The Margin for Error in Timing the Release for Double Layout Somersault Dismounts from High Bar

Abstract

Introduction: In the high bar competition in Men's Artistic Gymnastics the backward giant circle is used prior to a dismount in order to generate the required release characteristics. Currently there are two distinct (traditional and scooped) techniques used in the accelerated backward giant circle prior to the double layout somersault dismount. Hiley (1998) showed that each of the techniques was more than capable of producing the rotation required for a double layout somersault dismount. Since the scooped technique is less aesthetically pleasing and may be liable for score deductions by some judges, it is likely that there is some technical advantage associated with this technique. It is speculated that the scooped technique allows a greater margin for error in timing the release for a double layout somersault dismount. This study investigated this by comparing the margin for error in timing the release from traditional and scooped giant circles. Methods: All high bar performances from the Sydney 2000 Olympic games were recorded using two digital camcorders. The last giant circle and the whole of the flight phase of six double layout dismounts (three traditional and three scooped) were analysed. Fifteen body landmarks were digitised in each video field along with the centre of the bar between the gymnast's hands. The two sets of digitised data were used to reconstruct the three-dimensional coordinates of the landmarks using the Direct Linear Transformation technique. Inertia parameters for gymnasts were determined from anthropometric dimensions obtained in the three-dimensional analysis using the mathematical model of Yeadon (1990). Whole body mass centre location and angles describing the orientation and configuration of the gymnast were determined throughout and the angular momentum during the flight phase was calculated (Yeadon, 1990). A simulation model of a gymnast and high bar (Yeadon and Hiley, 2000) was driven using the joint angle time histories obtained from the video analysis. Bar stiffness was determined from static loading. The values for bar stiffness, segmental masses and initial angular velocity in the giant circle were adjusted in order to minimise the difference between recorded and simulated whole body rotation angle, bar displacement and linear and angular momentum at the point of release from the bar. The margin for error was calculated as a release window time interval within which appropriate linear and angular momenta for a double layout somersault dismount were achieved in a simulation. Results and Discussion: On average the simulation model was able to estimate the whole body rotation angle to within 1.8° and the bar displacements to within 0.013 m. The release window was based on the requirement of the horizontal release velocity lying between 0.35 m/s and 2.3 m/s and the angular momentum being sufficient to produce at least 1.4 straight somersaults during flight. The average release windows for the traditional and scooped backward giant circles were 72 ms and 135 ms respectively. The scooped technique results in a bar motion which, coupled with the changes in body shape, produce a less curved path of the mass centre in the last part of the giant circle. As a consequence the flight trajectory is not as sensitive to release timing. This explains why the scooped giant circle has been adopted by the majority of gymnasts in preference to the traditional giant circle. Thus the gymnasts with the best performances may not be those who are able to time the release most accurately. Rather they may be the ones who use a technique that is more forgiving of errors in timing. Acknowledgements: This project was funded by Pfitzer through the IOC Medical Commission.