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.     

Human perceptions of artificial surfaces for field hockey

Measuring the performance of a sports surface is typically derived from a series of field and laboratory tests that assess the playing properties under simulated game conditions. However, from a player’s perspective their own comfort and confidence in the surface and its playing characteristics are equally if not more important. To date no comparative study to measure playing preference tests has been made. The aim of this research was to develop a suitable method for eliciting player perceptions of field hockey pitches and determine the key themes that players consider when assessing field hockey pitches. To elicit meaningful unbiased human perceptions of a playing surface, an individual subjective analysis was carried out, using interviews and inductive analysis of the recorded player statements. A qualitative analysis of elite hockey players (n = 22) was performed to obtain their perceptions immediately after a competitive match. The significant surface characteristics that emerged as part of an inductive analysis of their responses were grouped together and formed five general themes or dimensions: player performance, playing environment, pitch properties, ball interaction and player interaction. Each dimension was formed from a hierarchy of sub-themes. During the analysis, relationships between the dimensions were identified and a structured relationship model was produced to highlight each relationship. Players’ responses suggested that they perceived differences between pitches and that the majority of players considered a ‘hard’ pitch with a ‘low’ ball bounce facilitating a ‘fast’ game speed was desirable. However, further research is required to understand the relative importance of each theme and to develop appropriate measurement strategies to quantify the relevant engineering properties of pitch materials.     

Device for on-the-water measurement of rowing output

All those who compete in the sport of rowing have used the land rowing machine, Ergometer (commonly called the ‘erg’), manufactured by Concept II (Morrisville, Vermont, USA). Ergon is the Greek word for work, hence the Ergometer measures work. Rowers are commonly ranked according to their ‘erg score.’ The fault in this ranking is that the land Ergometer cannot account for many of the important technical aspects associated with rowing on the water. The goals of this project were to (1) develop a system for on-the-water measurement of work during rowing and then (2) demonstrate the potential of such a system to quantify performance and improve rowing technique. To achieve these goals, force was measured using strain gauges glued to the shaft of the rowing oar and angular displacement was measured using a potentiometer. The force and displacement measurements were sent to a microcontroller, which calculated the total work done in a particular stroke, as well as other parameters, and displayed the values to the rower. The parameters were used to evaluate the performance of three collegiate rowers on the water. The data were also used to plot force profiles, which were reviewed with each rower and the coach to illustrate the rowers’ habits and facilitate improving technique. One rower was ‘tutored’ with the device through five on-the-water practices, after which his force profiles and parameter values demonstrated significant improvement. The device not only provided a standard to which all rowers were compared on the water, but also supplied the rowers with important information on technical aspects of their strokes and pacing themselves.     

Soccer ball modal analysis using a scanning laser doppler vibrometer (SLDV)

Soccer equipment manufacturers invest significant amounts of time and money researching and developing soccer balls, using advanced materials and constructions in an attempt to create a ball that has better flight and impact characteristics. An important consideration in any structure subject to dynamic or impact loading is its mechanical response. The recent development of non-contact optical vibration measurement tools such as the SLDV have made the accurate measurement of such responses possible. The technique of vibrometry utilises the Doppler principle to provide a measure of the surface velocity at the point at which a laser beam is incident. The SLDV benefits from its non-contact and non-marking method, and the speed and ease with which measurements can be recorded. This paper reports the method and results from a study aimed at determining the dynamic responses of two different soccer balls. The balls were excited using an acoustic source and the velocity of each ball’s surface at a series of points was recorded. The natural frequencies and vibration mode shapes were identified and a comparison made between the responses of each ball. Significant mode shapes were observed between 150 Hz and 1500 Hz. At the lower frequencies, the mode shapes were observed to be independent of the outer panels, based more on the structure of the ball as a whole. At higher frequencies, one of the balls tested showed mode shapes centred on individual panel oscillations. The soccer balls tested show some noticeable differences in mode shapes.     

Basketball shooting strategies — the free throw,direct shot and layup

A rationale and geometric parameters for optimal basketball shooting are provided. The premise is that shots requiring the least energy are the easiest to control and thus have the greatest probability of success. The kinematics of the ball movement are modelled and simulated for the free throw, for the direct shot, and for the bank shot off the backboard (the ‘layup’). For the layup, the analysis includes the effects of friction, ball inertia, ball spin and impact restitution. The results provide a means for shot planning and for coaching to improve shooting technique. The advantage of the layup for close-in shooting is demonstrated. Results of numerical parameter studies are also presented, demonstrating the ranges of allowable shooting error for the various shots, and thus also identifying the shots with highest probability of success.     

Modelling the mechanical characteristics and on-snow performance of snowboards

Models were developed for calculating the mechanical characteristics and the on-snow performance of snowboards.The snowboards are constructed of layers of materials which may include wood, foam, honeycomb, fibre-reinforced composites and polymeric materials.The models pertaining to the mechanical characteristics provide the bending and torsional stiffnesses, the flex and the twist.A computer code (Snowboard-MECH) was written which yields numerical values for these characteristics.The model for on-snow performance simulates the travel of a snowboarder of given height, weight and skill level, down an S-shaped course.A second computer code (Snowboard-TURN) was written in support of this model; this calculates the time it takes the snowboarder to complete the course.The two computer codes were verified by comparing their outputs with laboratory data and with data generated by a snowboarder completing a prescribed S-shaped course.The results generated by the models and the data are in agreement, lending support to the models and the corresponding computer codes.A procedure is described by which the computer codes developed in this study can be utilized in the design of snowboards.     

Quantitative understanding of the fly casting stroke through measurements and robotic casting

A stumbling point for many learning to fly fish is being able to fly cast well enough to ‘present’ a fly to a feeding fish. Even among more skilled fly fishers, learning to fly cast better is often a bottleneck towards advancement in the sport. Fly casting instruction today relies on the visual inspection of the fly casting stroke and the resulting ‘loop’ of fly line. These qualitative visual cues help fly casting instructors spot the strengths and weakness in a student’s casting stroke. We introduce two novel technologies for fly casting instruction that result in aquantitative understanding of the fly casting stroke. In particular, we describe a novel robot that is able to replicate standard overhead casts. This achievement is made possible by measuring the casting stroke using a small (MEMS) rate gyro to record the angular velocity of the fly rod in the casting plane. The robot is then programmed to replicate this angular velocity history. Potential uses of this robot include an objective means to assess fly rod, fly line and leader designs, as well as new methods for fly casting instruction.     

Athlete and coach perceptions of technology needs for evaluating running performance

Athletes and their support team utilise technology to measure and evaluate technique and athletic performance. Existing techniques for motion and propulsion measurement and analysis include a combination of indirect methods (high-speed video) and direct methods (force plates and pressure systems). These methods are predominantly limited to controlled laboratory environments (in a small area relative to the competition environment), require expert advice and support, and can take significant time to evaluate the data. Consequently, the more advanced measurement techniques are considered to be restricted to specific coaching sessions, or periods in the year leading up to competition, when the time and expertise of further support staff are available. The more widely used, and simple, devices for monitoring ‘performance’ during running include stopwatches, GPS tracking and accelerometer-based systems to count strides. These provide useful information on running duration, distance and velocity but lack detailed information on many key aspects of running technique. In order to begin the process of development of more innovative technologies for routine use by athletes and coaches, a study was required to improve the understanding of athletes’ and coaches’ perception of their requirements from measurement technology. This study outlines a systematic approach to elicit and evaluate their perceptions, and presents the findings from interviews and a questionnaire. The qualitative data are presented as a hierarchical graphical plot (structured relationship model) showing six general dimensions (technique, footwear and surface, environment, performance, injury and cardiovascular) and shows the development of these general dimensions from the interviewee quotations. The questionnaire quantitative data enhances the study by further ranking characteristics that arise from the interviews. A contrast is shown between short and longer distance runner groups, as might be expected. The current technology available to elite runners is briefly reviewed in relation to the 22 characteristics identified as important to measure. The conclusions highlight the need for newer technologies to measure aspects of running style and performance in a portable and integrated manner, with suggestions as to size and weight likely to be acceptable to users for emerging devices.     

Colour-based rigid body tracking using three-dimensional graphics models

This paper introduces the first stage of a new model-based approach to three-dimensional (3D) human movement tracking. A ‘generate-and-test’ matching procedure was adopted by matching rendered images of a 3D computer graphics model of the human body to target images of rigid body motion. The set of pixels to be compared were just those corresponding to the model of the body in the rendered images. The matching criterion to optimize model position and orientation was based on the minimisation of the RGB (red-green-blue) colour difference between generated model images and associated target images. The method was able to track synthetic image sequences of a half twisting somersault accurately with root-mean-square (rms) errors of less than 5 mm and 0.3∘ for position and orientation estimates respectively. The suitability of the proposed approach for rigid body motion tracking was supported by additional tracking experiments on video image sequences of ‘wooden cross’ trajectories. Comparisons of tracked estimates against manual digitizing estimates returned relatively small rms difference values on both side somersault and twisting somersault movements. The proposed approach has the potential to track video images of a human torso using a rigid body model and hence to track articulated movements by successively adding segments to the model in a hierarchical manner.     

Flight dynamics of an American football in a forward pass

The motion of an American football in a forward pass is discussed in this paper. It was investigated by using wind-tunnel aerodynamic data in a numerical integration of the full nonlinear equations of motion, and by application of the small-angle theory for the atmospheric motion of an axisymmetric spinning body. The numerical simulations agree with certain observed features such as the range, flight duration, and ratio of the spin and precession frequencies. The analytic results reveal functional dependences of the flight parameters on the aerodynamics and give insights into the physical effects that occur. Both approaches show a feature that is known as ‘drift’ in the science of ballistics, namely that a long, highly arched trajectory of a spinning body does not lie in a vertical plane, but rather turns slightly to the left or right, depending on the direction of the spin vector and on the magnitudes of the aerodynamic loads.     

Dynamic behaviour of soils used for natural turf sports surfaces

The modulus and damping properties of soils in compression are a function of soil type, water content, stress history and loading rate. To model human–surface interaction with natural turf sports surfaces, stiffness and damping properties must be determined at dynamic loading rates. Two contrasting soil types, a Sand and a Clay Loam, commonly used in sports surfaces were loaded uniaxially to 2 kN at loading rates between 0.6 and 6 kN s⁻¹ in modified dynamic soil testing apparatus. Soils were compacted prior to loading but initial cycles resulted in viscoplastic deformation, with strain accumulation with repeated cycles of loading. Ultimately a resilient, viscoelastic steady-state equilibrium with loading was established. Resilient modulus and damping ratio varied with soil type, water content, stress history and increased significantly with loading rate. The resilient modulus of the Sand soil, typical of modern free-draining sand construction natural turf sports surfaces, was significantly greater than that of a Clay Loam soil more characteristic of traditional natural turf surfaces; reducing water content caused an increase in modulus and a decrease in damping ratio in the Clay Loam soil. Determination of these properties provides initial data for the modelling natural turf surface behaviour in terms of both ball and human interactions, with further research required to determine the effect of both grass roots and leaves on mechanical behaviour.     

The role of engineering in fatigue reduction during human locomotion — a review

The purpose of this review is to discuss how an athlete’s fatigue can be limited by using recent innovations in sports engineering. The review focuses on human locomotion, i.e. mainly fatigue during endurance sports. First, through a general definition and illustrations of means of locomotion such as running, cycling, walking/hiking or speed skating, several aspects of fatigue reduction will be presented. With regards to the mechanical stress, it has been shown that (i) contrary to ‘invitro’ experiments and, in comparison with hard shoes, soft shoes do not appear to reduce impact forces during running and (ii) too much cushioning can have side effects in terms of energy cost and thus in terms of fatigue in running and mountain biking. On the contrary, the equipment weight-that also depends on the weight repartition may have dramatic effects in terms of fatigue. Any equipment allowing better mechanical efficiency (e.g. chainrings, klapskate) or work distribution (e.g. walking with poles) can potentially reduce an athlete’s fatigue under similar conditions without this equipment. However, among elite athletes, the use of technical innovation does not seem to affect fatigueper se but provides performance improvement with similar fatigue occurrence. It appears that fatigue-related improvements caused by technical innovations only occur among sportsmen exercising for leisure. In the second part of this review, recent textile innovations aimed at decreasing fatigue by the use of elastic compression stockings or at regulating temperature will be discussed. Finally, two methods designed to improve recovery after training or competition (elastic compression and electromyostimulation) will be discussed. Both these techniques are widely used by elite athletes despite relatively poor scientific evidence of their efficiency, with the exception of recovery after eccentric exercise.     

Investigation of snowboard stiffness and camber characteristics for different riding styles

Previous research has indicated that the flex pattern and camber of a snowboard are crucial to its perceived “feel”, or the physical and psychological feedback given to the rider whilst snowboarding. These features are the primary cause of variation in snowboard performance for different riding styles. Consequently, this article deals with the identification of stiffness and camber characteristics for freestyle, freeride and versatile test boards, and their statistical correlation to a comprehensive list of qualitative feel-based performance requirements. It has been determined that the test boards spanning the major styles all possessed similar bending profiles, that were highly representative of each snowboard’s respective thickness distribution. The torsional stiffness curves however appeared to be driven by the composite architecture used in construction. Unsurprisingly, the freeride test board showed the greatest level of overall stiffness. The versatile board exhibited the greatest fluctuation in bending stiffness along the chord, whereas the freestyle profile was far more even throughout, with less variation from tip to tail. All of the subjective performance parameters except forgiveness showed positive associations to the body stiffness and camber, with manoeuvrability exhibiting the strongest correlations. The forgiveness showed the exact opposite trend, implying that higher levels of flex and less camber promotes a forgiving snowboard.     

Topspin in putters — a study of vertical gear-effect and its dependence on shaft coupling

Imparting topspin on a golf ball from putter impact can be achieved either by oblique impact from negative-lofted putter faces or by vertical eccentric impact (commonly referred to as ‘vertical gear-effect’). Negative loft gives a small amount of topspin but should preferably be combined with positive putter-head trajectory to give the ball lift at impact. Vertical gear-effect can provide high spin rates for impacts above the sweet spot and desirably gives the ball a small upward lift at impact. This paper outlines the theory of spin generation in putter impact, discusses how high vertical gear-effect can be implemented and considers the effect that such designs have on putt length control, directional accuracy and impact vibration. Ballistic measurement techniques to validate putter designs are described and an unexpected experimental result dependent on shaft coupling is analysed.     

Estimation of reaction forces in high bar swinging

Reaction forces experienced by gymnasts swinging on the high bar may be determined indirectly using inverse dynamics analysis or may be measured using strain gauges. The accuracy of inverse dynamics analysis may be poor because of errors in the estimated inertia parameters and in the accelerations obtained from digitized data. On the other hand the use of strain gauges is not always possible in elite competition. This paper presents a method for estimating the reaction forces based on the linear displacements of the bar. The bar was modelled as a point mass attached to horizontal and vertical linear springs (obeying Hooke’s law) with stiffness coefficients determined from static loading. The stiffness coefficients of the bar were determined with three different tensions in the stabilizing cables of the high bar. A force and video analysis of backward giant circles was performed. Estimates for the reaction forces were obtained by multiplying the bar displacements from the video analysis by the stiffness coefficients determined from the static loadings. Comparisons were made between the estimated reaction forces and the reaction forces recorded using strain gauges attached to the high bar. Varying the tension in the stabilizing cables of the high bar did not effect the stiffness of the bar. Root mean squared differences between estimated and recorded reaction forces were on average within 99 N for three ‘regular’ and three ‘accelerated’ giant circles. This was less than 3.5% of the range of forces recorded. The bar displacement method was able to estimate the peak reaction forces to within 7% on average, which compares favourably with 24% reported by Gervais (1993) using inverse dynamics.     

Comparison of numerical and analytical solutions for fly casting dynamics

This paper presents an approximate analytical model of the dynamics of a tapered fly line during a standard overhead cast. During casting, the line forms a nonlinear propagating wave that is frequently referred to as a ‘loop’ by fly casters. The geometry of the loop is described by three distinct parts: a straight bottom segment (attached to a stationary fly rod), a semi-circular segment that is propagating (i.e. the loop), and a straight top segment that is also propagating, (i.e. the traveling line). A fly (particle) is attached at the end of the traveling line. A work-energy balance yields the velocity of the fly as a function of the length of the traveling line. For a uniform fly line (level line), a closed-form solution is found, while for a tapered fly line, the solution is obtained by quadrature. A critical loop diameter arises in the analysis, and it determines whether the final velocity of the fly is greater or lesser than the initial velocity of the traveling line. The analytical solutions are critically compared against numerical solutions of a general model for fly line dynamics that relaxes many of the assumptions employed in the analytical model. The agreement between the two solutions remains close during the loop propagation phase, provided a significant amount of fly line remains in the traveling line. However, as the traveling line vanishes and the loop ‘turns over’, the two solutions diverge abruptly due to the many simplifying assumptions employed in the analytical model.     

Parameter study using a finite element simulation of a carving Alpine ski to investigate the turn radius and its dependence on edging angle,load, and snow properties

For ski manufacturers, it is important to know how a given ski-binding system performs under different loading conditions. Important performance parameters are the ski deformation and the resulting turn radius. This study focuses on carving turns. The aims of this study were: (1) to investigate the dependence of the turn radius on edging angle, load on the binding, and snow hardness using a finite element (FE) simulation, and (2) to compare the results with predictions of a frequently used model introduced by Howe. The FE simulation used a quasi-static approach (similar to Howe’s model), but the ski–snow interaction model incorporated the groove that forms in the snow during a carved turn. Up to edging angles of 40°, the results of the FE simulation agreed well with Howe’s model. However, for large edging angles (>50°) the calculated turn radius leveled out, whereas Howe’s model tends to zero. This effect was more pronounced for soft snow than for hard snow conditions. Increasing forces on the binding caused a decrease in the calculated turn radii. In summary, the FE simulation showed that particularly at large edging angles the groove in the snow needs to be considered in models of the ski–snow interaction or in computations of the turn radius.     

Three-dimensional analysis of blade contact in an ice hockey slap shot,in relation to player skill

The purpose of this study was to examine the three-dimensional movement profile of the blade during a stationary slap shot, as a function of player skill level. A total of 15 subjects participated; eight were classified as elite and the remaining seven were recreational. Performances were evaluated by simultaneously recording the movements of the stick’s lower shaft and blade with high-speed video (1000 Hz), the time of stick-ground contact with two uniaxial forceplates and time of blade-puck contact with a uniaxial accelerometer mounted within the puck. Data were analysed with a two-way MANOVA for several dependent variables including linear kinematics, temporal phase data and global angles. The results indicated that skill level affected blade kinematics, with elite shooters tending to alter timing parameters (i.e. phase length), magnitude of linear variables (i.e. displacement, etc.) and the overall blade orientation to achieve a higher velocity slap shot. These analyses identified a unique ‘rocker’ phase within the execution of the slap shot in both groups.     

Effect of gear ratio on peak power and time to peak power in BMX cyclists

The aim of this study was to ascertain if gear ratio selection would have an effect on peak power and time to peak power production in elite Bicycle Motocross (BMX) cyclists. Eight male elite BMX riders volunteered for the study. Each rider performed three, 10-s maximal sprints on an Olympic standard indoor BMX track. The riders’ bicycles were fitted with a portable SRM power meter. Each rider performed the three sprints using gear ratios of 41/16, 43/16 and 45/16 tooth. The results from the 41/16 and 45/16 gear ratios were compared to the current standard 43/16 gear ratio. Statistically, significant differences were found between the gear ratios for peak power (F(2,14)?=?6.448; p?=?.010) and peak torque (F(2,14)?=?4.777; p?=?.026), but no significant difference was found for time to peak power (F(2,14)?=?0.200; p?=?.821). When comparing gear ratios, the results showed a 45/16 gear ratio elicited the highest peak power,1658?±?221?W, compared to 1436?±?129?W and 1380?±?56?W, for the 43/16 and 41/16 ratios, respectively. The time to peak power showed a 41/16 tooth gear ratio attained peak power in ?0.01?s and a 45/16 in 0.22?s compared to the 43/16. The findings of this study suggest that gear ratio choice has a significant effect on peak power production, though time to peak power output is not significantly affected. Therefore, selecting a higher gear ratio results in riders attaining higher power outputs without reducing their start time.     

Profiling the physical load on riders of top-level motorcycle circuit racing

Manoeuvring a motorcycle at high-speed in official competition has been shown to expose riders to substantial and complex physiological and psychological demands, however few studies have analysed the physical load experienced by professional racers. This study aimed to quantify the physical stress experienced by riders and explore relationships between performance related variables (i.e. crashes). Performance and braking data were collected from official race reports from 2013 to 2015 of the top class of the FIM Road Racing Grand Prix World Championship. Top-level riders are exposed to a considerable volume (175 ± 42 brakes and 372 ± 48 leans to corner per race) of high intensity actions (>40% of brakes initiated at speeds higher than 260 km.h^?1, and 13.2% over 300 km.h^?1), where 1 out of every 4 braking actions generated inertial stresses greater than 10 m.s^?2. Furthermore, the mean speed across competitions increased over the years (from 161.7 ± 6 km.h^?1 to 164.5 ± 6 km.h^?1), however no clear relationships between the amount of crashes and competition-related factors were found. Given the findings it would seem that riders could benefit from strength training specifically designed to prepare the body to counteract the repetitive inertial stresses of racing.