊柱弯曲角度与躯干活动特征的相关性。结果:后搬左侧腿时的活动幅度显著小于后搬右侧腿(P<0.01),对应躯干向左扭转的幅度显著大于向右扭转幅度(P<0.05)。侧搬腿时躯干活动幅度越大对应的躯干扭转角度越大。胸曲角度与右侧搬腿活动幅度角存在正相关(P<0.05),与右侧搬腿躯干扭转角之间为显著负相关(P<0.05),腰曲角度与左侧搬腿活动幅度角之间存在显著正相关(P<0.05),与右侧搬腿躯干扭转角之间存在显著负相关(P<0.05)。肌肉力量方面,胸曲角度越大,3个位置躯干后伸力矩峰值越小。侧屈力量上,运动员绝大多数角度下的右屈力量显著大于左屈力量。胸曲角度、腰°曲角度分°别与不同躯干侧屈角度下右屈力矩峰值存在显著负相关。腰曲角度与左屈0、15°、30和右屈15°位置的躯干左屈力矩峰值存在显著负相关。结论:艺术体操运动员躯干两侧活动度和肌肉力量存在不对称,后伸幅度左侧大于右侧,侧屈肌力右侧大于左侧;但这种不对称与脊柱额状面上异常弯曲无明显关系;集中于躯干右侧和躯干后伸动作的训练,可能是导致胸曲变直的原因。     

Does shortening the pitch make junior cricketers bowl better?

In order to get bounce and movement seam bowlers need to bowl the ball “into” the pitch. Standard deliveries by elite players are typically projected at around 7° below horizontal. In contrast, young players currently often need to release the ball almost horizontally in an effort to get the ball to bounce close enough to the batter. We anticipated that shortening the pitch could be a simple way to help young bowlers to release the ball at a better angle and with more consistency. Twenty county or best in club age group under 10 and under 11 seam bowlers were analysed bowling indoors on two different pitch lengths. They were found to project the ball on average 3.4° further below horizontal on a 16 yard pitch compared with a 19 yard pitch, while ball speed and position at release changed negligibly. Pitch length did not affect the consistency of the release parameters. The shorter pitch led to a ball release angle closer to that of elite bowlers without changing release speed, and this should enable players to achieve greater success and develop more variety in their bowling.     

Kinematic effects of a short-term fatigue protocol on punt-kicking performance

The punt kick is a fundamental skill used in several team sports; however, there has been a lack of research on how fatigue affects its technique. The purpose of this study was to determine the effects of short-term fatigue on punt-kicking performance. Eight elite and sub-elite Australian Football players performed maximal drop punt kicks on their preferred leg prior to, during and after a match-specific fatigue protocol. Optotrak Certus collected kinematic data from kick foot toe-off until ball contact. Repeated-measures analysis of variance showed a significant increase in 20 m sprint times after each short-term protocol, indicating fatigue. Foot speed did not significantly change with fatigue; however, increases in the range of motion at the pelvis and kicking thigh, along with increases in kicking thigh angular velocity, occurred. For the support leg, maximum knee flexion angular velocity increased while there was greater flexion found at the knee and hip, and greater range of motion at the knee. Players are able to make kinematic adaptations in order to maintain foot speed while punting for maximal distance after short-term efforts.     

Kinematic comparison of the preferred and non-preferred foot punt kick

Kicking with the non-preferred leg is important in Australian Football and becoming important in the rugby codes. The aim of this study was to examine differences between preferred and non-preferred leg kicking in the drop punt kick. Seventeen elite Australian Football players performed kicks with the preferred and non-preferred leg. Optotrak Certus collected kinematic data of the kick leg and pelvis (200 Hz) from kick leg toe-off until ball contact. Foot speed, knee and shank angular velocity at ball contact, and pelvis range of motion were significantly larger for the preferred leg (P < 0.05). In contrast, hip and thigh angular velocity at ball contact and hip range of motion were significantly larger for the non-preferred leg. This indicates different movement patterns, with preferred-leg kicks making greater use of the pelvis, knee, and shank while non-preferred leg kicks rely relatively more on the hip and thigh (P < 0.05). Reasons for this difference might be due to locking degrees of freedom or sub-optimal sequencing in the non-preferred leg. The thigh-knee continuum identified by Ball ( 2008 ) was also evident in this study. Findings have implications for training non-preferred leg kicking for performance and injury prevention.     

Bowling action and ball flight kinematics of conventional swing bowling in pathway and high-performance bowlers

ABSTRACT

When executed correctly, swing bowling has the potential to influence the outcome of a cricket match, yet little is known about the required bowling action and ball flight characteristics. This study aimed to describe the bowling action and initial ball flight characteristics as well as to identify variables that may be associated with increased swing in pathway and high-performance medium and fast pace bowlers. A 17-camera Vicon motion analysis system captured retro-reflective markers placed on the upper-body of participants and new cricket balls to quantify bowling action and initial ball flight kinematics. Bowlers delivered the ball with their forearm and hand angled in the direction of intended swing with an extended wrist flexing through the point of ball release. Bowlers who produced more swing had increased seam stability, possibly linked to a lower wrist and ball angular velocity. It is believed that swing increases with seam stability, however, optimal ranges may exist for seam azimuth angle, ball angular velocity and release speed. These findings may assist coaches to optimise the performance of bowlers, however, future research should use bowlers who play at higher levels to investigate swing bowling at greater speeds.     

High-speed video image analysis of ski jumping flight posture

Ski jumping flight posture was analyzed for achieving large flight distance on the basis of high-speed video images of the initial 40 m part of 120-m ski jumping flight. The time variations of the forward leaning angle and the ski angle of attack were measured from the video images, and the aerodynamic forces were calculated from the kinematic data derived from the images. Some correlations were investigated between the initial-speed corrected flight distance and such parameters as the angles of jumper, the initial transition time and the aerodynamic force coefficients. The result indicated that small body angle of attack was a key for large flight distance in the initial phase of flight because of small drag force, and that the most distinctive fault of beginners was too large body angle of attack and ski angle of attack leading to aerodynamic stall. Too small drag force does not give an optimal condition for large flight distance because the lift force is also too small. The ratio of the lift to the drag was larger than 0.95 for advanced jumpers.     

太极拳蹬腿动作的下肢肌电活动规律、关节运动类型和平衡控制特征

目的:检测太极拳蹬腿动作支撑腿和动作腿的协调活动,揭示中枢双重命令下的下肢运动控制的特征.方法:太极拳运动员和初学者各10人,分两组.记录太极蹬腿动作时下肢肌肌电图、双下肢关节的角运动、足底中心压力的移位.每次试验8 s完成,重复5次.统计处理后,做肌电、运动和平衡分析.鲒果:两组间支撑腿的EMG、关节活动和COP位移出现了在形态上和幅度上的差别,但是在动作腿多表现在幅度上的差别.运动员支撑腿的平均EMG都高于初学者,只有股直肌有显著差异;运动员膝和髋关节的平均最大运动角度小于初学者,踝关节的平均最大运动角度稍稍比初学者大,只有髋关节的平均最大运动角度较为显著.运动员动作腿的平均EMG只有股直肌和胫骨前肌显著地高于初学者,而臀中肌显著地低于初学者;所有关节的平均最大运动角度都是运动员的显著大于初学者.平均足底中心压力的侧方和前后方位移都是运动员的显著大于初学者.运动员动作腿的起始运动约250～350ms,滞后于支撑腿起始运动的延迟时间.结论:运动员和初学者都可以用踝-髋策略来调节单腿直立的姿势平衡,但是运动员能够启动一个根据任务需要的前馈控制技术,通过下肢肌的积极活动,预先形成一个对抗蹬腿反作用力干扰的姿势稳定.因此,训练太极拳可以获得这个前馈控制技术.持续降低重心时,初学者的蹬腿和支撑两任务间出现了相互冲突.     

旋风脚支撑腿膝关节的受力及损伤机制分析

旋风脚在武术竞技套路中是最常见且难度系数较其他腾空动作要高的腾空动作之一,是在武术套路中经常被采用的一种腾空动作,因此运动员的受伤概率相对较多.文章通过对旋风脚支撑腿膝关节的受力及损伤机制进行分析,为习练者提供正确的训练方法,以预防旋风脚因支撑腿膝关节的错误受力而受到的损伤.     

An overview of cricket ball swing

The aerodynamic properties of a cricket ball have intrigued cricket players and spectators for years, arguably since the advent of the game itself. The main interest is in the fact that the ball can follow a curved flight path that may not always be under the control of the bowler. The basic aerodynamic principles responsible for the nonlinear flight or ‘swing’ of a cricket ball were identified decades ago and many papers have been published on the subject. Over the last 25 years or so, several empirical investigations have also been conducted on cricket ball swing, which revealed the amount of attainable swing and identified the parameters that affect it. Those findings are reviewed here with emphasis on phenomena such as late swing and the effects of humidity on swing. The relatively new concept of ‘reverse swing’, how it can be achieved in practice, and the role in it of ‘ball tampering’, are also discussed in detail. In particular, the ability of some bowlers to effectively swing an old ball in the conventional, reverse and the newly termed ‘contrast’ swing mode is addressed. A discussion of the ‘white” cricket ball used in the 1999 and 2003 World Cup tournaments, which supposedly possesses different swing properties compared to a conventional red ball, is also included. This is a current overview of cricket ball swing rather than a detailed review of all research work performed on the topic. The emphasis is on presenting scientific explanations for the various aerodynamic phenomena that affect cricket ball swing on a cricket ground.