In this research, a fully automatic inertial motion capture system for the determination and analysis of kinematic motion parameters in ski jumping was developed. Two databases were created for the implementation of the measurement system: one basic database acquired in a laboratory setting and one database acquired during a summer ski jump season on an actual ski jumping slope. First, the former database was used to set up the fundamental data processing method. Next, this method was extended to derive jump kinematics for motion analysis in the larger summer jumping data set. Data analysis showed that the determined body kinematics varied largely in heading angle due to variances in the magnetic field near the top of the ski jumping hill. Therefore, a novel method for the additional compensation of magnetic disturbances was added to the processing framework. The resulting system output data indicated that the final body orientations, joint positions and joint angles were of good and meaningful accuracy. The enhanced inertial capture system consequently constitutes a reliable and very accurate tool to evaluate ski jumps from inertial sensor data under high data comparability and repeatability within different athletes and capture sessions.
Simple manipulation of force–time input is a potential strategy to increase the biofidelity of running footwear mechanical ageing. The purpose of this study was to compare a Dwell protocol, which incorporated a recovery period characteristic of the float phase of running, to traditional sinusoidal ageing. A second aim was to use the protocol to compare the mechanical ageing performance of foam, a halved commercial running shoe, and a cylindrical plug cut from a running shoe to quantify effects due to testing geometry and to estimate the contribution of midsole foam to shoe energy management. Dwell was more biofidelic and less aggressive than Sine because (1) net displacement and energy absorption were greater than Sine and (2) net displacement and energy absorption decreased at a slower rate than Sine. Using a 60 mm diameter cylindrical plug to estimate the performance of a halved shoe with 100 mm contact area led to 20% overestimation of energy absorption. Comparing the performance of a slab of foam and a cylindrical plug cut out from a shoe, the midsole was estimated to manage 90% of the energy. Differences between sample types were also related to stiffness, yield behavior, and resulting hysteresis curve shapes, which revealed that the outsole improved sample deformation and durability. Overall, results supported that Dwell improved the biofidelity of mechanical ageing, testing geometry is an important consideration in experimental design, and most of the energy was managed by the midsole.
Aerodynamic effects play an important part in any sport where the ball experiences significant periods of free flight. This article investigates the aerodynamic forces generated when a football is spinning quickly to generate swerve and more slowly to generate more erratic flight. The work reports on the application of an experimental method that measures the aerodynamic loads on a non-spinning, slowly spinning and fast spinning football, using a phase-locked technique so that orientation-dependent and steady ‘Magnus’ forces can both be determined. The results demonstrate that the orientation-dependent aerodynamic loads, widely seen in non-spinning data in the literature, surprisingly persist up to the highest spin rates reported. When predicting ball flight, it is generally assumed that at low spin rates a quasi-static assumption is acceptable, whereby forces measured on a non-spinning ball, as a function of ball orientation, apply for the spinning case. Above an arbitrary spin rate, the quasi-static assumption is replaced with the assumption of a steady ‘Magnus’ force that is a function of spin rate and ball speed. Using a flight model, the quasi-static assumption is shown to be only applicable for the lowest spin rates tested and the assumption of a steady ‘Magnus’ force is only applicable at the highest spin rates. In the intermediate spin rates (20–40 r/min), the persistence of the orientation effects is shown to have sufficient effect on the flight to be an important additional consideration.
Following a review of the key determinants of successful rowing, a wireless body sensor network was developed to monitor boat and body segment acceleration and surface electromyography in major muscles recruited during the rowing stroke cycle. Its design was optimised to yield maximum information about the rowing stroke cycle from fewest sensors and minimise the power consumption of the nodes. The system was validated against the Qualisys motion capture and high-speed camera system with most Pearson correlation coefficients in excess of r = 0.8. On-land ergometer experimentation allowed muscle recruitment over the stroke cycle to be studied, with data from multiple experiments combined using correlation of the acceleration signatures of back and thigh nodes (r = 0.95). It was demonstrated that it was possible to identify one of the common rowing errors of ‘shooting-the-slide’ from the data collected, and that a marked decrease in correlation of good-to-bad technique over the drive phase of the stroke (0.95 reducing to 0.34 in the experiment undertaken) could be used to indicate the presence of this error. Extension of the wireless body sensor network to encompass boat and two oarsmen was demonstrated, allowing correlation of their rowing signatures to be studied, indicating their cohesion as a crew.
Judo is a martial art that was created as a physical, intellectual and moral education method in Japan. In competition matches, Judo is a combat sport where two athletes fight against each other. Judo matches are ruled by different scores, penalties and durations, which change regarding the age and gender of the competitors. There is a need to record the actions in favour of or against a judoka during a match in order to create an efficient training programme as well as technical and tactical development strategies for each competitor. In this work, a technological solution is presented; it records each athlete’s matches and scores, penalties, pauses during the match and its actual length of time. These aspects can help to create charts reflecting efforts made by the judoka. The research is focused on the support of the technical–tactical analysis of judo matches, taking into account recent information technology and communications trends: (1) the solution is developed for mobile devices which use the Android operating system, (2) the solution takes advantage of Cloud computing to allow ubiquitous access to the data and (3) the desktop component of the solution is portable to many computer systems because it has been developed using the Java programming language. The initial results show how the technological solution can be used for improving the performance of the athlete by providing feedback of the behaviour of the judoka during each match.
The attention given to brain injury has grown in recent years as its effects have become better understood. A desire to investigate the causal agents of head trauma in athletes has led to the development and use of several devices that track head impacts. In order to determine which devices best measure these impacts, a Hybrid III headform was used to quantify the accuracy for translational and angular accelerations. Testing was performed by mounting each device into the helmet as instructed by its manufacturer, fitting the helmet on the headform, and impacting the helmet using an impulse hammer. The root mean square error for the peak translational acceleration varied with location. The worst root mean square error for a head-mounted device was 74.7% while the worst for a helmet-mounted device was 298%. Head-mounted devices consistently outperformed those mounted in helmets, suggesting that future sensor designs should avoid attachment to the helmet. Deployment to a high school football team affirmed differences between two of the device models, but strongly indicated that head-mounted systems require further development to account for variation between individuals, the relative motion of the skin, and helmet–sensor interactions. Future work needs to account for these issues, refine the algorithms used to estimate the translational and angular accelerations, and examine technologies that better locate the source of the impact.
Coast-down techniques are widely used on bicycles and motorized vehicles in order to estimate retarding forces and respective coefficients. The mathematical model behind coast-down data analysis is usually based on the assumption that both drag and rolling-resistance coefficients do not depend on the vehicle speed. This assumption restricts the model validity to the specifically tested range of speeds and provides averaged values for the force coefficients. In the attempt to overcome this limitation, the proposal of a complete polynomial equation of motion is developed, evaluated and discussed through a human-powered vehicle case study. The analysis points out that the extended model is adequate for experimental data fitting and could potentially provide a more reliable power–speed prediction outside the testing range. However, the expressions included in the model in order to account for speed-dependent coefficients are first approximation with limited capability to represent these complex phenomena. As a consequence, further experimental testing is needed in order to achieve a validation. Advantages and side effects of both the classical and the complete polynomial models are discussed, concluding that the two approaches could be complementary and could answer different needs that specifically depend on the purpose of the coast-down analysis.
The crank angle is an important outcome in biomechanical analyses of cycling. Wireless inertial and magnetic measurement systems are unobtrusive and have the potential to measure crank angles more advantageously than ergometers, encoders or cameras. However, magnetic field disturbances and large centripetal accelerations during pedaling introduce tracking errors. The aim of this study was to validate two magnetometer-free sensor-to-body frame alignment methods for tracking the bicycle crank angle using wireless inertial and magnetic measurement systems. A passive complementary filter is presented for tracking the crank angle using an inertial and magnetic measurement system mounted on the bicycle frame and another on the crank arm. Sensor-to-body frame alignment is performed for both inertial and magnetic measurement systems using functional calibration techniques that do not require magnetometer measurements. The filter also performs dynamic tracking of the crank arm inertial and magnetic measurement system without magnetometer data by exploiting domain constraints and compensating for centripetal accelerations. The filter was validated at a slow, medium and fast pedaling cadence using stereophotogrammetry. The filter produced absolute errors of 1.3° ± 0.9° or less in all three tests. In contrast, large and variable absolute errors (11.6° ± 7.6°, 14.2° ± 10.7° and 14.0° ± 10.2°, respectively) were found with a standard passive complementary filter using a traditional static pose calibration that relies on magnetometer data. The proposed filter operated with low and consistent errors despite the presence of magnetic interferences, whereas traditional magnetometer-based approaches produced unacceptable results. This study contributes toward the ultimate goal of outdoor cycling analysis using inertial and magnetic measurement system technology by accomplishing magnetometer-free frame alignment and centripetal acceleration compensation when tracking crank angles.
We consider the rope climber fall problem in two different settings. The simplest formulation of the problem is when the climber falls from a given altitude and is attached to one end of the rope while the other end of the rope is attached to the rock at a given height. The problem is then finding the properties of the rope for which the peak force felt by the climber during the fall is minimal. The second problem of our consideration is again minimizing the same quantity in the presence of a carabiner. We will call such ropes mathematically ideal. Given the height of the carabiner, the initial height and the mass of the climber, the length of the unstretched rope and the distance between the belayer and the carabiner, we find the optimal (in the sense of minimized the peak force to a given elongation) dynamic rope in the framework of nonlinear elasticity. Wires of shape memory materials have some of the desired features of the tension–strain relation of a mathematically ideal dynamic rope, namely, a plateau in the tension over a range of strains. With a suitable hysteresis loop, they also absorb essentially all the energy from the fall, thus making them an ideal rope in this sense too.
In this theoretical article, the force-elongation behaviour of a climbing rope in a heavy fall is investigated and compared with experiments. The experiments show that the state-of-the-art viscoelastic description of a climbing rope with time-independent friction is not able to explain the rope tension as a function of time. A proper description has to take into account time-delayed friction, that is, a transition from a low-friction regime to strong friction near the force maximum which leads to a fast relaxation of the rope into its equilibrium position. Furthermore, a climbing rope has to be described by a nonlinear tension with increased stiffness for large elongations in order to agree with experiments with varying fall masses. Finally, observed second-mode force oscillations are explained by a continuum description of the rope taking into account its mass.
AI-Virtual Trainer is an educative system using Artificial Intelligence to propose varied lessons to trainers. The agents of this multi-agent system apply case-based reasoning to build solutions by analogy. However, as required by the field, Artificial Intelligence-Virtual Trainer never proposes the same lesson twice, whereas the same objective may be set many times consecutively. The adaptation process of Artificial Intelligence-Virtual Trainer delivers an ordered set of exercises adapted to the objectives and sub-objectives chosen by trainers. This process has been enriched by including the notion of distance between exercises: the proposed tasks are not only appropriate but are hierarchically ordered. With this new version of the system, students are guided towards their objectives via an underlying theme. Finally, the agents responsible for the different parts of lessons collaborate with each other according to a dedicated protocol and decision-making policy since no exercise must appear more than once in the same lesson. The results prove that Artificial Intelligence-Virtual Trainer, however perfectible, meets the requirements of this field.
The aim of this study was to determine the effects of using an electrical heating garment during a 30-min recovery period after a standardized swimming warm-up on subsequent swimming performance and upper body power output. On two occasions, eight male and four female elite competitive swimmers completed a standardized swimming warm-up, followed by a 30-min passive recovery period before completing maximal plyometric press-ups and a 50-m freestyle swim. Plyometric press-ups determined starting strength, peak force and peak concentric power. During the recovery period, participants wore tracksuit bottoms and (1) a standard tracksuit top (CON) or (2) jacket with integrated electric heating elements (HEAT). The overall results demonstrated a trend of a relevant (>0.4%) improvement in the 50-m freestyle performance of 0.83% (p = 0.06) in HEAT versus CON. In male participants, performance in the 50-m freestyle significantly improved by 1.01% (CON 25.18 ± 0.5 s vs HEAT 24.93 ± 0.4 s; p < 0.05), whereas female participants only showed a trend for an improvement of 0.38% (29.18 ± 0.5 s vs 29.03 ± 1.0 s; p = 0.09), in HEAT compared with CON, although statistical power for the latter test was low. Male participants’ starting strength, peak force and peak concentric power were 16.5 ± 13%, 18.1 ± 21% and 16.2 ± 21% greater, respectively, in HEAT compared with CON (all p < 0.01). In conclusion, external heating of the upper body between completion of the warm-up and performance through the utilization of an electrically heated jacket improves plyometric press-up power output and force production, as well as sprint swimming performance in males. This provides justification for future enhancement opportunities in sporting performance through the utilization of external heating systems. Optimization of the heating system for specific sports is required.
Due to different design parameters, there is a large variety of artificial turf configurations on the market for soccer. The ultimate aim for any player surface is to maximize the performance and to minimize injuries. The aim of this study is to develop and validate the Football Turf Performance Questionnaire which measures the performance of an artificial turf soccer pitch and to identify predictors for both the overall performance and sliding friendliness based on the players’ perceptions. Three types of artificial turf configurations were evaluated by an elite soccer team in five different trials. Statistical analyses were performed to check the reliability, the classification into factors and identification of predictors, respectively. The best predictors of the total judgement are the descriptors ‘hardness of the field during falling and during sprinting’ and ‘traction during stopping’ and the indicators ‘traction’ and ‘shock absorption’. For sliding friendliness solely, the best predictors are the descriptor ‘burning feeling of the skin after a sliding movement’ and the indicators ‘skin irritation’ and ‘traction’.
The sport of curling has a long history over 500 years and, consequently, a variety of information and experiences have been accumulated on the technique, strategy, coaching, and other facets of the sport. However, very few detailed scientific or quantitative investigations have been made, especially on the stone dynamics, such that a fundamental understanding of the dynamics has yet to be achieved. This report summarizes the previous theoretical and experimental studies of stone dynamics and aims at making clear the areas yet to be solved.
Brain injuries are prevalent in the sport of American football. Helmets have been used which effectively have reduced the incidence of traumatic brain injury, but have had a limited effect on concussion rates. In an effort to improve the protective capacity of American football helmets, a standard has been proposed by National Operating Committee on Standards for Athletic Equipment that may better represent helmet-to-helmet impacts common to football concussions. The purpose of this research was to examine the National Operating Committee on Standards for Athletic Equipment standard and a new impact method similar to the proposed National Operating Committee on Standards for Athletic Equipment standard to examine the information these methods provide on helmet performance. Five National Operating Committee on Standards for Athletic Equipment–certified American football helmets were impacted according to the National Operating Committee on Standards for Athletic Equipment standard test and a new method based on the proposed standard test. The results demonstrated that the National Operating Committee on Standards for Athletic Equipment test produced larger linear accelerations than the new method, which were a reflection of the stiffer compliance of the standard meant to replicate traumatic brain injury mechanisms of injury. When the helmets were impacted using a new helmet-to-helmet method, the results reflected significant risk of concussive injury but showed differences in rotational acceleration responses between different helmet models. This suggests that the new system is sensitive enough to detect the effect of different design changes on rotational acceleration, a metric more closely associated with risk of concussion. As only one helmet produced magnitudes of response lower than the National Operating Committee on Standards for Athletic Equipment pass/fail using the new system, and all helmets passed the National Operating Committee on Standards for Athletic Equipment standard, these results suggest that further development of helmet technologies must be undertaken to reduce this risk in the future. Finally, these results show that it would be prudent to use both standards together to address risk of injury from traumatic brain injury and concussion.
This study aimed to investigate the effects of two functional sport shirts with different fiber compositions (polyester: 100% polyester vs polyester–lyocell combination: 67%–33%) on thermoregulation and wearing comfort during treadmill walking at an average intensity under moderate environmental conditions. It was hypothesized that the hydrophilic lyocell fibers would benefit sweat evaporation and, thus, provide a superior cooling effect. Using a repeated-measures study design, core, surface and between skin-and-shirt temperatures were measured in 11 men while wearing either the polyester or polyester–lyocell shirt. Additionally, sweat loss, heart rate and subjective perception of comfort were determined. In spite of significantly greater sweat production, relative humidity was lower with the polyester–lyocell shirt. In the later phases of the walking intervention, the temperatures were consistently higher with polyester–lyocell, although between-shirt differences failed to reach significance. These results suggest that greater water retention limits the thermoregulatory efficiency of cellulosic fibers when excessive sweat production occurs.
The aim of this study was to examine the possibility of using data collected with an electronic training system to determine the influence of a shooter’s heartbeat on shooting precision. Shooting sessions of a rifle in prone position were studied with the use of an electronic training system. As a case study, results of an experienced shooter were analyzed. Fast Fourier transform was applied to raw data extracted from the system and then results were interpreted. The spectrum obtained revealed a wide peak at the frequency f = 2.6 Hz that was considered as the second harmonics of the average frequency corresponding to the heartbeat decreasing down to 69 beats/min when releasing a shot. The session finished with a very modest score of 611.3 points. When a small intentional change in the shooter’s equipment (a sling position) was introduced, the spectrum obtained did not reveal any peaks and the shooter reached a much better score of 621.8 points. The use of fast Fourier transform analysis is proposed as a new tool for Olympic rifle shooters and coaches. This new tool does not require any complicated procedures and provides quantitative information on the influence of a heartbeat on the stability of a shooter’s aim.
The performance of five different bat designs, from different eras spanning from 1905 to 2013, was assessed to address the question whether the changes in bat design over the years have resulted in a performance advantage to the batsman. Moment of inertia and ‘freely suspended’ vibration analysis tests were conducted, as these physical properties have been directly associated with rebound characteristics of the bats. Results showed that changes in the blade’s profile such as distribution of the blade’s weight along the edges and closer to the toe have resulted in a clear performance advantage of the newest bats in comparison with older designs. These results add to the weight of evidence in cricket that the game has changed to the benefit of the batsman and additional changes to bat design are conceivable as modern engineering tools are applied to further optimise performance.
The rolling resistance of skis used in roller skiing competitions should resemble the gliding resistance of cross-country skis to allow specific training and moving patterns for cross-country skiing and to guarantee equal opportunities for athletes in roller ski races. Therefore, the purpose of this work was to develop a portable rolling resistance meter to precisely measure the rolling resistance of roller skis. Measurements were based on recordings of the angular deceleration of a flywheel due to the rolling resistance between a roller ski’s wheel and the flywheel’s steel surface. Rolling resistance coefficients of four roller ski types ranged between 0.019 and 0.025. Measurements of the rolling resistance coefficient showed a precision of 1.26%. Substantial rolling resistance coefficient variations (10%) were observed for wheels of the same type. Furthermore, the rolling resistance coefficient was found to be negatively correlated with normal load or ambient temperature. The proposed rolling resistance meter is appropriate to determine the rolling resistance coefficient of roller skis’ wheels precisely.
Even if it makes a smaller contribution than aerodynamic drag, rolling resistance plays a non-negligible role in the efficiency of human-powered vehicles, whether they are designed for daily commuting or to set speed records. The literature, experimental evidence and models show that the rolling resistance coefficient of cycling wheels strongly depends on the supported load, suggesting that the number of wheels and the load distribution could play a role in vehicle design and in road-test data analysis. Starting with an in-depth look at the relationship between a single wheel and overall vehicle rolling resistance coefficients, an analysis is proposed and discussed with the aim of minimizing the rolling resistance of a vehicle. Finally, a parametric surface response model for rolling resistance is obtained as a function of wheel size and the number of wheels. The overall analysis overturns the popular assumption according to which ‘the more wheels, the more rolling resistance’, at least according to a strict definition of the phenomenon.
The soccer ball is one of the important pieces of equipment in the game of soccer. It undergoes various forms of impact during the game. In order to numerically investigate the occasions of ball impact such as soccer heading, a validated finite element model of a soccer ball is required. Therefore, a model was developed incorporating material properties obtained from literature. To ensure the accuracy of the model, it was validated against an established soccer ball model and experimental data of the coefficient of restitution, contact time, longitudinal deformation and reaction force. In addition, a parametric study of the mesh density was also performed to determine the optimal number of elements. The developed soccer ball model was found to be in a good agreement with the literature and experimental data. This suggests that, the soccer ball model is capable of replicating the impacts of interest. This article details the development of the model and the validation processes.
The rotational stiffness of footwear has been previously shown to have an effect on ankle kinematics and injury risk, but this relationship has not yet been modeled. The aim of this study was to derive equations from experimental data that were able to predict ankle kinematics under various torsional stiffness constraints and use these equations to estimate ligament strains. Three athletic tapes were tested for their ability to constrain the ankle during external rotation. Six subjects then performed a voluntary external foot rotation using the selected tape designs to constrain the ankle, as well as with no constraints. The motion of the calcaneus with respect to the tibia (tibiocalcaneal motion) from 0° to 15° of tibia rotation and predictive equations were determined to establish tibiocalcaneal rotation, eversion, and flexion as a function of gross tibia motion and tape stiffness. These predictive equations were then used to drive a computational model in which ankle ligament strains were determined at 15° of tibia rotation and for ankle constraint stiffness ranging from 0 to 30 N m/deg. The three tapes provided significantly different constraint stiffnesses during external foot rotation. There was no statistical effect of ankle constraint on the dorsiflexion response of the ankle (p = 0.461). In contrast, there was an effect of constraint stiffness on tibiocalcaneal external rotation (p < 0.001) and tibiocalcaneal eversion (p < 0.001). Results of the model simulation revealed the highest ligament strains in the anterior tibiotalar ligament and anterior tibiofibular ligament. Anterior tibiotalar ligament strain increased with increasing constraint stiffness, while there was little effect of constraint stiffness on anterior tibiofibular ligament strain. Results from this study could aid in the design of footwear, as well as the analysis of clinical injuries.
Surfaces of artificial turf have been continuously improved to resemble the characteristics and properties of natural grass. Nevertheless, these improvements are still unable to prevent the turf from reaching higher temperatures than natural grass. This situation results in customer dissatisfaction, decreased performance and the possibility of causing heat-related injuries. The aim of this study was to check how various structural components such as the type of fibre, the type of infill, the age of the turf and the hours of use influence the temperature (°C) of artificial turf football fields. In situ tests were performed using an infrared thermographic camera according to the standard ISO 18434-1:2005 and the normative standard of the Fédération Internationale de Football Association for the certification of artificial turf football fields. The results show higher temperatures in artificial turf fields built with styrene–butadiene rubber and fibrillated fibres. This shows that the type of infill and fibre affects the temperature of third-generation artificial turf fields, the thermoplastic rubber and the monofilament fibres being the components that contribute significantly to the reduction of the temperature.
We established a set of analytical equations that constitute the biomechanical framework for the optimal design of plate-loaded strength training machines. Specifically, we assessed the effect on the exercise kinetics of a change in the distance dP between the site P of the resistance lever where the weight plates are loaded and the axis of rotation of the lever. To this end, the distance dP was increased, while keeping the value of the resistance torque R unchanged by a simultaneous decrease in the mass mP of plates loaded on the lever (dPmP = const). A progressive increase in dP (under the condition dPmP = const) yielded a sharp decrease, followed by a steady increase, in the moment of inertia of the loaded resistance lever (relative to its axis of rotation). The impact of this change on the kinetic effects related to the inertia of the moving equipment masses (inertial effects) has been discussed for maximal and explosive exercises, and for sub-maximal exercises executed at controlled cadence. We also detected a specific value of dP for which the torque related to the inertial effects, expressed as a percentage of R , turns out to be independent of the selected level of external resistance. This condition precisely reflects the linear-dynamic condition that occurs when lifting free weights.
Like most sports, alpine skiing has international regulations – its regulations specifically designed by the FIS, that is, the Fédération Internationale de Ski or International Ski Federation– aimed at coordinating competitions and rating athletes. FIS points, as they are called, represent the core of the rating system, as they facilitate the rating of athletes involved in competitions for each of the five alpine skiing disciplines, that is, slalom, giant slalom, super-G, downhill, and combined. The objective of this article is to analyse the current rating system, giving special attention to the FIS points’ construction and updating system and focusing on the potential weaknesses. Two major weaknesses emerge from this analysis: (1) the questionable update process of the FIS points, based on the average of the best two results obtained in a discipline of interest, and (2) the lack of a general rating of athletes based on their eclecticism, that is, the ability to obtain good results in as many different disciplines as possible. The second part of the article presents some proposals for sorting out the above weaknesses. The description therein is supported by several practical examples, based on real and hypothetical data.
The aim of this research was to indicate improvements in 4-km cycling performance that may be gained as a function of reduced frontal surface area (A) when Union Cycliste Internationale rule 1.3.013 is contravened. In 10 male cyclists age 26 ± 2 (mean ± standard deviation) years, height 180 ± 5 cm and body mass 71 ± 6 kg, entire cycling posture was rotated forward from where the nose of the saddle was 6 cm rearward of the bottom bracket spindle (P6) to 4, 2 and 0 cm (P4, P2 and P0); contravening Union Cycliste Internationale rule 1.3.013. Using computerised planimetry, A was estimated and a forward integration model was compiled to simulate 4-km track cycling end time (T4km) when a fixed power profile was applied. At P2, there was a significant but non-meaningful reduction compared to P6 (p < 0.05, d < 0.02). There were small but significant reductions in A and T4km between P6 and P0; –0.007 ± 0.004 m2 and –1.40 ± 0.73 s, respectively (p < 0.001, d = –0.259). There were no significant differences between P4 and P6 for A and T4km. These results suggest that at the most forward position (P0), a small but significant increase in 4-km performance can be expected compared to the legal position (P6). Moreover, the mean difference in T4km between P6 and P0 is greater than the winning margin at the Union Cycliste Internationale 4-km pursuit world championships four times in the previous 10 years.
To assess ball performance for research and development purposes requires greater understanding of the impact conditions a tennis ball experiences in professional tournament play. Ball tracking information taken from three consecutive years of an ATP 250 tour event played on hard court was analysed. The frequency of first serves, second serves, racket impacts and surface impacts was assessed per game and extrapolated to show how many impacts a single ball is subjected to. Where applicable the pre- and post-impact velocities and angles were found, and the distribution of each was analysed. In total, data from 65 matches comprising 1505 games were analysed. On average, each game contained 70.26 (±16.23) impacts, of which 9.23%, 3.16%, 37.78% and 49.83% were first serves, second serves, racket impacts and surface impacts, respectively. As a result, assuming all balls in play are used evenly, a single ball is expected to be subjected to 105 (±24) impacts over the course of the nine games that it is in play. The results of the investigation could be used to design a wear protocol capable of artificially wearing tennis balls in a way that is representative of professional play.
The use of representations of physiological parameters to an athlete and coach during training is becoming increasingly common. Their utility is enhanced when the appropriate data are captured and communicated in real time for the athlete to make training adjustments immediately. The aim of this work was to develop a biofeedback tool for ergometer rowing by creating a data acquisition system, data analysis and interpretation that could be conducted in real time and a feedback system with appropriate cues to the athlete. This 14-year study resulted in a set of measured parameters with inferred correlations between the directly measured parameters acquired during the activity and performance and injury outcome measures. These parameters were represented through a customisable visual display in real time during ergometer training. An athlete and coach open survey was conducted to assess the utility of the biofeedback tool. This survey found that all parties valued the feedback system since it provided a common language to identify body motion and performance parameters in a way that was accessible and meaningful to all parties as well as available during training and coaching. Athletes noted that it helped them to understand body segment motion and its relation to performance, and both coaches and medical staff valued this in enhancing performance and monitoring injury and injury prediction. There was also speculation that the system helps to underpin coaching practice and its translation to the team. The biofeedback tool has been adopted by the British elite rowing squad.
Data acquisition and analysis are an intrinsic part of motorsport, helping a race team objectively evaluate the performance of both their car and driver. Over time, data acquisition has become almost universally employed through all levels of racing. While large teams in the sport’s highest ranks have many resources to derive answers from these data, users in more minor ‘stepping stone’ categories often find themselves unable to successfully exploit the full potential of the information gathered because of its volume and their limited resources. Further to issues associated with the volume of data, recent trends in racing have seen cuts to the time available for driver and car testing through all levels of the sport to reduce escalating competition costs. While users are faced with ever more data and less time in which to extract useful information, the tools provided by commercial analysis packages have shown little development. This article describes the investigation into a new three-dimensional graphical display method, which aims to help the user more rapidly assimilate acquired motorsport data to the race car producing it. The first two preliminary stages of development of this system are presented, demonstrating the ability of the system to operate with two levels of complexity, which might be considered to suitably represent different levels of user. Together, results from both demonstrate the system’s potential for further development as a useful tool for accelerating a race team’s analysis of acquired data.
Sporting was solely considered to be based on talent and physical capabilities in the past. Adaption of computer-aided engineering, particularly computational fluid dynamics, in sports-engineering has made significant advancements by developing concentrated techniques that could help individuals to reach their peak performance. Studies show that physical performance could be mainly limited by three main components, namely, muscular, cardiovascular and pulmonary systems. Due to inevitable limitations that exist in the pulmonary system, researchers are more concerned in training respiratory muscles. Inspiratory-muscle training is a well-known technique in many sports, particularly in high-intensity breathing-related sports such as rowing, cycling and swimming that require an individual’s aerobic capability and respiratory system with a high-minute ventilation to sustain exhaustive breathing scenarios. This article describes inspiratory-muscle training dynamics followed by a methodology for three-dimensional lung model to understand the interdependence of several control parameters for comparative performance, thereby generating an inverse control model for potential performance improvement criteria. The three-dimensional lung model is developed based on Visible Human Project® database, which provided detailed anatomical dimensions. The shape functions are constructed using cubic splines to fit tomographic slices. Parametric studies using variables such as pressure exerted by chest cavity on lungs, lung compliance, fluid-flow/volume, average elasticity for inspiratory-muscle training and breathing-time constants are conducted. Our hypothesis is based upon synchronising the position of lung centroids with working stroke execution, which can result in enhanced swimming performance. Simulation results showed that lung centroid could vary from 109.95E–5 to 109.99E–5 m, proving that there is a possibility to change the swimmer’s floatation angle by 0.036% during each swimming cycle. The lung centroid could be varied optimally by controlled breathing patterns. A typical swimmer with 25°–35° floatation angles can increase or decrease the floatation angles during recovery and gliding phases, respectively, by synchronising breathing patterns with the stroke during different phases of swimming cycle. Previous studies showed that the distance between lung centroid and body gravity can change up to 1.5 mm. Results obtained from our model equations showed that the change in displacement of lung centroid is 1.099 mm. Therefore, the variation of accuracy of our results is about 27% from the previous studies. However, results generated from our studies are generic, that is, results are gender independent, and the effect of body-to-lung ratio in stroke execution is not taken into consideration. These factors potentially provide a platform for further improvement in our simulation models.
In this study, free-surface effects on swimming are investigated by the application of the computational fluid dynamics method for the first time. The major goal of this study is to represent a new methodology to numerically investigate free-surface effects on swimming. Utilizing a two-dimensional solver with steady flow conditions, the numerical results for swimming at a fully submerged level are validated with the data presented by previous researchers. The validity of the results is also examined through the study of mesh independency and the control of a critical turbulence feature, entitled as non-dimensional wall distance (y+). Finally, for the analysis of swimming at the free-surface level, a two-dimensional time-dependent solver with a well-known multiphase mathematical model is implemented to simultaneously investigate two-phase flow interactions and wave propagation in the proximity of the swimmer’s body. The development of different flow topology features, including major vortex cores and secondary recirculation zones as well as turbulence mixing and flow updraft and downdraft, are investigated and used to compare free-surface swimming against fully submerged cases. While the drag coefficient continuously decreases for higher advance velocities for a fully submerged case, a gradual augmentation is observed for the drag coefficient at a free-surface swimming level. The obtained results suggest that while the proportion of wave drag is ignorable at low swimming speeds below 1 m/s, in the case of higher speeds, its amount enhances significantly and constitutes about 15% of the total drag. Moreover, the proposed methodology is demonstrated to be efficient in the simulation of flow characteristics and phase interactions in swimming at the free-surface level.
Full-face helmets are designed to protect against head and face injuries during downhill and free-ride mountain biking. This study assessed whether multiple impacts and helmet type are related to the protective properties of full-face helmets. A drop tower fitted with a helmeted headform simulated impacts to the chin following a forwards fall. Four models of full-face mountain biking helmets were tested. Three repeated trials were completed for each helmet at four impact velocities. Outcome variables included head injury criterion score, peak force, and peak acceleration. Peak accelerations for all trials were below the 300 g pass/fail criterion used in some testing standards. Multiple impacts reduced helmet protective properties, most noticeably at the higher impact velocities (increases in impact severity measures ranging from 11% to 22% for low and 17% to 49% for higher impact velocities). However, the effects of multiple impacts were smaller than the differences observed across individual helmet types. Helmet protective properties were associated with local chin bar characteristics, most notably chin bar length at higher impact velocities. Towards the goal of reducing overall head/brain injury risk in cyclists, there may be value in complimentary messaging about the importance of repeated impacts and helmet type on the protective properties of downhill mountain biking helmets.
Footwear fit is very important in tennis, directly influencing comfort, security and performance. Within the current literature, there are no in-depth studies regarding the fit of tennis shoes, resulting in a lack of knowledge regarding the effect of player expertise on fit preference. Therefore, the main purpose of this study was to determine optimal inner-shoe dimensions for tennis players. A total of 34 tennis players were recruited and divided into two groups based on frequency of play (occasional and regular). Each subject’s feet were measured, and they were then asked to assess each of the four tennis shoes, which varied in dimension, through the use of a questionnaire. A repeated measure analysis of variance and Pearson’s correlation coefficient were performed to analyse shoe–foot dimensional difference and subjective fit rating. The analysis of variance revealed significant differences on fit rating between shoes. Correlations were found between shoe–foot dimensional differences at length, metatarsal width and metatarsal girth. The optimal shoe length was determined to be nearly 10 mm longer than the foot for both occasional and regular players; the optimal shoe metatarsal width was 8.4 mm less than the foot for regular players; the optimal shoe metatarsal girth was 9.5 mm less than the foot for occasional players and 14.7 mm less than the foot for regular players.
In the world of fast-growing technology, switch from traditional wooden and metallic sports racquets to next generation powerful racquets is inevitable with the advent of carbon fibres, which offer benefits like increased strength, stiffness, impact, and efficient vibration and damping properties. The introduction of carbon fibres, however, comes with challenges of choosing a right matrix system that, in combination, provides the best solution without sacrificing performance. Non-crimp fabric thin C-Ply composites have the potential to suppress the micro cracks and delamination until the material’s ultimate strength. But still, their usage and the possible advantages they can offer in sports applications like tennis racquets, badminton racquets or table tennis bats and so on are yet to be explored. This article aims at exploring the niche benefits offered by thin C-Ply™ carbon fibres in combination with thermoset and thermoplastic matrices in sports applications, especially racquets. The composites comprised multi-axial reinforcement fabrics/non-crimp fabrics infused with a room-temperature cure epoxy or a thermoplastic resin having low mix viscosity (200 cps) suitable for vacuum-assisted resin infusion. The mechanical properties of carbon fibre thin C-Ply/(thermoplastic or thermoset) composites pivotal in racquets, like tensile and flexural stiffness and modulus, have been determined experimentally. Double cantilever beam Mode I tests are also carried out to determine the bonding strength between the plies and the matrix interface as most of the failures in sports equipment are accompanied by either bond failures or imperfections within the structure. The findings of testing of various specimens are presented and discussed.
The material selection for shoe soles is important as it determines the long-term performance of sports shoes, especially the performances of athletes’ shoes with respect to comfort during walking, running and jumping. An effective approach is developed to establish a strong interface between the carbon nanotube and high-density polyethylene/ethylene propylene rubber matrix by introducing electron beam radiation to the nanocomposite as a crosslinking technique. This study focuses on the carbon nanotube variation in the polymer matrix of high-density polyethylene and ethylene propylene rubber. The mechanical properties of high-density polyethylene/ethylene propylene rubber–carbon nanotube nanocomposites with different carbon nanotube contents were investigated at 0.5, 1, 3 and 5 wt% of carbon nanotube content. The combinations of nanofillers and polymer matrix stimulate the performance of sports shoes soles since each of them exhibits superior properties. The aim of this article is to find the optimum carbon nanotube content over the mechanical properties of electron beam–irradiated high-density polyethylene/ethylene propylene rubber nanocomposite for shoe soles. These irradiated nanocomposites are melt blended before compression moulding of the specimens. The specimens were then irradiated under electron beams at 100 kGy. The irradiated nanocomposites were tested for their tensile, impact, hardness and wear properties. The morphology of the tensile failure fracture was analysed under a field emission scanning electron microscope. The addition of carbon nanotubes improved the mechanical properties of the samples for both unirradiated and irradiated nanocomposites; however, they dropped after 3 wt% of carbon nanotube content. The carbon nanotube content at 3 wt% was found to be the most effective in enhancing the mechanical properties, particularly wear in irradiated nanocomposite, due to the better crosslinking and carbon nanotube dispersion.
Turnover of a badminton shuttlecock is the flipping motion of the shuttlecock after its initial contact with the racket. During the process, the shuttlecock experiences a large change in heading. In this article, the turnover stability of the shuttlecock is investigated through experiment and simulation. Three types of badminton shuttlecocks are experimentally evaluated: one feather shuttlecock (Li-Ning A+600) and two synthetic ones (Yonex Mavis 350 and Mizuno NS-5). The experimental results are applied to a response model that takes the form of an under-damped second-order transfer function. This angular response model is then used for the identification of the turnover parameters: the damping ratio and the time constant. The identified parameters are subsequently used as input for building a response function to predict the turnover angular behaviour of the shuttlecock. The feather shuttlecock, which has the highest damping ratio and the lowest time constant, is the shuttlecock with the best turnover stability. Finally, the simulated pitching moment components of the feather shuttlecock are evaluated.
The study of teammates’ interaction on team sports has been growing in the last few years. Nevertheless, no specific software has been developed so far to do this in a user-friendly manner. Therefore, the aim of this study was to introduce a software called the Performance Analysis Tool that allows the user to quickly record the teammates’ interaction and automatically generate the outputs in adjacency matrices that can then be imported by social network analysis software such as SocNetV. Moreover, it was also the aim of this study to process the data in a real-life scenario, thus the seven matches of the German national soccer team in the FIFA World Cup 2014 were used to test the software and then compute the network metrics. A dataset of 3032 passes between teammates in seven soccer matches was generated with the Performance Analysis Tool software, which permitted a study of the network structure. The analysis of variance of centrality metrics between different tactical positions was made. The two-way multivariate analysis of variance revealed that the strategic position (
A photoelectric detection algorithm for measuring football bounce rate based on horizontal displacement compensation has been developed. This algorithm is able to correct the horizontal movement of a free falling object affected by breeze or wind. The horizontal deviation between the football center and the gravity line during the first free fall was calculated, according to which test passes were determined. If a test satisfies the passing standard, then the first rebound height was compensated by horizontal displacement. A previously developed football bounce rate detector was used for experiments, and the results showed that the football bounce rate photoelectric detection algorithm based on horizontal displacement compensation can effectively overcome the impact of a range of breeze or wind, and the absolute detection errors were within the range of 1%.
The present paper discusses the use of a Kalman filter-based method to identify fall events during rock climbing activity. The proposed technique relies on the acquisition of three-axis acceleration and altitude by means of a data logger integrated within the climber’s sit harness. Time-domain results exhibit the working principle of the algorithm. Furthermore, the data provided by eight climbers is analysed and discussed to validate the method.
Shock absorbance, or force reduction, is the most significant parameter in sport surfaces which has been used as an injury prevention criterion. Many sport federations like the International Association of Athletics Federations, the International Federation of Association Football and the International Hockey Federation have arranged force reduction tests for sport surfaces which are performed by an apparatus called the Artificial Athlete Berlin. As this apparatus has been designed for simulating a normal subject at usual conditions, some major details are neglected. In this article, a finite element model, which included the human lower limb and a standard sport surface, was developed and is capable of extracting force reduction parameters in various sport conditions. The viscoelastic behavior of the sport surface was extracted by compression stress-relaxation tests with various strain rates to import into the finite element model. To calculate the shock absorbance of the sport surface, the contact pressure versus time curves were plotted for the top and bottom layers of the sport surface. The difference between peak values of curves was extracted as the sport surface shock absorbance ability. To validate the proposed model, a finite element model which included the Artificial Athlete Berlin apparatus was simulated. The results present an excellent correlation between the proposed and the Artificial Athlete Berlin apparatus models. Also, the shock absorption value obtained by the proposed model was close to the average value reported by the ASTM F2772 standard which the sport surface meets.
Major international target archery competitions usually include a 72-arrow ranking round and then one-on-one knockout matches conducted over a small number of arrows until one archer remains. This article considers the relation between an archer’s placing in the ranking round and the likelihood of that archer finishing with a high place following the one-on-one matches. The archer’s ranking round score has been used as an indication of the archer’s ability in the matches and used to calculate the probability of the archer winning sufficient matches in succession to succeed in the competition. It has been found that the probability of the archer winning the competition decreases exponentially with ranking place. This has been compared with the results from all major international target archery competitions between 2000 and 2014 inclusive and provides a good match. Given the importance of the ranking round, it is suggested that an archer needs to finish in about the top 8 places in the ranking round if the archer is to have good prospects of winning a medal. The score trend for eighth place provides an indication of the likely score required in future competitions, such as the 2016 Olympic Games.
The agility T-test and countermovement jump test have long been used to examine the agility of athletes. However, for some sports, newer systems of evaluation are being designed for specific movements. The goal of this study was to design a blocking agility system and apply it to analyzing the efficiency of 6 weeks of plyometric training on volleyball players. A total of 26 male volleyball players in Taiwan participated in the study. The participants were divided into a plyometric training group and a control group. The agility T-test, countermovement jump test, and blocking agility test were used to examine the influence of plyometric training on the blocking agility of volleyball players. A single-factor analysis of covariance was applied to obtain the variables for the two groups. There was no significant difference between the groups on the agility T-test. On the countermovement jump test and blocking agility test, the plyometric training group performed significantly better than the control group. Also, the power values of blocking agility were higher than 90%, which demonstrated very good validity. The results of this study indicate that appropriate plyometric training can increase the rate of force development for vertical jumps and significantly enhance the combined agility of volleyball players in terms of lateral-movement speed and quickness, which enable players to rapidly perform blocking actions.
The objectives of this study were to assess volleyball speed and impact force and to analyse the differences between these properties. Three types of volleyballs were used in this study: MVA200, weighing 270 ± 10 g; Prototype Ball A (Type A), weighing 270 ± 10 g; and Prototype Ball B (Type B), weighing 340 ± 10 g. Vertically downward 3-m impact tests were conducted using a serving machine, force plate, and radar speed gun. Contact time, ball speed, mean force, peak force, total impulse, initial momentum, incident impulse, and lost momentum were calculated. Intraclass correlation coefficients were calculated to evaluate the reliability of the data, and one-way analysis of covariance and Scheffe’s post hoc analysis were used to analyse the variables of the three ball types. The paired samples t-test was used to compare the difference between initial momentum and incident impulse. The results indicated that the intraclass correlation coefficients of the three ball types were 0.998 (MVA200), 0.997 (Type A), and 0.999 (Type B). Type B considerably surpassed Type A and MVA200 in mechanical factors, and Type A was significantly superior to MVA200 in incident impulse and lost momentum. The results indicated that different volleyballs of the same size, weight, and internal air pressure have dissimilar mechanical features and implied that slight adjustment to ball structure can cause substantial changes in the specific characteristics. In addition, the mass increased the lost momentum, which might cause the ball to bounce unpredictably.
Concussion has become a prevalent injury in the sport of American football, and its severity can be influenced by the mass of the impactor, velocity, compliance, and direction of impact. As a result, it is important to characterize how American football helmets perform against these impact characteristics. The purpose of this research is to examine how an American football helmet performs across velocities and impact angles which can occur in the sport of American football. The methods used a combination of Hybrid III headform impacts combined with a finite element modeling approach to find the brain deformation variables known to be associated with concussion. At the 9.5 m/s impacts, the brain deformation metrics showed an increase in risk of concussion. Also, the region of the brain with the largest magnitude deformation shifted with differing velocities when analyzed using maximum principal strain but not von Mises stress. The results indicate that impact conditions (location and velocity) can influence the regional brain strains.
Football fields of artificial turf are in constant evolution. The resulting improvements have given rise to a large diversity of structural components. There are various types of infill and fibre for artificial turf and different designs and materials for the support structure (sub-base and elastic layer). The design of the sub-base and the presence or absence of the elastic layer can influence turf performance and the surface’s useful lifetime. The aim of this study was to assess in situ the effect of the various support structures on the mechanical properties of artificial turf after deterioration caused by wear for a year. The assessed properties were force reduction (%), standard vertical deformation (mm), rotational traction (N·m), vertical ball rebound (%), and ball roll (m), according to the requirements in norm EN 15330-1:2007. The results demonstrate the effect of the structural base on the mechanical and functional performance of football fields of artificial turf, as well as the significant deterioration of the properties over a year which varied between 3.14% and 8.92% with regard to the installed system. These results show that the support structure that provides the greatest durability and adequate behaviour of the mechanical properties over time is that which has a sub-base of compacted gravel under an elastic layer.
Wind-tunnel experimental measurements of drag coefficients for non-spinning Jabulani and Brazuca balls are presented. The Brazuca ball’s critical drag speed is lower than that of the Jabulani ball, and the Brazuca ball’s super-critical drag coefficient is larger than that of the Jabulani ball. Compared to the Jabulani ball, the Brazuca ball suffers less instability due to knuckle-ball effects. Using drag data, numerically determined ball trajectories are created, and it is postulated that although power shots are too similar to note flight differences, goalkeepers are likely to note the differences between Jabulani and Brazuca ball trajectories for intermediate-speed ranges. This latter result may appear in the 2014 World Cup for goalkeepers used to the flight of the ball used in the 2010 World Cup.
American football helmets are subjected seasonally to a myriad of environmental conditions from expected use and storage and yet are reused without a relational understanding between service life degradation and changes in impact performance. Comprehensive investigations could link rates and degrees of material degradation to scientifically and clinically meaningful changes in helmet performance. Therefore, the purpose of this research was to preliminarily quantify the effects of accelerated weathering on (1) colorimetric, chemical, fluorescent, and thermal properties; (2) surface and bulk mechanical properties; and (3) impact performance of an American football helmet outer shell material. Helmet-grade plaques were exposed to 480 h of accelerated weathering. Surface-specific shifts (p < 0.05) in colorimetric, chemical, fluorescent, thermal, and mechanical properties were observed at the plaque surface. Plaque-derived tensile specimens underwent monotonic tensile testing, and the photodegraded ~1% of the Weathered plaque surface thickness led to 10%, 12%, and 9% increases (p < 0.05) in Young’s modulus, yield stress, and ultimate tensile stress, respectively. Impact performance was analyzed with a protocol attempting to employ expected on-field impact conditions. Weathered and Non-weathered helmet surrogate systems managed impact energy progressively less effectively across five repetitive trials (p < 0.05); yet the absence of significant Weathered differences demonstrated that the plaque–foam systems performed similarly. Results identified a battery of diagnostic tools to characterize the degradation of outer shell material exposed to accelerated weathering. Thus, the comprehensive approach herein may be used toward the evaluation of additional service life exposures, as well as examine on-field deterioration of full helmet outer shells.
This study investigated the reliability of the recently released low-cost NaturalPoint OptiTrack 250e camera system across different measurement designs. Results are compared to an already well-established motion capture system from Vicon Motion Systems Ltd (Oxford, UK). The OptiTrack performed well across measurement conditions. Provided with the AMASS software kit from C-Motion (Germantown, MD, USA), nine distances from three rigid bodies (ten markers) were used to calculate measurement accuracy. Independent t-tests, a one-way multivariate analysis of variance, intra-class correlation coefficients, and the standard error of measurement were computed for all conditions to evaluate the differences and the reliability of the systems. The results suggest that the NaturalPoint OptiTrack 250e camera system is a reliable working system that can certainly be used in biomechanics and other related fields.
This work reports the evaluation of the mechanical behaviour of Telemark ski boots, by means of an integrated approach, considering polymeric material characterisation, reported in a previous study (Part I), and numerical structural analysis, reported in this study (Part II). Telemark boots entail a complex procedure for analysis of the mechanical response, with regard to both material assumption and overall structural behaviour, and represent a reference problem within sky footwear in consideration of this peculiar complexity. A visco-elastic constitutive model is formulated to describe the material mechanical response defined in accordance with experimental test performed. Solid models define the morphology of the ski boots and represent the basis for numerical modelling. Specific boundary conditions are assumed to mimic the binding effect. The numerical analysis leads to an interpretation of the global and local responses of a specific Telemark ski boot, considering material properties and structural conformation. The results provide valid information on the ski boot mechanical response, taking into account also the effects of temperature on material response and strain rate with regard to loading conditions. The evaluation of variations in shape and material of the different components can be performed representing a fundamental support for the design.
This study reports the first part of the analysis for the evaluation of the mechanical behaviour of ski boots by means of an integrated approach that considers polymeric materials characterization, in Part I, and numerical structural analysis, in Part II. In the present Part I, different techniques are adopted to characterize the mechanical behaviour of the polymeric materials used for ski boots, to define the elastic, visco-elastic, temperature and weathering-dependent characteristics. Experimental data provide fundamental information on mechanical response, in particular taking into account the effect of the environmental conditions, due to temperature variation, ultraviolet radiation and water absorption, which are correlated to the definition of reliability and durability of the materials. In more detail, experimental results from tensile tests and dynamic mechanical analysis are reported, evaluating mechanical response and chemical conformation of the polymers. Materials properties are correlated with the specific use conditions and boot structure, to be able to evaluate and preserve overall performances and general safety requirements of ski boots. This activity represents a reference procedure for the evaluation of the material mechanical behaviour that must be considered within the structural analysis.
Despite the potentially negative effects on play performance and safety, little is currently known about the spatial and temporal variability in the properties of artificial turf pitches. The primary purpose of this study was to quantify the spatial and temporal variations in surface hardness across a 5-year-old third-generation artificial turf pitch over full year cycle. The secondary purpose was to investigate the key variables that contributed to these variations in surface hardness using a correlation approach. Surface hardness (2.25 kg Clegg impact hammer, average of drops 2–5), ground temperature and infill depth were measured at 91 locations across the third-generation artificial turf pitch in 13-monthly test sessions from August 2011 to August 2012 inclusive. For each month, rainfall in the 24 h prior to testing and pitch usage statistics were also obtained. Shockpad thickness was obtained from measurements taken when the carpet was replaced in 2007. Spatial and temporal variations were assessed using robust statistical measures while Spearman correlation was used to assess the contributions of the secondary variables to surface hardness variability. The results indicated that spatial variation in surface hardness exceeded temporal variation; the former demonstrated a median absolute deviation of 12 ± 1 G across the pitch in any test session while the median absolute deviation for the latter was only 4 ± 2 G across the 13 test sessions. Spatial variation in surface hardness was moderately correlated with shockpad thickness and weakly correlated with infill depth (both negative). These results reinforce the importance of monitoring spatial and temporal variations in play performance variables for third-generation surfaces as well as providing support for the role of maintenance in minimising the spatial variation.
A sprint kayak experiences an unsteady flow regime due to the local influence of the paddle. However, kayak designs are usually optimised for steady-state, naked hull resistance. To determine whether unsteady paddle effects need to be included in kayak design, the hydrodynamic interactions between a kayak paddle and a hull are assessed using computational fluid dynamics. A body force model of a drag-based paddle stroke is developed using a blade element approach and validated against experimental data. This allows the paddle-induced local velocities to be simulated without the need to fully resolve the detailed flow around a moving paddle geometry. The increase in computational cost, compared to the naked hull simulation, is 8%. A case study investigating the impact of different paddle techniques on the hydrodynamic forces acting on a self-propelled kayak is conducted. A 0.23% difference in self-propelled resistance was observed, while an estimated 0.5% additional increase can be attributed to paddle-induced draught increases. An estimate of small changes in resistance on race times indicates that reductions of even a fraction of a percent are worth pursuing, indicating that the developed methodology may provide a useful design tool in the future.
In soccer, it seems relevant to understand the relationship between the ball recovering and the subsequent success or failure of attacking play. However, few studies have considered the links between the type of ball recovery in different pitch zones, the competition stages and the overall teams success. The present study aims to analyze the attacks (n = 1619) carried out by the semi-finalist teams in the 2010 FIFA World Cup in order to explore ball recovery patterns as a performance indicator. SoccerEye observational instrument, SoccerEye recording software, Sequential Data Interchange Standard-Generalized Sequential Querier (SDIS-GSEQ) and SPSS analytic software—one-way analysis of variance, two-way analysis of variance and regressions—were applied. Direct ball recovery, in specific by interception and defensive behavior followed by a pass, was the mostly frequent behavior, with the later inducing attacking play efficacy (p < 0.017). Differences were detected between the group and play-off stages with regard to the types of direct ball recoveries. The ball was most often regained in defensive and mid-defensive central zones, evidencing differences to all other pitch zones (p ≤ 0.001). Throw-ins were the only type of ball recovery that differentiated the semi-finalists, namely Germany and Spain (p < 0.009). It was found that recovering directly the ball possession in mid-defensive central zones increases attacking efficacy. Consequently, coaches should consider this tactical determinant in order to organize the training process. Specifically, it is fundamental to improve the collective defensive organization protecting central strip zones and simultaneously performing high-pitched pressure to constrain the ball carrier.
This article presents a study of torsion stiffness of a specific racing cross-country ski boot for the skating technique conducted by means of numerical analyses and measurements. Its aim is to determine relative torsion stiffness contributions, relative mass contributions, and the ratios between them (torsion stiffness/mass ratios) for individual boot components of the torsionally most deformable part of the boot. These are basic data for torsion stiffness–mass optimization of the boot. For acquiring these data, a complex finite element model of the cross-country ski boot and an artificial silicone foot were created in different versions after an existing device designed for measurement of stiffness properties of the boots. Material properties employed in the model were acquired experimentally. The confirmed model was used for determination of the torsion deformation contributions of different regions of the boot. Focus was given to the middle region, whose contribution is the largest. The aforementioned data were determined for individual boot components of this region. The soles, which contribute the most to the middle region’s torsion stiffness, turned out to have the highest potential for torsion stiffness–mass optimization, because of their lowest torsion stiffness/mass ratio and highest mass contribution. The shoe-upper has the highest torsion stiffness/mass ratio and is, therefore, the most worthwhile to be enlarged. The torsion stiffness/mass ratio of the strengthening bands is lower than expected and could likely be increased by their positioning.
Modern arrow shafts are usually tubular and are constructed using high-strength materials, with most competition arrows now using carbon fibre composites. The need to mount the arrow components (and in particular the arrow point) internally and the need to retain sufficient wall strength to avoid crushing combine to set design limits on the arrow’s mass–diameter relationship for a given arrow shaft material. This article considers those design limits and the consequent selection of the optimal arrow shafts to use for the various types of major archery competitions, depending upon the major score-detracting factors. It is shown that for a given arrow shaft material, a simple set of rules can be used for the selection.
Wrist injuries during snowboarding are very common. An instrumented snowboarding glove was developed to measure flexion/extension of the wrist in the sagittal plane, as well as forces and moments at the hand and wrist joint during snowboarding. On-slope data were analyzed from 128 falls resulting in hand impacts for 20 snowboarders. Impact forces and wrist extension moments varied widely by age, experience level, and fall direction. Backward falls resulted in significantly higher maximum force than forward falls (p = 0.038). Adults had significantly higher maximum force (p = 0.026) and maximum extension moments compared to young adults (p = 0.049). Beginners suffered more impacts that resulted in higher maximum loads generated and wrist angles that did not reach terminal extension. A significant percentage of all falls resulted in wrist extension near terminal extension. This study provides novel hand and wrist biomechanical data in snowboarding falls that can be used to guide the development of wrist protector standards and products.
Wetsuits are an integral part of surfing especially in the southern regions of Australia. There is currently little information about mechanical, comfort and thermal properties of wetsuits. There is a demand from wetsuit manufacturers to better understand the neoprene properties and wetsuit performance. The performance characteristics of eight top-selling wetsuits, from both high end and low end of the market, were examined. These characteristics include thickness, elasticity, bursting strength, hydrophobicity, thermal conductivity and seal strength. Tensile assessment revealed that neoprene foam was strong and its stretch recovery was well beyond 1.6 times of the original length. Neoprene was found to be hydrophobic with very low surface energy. High-end wetsuits with higher thickness showed slightly higher thermal resistance than low-end wetsuits, indicating that both thickness and bulk density of neoprene influenced thermal properties. High-end wetsuits with fluid seal were stronger than low-end wetsuits with stitched seal.
This study examined the mechanical behaviour of the Japanese bo during simulated attack and defence manoeuvres with the aid of finite element analysis. The bo properties varied were handgrip location along the bo shaft and shaft diameter. It was found that an optimal attacking response could be achieved for the following factors: (1) the striking point on the attacking bo, (2) the holding point on the attacking bo, and (3) the diameter of the attacking bo. In addition, the defending response was optimal when defending with an attacking stance. Optimal bimanual grip locations were identified to be in agreement with common practices exhibited by karate practitioners. It was also found that bo geometric construction properties substantially modified the mechanical response. Further empirical testing is needed to verify the finite element analysis findings.
This article presents a novel video analysis system for coaching tennis players of all levels, which uses computer vision algorithms to automatically edit and index tennis videos into meaningful annotations.
Existing tennis coaching software lacks the ability to automatically index a tennis match into key events, and therefore, a coach who uses existing software is burdened with time-consuming manual video editing. This work aims to explore the effectiveness of a system to automatically detect tennis events. A secondary aim of this work is to explore the benefits coaches experience in using an event retrieval system to retrieve the automatically indexed events. It was found that automatic event detection can significantly improve the experience of using video feedback as part of an instructional coaching session. In addition to the automatic detection of key tennis events, player and ball movements are automatically tracked throughout an entire match and this wealth of data allows users to find interesting patterns in play. Player and ball movement information are integrated with the automatically detected tennis events, and coaches can query the data to retrieve relevant key points during a match or analyse player patterns that need attention. This coaching software system allows coaches to build advanced queries, which cannot be facilitated with existing video coaching solutions, without tedious manual indexing. This article proves that the event detection algorithms in this work can detect the main events in tennis with an average precision and recall of 0.84 and 0.86, respectively, and can typically eliminate manual indexing of key tennis events.
The traction developed at the shoe–surface interface can have a significant influence on a player’s injury risk and performance in tennis. The purpose of this study was to investigate shoe–surface traction on a dry acrylic hard court and two artificial clay court tennis surfaces in dry and wet conditions. A laboratory-based mechanical test rig was developed to measure the traction force developed at the shoe–surface interface. Linear regression analysis was used to examine the relationship between normal force and three measures of traction: initial stiffness, peak traction force and average dynamic traction force. The normal force did not significantly influence the initial stiffness for the shoe–surface system on the acrylic hard court but did on the artificial clay surfaces. The infill particle size and the addition of moisture influenced the traction developed on the artificial clay surfaces. Small, dry particles developed greater traction and with a sufficiently high applied normal force will provide traction comparable to that on an acrylic hard court. However, increased particle size and/or the presence of moisture generally reduced traction. Strong and significant positive linear relationships were found between peak traction force and average dynamic traction force for all surface types and conditions. This study improves the understanding of the influence surface characteristics have on shoe–surface traction mechanisms. Once traction mechanisms are understood, surface properties and/or footwear can be effectively changed to maximise performance and/or minimise injury risk.
A wireless sensor system has been used to calculate measurable performance parameters throughout a swimmer’s tumble turn. The parameters to be measured have been specified by the users (coaches, biomechanists and swimmers) of the system. The findings suggest that the wireless sensor network can be used to determine the approach time, contact time, glide time, kick time and stroke time to within 0.07 ± 0.16 s of the results obtained using manual digitisation of video images obtained from an underwater camera. It is concluded that it is possible to determine the swimmer’s time, orientation and velocity throughout the turn using the implemented inertial navigation system.
An arrow exiting a recurve archery bow flexes laterally. This is important in ensuring that the rear of the arrow clears the bow without obstruction and is a consequence of the manner by which the string leaves the archer’s fingers. Pekalski and then Kooi and Sparenberg modelled the arrow behaviour during the bow’s power stroke using a flexible beam. In this article, the method used by Kooi and Sparenberg has been extended to remove subjective components, to include the carbon fibre composite arrows now used almost exclusively in competition and to consider the arrow after it has left the bow. The various user-selectable parameters have been examined to ascertain their impact on archer performance. The modelling was tested against measured parameters of a number of expert archers and against the use of the recurve bow in a shooting machine.
A wireless sensor network has been developed and used to monitor the important performance parameters pertaining to a swimmer’s start. The variables identified as important include time to back foot leaving the block, time to hip entry into the water, time to first kick, time to first stroke, number and rate of the underwater kick and stroke count and rate. These parameters were specified by the users (coaches, biomechanists and swimmers) of the system. The measurements were validated against the vision analysis system currently used during in-water training with the national swimming team. From the results, it can be suggested that the wireless sensor network can be used as an automated system for monitoring performance parameters considered of importance to the user during the swimming start.
Swing describes the lateral deviation of a cricket ball in its trajectory towards the batsman. Conventional swing is effective with a new, or well-preserved, ball, and the fluid dynamics governing this phenomenon was first explained in 1957. In 2012, many test-match fast bowlers are able to swing, at high speed, an older ball in the reverse direction. This reverse swing of a ball aged under match conditions has never been explained fully. A cricket ball is asymmetric with six seams of 80–90 encircling stitches, protruding approximately 1 mm proud of the surface. Both conventional and reverse swings are a consequence of asymmetrical flow separation leading to a skewed wake and a net pressure force on the ball perpendicular to the flight trajectory. Here, experimental evidence is presented for the first time showing that the formation of a laminar separation bubble is the prominent flow feature creating the flow asymmetry for reverse swing. A new flow visualisation technique to capture the fluid dynamics of boundary-layer separation using an infrared camera is also introduced here.
The aim of this study was to determine whether dynamic breast properties could be used as objective measures of discomfort in the breast during running. Relative breast motion was measured in eight women with breast sizes ranging from 32A to 34G while running on a treadmill at 10 and 14 km·h–1 wearing either no bra, an everyday bra or an encapsulated sport bra. Kinematic data was converted to dynamic strain, max, and differentiated twice to give maximum dynamic acceleration, amax. Discomfort scores from 0 to 10 (comfort to discomfort) were recorded after each test. Discomfort was found to increase with both max or amax; additionally max and amax generally demonstrated a positive linear relationship for all participants. Discomfort score and max increased with breast size, while discomfort score and amax decreased with the use of a bra. A transition between comfort (scores between 0 and 5) and discomfort (scores between 6 and 10) was approximated on the basis of max and amax and tested against the real score given by the participants. The simple model agreed with the participants’ perceptions of discomfort in 77% of cases and was 10.5 times more likely to predict the classification correctly than incorrectly. It was concluded that breast discomfort during exercise is a function of both max and amax, and strategies to decrease discomfort in the breast during exercise should aim to minimize both parameters.