The aim of the study was to compare the power output during indoor sprints on a SKILLRUN^TM treadmill with the power output expressed in outdoor sprints pushing an instrumented sled. The SKILLRUN^TM has been chosen because it is able to simulate the outdoor sprint pushing a sled setting different loads and providing performance output data like speed and power. Two athletes were involved in this pilot study and were asked to perform indoor and outdoor sprints with the same overloads. Two dynamometric handles were designed and applied both on the treadmill for the indoor sprints and on the sled for the outdoor sprints. Power data were calculated throughout the force measured at the handles and the speed collected during the sprints. Kinematics data of trunk and lower limbs were also calculated by means of a set of inertial sensors (Xsens, Enschede, The Netherlands). The power–speed and the load–speed curves together with the kinematics results derived from the indoor and outdoor tests were compared, showing, in general, a good agreement between the indoor and outdoor conditions. These results highlighted the validity of the SKILLRUN^TM treadmill in simulating a sprint with overloads. Full article

Auxetic materials have a negative Poisson’s ratio, meaning they contract laterally during axial compression. Auxetics can also absorb more energy during impacts than conventional materials. Auxetic foam was fabricated by volumetrically compressing open cell foam to buckle cell ribs and impart a re-entrant cell structure, then the imposed structure was fixed by heating and cooling. Passing pins through the foam allowed localised control over compression during fabrication, producing gradient foam with regions with differing Poisson’s ratios and stress vs. strain relationships. Uniform sheets had volumetric compression ratios of three, gradient sheets had volumetric compression ratios of one (unchanged) or three in different regions. One participant jumped barefoot on all foams, cut out to fit pressure sensors; another ran wearing shoes containing uniform converted and unconverted foam insoles. Pressure distribution was measured underneath the foams and foam insoles. Peak pressure was lowest underneath converted foams, warranting further investigation with more participants. Full article

Although accelerometers’ responses during running are not perfectly understood, they are widely used to study performance and the risk of injury. To outline the typical tibial acceleration pattern during running, this study aims to investigate the repeatability of acceleration signals with respect to the ground reaction force waveforms. Ten amateur runners were asked to perform ten trials along a straight line. One participant was asked to perform this protocol over ten sessions. Tibial accelerations and ground reaction forces were measured during the stance phase. The coefficient of multiple correlation R was computed to study the intra- and inter-test and subject repeatability of accelerometric and force waveforms. A good (R>0.8) intra- and inter-test repeatability was observed for all measured signals. Similar results were observed for intra-subject repeatability. A good inter-subject repeatability was observed only for the longitudinal acceleration and vertical and antero-posterior forces. Typical accelerometric signatures were outlined for each case studied. Full article

Variability in the running surface can cause an athlete to alter their gait. Most literature report running on grass, a treadmill or athletics running tracks using inertial sensors. This study compares the signals obtained by 9 degrees of freedom (DOF) inertial-magnetic sensors incorporating an accelerometer (±16 g), gyroscope (±2000°/s) and magnetometer (±8 gauss). The sensors were placed on the participant’s shank, knee, lower spine and upper spine, and the participants were asked to run on three different surfaces (running track, hard sand and soft sand). The calculated player loads for a 400 m run on each surface type was very similar. The mean and standard deviation values were 577 ± 130, 581 ± 128, 568 ± 124 for soft sand, hard sand and the running track, respectively. This did not correlate with the participant’s self-assessment RPE (Rate of perceived exertion), which demonstrated running on soft sand to be significantly more challenging, yielding a mean and standard deviation of 5.3 ± 2.5 (Hard to Very Hard). Soft sand running had a decreased swing time duration but increased variability (0.44 ± 0.02 s—Swing Time, 6.5 ± 1.1%—CV), hard sand running had the longest swing and intermediate variability duration (0.46 ± 0.02 s—Swing Time, 3.30 ± 2.58 %—CV) and running track running had the medium swing time but lowest variability (0.45 ± 0.02 s, 2.7 ± 0.9%—CV). Gait dominance was not consistent across the surfaces for each participant and remained below a ratio of 0.4. These results provide an insight into how athletes modify their gait mechanics to accommodate different running surfaces. Full article

A previous study reported that habitually barefoot Kenyan distance runners tend to use a mid-foot strike or a forefoot-heel strike (FHS). Current findings indicate FHS helps enhance Kenyans’ running performance. However, no study has investigated how FHS modulates leg stiffness (k_leg) and altered running velocity with changes in k_leg. Because vertical displacement of the centre of mass and k_leg during hopping are applicable to the running process, this study investigated how FHS affects k_leg and hopping frequency (f_hopping) during hopping. Subjects hopped at 2.2 Hz with normal hopping (NH-2.2Hz) and at a comfortable frequency with FHS (FHS-CF). According to each subject’s comfortable frequency at FHS-CF, they were divided into higher (HG, 2.49 ± 0.11 Hz) and lower (LG, 2.16 ± 0.19 Hz) groups. With FHS-CF, the flight duration in HG was significantly shorter than that in LG. k_leg in HG was greater than that in LG. Negative work in the first half of the stance phase and positive work in the second half of the stance phase at all three joints were smaller in HG than in LG. The touchdown angle was larger and angular displacements at the joints were smaller in HG than in LG. The findings indicate that when hoppers used FHS, they increased their preferred f_hopping by stiffening their leg joints during the stance phase and jumping with a lower height than in normal hopping; additionally, it is important to increase the touchdown joint angle for a stiffened joint. Full article

The purpose of this study was to elucidate pelvic orientation angles using a single lower back-mounted inertial sensor during sprinting. A single inertial sensor was attached to each sprinter’s lower back, used to measure continuous pelvic movements including pelvic obliquity (roll), anterior-posterior tilt (pitch) and rotation (yaw) during sprinting from a straight to bend section. The pelvic orientation angles were estimated with the three-dimensional sensor orientation using a sensor fusion algorithm. Absolute angles derived from the sensor were compared with angles obtained from an optical motion capture system over a 15 m length. The root mean squared error between the sensor and motion capture data were 4.1° for roll, 2.8° for pitch and 3.6° for yaw. Therefore, the sensor was comparable to the motion capture system for tracking pelvic angle changes. The inertial sensor is now supported as a valid tool to measure movements of the pelvis during sprinting. Full article

The aim of this project was to evaluate effects of backpacks with different design intended for use during cycling on skin-close temperature and relative humidity, oxygen uptake, heart rate and aerodynamic drag. Seven subjects took part in the study cycling on a mountain bike mounted on a “smart trainer” placed on a force plate in a wind tunnel. Three series of experiments were carried out: without backpack, with conventional backpack and with a backpack having innovative rear panel design. As hypothesized, the results showed that an innovatively designed backpack with the ducts deflecting part of the airflow towards some areas of the user’s back provided lower temperature and relative humidity for the microclimate compared to a conventional backpack without airflow channels. Further, reference tests without any backpack resulted in the lowest temperature and humidity. However, no differences were found between the three tests for oxygen uptake, heart rate and aerodynamic drag. Full article

This study investigated the effects of road surface (tarmac, gravel, cobblestones), load case (single passenger, two passengers), tire pressure (3.0, 4.0, 5.0 bar), and cycling velocity (10.0, 17.5, 25.0 km/h) on the whole-body vibration of children being transported in a bicycle trailer. Two types of passive dummies were utilized to mimic a baby and a toddler passenger in terms of weight and height. Road type and cycling velocity caused statistically significant change on the magnitude of whole-body vibrations. Overall, vibration total values were on the “uncomfortable” level of the vibration discomfort scale or even above. The major limitation of the study is the application of passive dummies, which might not represent the biodynamics of the target population. Full article

The aim of this research was to study the effects of cycling gloves on hand-arm vibrations in realistic load scenarios. A test has been performed in the laboratory, a road bicycle handlebar was mounted to the hydraulic cylinder of a universal testing machine, and the bicycle was fixed on an indoor trainer. Tests were executed for three different hand sizes (small, medium, large), three different frequency ranges (15–25, 35–45, 85–95 Hz), with two different types of gloves (gel-padded; non-padded) and without gloves. The amplitudes and each frequency bands were obtained from a previous field test. Hand-arm vibrations were quantified by means of root mean square values of the frequency-weighted accelerations measured at the subject’s wrist joint. Analysis of variance (ANOVA) showed no significant effect of gloves in reducing vibration transmissibility. Full article

High-power bicycle disc braking can create excessive temperatures and boiling brake fluid, resulting in performance degradation and damage. The goal of this work is to understand brake friction performance and thermal behavior for bicycle disc brakes. A previously described disc braking dynamometer is used to assess brake pad performance of sintered metallic brake pads, organic brake pads, and ‘power’ organic pads in up to 400 W of braking power. The friction coefficient is found to be dependent on both temperature and normal force. Friction curve fits are provided for temperatures between 300 K and 550 K. Organic and ‘power’ organic pads are found to have similar behavior, and have higher friction coefficients compared to metallic pads. Further, brakes on an instrumented bicycle are tested in outdoor field trials during downhill descent. A MATLAB thermal model successfully predicts the downhill field brake disc temperatures when using the friction data curve fits. Full article

The practice of road cycling is often associated with low levels of comfort for the cyclist and can be a physically painful experience on bad roads. Apart from cushioning in the saddle, applying handlebar tape, or reducing tyre pressure, a road bicycle offers in itself few options for comfort improvement, as it is primarily designed for performance, with emphasis on low mass and high stiffness. However, a range of components exist (e.g., suspension stems and seatposts) that can be fitted to a road bicycle, which can potentially improve comfort. In this context, the aim of this study was to assess the effectiveness of suspension stems in reducing the vibration transmitted to a cyclist’s hands in the case of impact loading. The results showed an important reduction in the vibrational energy transmitted to a cyclist’s hands with two commercially available suspension stems compared to a regular stem. Full article

Here we seek to control mechanical power output in outdoor cycling by adjusting commanded cadence of a cyclist. To understand cyclist’s dynamic behavior, we had one participant match their cadence to a range of commanded cadences. We then developed a mathematical model that predicts the actual mechanical power as a function of commanded cadence. The average absolute error between the predicted power of our model and the actual power was 15.9 ± 11.7%. We used this model to simulate our closed-loop controller and optimize for proportional and integral controller gains. With these gains in outdoor cycling experiments, the average absolute error between the target and the actual power was 3.2 ± 1.2% and the average variability in power was 2.9 ± 1.3%. The average responsiveness, defined as the required time for the actual power to reach 95% of the target power following changes in target power, was 7.4 ± 2.0 s. Full article

Steel, being the most commonly used bicycle frame material, has a major role to play in future developments within the bicycle industry, and there is scope to enhance the role of engineering in the development of steel bicycles. This paper introduces The Steel Bicycle Project (TSBP), an open-ended project which aims to raise awareness of engineering principles that relate to steel bicycle frames and aims to support frame builders in designing and fabricating better and safer products. In this paper, we give details of the main project themes (Design and simulation, Materials and fabrication, Testing and measurements, Knowledge and education) and outcomes. We also present some initial activities from the early stages of the project and will discuss general models to bring together key partners under the umbrella of the sports engineering community. Full article

In speed skating, environmental circumstances and the near-frictionless movement of the skate in a fore–aft direction over the ice make it difficult to measure technical performance parameters on a regular basis while training in an indoor speed skating rink. SkateView has been developed to overcome these challenges, comprising of two IMU’s (Inertial Measurement Unit), ultra-light force sensors, a mobile phone and an app providing feedback to coach and skater. The feedback, directly on the ice or shortly after a training session, consists of basic parameters like ice contact time, stroke frequency and lap times, and more parameters can be added. Stroke frequency is an important performance parameter, which is presented on a stroke–by–stroke basis and provides a direct insight into the activity. Full article

Figure roller skating is a discipline composed of various movements which involve jumps, artistic figures and spins in a seamless program which has both technical and shapely difficult. A biomechanical analysis of a double salchow was performed using a 2D video analysis of one European and in two Italian roller skaters. On average, the high level (HL) roller skater showed a horizontal velocity of the center of mass higher than the average, especially in the prop stage, whereas the medium level (ML) and low level (LL) athletes reduced their velocity significantly. The spin angular velocity of the ML and LL skaters was always higher than of the HL. This phenomenon would seem to be a compensatory strategy for a lower jump height, with a reduced trunk-thigh angle and less thigh lever arm (coxo-femur/knee joints) during the take-off and landing phases of the double salchow jump. Full article

The sport of curling is played on an ice surface with raised ice pebbles and uses curling rocks made of granite. The effect of sweeping is thought to straighten the rock’s projected curved path and increase the distance travelled. Recent anecdotes suggest that sweeping from the center of the running surface with the direction of rotation and curl is thought to increase the amount of curl, whereas sweeping against and opposite the curl is thought to decrease the amount of curl. The purpose of this study is to observe the topography of the ice surface while comparing scratch measurements from different broom materials. Nine conditions were replicated: nipped pebble, rock traversing the ice, and seven broom conditions. Replicas of the ice were created with vinyl polysiloxane and observed with an optical microscope. Roughness profiles of the replicas were measured, and broom materials were compared using data from an optical profiler. Full article

Jump analysis in figure skating is important. Recovering the 3D pose of a figure skater has become increasingly important. However, issues such as restrictions from an athlete’s clothing, self-occlusion, abnormal pose and so on will result in poor results. This paper proposes a multi-technology correction framework to obtain a 3D human pose. The framework consists of three key components: temporal information-based mutational point correction, multi-perspective-based reconstructed point selection and trajectory smoothness-based inaccurate point correction. Firstly, temporal information is used to correct the mutational points at the 2D level. Secondly, a multi-perspective is used to select the correct spatial points at the 3D level. Thirdly, trajectory smoothness is used to correct inaccuracies at the 3D level. This work will serve the purpose of displaying the 3D animated pose of a figure skater. The quality grade of the result rate on the test sequences is 87.25%. Full article

The purpose of this study was to demonstrate the feasibility of measuring and analyzing characteristics of figure skating jumps using wearable sensors. One elite figure skater, outfitted with five inertial measurement units (IMUs), performed flip jumps with single, double, and triple revolutions. Take-off event and flight phase of each trial were under analysis. Kinematic differences among jumps with variant revolutions as well as key factors for performing successfully landed triple jumps were determined by IMU signals. Compared with a video-based method, this study revealed the following characteristics that coincide with previous studies: at take-off event, the skater performed pre-rotation and took off with preferred postural positions as revolutions increased (p < 0.01); during flight, the skater struggled more to maintain the smallest inertial of moment as revolutions increased (p < 0.01); in order to perform successfully landed jumps, it was crucial that the skater improved the control of preparation for flight at take-off (p < 0.05). Full article

In the laser-run trial in modern pentathlon, athletes must perform series of five successful shots with a laser pistol. A miss does not lead to a penalty but costs the time needed to lower the arm, charge the weapon and raise the arm. Pentathletes face the following dilemma: is it better to shoot fast or accurately? We investigate experimentally the effect of the shooting cadence on the accuracy. We then predict the consequence of this unavoidable speed-accuracy tradeoff in terms of total time needed to succeed the specific trial of laser-run. We find an optimal shooting cadence for each athlete, which minimizes this time. Full article

Archery is a quasi-static sport. Nevertheless, it requires maximum concentration, as well as precision from the archer. Previous research used combinations of several sensors, video analysis and electromyography to analyse the motion sequence and to identify parameters leading to a worse score. Therefore, the aim of this study is to verify if solely an acceleration sensor on the archer’s hand, without complex data processing, could be used to set up a feedback system. For testing, six participants with a three dimensional acceleration sensor on each hand shot indoors at a vertical triple target. The parameters analysed were the duration of the movement, the range of motion and the coefficient of variation. The results indicate that the analysis of the coefficient of variation shows no correlation with the score reached, whereas the analysis of the duration and the range of motion does. Full article

The aerodynamic characteristics of archery arrows fletched with two types of straight vanes, for which the area is different, were studied. The arrows’ pitching moment (C_M), lift (C_L) and drag (C_D) coefficients were measured in the 60 × 60 cm Magnetic Suspension and Balance System (MSBS) from JAXA. At a Reynolds number of Re = 1.2 × 10⁴, the values of C_D were 1.56 and 2.05 for the short and large vanes, respectively. In a second experimental procedure, the arrows’ deceleration in free flight was measured by inserting an acceleration sensor inside their shafts. For shots with an initial velocity of around 56.4 ms⁻¹, a velocity decay of around 8% was measured. A turbulent–laminar boundary layer transition during free flight was found for shots with an average Re = 1.8 × 10⁴. Lastly, through numerical computations, the area difference of the two vanes was analyzed to verify the importance of C_M and C_L during the arrows’ flights. Full article

The appropriate selection of arrows in the sport of archery is important to the achievement of high-quality results. In this regard, a shooting machine that is compatible with the wide variety of available bows and arrows is necessary. However, bow strength and arrow length vary among different athletes. It is also important to develop a shooting machine that reproduces the movement of the right fingers that releases an arrow, and the forward jump of a bow after shooting an arrow. In this study, a shooting machine was developed that considered these factors. Its efficacy was examined in terms of its ability to determine the characteristics of each arrow, and to distinguish between normal and flawed arrows. Based on the experimental results, we identified the factors that affected the shooting accuracy of arrows. In addition, the developed shooting machine was able to distinguish between normal and flawed arrows. Full article

Experimental analyses of motions of a double-leg circle were conducted for a smooth and dynamic movement. A motion capture system provided the data for two different gymnasts; one is well trained and the other has an average skill level. Lissajous analysis was done for a tip-toe circling motion and a rolling motion around a longitudinal axis of a body. The results show that synchronization between the tip-toe circling and the body-rolling around the body’s longitudinal axis is crucial. Muscle activity was also analyzed from electromyogram data when the gymnasts performed double-leg circles, and the muscle activity characteristics of synchronized rolling-type circles were uncovered. Full article

In gymnastics, the skeleton of the athletes can be estimated from many points with three-dimensional coordinate data by measurement control using Laser Imaging Detection and Ranging (LIDAR), and the motion can be derived. However, the system cannot know what kind of load is being put on the athletes’ bodies. Additionally, it is not possible to know in detail how top-level athletes handle apparatus. Therefore, it is important to understand the dynamic response of the apparatus to the athlete’s motion. This study shows that the apparatus’s motion can be identified by performing a static load test using a multi-sensing system that can sense how the bar deforms during a game and determine the apparatus’s motions as an inverse analysis. Full article

A fully coupled model of an athlete’s muscular force output combined with a load resistance is developed and investigated in context of ergometer rowing. The athlete force is based on a simple Hill equation hyperbolic-in-speed, and parabolic-in-length model. Coupling this force function with the dynamics of the ergometer load and inertia and athlete’s own body mass inertia produces a trajectory of the resultant motion in force-speed-length space. The coupled equations were solved using a first order time-marching procedure, and iteratively calculated starting conditions based on ergometer spin-down during the recovery period between strokes. The results agree well with experimental measurements available from Kleshnev particularly given the relatively simple, and untuned, athlete force model used. Changing the load resistance changed the trajectory of the stroke, with qualitative agreement with the expected outcomes. Full article

We examined the association between changes in swimming velocity, vertical center of mass (CoM) position, and projected frontal area (PFA) during maximal 200-m front crawl. Three well-trained male swimmers performed a single maximal 200-m front crawl in an indoor 25-m pool. Three-dimensional (3D) shape data of the whole body were fitted to 3D motion data during swimming by using inverse kinematics computation to estimate PFA accurately. Swimming velocity decreased, the vertical CoM position was lowered, and PFA increased with swimming distance. There were significant correlations between swimming velocity and vertical CoM position (|r| = 0.797–0.982) and between swimming velocity and PFA (|r| = 0.716–0.884) for each swimmer. These results suggest that descent of the swimmer’s body and increasing PFA with swimming distance are associated with decreasing swimming velocity, although the causal factor remains unclear. Full article

The swimming turn is one of the important factors in producing results in a race. Knowing the mechanical quantities in turns is useful to quantify the turning technique. However, experimental measurements often require considerable time and costs. The aim of this study was to construct a simulation model of a flip turn in the crawl stroke by extending the swimming human simulation model SWUM. The joint motion was created based on the standard crawl motion and a turn commentary video on the Internet. Furthermore, the contact with the wall was represented as forces by virtual springs and dampers and the frictional forces. As a result of simulation, a successful turning motion was confirmed. It was also found that the simulated contact time, the maximum force, and the impulse were within the ranges of the previous research. Full article

This study investigates differences in propulsive force between the water surface and underwater conditions in the flutter kick swimming technique. The subjects were well-trained university male swimmers. A towing device was set up in a 25 m swimming pool to measure the towing force and velocity of the swimmer under two conditions: the swimmer was near the water surface and at a depth of 0.60 m. The swimmers performed the gliding trials and the kicking trials with maximum effort with five towing velocities from 1.2 to 2.4 m/s. The passive drag and the resultant force of the propulsive and drag forces in kick swimming were formulated, respectively. The propulsive force was calculated from the difference between the two formulas. A difference of the propulsive force under conditions in high swimming velocity was observed. This suggests that the water surface condition has advantages of raising the foot above water. Full article

Many studies have investigated the forces acting on a football in flight and how these change with the introduction or modification of surface features; however, these rarely give insight into the underlying fluid mechanics causing these changes. In this paper, force balance and tomographic particle image velocimetry (PIV) measurements were taken on a smooth sphere and a real Telstar18 football at a range of airspeeds. This was done under both static and spinning conditions utilizing a lower support through the vertical axis of the ball. It was found that the presence of the seams and texturing on the real ball were enough to cause a change from a reverse Magnus effect on the smooth ball to a conventional Magnus on the real ball in some conditions. The tomographic PIV data showed the traditional horseshoe-shaped wake structure behind the sphere and how this changed with the type of Magnus effect. It was found that the positioning of these vortices compared well with the measured side forces. Full article

This paper presents the first scale resolving computational fluid dynamic (CFD) investigation of a geometrically realistic feather shuttlecock with rotation at a high Reynolds number. Rotation was found to reduce the drag coefficient of the shuttlecock. However, the drag coefficient is shown to be independent of the Reynolds number for both rotating and statically fixed shuttlecocks. Particular attention is given to the influence of rotation on the development of flow structures. Rotation is shown to have a clear influence on the formation of flow structures particularly from the feather vanes, and aft of the shuttlecock base. This further raises concerns regarding wind tunnel studies that use traditional experimental sting mounts; typically inserted into this aft region, they have potential to compromise both flow structure and resultant drag forces. As CFD does not necessitate use of a sting with proper application, it has great potential for a detailed study and analysis of shuttlecocks. Full article

The following considers drag measurements of baseballs with backspin (spin axis horizontal and normal to trajectory) and gyro spin (spin axis parallel to trajectory) orientations. Balls were propelled through still air in a laboratory setting at 36 m/s and spin ranging from 1250 rpm to 1750 rpm. Balls were projected with backspin and gyro spin in the two- and four-seam orientations. Speed and position sensors measured the speed and location of the balls at three locations from which the coefficient of drag and lift were found. Drag was observed to depend on spin rate, spin axis and seam orientation. The largest and smallest coefficient of drag was found with the gyro four-seam and two-seam spin orientation, respectively. Drag was observed to correlate with seam height with back spin, but not with gyro spin. Lift was observed for baseballs with back spin, but not with gyro spin. Full article

In this paper, we summarize our recent research work on soccer balls. Employing wind tunnels and analyses of simulated trajectories, we have gained an understanding of how various surface features influence soccer ball aerodynamics. Wind tunnels provide aerodynamic coefficients for non-spinning soccer balls. The coefficients then help determine the trajectories of various simulated kicked balls. Surface features include panel texturing, seam width, and seam depth. We have determined that small changes in surface texturing can lead to hard-kicked soccer balls experiencing lateral deflections as large as 10%–20% of their horizontal ranges. We have also found that the critical Reynolds number for soccer balls is more strongly correlated with seam width than with seam depth. Full article

The purpose of this study is to investigate the difference in aerodynamic properties between the feather shuttlecock and the synthetic shuttlecock. In particular, we focus on the aerodynamic stability of the two types of shuttlecock during impulsive change of an angle of attack (flip movement). Wind tunnel experiments are performed by using two types of the badminton shuttlecock (feather and synthetic shuttlecocks) to measure the fluid forces, and to visualize the flow fields around the shuttlecock. It is confirmed that the pitching moment coefficient at a near-zero angle-of-attack for feather shuttlecock is larger than that for synthetic shuttlecock. The results indicate that the feather shuttlecock demonstrates high stability in response to the flip phenomenon. Full article

Volleyball is a sport that starts with a serve, so effective service is essential to win the game. The trajectory of the ball is complicatedly affected by the fluid force, which depends on the speed, spin speed, and panel shape. To understand the aerodynamic characteristics of the ball and to propose an ideal serve method, we measured the fluid force and flight trajectory. The fluid force applied to the ball was measured at a wind speed of 4–30 m/s in the wind tunnel. The fluid force on the ball was strongly dependent on the ball type and orientation of the panel. In the flight trajectory measurement, the trajectory of the ball was measured using a high-speed camera under controlled speed and spin speed using a shotting machine. The effect of the panel orientation shown by the fluid force measurement was consistent with the results of the trajectory analysis, clarifying the importance of the panel orientation in serving. Full article

The soccer ball panel pattern, which changes every World Cup, greatly affects the ball’s aerodynamics and flight characteristics. In this study, the fluid force of 11 soccer balls with different panel patterns was measured by wind tunnel tests. The drag crises with different Reynolds numbers were confirmed depending on the panel shape. To understand this, the shapes of panel grooves were measured and the relationship between them was investigated. The flow separation point was also visualized by the oil film method and the particle image velocimetry (PIV) analysis. The separation points were confirmed to be different depending on the panel groove by the oil film method in a supercritical Reynolds region. The flow separation points were found to be almost the same position in the subcritical and supercritical state and to be partly different around the Reynolds number of drag crisis. Full article

Using the world’s largest magnetic suspension and balance system (MSBS) and a low-turbulence wind tunnel, we successfully measured the aerodynamic forces acting on a non-spinning women’s javelin. It was found that the drag and the lift increased as the angle of attack was increased up to 18°. The pitching moment increased for angles of attack up to about 9°, and then decreased, becoming negative above 12°, indicating nose-down rotation. We used a pseudo supporting rod to simulate a javelin attached to a support, as used in a conventional setup, and confirmed that this interferes with the javelin by creating differences between the aerodynamics forces acting on the javelin with and without the pseudo supporting rod. Full article

The trajectory of a soccer ball, kicked with a spin to curve it into the goal, is strongly influenced by aerodynamic factors such as the Magnus force. Several studies using a wind-tunnel and high-speed cameras have investigated the Magnus force acting on a spinning soccer ball. However, the exact effect of the Magnus force on the trajectory of a spinning soccer ball in free flight remains unclear. This study set out to use an optical three-dimensional motion-capture system to record the details of the flight of such a spinning soccer ball. The maximum curvature of the ball’s trajectory occurred in the middle of its flight. The sideways-directed Magnus force acting on the ball decreased as the ball’s speed decreased during the entire flight. Thus, it was concluded that the deflection of the trajectory of the ball decreases as the sideways-acting force decreases throughout the flight. Full article

The swing is a key movement for golf. Its in-field performance could be estimated by embedded technologies, but often only vertical ground reaction forces (VGRF) are estimated. However, as the swing plane is inclined, horizontal ground reaction forces (HGRF) are expected to contribute to the increase of the club angular velocity. Thus, this study aimed at investigating the role of the HGRF during the golf swing. Twenty-eight golf players were recruited and performed 10 swings with their own driver club, in a motion analysis laboratory, equipped with a full body marker set. Ground reaction forces (GRF) were measured with force-plates. A multibody kinematic optimization was performed with a full body model to estimate the instantaneous location of the golfer’s center of mass (CoM). Moments created by the GRF at the CoM were investigated. Results showed that horizontal forces should not be neglected regarding to VGRF because of their lever arm. Analyzing golf swing with only VGRF appeared not enough and further technological developments are still needed to ecologically measure other components. Full article

Current custom fitting guidelines for golf clubs suggest the smallest change in club length from a standard length iron should be 6 mm (1/4”). However, no previous research suggests why this length change is used. This study aims to identify the minimum noticeable difference in the length of 7-iron clubs using just noticeable difference analysis techniques. Fifty golfers of varying ability were asked to compare a standard length 7-iron to test 7-irons of varying lengths, regarding changes in the perception of club length and body position at address. Irrespective of golfing ability, golfers could perceive a just noticeable difference of 13 mm (1/2”) from the standard length club. However, when asked if changes in body position were present, category 1 golfers noticed differences with a 6 mm change in club length and category 2 golfers noticed differences with a 13 mm change. No changes in body position were perceived by highly handicapped golfers. Full article

In this study, a dynamic golfer model was used to investigate the influence of the golf shaft’s balance point (i.e., center of mass) on the generation of clubhead speed. Three hypothetical shaft designs having different mass distributions, but the same total mass and stiffness, were proposed. The golfer model was then stochastically optimized 100 times using each shaft. A statistically significant difference was found between the mean clubhead speeds at impact (p < 0.001), where the clubhead speed increased as the balance point moved closer to the grip. When comparing the two shafts with the largest difference in balance point, a 1.6% increase in mean clubhead speed was observed for a change in balance point of 18.8 cm. The simulation results have implications for shaft design and demonstrate the usefulness of biomechanical models for capturing the complex physical interaction between the golfer and golf club. Full article

The purpose of the study was to determine the influence of grip mass on driver clubhead kinematics at impact as well as the resulting kinematics of the golf ball. Three club mass conditions (275, 325, and 375 g) were tested by 40 experienced golfers (handicap = 7.5 ± 5.3) representing a range of clubhead speeds (36 to 54 m/s). Each participant executed 12 drives per condition using matched grips and shafts and a single clubhead. Club mass was modified by inserting 50 g and 100 g into the grips of the two heavier conditions. The heaviest condition was associated with the slowest clubhead speed (p = 0.018) and highest vertical launch (p = 0.002), which resulted in no net influence on driving distance (p = 0.91). Lateral dispersion was greatest with the 325 g condition (p = 0.017), as was horizontal impact spot variability on the driver face (p = 0.031). Findings at the individual golfer level were not reliable enough to suggest that grip mass could be effectively used in a fitting environment to either shift ball flight tendencies or improve consistency. Full article

Golf is a sport which requires players to use ground interaction to generate clubhead speed in order to propel the ball towards the target. Force platforms are a technology which can be used to measure these ground reaction forces. Golfers generate force through a combination of jumping, sliding or twisting actions during the swing. Understanding how golfers generate these forces and if there are any groups which golfers could be clustered into could be used to enhance golf instruction as well as clubhead design or fitting practices for golf equipment. A total of 105 right-handed experienced golfers (handicap mean = 8.32 ± 8.31) consented to participate in the study of different swing speeds (31 below 95 mph, 41 over 105 mph and 33 between 95 and 105 mph). A calibrated single force plate was used for the test which sampled at 1000 Hz and recorded force and moment data in three axes. After a self-guided warm up, the players were instructed to hit five 7-iron shots and five drives to the best of their ability in an indoor hitting bay which used a launch monitor to record the club delivery and ball flight information. It was found that handicap or swing speed did not dictate the primary force production mechanism (sliding, jumping or twisting/spinning). This knowledge could aid engineers to design equipment better suited to the individual and help coaches build individualized programs to create power and clubhead speed in all players. Full article

We analyzed the relationship between the cooperative actions of golf swings and the differences in swing trajectory. To extract cooperative actions from different swings, we acquired swing data in an experiment on an experienced golfer who swung with two different trajectories. We measured the swings with motion capture system (VICON). We built an observance matrix from the collected positional data and conducted singular value decomposition (SVD) on it. The SVD yielded the cooperative actions as independent modes. Next, we compared the cooperative actions of different swing trajectories in the main mode. The results indicate that the analysis of the golf swing could be divided into a dominant behavior and an accompanying behavior. Full article

The purpose of this study was to determine the effect of modifying whole club moment of inertia (MOI) on clubhead delivery, thorax and wrist kinematics. Seven skilled golfers hit ~10 shots with two driver conditions (MOI difference ~400 kg∙cm²). A GOM system tracked the clubhead at impact and a 12-camera Vicon system was used to determine golfer biomechanics. Paired sample t-tests were conducted to quantify the effect of MOI on clubhead delivery, whilst biomechanical differences during the downswing were determined using statistical parametric mapping. Increasing MOI significantly reduced clubhead velocity (p = 0.001) but had a small and non-significant effect (p ≥ 0.294) on clubhead direction and orientation. The increase in MOI significantly decreased lead wrist flexion, thorax lateral bend and thorax axial rotation velocities during the downswing. The timing and magnitude of the decreases in both thorax velocities, suggests that these were contributing factors of the observed decrease in clubhead velocity. Full article

The aim of this study was to introduce a new activity-based balance index by using accelerometer data. Twenty-seven junior soccer players from the Iranian premier league were selected. Four functional tests, consisting of one leg stance, dynamic Y balance, running and dribbling tests, were conducted to assess the players’ balance, activity and skill. During these four tests, besides their relative scores, the acceleration of their body center was also recorded. Activity-based balance index (ABI) was calculated using these acceleration data. The results showed positive correlations between ABI and both static and dynamic balance scores. Additionally, negative correlations were found between ABI and dribbling scores, which demonstrate the agility required for this skill. It seems that this new index achieves the evaluation of both the balance and the skill level of soccer players. Perhaps this is a new way of talent identification and also a re-development of balance tests from traditional to modern. Full article

Passing a ball is a central aspect in the game of American Football. However, current passing machines do not fulfill the high quality standards for adequate catch training. The goal was to realize a passing machine that could do precise and accurate passes in a fully automated way in order to create high quality automated catch training. Automation was carried out to a degree that the release angle in terms of azimuth and elevation, release velocity and the release spin of the ball could be controlled via a wireless device within a reasonable range. Additionally, a pass prediction model was developed to determine where the pass went to and which height to catch it by least squares fit of 225 sample points with a second order function (R2>0.99). Normalized precision and accuracy of the machine were verified in an experiment with precision being less than 1% and accuracy less than 3% for more than 90% of all relevant passes. Full article

Scrums play a major role in Rugby Union games, and are historically known as a showdown between the two packs of opposing teams, composed of their eight forwards players organized in a 3-4-1 configuration, respectively. We investigate scrum mechanics by working with professional male forward players from Racing 92, a high-level French Rugby club, and measuring the forces they apply on the French Rugby Federation instrumented scrum machine. Signal analysis reveals two major phases in the force production during a scrummaging effort: an impulsive engagement force, and then a force sustained for a few seconds. We experimentally compare individual performances of the engagement phase. We discuss the influence of the mass and the engagement speed of the players, and we introduce the model we are investigating to describe the individual impact on a scrum machine. We expect this model to be the elementary component of a collective model of a pack. Full article

This paper describes the non-parametric shape optimization process for a football boot bottom plate. The non-parametric shape optimization process changes the nodes’ location of a model and outputs an optimum shape, which satisfies an optimization objective. The methodology presented in this study was able to change the shape of the football boot bottom plate, especially the dimensions of key features, to achieve four different target bending stiffnesses. Tosca Structure sensitivity-based shape optimization was used to perform the optimization process and output optimum bottom plates. Future research is needed to investigate the accuracy of the process in comparison with that of the previously developed parametric optimization process. Full article

A simulation-driven design process is proven to generate improved, more robust, and cost-effective designs within a shorter design cycle. Incorporating simulation and optimization early in the design cycle helps shape the concept designs so fewer iterations and rework are necessary as the design matures. For this case study, a portable basketball hoop system is chosen for several reasons. This is a product that is common in everyday life, easily understood, and has several design challenges. To achieve the various design goals for this product, several optimization tools and simulation disciplines are coupled: multibody simulation to determine the kinematics and dynamics; finite element analysis to find displacements and stresses caused by external loads; topology optimization to define the essential structure to efficiently support the loads the product endures throughout its life cycle; and finally, multimodel optimization to consider all the loads when the structure is in several configurations during the optimization process. Full article

A kinetic model of the shooting arms has estimated arm joint torques for one-hand set- and jump-shots in basketball. The dynamic model has three rigid planar links with rotational joints imitating an upper arm, forearm and hand with shoulder, elbow and wrist joints. In general shots controlled by hand, forearm and upper arm motions, there are many torque combinations of shoulder, elbow and wrist joints to produce shooters’ desired ball-release speed, angle and backspin angular velocity. The minimum of the sum of squares of the torque combinations exists at ball-release, when the release angular velocities of the hand and forearm are equal, and the release angular accelerations of the hand and forearm are also equal. Each torque of the shooting arm joints for the set-shot with upward shoulder speed is smaller than that for the jump-shot. Shoulder, elbow and wrist torques increase in proportion to horizontal shot distances. As release backspin angular speed increases, each of the shoulder, elbow and wrist torques also increases. The torques of the shoulder, elbow and hand affect the horizontal shot distance and the ball-release backspin. Full article

The aim of this study was to clarify the major differences in the electromyographic (EMG) activities in the hip joint required to achieve a non-rotational (NR) shot as compared with an instep kick from the spatiotemporal data. For this purpose, simulated EMG activities obtained from NR shots and instep kicks were analyzed using principal component analysis (PCA). The PCA was conducted using an input matrix constructed from the time-normalized average and the standard deviation of the EMG activities (101 data x (15 muscles; iliacus, gluteus maximus, rectus femoris, biceos femoris, vastus lateralis, vastus medialis, vastus intermedius, semimembranosus, semitendinosus, sartorius, tensor fasciae latae muscle, adductor magnus muscle, adductor longus muscle, gasctrocnemius, and tibialis anterior)). The PCA revealed that the 3rd, 4th and 8th principal component vectors (PCVs) of the 10 generated PCVs were related to achieving the NR shot (p < 0.05). Full article

Nine soccer balls were tested for their friction against a leather sheet, using a force plate. An average normal force of 63.6 N was applied and the movement of the ball had an average velocity of 15 mm/s. Each test was repeated 15 times and the average Coefficient of Friction (COF) was reported. The following results were obtained: Jabulani (COF: 0.62 ± 0.05); Fracas (COF: 0.41 ± 0.01); Ordem 3 (COF: 0.63 ± 0.02); Teamgeist (COF: 0.38 ± 0.01); Brazuca (COF: 0.45 ± 0.01); Kopanya (COF: 0.39 ± 0.01); React (COF: 0.37 ± 0.01); Finale 15 (COF: 0.39 ± 0.06); Vintage T-panel leather ball (COF: 0.41 ± 0.02). Overall, the COF of all balls tested ranged between 0.37 and 0.62. The Finale 15 ball showed a decreasing COF trend with repeated trials and the React ball produced pronounced slip-stick phenomenon. Full article

The rotation of a soccer ball is affected by several factors, such as impact point and foot posture, which are generated by joint torque in the lower limb. This study aimed to investigate joint torque in the lower limb that generates foot posture and swing trajectory, and compare three types of kicks before and after a practice period for participants to learn to control the ball rotation. An optical three-dimensional motion capture system was used to record the kicking motion of the participants. The results indicate that the adduction torque of the hip joint at the moment of impact decreased for curve kicks (from 0.56 to 0.25 Nm/kg) and increased for knuckle kicks (from −0.09 to 0.37 Nm/kg). We considered that the curve and knuckle kicks swing towards the inside (because of their positive values in the post experiment) with hip joint adduction before impact to control ball rotation. Full article

Rugby Union is a collision sport, with both player to player and player to pitch impacts being frequent. Current test standards for padded clothing in rugby use impact surrogates, which may not accurately replicate the human response. Modern technologies use silicone elastomers to represent human soft tissue when testing padding, however many commercially available silicones do not match the load response seen by human tissue. This paper describes the fabrication and validation of a bespoke formulation of commercially available silicone elastomer and deadener concentrations that portray a similar load response to relaxed organic muscle tissue. The mechanical responses, both at quasi-static and dynamic strain rates, have been compared, with improved, more representative behaviour being presented. The validation of this silicone elastomer formulation is important in developing a more biofidelic impact surrogate for the assessment of padded clothing in rugby. Full article

The aim of this study is to investigate the link between the cushioning feature of running shoes in objective and subjective measurements (OM and SM). In OM, four insoles materials were chosen after impact tests (S1 = 12.6 g, S2 = 7.2 g, G = 11.54 g, and E = 32.41 g). In SM (n = 19), perceived cushioning comfort of insoles was measured using pairwise comparison tests and a Visual analogue scale (VAS) during running. Lower impact peak (IP) leads to greater perceived comfort of cushioning only between S1, S2 and G. But insole E with the highest IP was rated as the most comfortable in cushioning. Its relationship can be explained by associating acceleration magnitudes from the beginning contact to the IP in two possible ways: i) participants did not reach the critical impact peak in SM or ii) participants perceived the critical impact peak, but other factors such as energy rebound and perceived stability influenced their rating in the pairwise comparison tests. Full article

“Ride” has been established to subjectively describe the heel-to-toe transition during walking and running. Recently, a study was published aiming to quantify “ride” by linking it to the maximum velocity of the anterior-posterior (AP) progression of the center of pressure (COP) during the first 30% of the stance phase. While that study investigated the parameter when running at a constant velocity of approximately 3.5 m/s (i.e., 12.6 km/h), this study was carried out to evaluate the influence of running velocity on “ride” when running. Five healthy participants performed runs on a treadmill at 8, 10 and 12 km/h with three different running shoes, and their plantar pressure was measured at 300 Hz using pressure-sensing insoles. “Ride” was calculated as suggested by the previously mentioned study. In two of the three shoes, “ride” decreased with increasing running speed. Between the shoes, however, there is no clear image of how the shoes influence this parameter. Full article

While it is assumed that pressure-sensing insoles are usually placed directly below the foot and on top of the shoes’ standard insoles, nearly no previously published study actually describes the procedure, which leaves a slight uncertainty. Therefore, the aim of this study was to evaluate whether the placement has an influence on selected parameters or not. Five healthy participants took part in the measurements and ran on a treadmill at a running velocity of 10 km/h with three different running shoes. Plantar pressure was measured using pressure-sensing insoles, which were once placed on top and once below the shoes’ standard insoles. Selected parameters were the maximum and mean pressure and the range of the center of pressure (COP) in anterior–posterior and medial–lateral directions. The results indicate that maximum and mean pressure decrease when the pressure-sensing insole lies below the shoe’s insole and the medial–lateral COP is the least effected parameter. Full article

Today’s development of running shoes is often supported by the assessment of biomechanical tests (BIOs) as well as material tests (MATs). In order to possibly reduce the number of relevant tests, the aim of this study was to find out whether there are correlations between the selected BIO and MATs. Therefore, four different running shoes were tested. For the BIO, the ground reaction force and tibial acceleration of 19 experienced runners were measured. The evaluated parameters were first peak, time to first peak, impulse during the first 75 ms of stance, maximum vertical ground reaction force, loading rate, mean peak acceleration and median power frequency. The MATs included compression tests and an impact test with and without insoles at the forefoot as well as the heel area. The results show that carrying out MATs (especially impact tests) without insoles give the most insight into the parameters analysed with the BIO. Full article

Running is a popular form of exercise, although runners are prone to injury from repeated impact. Running shoes can limit impact forces, but they deteriorate with use. Mechanical ageing typically involves repeatedly compressing the midsole while measuring the energy absorbed within compression cycles to assess degradation. Literature suggests mechanical aging often causes a higher rate of degradation than natural ageing. This work investigated the effect of introducing rest periods into mechanical ageing. Five shoes were mechanically aged using a sine plus dwell waveform (1.25 Hz, max. load 1.5 kN) for seven hours, equating to a simulated distance of 60 km. Three of the shoes were rested for 22 hours every 20 km. The shoes aged with rest periods absorbed more energy than their unrested counterparts for the first 10 km when testing recommenced. This finding has implications for the mechanical ageing, design and recommended lifespan of running shoes. Full article

For many runners, mechanical characteristics of running shoes, such as cushioning ability, are important in finding their suitable shoes. In addition to that, subjective comfort has come to be regarded as a non-negligible factor these days. According to previous studies, it has been found that more comfortable shoe conditions are associated with less oxygen consumption and fewer injury frequencies as compared to the less comfortable shoe conditions. However, there is also the fact that the shoes that they feel comfortable with are different from runner to runner, and it still remains unclear why the runners consider their shoes comfortable. Therefore, in this study, we tried to find the differences between several groups with different shoe preferences, applying an equilibrium-point (EP)-based muscle synergy analysis to know the reason why runners consider the shoes comfortable. As a result of the study, it was found that ankle EP velocity could distinguish between the groups classified by shoe preference. This fact indicates that some force-related parameters calculated from posture and stiffness affect the feeling of comfort. Full article

The objective of this study is to determine the impact of three alternative infills of various particle size on athlete performance and safety in a third generation (3G) synthetic fields. A complete randomized design composed of three different infill materials (thermoplastic elastomer, coconut and cork mixture, and recycled Nike shoes (Nano)) with all infills having the same infill depth, fiber length, fiber density, and shock pad. The study took place at the Center for Athletic Field Safety (CAFS) during the summer of 2017 in Knoxville, TN. Each plot received 120 traffic events with the CAFS traffic simulator. This study found that alternative infills do impact the safety and performance of the field, while showing a variation of performance properties among the alternative infills. The results of this study indicate that particle size and distribution of the infill plays a key role in the superior field performance in 3G turf. Full article

The objective of this study was to investigate the impact of brushing and infill maintenance of third generation (3G) synthetic turf on field safety. A split-plot randomized complete block design was used with six different fiber pile heights, infill depths, and shock pad combinations subjected to 120 games in the summer of 2017 at the Center for Athletic Field Safety (CAFS) in Knoxville, TN, USA. Traffic was applied with a CAFS traffic simulator. Half of the plots received maintenance every 20 games with a rotating power broom and infill applied to those below manufacturer’s recommendations. All 3G synthetic turf systems required maintenance to the same degree, and maintenance was necessary to keep surface hardness of 3G synthetic turf systems consistent and acceptable. Overall, field safety and consistency increased in this study due to maintenance, thus suggesting brushing and infill maintenance plays a vital role in maintaining high performance on 3G synthetic fields. Full article

Sand sports include running, volleyball, soccer, beach flags, ironman, and fitness training. An increased amount of soft tissue injuries have been widely reported. A novel technique of determining the surface stiffness of beach sand in-situ used a simple drop-test penetrometer. The relationship between drop height and the depth of penetration squared was linear (Pearson’s correlation coefficient r² > 0.92). The stiffness ratio between the soft dry sand and ocean-saturated wet sand compacted by eight hours of coastal water exposure was approximately seven, which was similar to previously reported stiffness measurements in a sand box. However, the absolute stiffness values were much smaller. While this technique was manually operated, an automatic system is postulated for future studies. Full article

The athletics track consists of multiple organic hydrocarbons and their derivatives, which are easy to release TVOC under specific conditions such as high temperature. Taking polyurethane athletics track as the research object, the TVOC release of an athletics track is carried out in a 0.1 m³ environmental chamber, and TVOC mass concentration detection is performed using a TVOC gas detector. The results show that the increase in ambient temperature will promote the release of VOCs from a PU athletics track, and the increase rate and decline rate of TVOC mass concentration will increase with the increase in ambient temperature. The increase in ambient temperature will result in a significant shortening of the rapid release of VOCs released from a PU athletics track and a prolonged slow-release period. The ambient temperature rises, the maximum and 24 h value of TVOC mass concentration of the PU athletics track are steadily increasing, and this trend is more significant in the high-temperature section. The research conclusions can provide a basis for the improvement of athletics tracks. Full article

Sports shoes used for hardcourt tennis vary greatly in outsole tread design. In this study, a series of experiments were conducted on individual shoe tread elements, replicating the tribological conditions they will experience during hardcourt step and slide movements. It was found that tread element orientation does not influence the friction during step movements, but has a moderate effect on the friction during hardcourt slides. This is considered to be due to differing amounts of wear and frictional heat experienced. Full article

The purpose of this study was to evaluate a bespoke spatial measurement methodology using Hall Effect Sensors (HES), i.e., utilizing inductance between a permanent magnet and sensor to indirectly measure the magnet position. The aim is to embed the magnet in a boot’s stud and use an array of sensors in the artificial turf. To evaluate the accuracy and applicability of a HES system in sports turf, two studies were carried out. To measure the spatial position vertically, a standard mechanical dynamic impact testing with the magnet embedded, and the sensors below the turf carpet, was compared to the gold standard optical reference measurement system (GOM UK Ltd.: Coventry, UK) . A second study evaluated the horizontal spatial accuracy for sensors in a variable array with a controlled incremental step movement of the magnet on a precise engineering workshop table. Full article

This paper compares four sport surface hardness impact test devices, for use on artificial turf (AT) surfaces to control safety. Sports governing bodies require sport surfaces to be assessed with the “Advanced Artificial Athlete” (AAA) mechanical test. The AAA data presented here demonstrate that this high energy test causes compaction of the particulate rubber infill during testing, such that the derived “field test value” is less relevant to the initial state of the surface and arguably also to player comfort. This paper reports on alternative impact test methods and their correlation to the AAA, including a novel comparison to the more portable Fieldtester. The potential use of a lightweight 0.5 kg Clegg Hammer for assessing the change in state of the infill and monitoring the effectiveness of field maintenance is also reported. These results expand our understanding of factors influencing surface hardness and safety, with useful implications for practitioners. Full article

High load quasi stress-strain (qSS) properties of professionally maintained natural turf (N-pro) was compared with eight natural, hybrid or artificial turfs: one professionally maintained natural turf in a sub field and one grown in a test field without maintenance, two hybrid turfs (one in the sub field and one grown in the test field without maintenance), three new artificial turfs (sand, rubber and sand/rubber infill) and one aged artificial turf (eight years old with sand/rubber infill). N-pro was characterized with a distinctive magnitude of plastic deformation and hysteresis profile, indicating its more energy absorbable properties compared to the artificial turfs. Apparent differences exist between N-pro and other natural turfs, suggesting factors such as daily maintenance work and sod compositions are very influential. Clear differences were also observed when the hybrid turf was professionally maintained. The aged artificial turf becomes substantially stiffer indicating usage over years affects the stiffness. Full article

This study was conducted to clarify the differences in sprint and change of direction performances on different futsal flooring systems (area-elastic (AE) vs. combined-elastic (CE)). Eight recreational athletes were recruited to perform the 505-agility test on three different EN 14904-certified futsal playing surfaces (AE, CE1 and CE2). All participants wore an identical footwear during the test. Timing-gate systems were utilized to record the time of 5-m sprint run-up and the change of direction components from the agility test. Participants were also requested to evaluate the perceived shoe-surface overall traction performance after each trial. The differences of performance across all surfaces were analyzed by one-way ANOVA repeated measures (p < 0.05). Results revealed that there was significant difference in change of direction performance between CE1 and CE2 surfaces (p = 0.04). It was also found that the mean score of the perceived traction performance evaluated by the participants were significantly different across all surfaces (p < 0.05). Full article

A thorough understanding of how the delivered face angle and club path of a golf club influences the initial launch direction of a golf ball can play a significant role in the design of various club types as well as help players and coaches better understand performance in the field. A theoretical model based on a Hertzian impact formulation with the inclusion of tangential compliance via Coulomb friction is compared to empirical results. This comparison demonstrates that the initial launch direction of a golf ball for a given club path and face angle can be sufficiently predicted by the theoretical model, providing insights into the mechanisms leading to different launch direction percentages relative to face angle for various club types. Additionally, the relationship between launch direction and the coefficient of friction is explored for various angles of incidence. Full article

In this paper, two simple and physically meaningful adjustments were made to a momentum-based clubhead-ball impact model to predict golf ball launch conditions with better accuracy. These adjustments were motivated by two shortcomings of the momentum-based impact model, namely the absence of shaft effects and golf ball deformation. Kinematic data from a golf impact motion capture experiment was used to empirically determine the parameter adjustments that minimized the ball speed and spin errors. It was found that the original model’s ball speed deficiency could be corrected by adding less than 3 g to the clubhead mass, and the amount of added mass correlated with the mass of the shaft. Additionally, the original model’s backspin and sidespin errors were significantly reduced by making a slight adjustment to the golf ball’s center of mass position relative to the impact location. Specifically, moving the golf ball center of mass approximately 0.5 mm downward and 0.07 mm towards the heel reduced the mean backspin and sidespin errors by approximately 85% each. Full article

The forgiveness of golf putters is traditionally achieved through weight distribution. Putters are often designed with large footprints, which help to increase the moment of inertia (MOI), but consequently move the center of gravity (CG) farther behind the face. The use of higher MOI putters will result in less ball speed loss on impacts away from the sweet spot (i.e., more forgiveness). It has been shown that certain face properties, such as milling patterns, grooves, or soft inserts, can be leveraged to have a similar effect. This paper explores the relationships between impact location, MOI, CG depth, discretionary mass placement, and launch direction for these putters. A novel design strategy is proposed. Minimizing CG depth for putters with ball speed normalizing face properties, even at the expense of MOI, can result in more consistent launch direction and distance control for the average player. Full article

: Equestrian polo is struggling to grow and attract young players due to the perception it is a game played by royals and the rich only, and is not a real sport. This study highlights the high level of skill and athletic challenge faced by the players. Literature is scarce for polo despite its global appeal and the high value of the game in terms of historical reach and investment by the polo community. The game is also unique in sports due to the multiplicity of interactions such as player–pony, pony–ground, player–mallet, and mallet–ball. This work introduces the basics of the game with a graphical interpretation of the motion of the mallet during play. The mallet is constructed of natural materials, the shaft from a rattan cane whilst the handle and head are crafted from hardwood. Using a materials analysis approach, a testing methodology is proposed that will enable quantifiable data to be produced based on the properties and performance of the mallet. The purpose of this is to enable benchmarking of the mallet based on the material properties and their assembled response to the testing. Quasi-static load tests using a universal testing instrument are followed by dynamic testing using inertial sensors. All testing is done in planes chosen to replicate the common lines of action of match play. The quasi-static tests enabled a value for stiffness (k), and the dynamic testing enabled a damping coefficient (c) to be calculated. These quantities will enable a quantitative measure for the properties and performance of any mallet and thereby remove the subjective nature of assessment. Subsequent study will then determine how these data correlate with the performance in play, as well as impact, trajectory, and fatigue responses. Full article

The objective of this study was to construct a finite element (FE) model of table tennis rubber (Sandwich rubber) with pimples structure, which can accurately estimate the rebound behavior of the ball at impact, and to investigate effects of its structure on ball rebound behavior. The sandwich rubber is composed of a combination of a rubber and foam layers. The FE model of the sandwich rubber was constructed with non-linearity, strain rate dependency, and energy absorption which were expressed based on the results of material tests. Impact analyses were conducted using the developed model of sandwich rubber and ball with different pimple heights. The simulation results of rebound behavior do not tend to be proportional to the pimple height. The trend of the rebound behavior was mainly affected by the amount of impulse during impact calculated using the horizontal component of the contact force which was varied with changes in pimple height. Full article

In this study, the finite element analysis of the string planes of badminton racquets was investigated to evaluate the effect of the mechanical characteristics of polymer strings. The nonlinear mechanical characteristics of commercially available polymer strings were obtained by the uniaxial loading tests experimentally. The effects of the strain rate on the mechanical characteristics of the polymer strings were also investigated to consider the dynamic effect on the numerical simulation. The numerical simulation code used to analyze the string planes of the badminton racquets was developed originally. A nonlinear elastic model (Yeoh model) was applied to the mechanical characteristics of the polymer string. Simulated results were compared with the experimental results. The effect of the mechanical characteristics of the polymer strings and the geometrical shape of the badminton racquets on the out-of-plane stiffnesses were investigated. Full article

The tension of strings on a badminton racket can be adjusted by players according to their personal experiences. The best way to execute such an adjustment remains unclear. A finite element model was employed in this study to investigate the effect of having nonuniform string tension on string-bed deformation, and the direction of force applied to shuttlecock head upon impact. The racket model was based on a commercially available racket with a simplified string-bed of 16 strings established using SolidWorks. A displacement was applied to the ball to simulate impacting on the string-bed. The simulations revealed that slightly lowering the tension of off-centered strings had a minimal effect on the von Mises stress distribution of the ball and string-bed. The off-centered impact caused comparable contact force magnitude but altered force direction. Further investigation is needed for understanding the effect of varying string tension on badminton racket performance. Full article

We aimed to clarify the effect of ball–racquet impact locations on the dynamic behavior of tennis racquet, the accuracy of shots and muscle activation of the forearm. Eight male intermediate tennis players performed ten forehand groundstrokes. A motion capture system was used to measure the motions of racquet, ball and human body at 2000 Hz, and electromyography (EMG) activities of wrist extensor and flexor muscles were measured simultaneously. The flight parameters of the ball were measured by ballistic measurement equipment. All shots were divided into tertiles based on ball impact location along the lateral axis of tennis racquet. We found that the off-center, upper-side impact induces a larger muscular activity in extensor carpi radialis. Passive radial deviation of the wrist occurring immediately after ball impact may account for this. Furthermore, the off-center, upper-side impact could be associated with a missed shot having a lower, outward ball launch angle. Full article

Because of the long history of the Finn Dinghy sailing class, the difference between a gold medal and a mediocre result often comes down to personal mistakes of the sailor, or to who has the most optimised equipment. Regarding the latter, the Finn class rules permit certain design variations of the hull, mast, sail and rudder. In the current contribution, we describe a method for developing a customised rudder system aimed at optimal performance during the Tokyo 2020 Olympics. Based on hydrodynamic analysis of existing rudder designs, an improved rudder geometry was developed. Based on the concept geometry, the rudder and tiller were structurally designed and manufactured to achieve high stiffness and sufficient strength, while respecting the minimum mass requirements as specified by the rules. Full article

Computational fluid dynamics is recently being considered as an interesting tool to predict and analyze surfboards’ hydrodynamic characteristics for the purpose of optimizing the design. In this paper we define a systematic methodology that could be used to measure forces and moments exerted by the fluid on the surfboard. We define a “surfboard attitude” matrix, for instance varying the angle of attack and the tip surfacing height, and we fill it with values of drag, lift and moment. With these data, we can calculate the position of the center of pressure and analyze static equilibrium conditions in the presence of external forces that represent the weight of a surfer. Full article

Diving consists of jumping into water from a platform, usually while performing acrobatics. During high diving competitions, the initial height reaches 27 m. From this height, the crossing of the water surface occurs at 85 km/h, and as such it is very technical to avoid injuries. Major risks occur due to the violent impact at the water entry and the formation and collapse of the air cavity around the diver. In this study, we investigate experimentally the dynamics of the jumper underwater and the hydrodynamic causes of injuries in high dives by monitoring dives from different heights with high-speed cameras and accelerometers in order to understand the physics underlying diving. Full article

The surfing performance of two shortboard fin types with surface features were compared to a standard (control) fin with a smooth surface using dynamic computational fluid dynamics (CFD) simulations. The fins with surface features included designs with a partially grooved and serrated surface (CR), and humpback whale-inspired fins with tubercles and other features (RW). Surfboard roll, pitch and yaw during cutback maneuvers were simulated based on field data from surfers of intermediate, expert and professional (WCT) skill level surfing on ocean waves. Sustained resultant forces relative to the rider direction were significantly different between fin types, and lowest for RW at WCT-level rotations. CFD results also revealed RW’s ability to dampen effects of turbulent flow. RW fins were always the last to stall during a turn, and always exhibited the most gradual stall. CR fins had significantly lower pre-turn drag, and the highest mean resultant forces during the turn. Overall, CR fins appear best for forward acceleration and hold on the wave, while RW fins appear best for maneuverability and stability. Full article

Compared to other Olympic sports, little research exists on competitive shortboard surfing—especially research comparing field and numerical data. In this paper, GPS sensors with 9-axis motion sensors were used to collect data on nearly 2000 surfed waves. Data were collected from four surfers of differing skill levels, ranging from intermediate/advanced (Level 6) to top-ranked professional (Level 9). The results revealed a positive correlation between surfer skill level and roll/pitch/yaw rates during a cutback. Some surfers used two different fin types: a standard commercial fin (C), and a 3D-printed, humpback whale-inspired fin (RW). Statistically significant cutback performance improvements were seen when surfers used the RW fin. Because of the skill level differences suggested by the field data, dynamic computational fluid dynamics (CFD) analysis was performed to simulate cutback maneuvers at three different rotation rates (roll/pitch/yaw). Sustained resultant forces relative to the rider direction were lower for RW fins during the turn, suggesting a less-skilled surfer could generate faster and more powerful turns using RW fins. Field results also confirmed that a skill Level 8 surfer performed closer to skill Level 9 when using RW fins, but not control fins. Surfers experienced more stability using RW fins, and CFD results confirmed RW’s ability to dampen the effects of turbulent flow. Full article

The purpose of this study was to investigate the effect of the air permeability of ski jumping suit fabric on aerodynamic characteristics. In the study, four types of fabric with different air permeabilities were installed onto a fabric-clothed elliptic cylinder, and the flow behavior around its surface was investigated through wind tunnel experiments. The stall was delayed by using the fabric with higher air permeability. The air flow permeated the surface of the elliptic cylinder through the fabric for the fabric with high air permeability. This air flowed out into the separation region through the fabric again, which suppress stall. The stall characteristics for the fabric-clothed elliptic cylinder were influenced by the air permeability of the fabric. The boundary layer thickness on the outer surface and the turbulence levels of the boundary layer affected the air permeability of the fabric. The higher air permeability fabrics improved the stall characteristics. Full article

The purpose of this study was to investigate the impact of blockage effect and Reynolds Number dependency by comparing measurements of an alpine skier in standardized positions between two wind tunnels with varying blockage ratios and speed ranges. The results indicated significant blockage effects which need to be corrected for accurate comparison between tunnels, or for generalization to performance in the field. Using an optimized blockage constant, Maskell’s blockage correction method improved the mean absolute error between the two wind tunnels from 7.7% to 2.2%. At lower Reynolds Numbers (<8 × 10⁵, or approximately 25 m/s in this case), skier drag changed significantly with Reynolds Number, indicating the importance of testing at competition specific wind speeds. However, at Reynolds Numbers above 8 × 10⁵, skier drag remained relatively constant for the tested positions. This may be advantageous when testing athletes from high speed sports since testing at slightly lower speeds may not only be safer, but may also allow the athlete to reliably maintain difficult positions during measurements. Full article

The spoiler on a go-kart is required to prevent the vehicle becoming airborne at speeds of 80 km/h or more. An optimal spoiler design balances this safety aspect with speed and fuel economy. This paper reports the results of a project to improve the aerodynamic aspects of a go-kart spoiler design using CFD Analysis. We investigated the design of a rear spoiler with three proposed angles (θ₁ = 9.5°, θ₂ = 19.5°, θ₃ = 29.5°). The drag force produced by each of the three designs is compared. Different computational results are discussed such as the air flow velocity, pressure and the applied forces in terms of CFD analysis using one-way fluid structure interaction (one-way FSI) to determine the spoiler stress, strain and drag coefficient. The findings of this paper have implications for the leisure and tourism industries, and may be applicable to other recreational vehicles’ spoilers. Full article

In marathon running, maintenance of body temperature is critical for peak performance. Rac