LATEST ARTICLES
Details of the latest articles published in the Journal. Includes the most recent InPress papers (uncorrected proofs of accepted papers awaiting publication in a Journal issue).
Date: Tue, 06 Jul 2010 18:39:00 GMT
Mechanical devices currently used to test sports equipment are limited to one or two and cannot replicate complete human movements. The purpose of this study was to investigate the capabilities of a six-degrees-of-freedom industrial robot (iRobot) to replicate the ground contact phase of human running. The objectives wereas follows: to quantify the repeatability of the iRobot system; to assess the ability of the system to replicate heelstrike running and forefoot running.
High-speed video and force plate data were collected for a single-subject heelstrike running and forefoot running. The iRobot was programmed to replicate the two footstrikes and then to perform 500 cycles of each. System kinematics and ground contact forces were recorded every tenth cycle.
The kinematic repeatability of the iRobot was extremely good (less than 2 mm mean standard deviation in all marker trajectories). The peak vertical ground reaction forces showed systemic trends specific to the footstrike; heelstrike 3 per cent decrease and forefoot 19 per cent increase over the 500 cycles. iRobot replication of the footstrikes met with some success, particularly for the forefoot running.
The iRobot generated highly repeatable kinematics and demonstrated potential for applications within the footwear industry. A number of improvements to the system were identified which could further improve its ability to replicate human running.
- Content Type Journal Article
- DOI 10.1243/17543371JSET59
- Authors
- J A Ronkainen, Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Loughborough, UK
- R F El-Kati, Department of Civil and Building Engineering, Loughborough University, Loughborough, UK
- P R Fleming, Department of Civil and Building Engineering, Loughborough University, Loughborough, UK
- S E Forrester, Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Loughborough, UK
Date: Tue, 06 Jul 2010 18:39:00 GMT
Swing, the sideways deviation of the cricket ball in flight, is a phenomenon which can be explained in terms of fluid dynamics. Conventional swing has been used since the beginning of the twentieth century and is effective with a new or well-preserved ball. A controversial form of swing emerged in Pakistan in the 1980s, featuring an older worn ball which, at a high speed, swung in the reverse direction. A cricket ball is asymmetric because of the the presence of a seam, which is made up of rows of prominent encircling stitches. For conventional swing, this seam trips into turbulence the boundary layer adjacent to one hemisphere of the ball which remains attached to a greater angle (about 120°) than does that on the other side (about 80°) where no seam is present to trip the laminar boundary layer. The result is asymmetrical separation, leading to a skewed wake and a net pressure force on the ball perpendicular to the flight trajectory. Reverse swing is thought to be a consequence of the fact that asymmetry inverts at a high speed if the seam thickens the turbulent boundary layer on one side of the ball. Although the fluid dynamics causes of both conventional and reverse swing are well known, this paper demonstrates clearly, by means of flow visualization and pressure measurements, the inversion of this pressure asymmetry at Reynolds numbers greater than 170×103.
- Content Type Journal Article
- DOI 10.1243/17543371JSET73
- Authors
Date: Tue, 06 Jul 2010 18:39:00 GMT
The sports ball market is a multi-million dollar industry; original equipment manufacturers are continually trying to develop sports balls and in order to achieve improvement in performance they often utilize launch and/or flight monitors to allow consistent measurement and benchmarking of their balls under test. This paper introduces a laser tracking system (LTS), which has been specifically designed for soccer ball tracking. This LTS combines two different concepts together in an innovative optical solution to allow the system to track an arbitrarily moving soccer ball in a completely non-contact and non-marking methodology, tracking a ball in real time up to approximately 10 m/s. The system was programmed to act as a launch monitor capable of reporting the ball launch velocity and launch angle. In order to achieve the fully functional LTS, the hardware and software choices are clearly outlined, as well as describing the tracking methodology used to achieve the real-time tracking capability.
- Content Type Journal Article
- DOI 10.1243/17543371JSET67
- Authors
Date: Mon, 07 Jun 2010 20:59:32 GMT
In cricket, expert batters must develop anticipatory skills to enable them to respond effectively to a delivery by the bowler. The batter is required to judge the delivery and to move into an appropriate position to respond to it within a limited time (i.e. the delivery transit time can be as little as 450,ms for fast-paced bowlers). In training, the batter therefore needs to face numerous deliveries to hone this skill. However, because of the natural variation that occurs in bowling and the high impact experienced by the bowler, bowling machines are often employed to provide numerous similar deliveries for practice and to minimize the occurrence of overuse injuries to the bowler. The purpose of the study presented within this paper was to investigate how the batter reacts differently when facing a bowler and when facing a bowling machine. In a controlled single-subject pilot study a batter faced an unfamiliar bowler and also faced a bowling machine. The batter and the bowler or bowling machine were synchronously filmed using high-speed video cameras operating at 500 frames/s and the reaction of the batter was analysed under both conditions. It was seen that the batter lifted his bat backwards significantly earlier (0.999,s as opposed to 0.838,s before ball release) and lifted his front foot significantly later (0.002,s as opposed to 0.153,s before ball release) when facing the bowling machine and when facing the bowler respectively.
- Content Type Journal Article
- DOI 10.1243/17543371JSET70
- Authors
Date: Fri, 14 May 2010 12:50:12 GMT
The aim was to determine whether increasing the stiffness of the shoe midsole supporting the metatarsophalangeal (MTP) joint could induce a better jumping and lateral cutting movement performance. 12 young team-sports players used two different shoe models (commercialized), with different sole bending stiffnesses. Two tests were performed: a multi-directional (Multi-D) sprint test including rapid lateral braking and cutting movements and a fatigue test including drop jumps (DJs) and countermovement jumps (CMJs) in pre- and post-fatigue conditions. A significant (p < 0.05) improvement was observed in the Multi-D test times with the stiffer midsole. Further, in fatigued conditions, the group with the stiffer midsole shoe showed a non-significant 9 per cent performance decrease in CMJs while this decrease was higher and significant (16.1 per cent; p < 0.05) for the compliant midsole group. Compared with the stiffer midsole, the compliant midsole yielded a significant decrease in the jump performance, highlighting the fact that a higher MTP midsole stiffness helped subjects to limit the effects of fatigue on jumping performance. Therefore, a higher midsole MTP stiffness is associated with better performance in indoor-sport-specific movements including fatigued conditions, which could be explained by a preserved dynamic interaction with the ground in these specific sport situations.
- Content Type Journal Article
- DOI 10.1243/17543371JSET69
- Authors
- N Tinoco, Laboratoire de Physiologie de l’Exercice, Université Jean Monnet Saint-Etienne, Centre Hospitalier Universitaire Bellevue, Saint-Etienne, France
- D Bourgit, SpringBoost SA, Saint-Sulpice, Switzerland
- J-B Morin, Laboratoire de Physiologie de l’Exercice, Université Jean Monnet Saint-Etienne, Centre Hospitalier Universitaire Bellevue, Saint-Etienne, France
Date: Fri, 14 May 2010 12:50:12 GMT
There are currently no restrictions on the coefficient of friction of tennis courts or strings. The aim of this paper was to determine the effect of friction on tennis ball impacts. Finite element models were used to determine the effect of friction for oblique spinning impacts both between a tennis ball and a rigid surface and between a tennis ball and the string bed of a freely suspended racket. The results showed that during an oblique impact a tennis ball can behave in any of the following ways: first, it can slide, second, it can slide and then ‘overspin’, or, third, it can slide, overspin, and then converge towards rolling. The ball will slide throughout the majority of impacts on the court during play. Therefore, the rebound topspin of the ball will increase with increasing court friction and the horizontal rebound velocity will decrease. The ball will roll off the string bed for the majority of groundstrokes and the rebound properties will effectively be independent of string-bed friction.
- Content Type Journal Article
- DOI 10.1243/17543371JSET66
- Authors
Date: Thu, 15 Apr 2010 13:24:03 GMT
Guest Editorial
- Content Type Journal Article
- Authors
Date: Thu, 01 Apr 2010 19:39:08 GMT
This paper describes a novel force acquisition system capable of measuring the force profiles of high-energy short-duration impacts. This force acquisition system was used to test dynamically a cricket leg guard and to create a contour map of the peak transmitted forces across the garment's surface. The cricket leg guard was found to provide most protection in the central shin and knee regions, areas most likely to be impacted normally and so to receive the highest-energy impacts. The use of this system will enable a dynamic test procedure to be developed to mimic impact conditions encountered during a game, allowing optimization of cricket pad designs for specific impacts.
- Content Type Journal Article
- DOI 10.1243/17543371JSET65
- Authors
- P J Walker
- S J Rothberg
- C E Holmes
- A R Harland
Date: Tue, 16 Mar 2010 15:52:02 GMT
Biofeedback systems have become a prominent component in the sports domain as a means of motor training and rehabilitation. This paper presents the development of a biofeedback prototype and system software framework facilitating its functionality in real time. The prototype incorporates an inertial measurement sensor unit, a wireless vibration stimulus module for vibrotactile biofeedback, and interactive system software behaving as the backbone of the system. The functionality of the prototype was tested with a stability test during which biofeedback was provided to improve postural control based on trunk tilt displacements. The test involved subjects standing in the tandem Romberg position during which their medial–lateral trunk tilt was measured, and postural sway biofeedback was conveyed via vibrotactile actuators placed on either side of the trunk. Two conditions were tested, namely eyes open and eyes closed, and postural sway with biofeedback was evaluated, as opposed to with no feedback. A 15.2 per cent sway reduction resulted in the eyes-open condition, and a significant reduction of 55.2 per cent was reported for the eyes-closed condition. The results demonstrate that instantaneous feedback provided via vibration stimulus can reduce postural sway based on trunk tilt measurements. Hence, the system's pertinence to comparable approaches employed in sports training and rehabilitation is foreseen.
- Content Type Journal Article
- DOI 10.1243/17543371JSET52
- Authors
- A U Alahakone
- A Senanayake
Date: Tue, 16 Mar 2010 15:52:02 GMT
In general, the path taken by the nocking point of an archery bow in the vertical plane is not a straight line perpendicular to the rest position of the string; it may vary significantly from that. Any deviation from a straight line at a draw length around the full-draw position will potentially lead to significant inaccuracy if the draw length varies by small amounts from arrow to arrow. This can occur for a compound bow if the cams do not come to their full-draw position simultaneously.
The path taken by the nocking point over the length of the bow's draw, and especially near the bow's brace height, can be expected to influence significantly the way that the arrow flexes and rotates about its centre of mass as it leaves the bow and enters the airstream. Hence it is of importance in relation to the arrow's position on the string relative to the bow's launcher (or arrow rest) at the brace height.
This paper provides a model for the nocking-point locus in the vertical plane. While examples are provided for several configurations of compound bow, it is generally applicable to longbows and recurve bows as well. It is noted that asymmetric degrees of freedom in the cam configuration of a compound bow are required if the nocking-point locus is to be both straight and perpendicular to the rest position of the string, and that this cannot be achieved for some compound-bow configurations or for a longbow or recurve bow unless the arrow pass is in the geometric centre of the string.
- Content Type Journal Article
- DOI 10.1243/17543371JSET58
- Authors
Date: Fri, 15 Jan 2010 20:26:36 GMT
The flow around a rowing oar blade during a stroke is highly complex owing to the proximity of the water surface and the rapidly changing blade flow incidence (here, greater than 180° in under 0.75 s). This flow is simulated using a computational fluid dynamics (CFD) model with a rotating subdomain for blade rotation coupled to a model of the shell velocity. Based on the shell velocity and a specified oar angular velocity, the CFD model calculates the highly unsteady three-dimensional flow, providing instantaneous drag, lift, and propulsive forces on the blade. The propulsive force drives the shell velocity model, which also accounts for the shell drag and the motion of the rowers relative to the shell. The dynamic blade–water interaction is depicted in six distinct flow regimes, characterized by the relative motion of the blade and the temporal influence of drag and lift. It is seen that the propulsive force generated by the blade is largely lift induced during the first half of the stroke. Dynamic stall behaviour of the blade characterizes the flow during the second half of the stroke, where drag increasingly influences the propulsive force. At the end of the stroke, the propulsive force is once again largely lift induced.
- Content Type Journal Article
- DOI 10.1243/17543371JSET57
- Authors
Date: Fri, 15 Jan 2010 20:26:36 GMT
Rowing injuries and performance have been attributed to the kinematics and kinetics of ergometer rowing. The aim of this study was to investigate these parameters on two commonly used rowing ergometers: one with a fixed-head design and one with a floating-head design. Using electromagnetic motion sensors and load cells, the kinematics and kinetics of ten elite male athletes (mean age, 22.8 ± 3.5 years) rowing on the two different ergometers were assessed. This revealed that the floating-head design produced a greater stroke length (p < 0.05) but higher stroke rate (p < 0.01) for the same rowing intensity. This was combined with significantly different rowing kinematics in which the fixed head had greater anterior pelvic rotation (p < 0.05) and greater femoral flexion (p < 0.05). The implications of these changes with respect to injury require further interpretation through a mathematical model. Since a full analysis comparing rowing kinematics on water with rowing ergometers has not been made here, no conclusions regarding which ergometer simulates rowing on water can be made.
- Content Type Journal Article
- DOI 10.1243/17543371JSET54
- Authors
- S Hislop
- K Cummins
- A M J Bull
- A H McGregor
Date: Wed, 02 Dec 2009 17:21:48 GMT
Accurate speed and split-time information on sprinters is crucial in coaching support. Furthermore, speed and stride parameters (i.e. contact time, stride frequency, and stride length) are important in research on the biomechanics of running. Existing speed-tracking systems for sprinting are expensive, unable to support multiple competing athletes, involve a complicated set-up procedure, or are not sufficiently accurate. This paper describes the design, evaluation results, and application scenarios of a novel, practical, and cost-effective light-sensor network system (commissioned at the National Indoor Athletics Centre, Cardiff, UK) that is capable of capturing criterion-comparable split-time information on simultaneously competing sprinters for long- and short-term coaching support and for biomechanics and sports science research purposes. This unique system is specifically designed to support coaching activities on a daily basis. It was also shown that the light-sensor network system can be integrated with other body-attached measurement systems to achieve continuous tracking of position, speed, and stride parameters of a race.
- Content Type Journal Article
- DOI 10.1243/17543371JSET55
- Authors
- L Cheng, Department of Computer Science, University College London, London, UK
- H Tan, Structure and Motion Laboratory, Royal Veterinary College, UK
- G Kuntze, Cardiff School of Sport, University of Wales Institute, Cardiff, UK
- I N Bezodis, Cardiff School of Sport, University of Wales Institute, Cardiff, UK
- S Hailes, Department of Computer Science, University College London, London, UK
- D G Kerwin, Cardiff School of Sport, University of Wales Institute, Cardiff, UK
- A Wilson, Structure and Motion Laboratory, Royal Veterinary College, UK
Date: Wed, 02 Dec 2009 17:21:47 GMT
A generic model of a rowing craft is presented and used to identify the mechanics of the rowing stroke that give rise to variations in the speed of a rowing shell, together with the causes and locations of maximum and minimum shell speeds through the stroke. The model is implemented computationally in a velocity prediction program which uses readily available measured data for the input and simulates the motion of the athlete using a seven-body-segment model. The rowing model is derived to avoid limitations that arise from the quasi-steady application of steady state data to the unsteady flow around the oar blades and includes hydrodynamic and aerodynamic resistance models. Propulsive drive forces arise as a result of the difference between the gate and handle forces due to the lever action of the oar. The surge motion is dominated by the inertial forces arising as a result of the athlete’s motion within the craft which are much larger in magnitude than the drive forces. The minimum surge speed occurs midway through the drive phase. Two distinct maxima in the surge speed occur: one at the end of the drive as the athlete comes to rest at the end of the stroke, and one during the recovery as the athlete’s seat attains the maximum speed backwards relative to the craft. The relative magnitudes of these peaks are mainly determined by the ratio of the drive time to the recovery time.
- Content Type Journal Article
- DOI 10.1243/17543371JSET49
- Authors
Date: Wed, 02 Dec 2009 17:21:46 GMT
The purposes of the study were to explain the double peak in the boat acceleration during the drive phase, to analyse the temporal structure of the stroke cycle, and to find correlations between the temporal structure and the boat type, rower gender, stroke rate, force profile, and effectiveness of rowing. Measurements of the boat acceleration, boat velocity, handle force, oar angle, and velocity of body segments were made in competitive rowing boats using a telemetry system. The accelerations of the whole system and of the rower's centre of mass (CM) were derived and used to define the temporal structure of the stroke cycle. Six microphases were defined during the drive phase, and three microphases were defined during the recovery phase. The relative magnitudes of the accelerations of the boat and of the rower's CM switched twice during the drive phase. During the ‘initial rower's acceleration’ and the ‘rower's acceleration’ microphases, the acceleration of the rower's CM was higher and, during the ‘initial boat acceleration’ and ‘boat acceleration’ microphases, the acceleration of the boat was higher. The presence of the initial boat acceleration microphase is an important indicator of the effectiveness of a rower's technique.
- Content Type Journal Article
- DOI 10.1243/17543371JSET40
- Authors
Date: Wed, 02 Dec 2009 17:21:37 GMT
ASTM F2333 is a test method for quantifying traction characteristics between an athletic shoe and a sports surface. This standard calls for normal loads of 500–3000 N to be applied between a footform and a playing surface. To assess the effect of varying the normal load on the traction coefficients between cleated athletic shoes and artificial turf surfaces, a new testing device was developed and used to collect traction data. Four different models of cleated athletic shoes were tested on FieldTurf™ at normal loads ranging from 222 N to 1776 N. Static, dynamic, and peak traction coefficient values were calculated for each condition. There was a significant difference in the slope of the load versus traction coefficient curve for loads below and above 888 N for all three variables measured. No significant differences in traction characteristics were found between shoes for loads below 888 N. Significant differences between the shoes were seen with loads above 888 N. However, buckling and potential permanent damage to the turf surface were seen at loads of 1776 N. The results suggest that traction data obtained on FieldTurf at loads below one body weight are not sensitive to different shoe designs. Therefore, the measurement of traction between cleated shoes and FieldTurf should be conducted at a load of at least 888 N, which is, in part, consistent with the default normal load of 1000 N, in ASTM F2333. However, a normal force of 3000 N defined in the standard for studying stopping may not be feasible without permanently damaging the turf surface.
- Content Type Journal Article
- DOI 10.1243/17543371JSET56
- Authors
- S Kuhlman
- M Sabick
- R Pfeiffer
- B Cooper
- J Forhan
Date: Wed, 02 Dec 2009 17:21:36 GMT
A calibration procedure was carried out to optimize the measurement accuracy of an application of force transducers to quantify the force magnitude and centre of pressure on the seat of a rowing ergometer. Known forces were applied to the system at specified locations, and the recordings were used to provide a solution in the least-squares sense for transforming the transducers’ voltage outputs to meaningful data. After calibration, the system was capable of measuring force to within 2 N of the applied load, identifying the position of force application to within 1.1 mm, and was more accurate than other apparatus described in the literature. The potential of the instrumentation for examining aspects of rowing technique in elite athletes was also demonstrated.
- Content Type Journal Article
- DOI 10.1243/17543371JSET39
- Authors
- A J Murphy, Department of Bioengineering, Imperial College London, London, UK
- S T H Chee, Department of Bioengineering, Imperial College London, London, UK
- A M J Bull, Department of Bioengineering, Imperial College London, London, UK
- A H McGregor, Biosurgery and Surgical Technology, Faculty of Medicine, Imperial College London, Charing Cross Hospital, London, UK
Date: Fri, 25 Sep 2009 16:53:44 GMT
This paper proposes a new model describing the dynamics of a rowing boat for general three-dimensional motions. The complex interaction between the different components of the rowers–oars–boat system is analysed and reduced to a set of ordinary differential equations governing the rigid motion along the six degrees of freedom. To treat the unstable nature of the physical problem, a rather simple (but effective) control model is included, which mimics the main active control techniques adopted by the rowers during their action.
- Content Type Journal Article
- DOI 10.1243/17543371JSET46
- Authors
- L Formaggia
- A Mola
- N Parolini
- M Pischiutta
Date: Fri, 25 Sep 2009 16:53:44 GMT
Biofidelic devices are used in the automobile industry to assess injury risk during a vehicular accident. Similar biofidelic devices may have broad applicability in the field of sports injury prevention and could be used to enhance player safety. Ankle sprains constitute one of the most common sports injuries. Past studies have suggested that high rotational traction at the shoe–surface interface may increase the likelihood of lower-extremity injury. Researchers have assessed this risk by measuring the peak torque during an applied rotation. On the other hand, ankle sprains may be dependent upon the amount of strain developed in the ankle ligaments during rotation of the foot–ankle complex and not the magnitude of torque. The current study quantifies the torsional stiffness of the human foot–ankle complex based on cadaver experiments. The development of a surrogate foot–ankle complex is then detailed and compared with the human response. Finally, the results of a rotational traction study on a couple of football shoe–surface interfaces are presented using the surrogate ankle. The testing resulted in a new outcome variable, namely the peak twist of the ankle, that may allow assessment of the risk of injury to the ankle due to excessive rotational traction at the shoe–surface interface.
- Content Type Journal Article
- DOI 10.1243/17543371JSET45
- Authors
- M R Villwock, Orthopaedic Biomechanics Laboratories, Michigan State University, East Lansing, Michigan, USA
- E G Meyer, Orthopaedic Biomechanics Laboratories, Michigan State University, East Lansing, Michigan, USA
- J W Powell, Department of Kinesiology, Michigan State University, Michigan, USA
- R C Haut, Orthopaedic Biomechanics Laboratories, Michigan State University, East Lansing, Michigan, USA
Date: Wed, 02 Sep 2009 19:41:08 GMT
Bowling machines are used in cricket training to improve a batsman's technique and prevent injury or fatigue to the bowler through overuse; however, existing bowling machines do not provide a realistic training environment that compares to the experience of facing a real bowler. This paper presents the design process undertaken to specify a novel bowling machine which is capable of recreating all common types of technically correct bowling deliveries. The design was implemented based on the requirements and specifications outlined by cricket coaches and players. A prototype was then manufactured and tested thoroughly in the laboratory and at the England and Wales Cricket Board's National Cricket Centre at Loughborough University. Results obtained have shown that the novel bowling machine is capable of recreating realistic bowling deliveries with the correct spin and speed characteristics.
- Content Type Journal Article
- DOI 10.1243/17543371JSET50
- Authors