To access, purchase, authenticate, or subscribe to the full-text of this article, please visit this link: http://dx.doi.org/10.1007/s12283-017-0234-1 Aerodynamics has such a profound impact on cycling performance at the elite level that it has infiltrated almost every aspect of the sport from riding position and styles, equipment design and selection, race tactics and training regimes, governing rules and regulations to even the design of new velodromes. This paper presents a review of the aspects of aerodynamics that are critical to understanding flows around cyclists under racing conditions, and the methods used to evaluate and improve aerodynamic performance at the elite level. The fundamental flow physics of bluff body aerodynamics and the mechanisms by which the aerodynamic forces are imparted on cyclists are described. Both experimental and numerical techniques used to investigate cycling aerodynamic performance and the constraints on implementing aerodynamic saving measures at the elite level are also discussed. The review reveals that the nature of cycling flow fields are complex and multi-faceted as a result of the highly three-dimensional and variable geometry of the human form, the unsteady racing environment flow field, and the non-linear interactions that are inherent to all cycling flows. Current findings in this field have and will continue to evolve the sport of elite cycling while also posing a multitude of potentially fruitful areas of research for further gains in cycling performance.
Tandem cycling enables visually impaired athletes to compete in cycling in the Paralympics. Tandem aerodynamics can be analysed by track measurements, wind-tunnel experiments and numerical simulations with computational fluid dynamics (CFD). However, the proximity of the pilot (front) and the stoker (rear) and the associated strong aerodynamic interactions between both athletes present substantial challenges for CFD simulations, the results of which can be very sensitive to computational parameters such as grid topology and turbulence model. To the best of our knowledge, this paper presents the first CFD and wind-tunnel investigation on tandem cycling aerodynamics. The study analyses the influence of the CFD grid topology and the turbulence model on the aerodynamic forces on pilot and stoker and compares the results with wind-tunnel measurements. It is shown that certain combinations of grid topology and turbulence model give trends that are opposite to those shown by other combinations. Indeed, some combinations provide counter-intuitive drag outcomes with the stoker experiencing a drag force up to 28% greater than the pilot. Furthermore, the application of a blockage correction for two athlete bodies in close proximity is investigated. Based on a large number of CFD simulations and validation with wind-tunnel measurements, this paper provides guidelines for the accurate CFD simulation of tandem aerodynamics.
Helmet design and development are an important tool to help mitigate the severity and frequency of head and brain injury in sport and everyday life. Helmet assessment protocols and standards often use the Hybrid III neckform as part of the impacting equipment even though it has a biased response that can affect the results. This research presents an unbiased neckform that can be used for the purposes of head impact testing that does not provide a mechanical directional bias to the impact result. A Hybrid III headform was impacted under a sporting impact protocol with a Hybrid III and an unbiased neckform. The resultant acceleration magnitudes were similar between the two necks, while larger differences (8 g and up to 4 krad/s2) were found between the acceleration components. The Hybrid III neck may have a more biased response for longer duration events (10 ms+) as this research considered only short duration impacts (5–10 ms).
The following compares the effect of differentiation methods used to acquire angular acceleration from three types of un-helmeted headform impact tests. The differentiation methods considered were the commonly used 5-point stencil method and a total variation regularization method. Both methods were used to obtain angular acceleration by differentiating angular velocity measured by three angular rate sensors (gyroscopes), and a reference angular acceleration signal was obtained from an array of nine linear accelerometers (that do not require differentiation to obtain angular acceleration). For each impact, three injury criteria that use angular acceleration as an input were calculated from the three angular acceleration signals. The effect of the differentiation methods were considered by comparing the criteria values obtained from gyroscope data to those obtained from the reference signal. Agreement with reference values was observed to be greater for the TV method when a user-defined tuning parameter was optimized for the impact test and cutoff frequency of each condition, particularly at higher cutoff frequencies. In this case, mean absolute error of the five-point stencil ranged from 1.0 (the same) to 11.4 times larger than that associated with the TV method. When a constant tuning parameter value was used across all impacts and cutoff frequencies considered in this study, the TV method still provided a significant improvement over the 5-point stencil method, achieving mean absolute errors as low as one-tenth that observed for the five-point stencil method.
A new measurement system (horizontal displacement, time of flight, synchronicity—HDTS) was investigated regarding the latest changes to the international evaluation rules in trampoline gymnastics. It allows for the real-time measurement of objective criteria, such as flight time and landing position, without affecting the gymnast. The aim of this study was to investigate the temporal and spatial accuracy of a measurement tool via cross-validation. Temporal precision was additionally tested via high-speed video landing and takeoff, while a three-dimensional motion capturing system was incorporated for spatial precision. The Bland–Altman “limit of agreement approach” was used for the assessment of congruence between the measurement systems. The new measurement system presented an average spatial deviation of 3.2 cm and a temporal deviation between − 5.8 and + 6.4 ms for the landing and − 11.3 and + 11.3 ms for the takeoff. Given its temporal and spatial accuracy in determining flight time and landing position as identified through cross-validation, the novel HDTS system proved to be suitable for its use in trampoline competitions.
Concussive and subconcussive sports-related head impacts are common in the United States, particularly in American football. Football helmets are constantly improving upon their predecessors and are proven to reduce head impact kinematics and the risk of sports-related head injury. All football helmets are required to pass certification testing overseen by the National Operating Committee on Standards for Athletic Equipment (NOCSAE) before they are permitted for use. A new advance in protective equipment involves coupling a helmet and shoulder pads as one connected piece of protective equipment. These protective gears cannot be tested using the standard NOCSAE method as they are worn over a user’s head, neck, and upper torso. We aimed to test the effectiveness of a prototype of a coupled, one-piece design, relative to a standard football helmet, using a custom drop tower method of testing. Relative to the standard football helmet, the coupled design reduced measures of peak linear acceleration at front, side, and rear impacts (p < .001) and peak rotational acceleration at all tested head locations (p < .004). The coupled design was also more effective than the standard helmet in attenuating the resultant upper neck force (p < .004) at all tested head impact locations and resultant upper neck moment at rear and side impact locations (p < .048). Future iterations of coupled, one-piece designs should use the results of this study to make improvements to the device, and further investigations on the effectiveness and safety implications of the protective gear are necessary.
This paper presents a method to estimate a time-sequential trajectory of the center of mass (CoM) of an athlete from a multi-view set of cameras. Collecting the CoM typically requires large-scale measuring systems or attaching sensors to the athletes. To mitigate such hardware limitations, the present study takes a multi-view video-based approach. The proposed method reconstructs subjects’ voxels from a set of multi-view frames and weights each voxel with body part-dependent weights to calculate a CoM. Our results, using real data measured in a studio, showed that the proposed method can estimate CoM within 20 mm concerning center of pressure measures.
We present a method for quantifying sacral kinematics during countermovement jumping (CMJ) using an inertial measurement unit (IMU). The IMU-derived sacral kinematic trajectories reproduced motion capture acceleration, velocity, and displacement to within mean (standard deviation) differences of 0.024 (0.088) m/s2, 0.023 (0.026) m/s, and 0.003 (0.032) m, respectively, across 252 jumps performed by 14 subjects. The method also quantified differences in maximum sacral displacement to within 1 % and differences in maximum propulsive velocity to within 0.7 % of motion capture estimates. This builds upon existing IMU-based methods for quantifying jump performance, which do not provide sacral kinematic trajectories. The utility of this method is demonstrated by its ability to discriminate jump performance metrics across a diverse subject population. In particular, we found that 21 participants adopted multiple strategies to maximize jump height in unloaded and loaded fresh conditions, but converged to a common strategy when jumping fatigued and under load. Changes in kinematic parameters were evident across conditions, and several changes were significantly associated with changes in jump performance (i.e., height). These parameters include changes in the depth of the countermovement, duration of the propulsive phase and maximum propulsive velocity. Collectively, these results point toward the future use of this method in naturalistic environments and for multiple objectives including biomechanical performance assessment and tracking, fatigue assessment, and jump training.
Determining an athlete’s speed from broadcast video is a common practice in sport. Many software packages that perform data extraction from video files are expensive; however, open source software is also available, but lacks published validation for speed measurements. The purpose of this research was to examine the error of speed measurements extracted from video during an ice hockey skating exercise using open source software. The subject completed four exercises, at two speeds recorded by broadcast cameras set at five angles. The speeds from the broadcast cameras were compared to speeds calculated from a high-speed camera placed orthogonally to the exercise. Speeds from the broadcast cameras correlated well with the high-speed video for motion more than 12 m away from the broadcast camera. When comparing all the measured speeds, no significant difference was found between the speeds calculated by the high-speed camera (slow: 4.46 m/s ± 0.2; fast: 7.2 m/s ± 0.7) and the speed calculated from the broadcast cameras (slow: 4.50 m/s ± 0.4; fast: 7.34 m/s ± 0.6) (p > 0.05). The open source method was found to be less accurate when the athlete was close to (within 12 m of camera position) or moving directly toward the broadcast cameras.
A low-speed wind tunnel investigation is presented documenting drag reduction to a golf driver club. Geometrical modifications (or elements) were attached to the golf driver. The size, spacing, and location of the elements were varied. Wind tunnel velocities spanned a range from the amateur to professional golfer. Measurements included both force balance and surface pressure accompanied by flow visualization to aid in flow diagnostics. The results indicated that a 40% reduction in drag can be achieved, primarily due to reduced pressure over the forward face of the crown and increased pressure over the crown’s aft extents. This reduction in drag was estimated to yield a 0.54 m/s (1.2 mph) club head speed gain, causing a 3.65 m (4 yds) increase in carry distance.
The purpose of this study was to define a method for the validation of a numerical model representing a snowboard structure undergoing the conditions of a carved turn. A static load bench was developed to expose a snowboard to in-situ conditions. The deformed shape of the structure was measured with the use of retro-reflective markers, whose positions in space were tracked by six cameras and determined by triangulation. The experimental set-up was idealized in a finite element model, representing the composite structure and the loading environment. The model was validated by comparing the measured and computed displacement fields. The congruence between the two deformed surfaces was expressed by statistical means and constitutes the target function for optimization frameworks. Additionally, the contact pressure at the ground interface was experimentally assessed with the use of pressure measurement tape and compared with the numerical predictions.
A non-harmful system to visualize the flow around an entire swimmer in a regular swimming pool is developed. Small air bubble tracers are injected through the bottom of the swimming pool in a prescribed measurement area. The motion of these bubbles, which will be largely induced by the swimmer’s motion, is captured by a camera array. The two-dimensional velocity field of the water at arbitrary planes of interest can be resolved using a refocussing method in combination with an optical visualisation method, based on particle image velocimetry, which is commonly used in fluid dynamics research. Using this technique, it is possible to visualize coherent flow structures produced during swimming; it is demonstrated here for the dolphin kick.
There is much debate around the role of shaft stiffness in the dynamic response of the club shaft during the golf swing. This study used a novel complex analysis to investigate within- and between-golfer differences in shaft strain patterns for three shaft stiffnesses. Twelve right-handed male golfers, with a handicap less than or equal to five, hit six shots with three driver clubs which differed only in shaft stiffness. Clubs were instrumented to record the shaft strain in the lead/lag and toe/heel directions. The analysis combined these perpendicular components into a single complex function, which enabled the differences between two swings to be characterised by a scale and a rotation component. Within-golfer strain patterns were found to be significantly more consistent than between-golfer, p < 0.01. Whilst some golfers displayed more similar patterns than others, there were no clear groups of golfers with similar patterns of shaft strain. Between the clubs, shaft strain patterns differed in the scale component, p < 0.01, rather than the rotation, p = 0.07.
Real-time monitoring and feedback of tibial acceleration using wireless skin mounted sensors may reduce the risk of tibial stress fractures in runners. The purpose of this study was to assess the agreement between a wireless accelerometer and a gold standard reference accelerometer, both skin mounted, in measuring peak axial tibial acceleration when treadmill running at a range of speeds. A research grade accelerometer was mounted to a wireless accelerometer and attached to the tibia. Peak positive tibial accelerations of 13 participants were compared at 2.5, 3.5 and 4.5 m s− 1. Intraclass correlation coefficients demonstrated good agreement, with limits of agreement showing accuracy to within 1.2–1.65 g. The wireless accelerometer has scope to be used as a tool to measure peak tibial accelerations during running for the purpose of real-time feedback in gait training systems.
In long-distance competitive cycling, efforts to mitigate the effects of air resistance can significantly reduce the energy expended by the cyclist. A common method to achieve such reductions is for the riders to cycle in one large group, known as the peloton. However, to win a race a cyclist must break away from the peloton, losing the advantage of drag reduction and riding solo to cross the finish line ahead of the other riders. If the rider breaks away too soon then fatigue effects due to the extra pedal force required to overcome the additional drag will result in them being caught by the peloton. On the other hand, if the rider breaks away too late then they will not maximize their time advantage over the main field. In this paper, we derive a mathematical model for the motion of the peloton and breakaway rider and use asymptotic analysis techniques to derive analytical solutions for their behaviour. The results are used to predict the optimum time for a rider to break away that maximizes the finish time ahead of the peloton for a given course profile and rider statistics.
This paper serves as a resource guide for Sports Engineering educators. The paper covers key topics in Sports Engineering, including ball impact, friction, safety and materials. A variety of resource types are presented to reflect modern methods of learning and searching for information, including textbooks, research and review papers, websites and videos. The field could benefit from more resources specifically designated for teaching Sports Engineering, particularly textbooks. (Autor).
To access, purchase, authenticate, or subscribe to the full-text of this article, please visit this link: http://dx.doi.org/10.1007/s12283-016-0219-5 Brain injury research in sport employs a variety of physical models equipped with accelerometers. These acceleration signals are commonly processed using filters. The purpose of this research was to determine the effect of applying filters with different cutoff frequencies to the acceleration signals used as input for finite element modeling of the brain. Signals were generated from reconstructions of concussion events from American football and ice hockey in the laboratory using a Hybrid III headform. The resulting acceleration signals were used as input for the University College Dublin Brain Trauma Model after being processed with filters. The results indicated that using a filter with a cutoff of 300 Hz or higher had little effect on the resulting strain measures. In some cases there was some effect of the filters on the peak linear (830g) and rotational measures (10004000 rad/s.sup.2), but little effect on the finite element strain result (approximately 26 %). The short duration and high magnitude accelerations, such as the puck impact, were most affected by the cutoff frequency of different filters.
In road cycling, the pacing strategy plays an important role, especially in solo events like individual time trials. Nevertheless, not much is known about pacing under varying conditions. Based on mathematical models, optimal pacing strategies were derived for courses with varying slope or wind, but rarely tested for their practical validity. In this paper, we present a framework for feedback during rides in the field based on optimal pacing strategies and methods to update the strategy if conditions are different than expected in the optimal pacing strategy. To update the strategy, two solutions based on model predictive control and proportional–integral–derivative control, respectively, are presented. Real rides are simulated inducing perturbations like unexpected wind or errors in the model parameter estimates, e.g., rolling resistance. It is shown that the performance drops below the best achievable one taking into account the perturbations when the strategy is not updated. This is mainly due to premature exhaustion or unused energy resources at the end of the ride. Both the proposed strategy updates handle those problems and ensure that a performance close to the best under the given conditions is delivered.
The torso angle of a cyclist is a key element to consider when attaining aerodynamic postures. For athletes competing in the tandem para-cycling category as the pilot or stoker, the torso angles are similar to those adopted by able-bodied athletes. However, their aerodynamic interaction is not yet fully understood. To date, there has been no study to identify aerodynamically advantageous torso angles for tandem athletes. In this study, numerical simulations with computational fluid dynamics and reduced-scale wind tunnel experiments were used to study the aerodynamics of tandem cyclists considering 23 different torso angle combinations. The sagittal torso angle combination of the pilot and stoker that yielded the lowest overall drag area of 0.308 m2 (combined pilot, stoker and bicycle) was 25° for the pilot coupled with 20° for the stoker. The results suggest that higher torso angles for the pilot have a lower impact on the overall drag area than equivalent torso angles for the stoker. This study suggests that a slight relaxation of pilot torso angle (which may help increase power output) may not penalise aerodynamics, in low (< 25°) sagittal torso angle ranges.
Sprint canoe paddling is a dynamic and complicated motion performed with the entire body of the paddler. Not only the upper limb motion, but also the motions of the trunk and lower limbs contribute to the propulsion. The objectives of this study were to simulate sprint canoe paddling, and investigate the contributions of the upper and lower limbs, and the trunk, to the propulsion during paddling. In the model, the paddler, paddle, and hull were represented as three rigid bodies, which were connected by virtual springs and dampers. The geometry of the paddler, paddle, and hull, as well as the joint motion of a paddler, was used in the model. It was found that the model could predict instantaneous hull velocity variation, although the average hull velocity was 8% lower than experiment. Two virtual paddling motions, “fixed lower limbs” and “fixed trunk,” were simulated. Comparing the measured original and the two virtual paddling motions, it was found that the lower limb motion during paddling contributed to the propulsion during the catch phase, when the blade entered the water until fully submerged (ratio of the contribution: 14% by upper limbs, 63% by lower limbs and 23% by trunk). It was also found that the upper limb motion contributed to the propulsion during the draw phase, when the paddler pulled the paddle backwards relative to the hull (54% by upper limbs, 30% by lower limbs and 16% by trunk), and that the trunk motion contributed to the propulsion just prior to the paddle exiting the water (7% by upper limbs, 30% by lower limbs and 63% by trunk).