THE EFFECT OF ELBOW AXIS DEFINITION ON THE CALCULATION OF FLEXION-EXTENSION AND ABDUCTION-ADDUCTION ANGLES FOR THE BOWLING ARM IN CRICKET

The standard protocols for testing whether a bowler is extending his/her arm illegally (by more than 15°) during the period from upper arm horizontal to ball release leave some flexibility of interpretation as to exactly how the axes should be defined. The purpose of this paper was to examine the effect of different elbow axis definitions on the flexion-extension and abduction-adduction angles calculated

Quantifying elbow extension and elbow hyperextension in cricket bowling: a case study of Jenny Gunn

In this study a method for determining elbow extension and elbow abduction for a cricket bowling delivery was developed and assessed for Jenny Gunn who has hypermobility in both elbows and whose bowling action has been repeatedly queried by umpires. Bowling is a dynamic activity which is assessed visually in real time in a cricket match by an umpire. When the legality of a bowler's action is questioned by an umpire a quantitative analysis is undertaken using a marker based motion analysis system. This method of quantifying elbow extension should agree with a visual assessment of when the arm is "straight'' and should minimise the effects of marker movement. A set of six markers on the bowling arm were used to calculate elbow angles. Differences of up to 1 degrees for elbow extension and up to 2 degrees for elbow abduction were found when angles calculated from the marker set for static straight arm trials were compared with measurements taken by a chartered sports physiotherapist. In addition comparison of elbow extension angles at ball release calculated from the markers during bowling trials with those measured from high speed video also showed good agreement with mean differences of 0 degrees +/- 2 degrees

Factors influencing performance in the Hecht vault and implications for modelling

This paper investigated the factors that influence Hecht vault performance and assessed the level of model complexity required to give an adequate representation of vaulting. A five-segment planar simulation model with a visco-elastic shoulder joint and a torque generator at the shoulder joint was used to simulate the contact phase in vaulting. The model was customised to an elite gymnast by determining subject-specific segmental inertia and joint torque parameters. The simulation model was matched to a performance of the Hecht vault by varying the visco-elastic characteristics of the shoulders and the arm–horse interface and the activation time history of the shoulder torque generator until the best match was found. Perturbing the matching simulation demonstrated that appropriate initial kinematics are necessary for a successful performance. Fixing the hip and knee angles at their initial values had a small effect with 3 less rotation. Applying shoulder torque during the contact phase also had a small effect with only a 7 range in landing angles. Excluding the hand segment from the model was found to have a moderate effect with 15 less rotation and the time of contact reduced by 38%. Removing shoulder elasticity resulted in 50 less rotation. The use of a five-segment simulation model confirmed that the use of shoulder torque plays a minor role in vaulting performance and that having appropriate initial kinematics at touchdown is essential. However, factors such as shoulder elasticity and the hands which have previously been ignored also have a substantial influence on performance

Maximising somersault rotation in tumbling

Performing complex somersaulting skills during the flight phase of tumbling requires the generation of linear and angular momenta during the approach and takeoff phases. This paper investigates how approach characteristics and takeoff technique affect performance with a view to maximising somersault rotation in tumbling. A five-segment planar simulation model, customised to an elite gymnast, was used to produce a simulation which closely matched a recorded performance of a double layout somersault by the elite gymnast. Three optimisations were carried out to maximise somersault rotation with different sets of initial conditions. Using the same initial linear and angular momentum as the double layout somersault and varying the joint torque activation timings allowed a double straight somersault to be performed with 19% more rotation potential than the actual performance. Increasing the approach velocity to a realistic maximum of 7ms 1 resulted in a 42% reduction in rotation potential when the activation timings were unchanged but allowed a triple layout somersault to be performed with an increase of 31% in rotation potential when activation timings were re-optimised.Increasing also the initial angular momentum to a realistic maximum resulted in a 4% reduction in rotation potential when the activation timings were unchanged but allowed a triple straight somersault to be performed with a further increase of 9% in rotation potential when activation timings were re-optimised. It is concluded that the limiting factor to maximising somersault rotation is the ability to generate high linear and angular velocities during the approach phase coupled with the ability to adopt consonant activation timings during the takeoff phase

THE EFFECT OF ALTERING STRENGTH AND APPROACH VELOCITY ON TRIPLE JUMP PERFORMANCE

The triple jump is an athletic event comprising three phases in which the optimal proportion of each phase to the total distance jumped, termed the phase ratio, is unknown. This study used a whole body toque-driven computer simulation model of all three phases of the triple jump to investigate the effect of strength and approach velocity on optimal technique. The strength and approach velocity of the simulation model was increased by up to 30% in 10% increments from baseline data collected from a national standard triple jumper. Increasing strength always resulted in an improved performance, increasing velocity also typically resulted in an improved performance but there was a point past which increasing velocity without increasing strength did not lead to an increase in performance. Increasing both strength and velocity by lo%, 20%, and 30% led to roughly equivalent increases in triple jump distance. The phase ratio employed by the simulation model typically became more balanced when the strength of the model was increased by more than its velocity

The effect of marker placement around the elbow on calculated elbow extension during bowling in cricket

The elbow extension angle during bowling in cricket may be calculated from the positions of markers attached around the shoulder, elbow and wrist using an automated laboratory-based motion analysis system. The effects of two elbow-marker sets were compared. In the first, a pair of markers was placed medially and laterally close to the condyles while in the second a triad of markers was placed on the back of the upper arm close to the elbow. The root mean square (RMS) difference in elbow extension angle between the two methods at four key instants was 8° for 12 fast bowlers and 4° for 12 spin bowlers. When evaluated against video estimates of the elbow extension angle for the fast bowlers, the elbow extension angle calculated using the pair method had an RMS error of 2° while the triad method had an RMS error of 8°. The corresponding errors for the spin bowlers were 3° and 5°, respectively. It is thought that the greater errors associated with the triad is a consequence of soft tissue movement in this dynamic activity. This is consistent with the finding of greater error for the fast bowlers compared with the spin bowlers

Coping with perturbations to a layout somersault in tumbling

Tumbling is a dynamic movement requiring control of the linear and angular momenta generated during the approach and takeoff phases. Both of these phases are subject to some variability even when the gymnast is trying to perform a given movement repeatedly. This paper used a simulation model of tumbling takeoff to establish how well gymnasts can cope with perturbations of the approach and takeoff phases. A five segment planar simulation model with torque generators at each joint was developed to simulate tumbling takeoffs. The model was customised to an elite gymnast by determining subject specific inertia and torque parameters and a simulation was produced which closely matched a performance of a layout somersault by the gymnast. The performance of a layout somersault was found to be sensitive to the approach characteristics and the activation timings but relatively insensitive to the elasticity of the track and maximum muscle strength. Appropriate variation of the activation timings used during the takeoff phase was capable of coping with moderate perturbations of the approach characteristics. A model of aerial movement established that variation of bodyconfiguration in the flight phase was capable of adjusting for takeoff perturbations that would lead to rotation errors of up to 8%. Providing the errors in perceiving approach characteristics are less than 5% or 5 and the errors in timing activations are less than 7 ms, perturbations in the approach can be accommodated using adjustments during takeoff and flight

Advances in the development of whole body computer simulation modelling of sports technique

© ACAPS, EDP Sciences, 2013. Computer simulation models have been used to address a range of research questions in sports biomechanics related to understanding the mechanics of sports movements, contributions to performance, optimisation of sports technique and control of sports movements. This paper will describe how theoretical models used in sports biomechanics have been developed at Loughborough University over the last 20 years, detailing their various components, subject-specific parameters, model evaluation, key findings and the strengths / limitations and how models could be further progressed in the future. With each model a four stage methodology has been used to answer specific research questions: development of the simulation model, determination of subject-specific parameters, evaluation of the model, and application of the model. These computer simulation models have provided insight into the mechanics behind sports movements that would not be possible through observing performance and have established the factors that limit optimal performance. In the future computer simulation models of sports movements will continue to develop in terms of sophistication to include elements such as joint compression and will provide further insight into the mechanics underlying sports movements

Evaluation of a torque driven simulation model of tumbling

The use of computer simulation models in studies of human movement is now widespread. Most of these models, however, have not been evaluated in a quantitative manner in order to establish the level of accuracy that may be expected. Without such an evaluation little credence should be given to the published results and conclusions. This paper presents a simulation model of tumbling takeoffs which is evaluated by comparing the simulation output with an actual performance of an elite gymnast. A five segment planar model was developed to simulate tumbling takeoffs. The model comprised rigid foot, leg, thigh, trunk + head and arm segments with two damped linear springs to represent the elasticity of the tumbling track / gymnast interface. Torque generators were included at the ankle, knee, hip and shoulder joints in order to allow each joint to open actively during the takeoff. The model was customised to the elite gymnast by determining subject specific inertia and torque parameters. Good agreement was found between actual and simulated tumbling performances of a double layout somersault with 1% difference in the linear and angular momenta at takeoff. Allowing the activation timings of the four torque generators to vary resulted in an optimised simulation which was some 0.32 m higher than the evaluation simulation. These simulations suggest that the model is a realistic representation of the elite gymnast since otherwise the model would either fail to reproduce the double layout somersault performance or would produce a very different optimised solution

A method for synchronising digitised video data

This paper presents a general method for synchronising digitised video data using a mathematical approach based upon the direct linear transformation reconstruction technique. The method was tested using digitised data from genlocked video recordings of gymnastic vaulting, tumbling, high bar and rings. The mean synchronisation error was less than 0.002 s for vaulting and less than 0.001 s for the other activities