David Kerwin

Reflective practice and the origins of elite coaching knowledge

This study examines the origins of elite coaching knowledge and the use of this knowledge in the construction of progressions in mens artistic gymnastics. The focus of the current study was first to establish where these elite coaches learnt the skill of coaching, and second to identify the methods currently used by these elite coaches to increase their knowledge base. Sixteen elite mens artistic gymnastic coaches were interviewed using a semi-structured technique. Following inductive content analysis the findings of this investigation were contextualized within the framework of experiential learning, reflective practice and the existing coaching literature. Specifically, these coaches displayed a high level of individuality in terms of how they learnt the skill of coaching. These coaches identified that knowledge acquisition was facilitated mostly through interactive coaching clinics and mentorships that promoted critical inquiry and active experimentation. These experiences allowed the coaches to develop learning through reflective practice within the training environment. Subsequent investigations are recommended to identify how this knowledge is integrated into the coaching process and applied in the development of gymnastic skills.

Modelling the flight of a soccer ball in a direct free kick

This study involved a theoretical and an experimental investigation of the direct free kick in soccer. Our aim was to develop a mathematical model of the balls flight incorporating aerodynamic lift and drag forces to explore this important set-play. Trajectories derived from the model have been compared with those obtained from detailed video analysis of experimental kicks. Representative values for the drag and lift coefficients have been obtained, together with the implied orientation of the balls spin axis in flight. The drag coefficient varied from 0.25 to 0.30 and the lift coefficient from 0.23 to 0.29. These values, used with a simple model of a defensive wall, have enabled free kicks to be simulated under realistic conditions, typical of match-play. The results reveal how carefully attackers must engineer the dynamics of a successful kick. For a central free kick some 18.3 m (20 yards) from goal with a conventional wall, and initial speed of 25 m·s−1, the balls initial elevation must be constrained between 16.5° and 17.5° and the ball kicked with almost perfect sidespin.

Measuring running speed using photocells

Photocell timing systems are used routinely to measure running speeds. In this study, the accuracy of such systems was evaluated using centre of mass speed estimates from three-dimensional video analysis as criteria. One subject ran at five nominal speeds (5-9 m x s(-1)) for each of five separations (1.6-2.4 m) between consecutive photocells. Running speeds were calculated from the photocell data using single beam and double beam systems. For single beam systems, the start of the first break of a beam and the start of the longest break of a beam were used as trigger criteria. For double beam systems, the first occurrence of both beams being broken and the start of the longest double break were used as trigger criteria. Root mean square speed errors were smaller for the double beam systems. The longest break criterion gave smaller root mean square errors than the first break criterion. In general, errors in speed were smaller for greater photocell separations. An error of 0.1 m x s(-1) was achieved using a single beam system set at hip height with a longest break criterion for photocell separations of around two stride lengths. The advantage of using a double beam system is that it achieves this accuracy without the need to adjust photocell separation for different stride lengths.

The conceptual process of skill progression development in artistic gymnastics

In this study, we examined the methods used and knowledge required by 16 elite mens gymnastic coaches in the development of skill progressions. Following in-depth interviews, a conceptual model representing the process of skill progression development was generated. We found that: (1) elite gymnastic coaches developed skill progressions through experimental practice, reflection and critical inquiry; (2) the development of skill progressions was underpinned by the coaches acquiring a mindset based on four further sub-components (i.e. skill progression refinement, current coaching knowledge, mental imagery and biomechanical understanding); and (3) coaches identified the importance of replication of the spatial and temporal characteristics of the final skill. The results are consistent with task analysis, reflective practice and the principle of specificity. Practically, these findings suggest the need to develop coaches with a more objective approach to skill progression development and a greater understanding of the controlling mechanisms inherent in such practices.

Biomechanical similarities of progressions for the longswing on high bar.

Based on specificity of training and biomechanical analysis, the aim of this study was to develop a method to rank selected progressions for learning the longswing on high bar. Four members of the Mens National Gymnastics Squad were recorded (50 Hz) performing three series of five longswings and eight progressions. Real world co-ordinates from the digitized data were determined using two-dimensional direct linear transformation. Biomechanical similarity between the functional phases of the longswing and the corresponding phases of the progressions were calculated. The functional phases were described as a hyperextension to flexion of the hip and hyperflexion to extension of the shoulder joints as the gymnast passed underneath the bar. Using a combined score of Difference and movement Variability a Specificity score was calculated for hip and shoulder angular displacements and velocities. An overall score based on the average of the four scores provided a ranked list of progressions based on their similarity to the target skill. The progression that showed the greatest similarity to the biomechanics of the longswing, and was therefore ranked first, was the chalked bar pendulum swing. The least similar progression, and, therefore, eighth ranked, was the chalked bar bent knee longswing. The hip kinematics were found to contribute most to the overall differences because the performance requirements of these progressions emphasize an increase in hip flexion during the ascending phase. The method described provides a means to quantify and rank progressions based on their kinematic similarity to the longswing.Abstract Based on specificity of training and biomechanical analysis, the aim of this study was to develop a method to rank selected progressions for learning the longswing on high bar. Four members of the Mens National Gymnastics Squad were recorded (50 Hz) performing three series of five longswings and eight progressions. Real world co‐ordinates from the digitized data were determined using two‐dimensional direct linear transformation. Biomechanical similarity between the functional phases of the longswing and the corresponding phases of the progressions were calculated. The functional phases were described as a hyperextension to flexion of the hip and hyperflexion to extension of the shoulder joints as the gymnast passed underneath the bar. Using a combined score of ‘Difference’ and movement ‘Variability’ a ‘Specificity score’ was calculated for hip and shoulder angular displacements and velocities. An overall score based on the average of the four scores provided a ranked list of progressions based on their similarity to the target skill. The progression that showed the greatest similarity to the biomechanics of the longswing, and was therefore ranked first, was the chalked bar pendulum swing. The least similar progression, and, therefore, eighth ranked, was the chalked bar bent knee longswing. The hip kinematics were found to contribute most to the overall differences because the performance requirements of these progressions emphasize an increase in hip flexion during the ascending phase. The method described provides a means to quantify and rank progressions based on their kinematic similarity to the longswing.

Minimising peak forces at the shoulders during backward longswings on rings

Abstract Many elite gymnasts perform the straight arm backward longswing on rings during their competition routines in order to satisfy specific judging requirements. Measured peak combined cable tension during a backward longswing is typically in excess of 9 bodyweights and forces of this magnitude have been associated with an increased risk of injury to gymnasts shoulders. This study investigated the contribution of longswing technique and the elasticity of the gymnast and rings apparatus to minimising loading at the shoulders. A three-dimensional video and cable tension analysis was conducted on a backward longswing performed by an elite gymnast. This analysis provided information regarding the motion of the rings cables, the gymnasts technique and the elasticity of the rings apparatus. A three-dimensional five-segment computer simulation model of a gymnast swinging on rings was developed. The inertial characteristics for the model were determined from anthropometric measurements of the gymnast and measurements taken directly from the rings apparatus. The simulation model was evaluated by comparing the backward longswing from the data collection with a simulation of the same performance. The root mean squared (rms) differences between the actual performance of the longswing and the simulation for cable tension, orientations of the gymnast and rings cables and the wrist to ankle length of the gymnast were 297 N, 3.3°, 1.1° and 0.06 m, respectively. During the simulated longswing the peak combined force at the shoulders was 8.5 bodyweights. Modifications to the evaluated simulation of the longswing were used to determine the effect of the gymnasts technique, his elasticity and that of the rings apparatus on peak shoulder force. Altering the gymnasts technique, by fixing the gymnast in a straight body configuration throughout the swing, increased the peak shoulder force by 2.56 bodyweights. Removing only the lateral arm movements, which form part of the gymnasts technique, also resulted in an increased peak shoulder force (0.73 bodyweights). Removing only the elasticity of the apparatus or gymnast from the evaluated simulation resulted in smaller increases in peak shoulder force (0.62 bodyweights and 0.53 bodyweights). Although the elasticity of the gymnast and apparatus contribute to minimising peak shoulder force, this study shows that the contribution of a gymnasts technique is considerably greater.

Estimation of reaction forces in high bar swinging

Reaction forces experienced by gymnasts swinging on the high bar may be determined indirectly using inverse dynamics analysis or may be measured using strain gauges. The accuracy of inverse dynamics analysis may be poor because of errors in the estimated inertia parameters and in the accelerations obtained from digitized data. On the other hand the use of strain gauges is not always possible in elite competition. This paper presents a method for estimating the reaction forces based on the linear displacements of the bar.The bar was modelled as a point mass attached to horizontal and vertical linear springs (obeying Hooke’s law) with stiffness coefficients determined from static loading. The stiffness coefficients of the bar were determined with three different tensions in the stabilizing cables of the high bar. A force and video analysis of backward giant circles was performed. Estimates for the reaction forces were obtained by multiplying the bar displacements from the video analysis by the stiffness coefficients determined from the static loadings. Comparisons were made between the estimated reaction forces and the reaction forces recorded using strain gauges attached to the high bar.Varying the tension in the stabilizing cables of the high bar did not effect the stiffness of the bar. Root mean squared differences between estimated and recorded reaction forces were on average within 99 N for three ‘regular’ and three ‘accelerated’ giant circles. This was less than 3.5% of the range of forces recorded. The bar displacement method was able to estimate the peak reaction forces to within 7% on average, which compares favourably with 24% reported by Gervais (1993) using inverse dynamics.

Indirect estimation of cable tension during gymnastic movements on rings

Knowledge of external forces acting on an athlete is often required to study performance and injury mechanisms, but direct measurements are difficult to obtain. While transducers in the rings cables typically measure external forces experienced by gymnasts performing static balances and swinging movements on rings, this solution is not always acceptable and an accurate technique that does not hinder the gymnasts’ performances is desirable. This study evaluates a video-based technique for estimating cable tension on the rings apparatus. Static loading of a rings frame coupled with a planar video analysis of the mandatory damped elastic devices (DEDs) provided a tension-deflection calibration curve. Three-dimensional video and cable tension data were obtained for two male gymnasts performing static balances and dynamic swinging movements. Cable tension was measured using a force link while a planar video analysis determined time histories of the DED deflections. Combined cable tension time histories were estimated fromrelative DED deflections coupled with the tension-deflection calibration curve and the orientation of the rings cables, and were compared to measured values to evaluate the proposed technique. For static balances the RMS difference between measured and estimated combined cable tension was 83 N. For dynamic swinging movements the maximum RMS difference was 189 N, equivalent to a 4% difference when expressed as a percentage of the peak value. The indirect video-based technique developed in this study accurately estimates combined cable tension throughout movements on rings and may be considered for studies where a remote measurement is required. There is potential for the technique to be extended to other sporting situations, where indirect accurate estimates of external forces acting on an athlete are needed.