TWIST LIMITS OF LATE TWISTING DOUBLE SOMERSAULTS ON TRAMPOLINE

The aim of this research study was to determine the twist limits for double somersaults on trampoline with the twist in the second somersault. An angle-driven computer simulation model of aerial movement was used to determine the maximum number of half twists that could be produced in a double somersault using asymmetrical movements of the arms and hips. Simulations of two limiting movements were found using simulated annealing optimisation to produce the required amounts of somersault, tilt and twist at landing after a flight time of 2.0 s. It was found that 3½ twists could be produced in the second somersault of a forward piked double somersault with arms abducted 8o from full adduction during the twisting phase and that 3 twists could be produced in the second somersault of a backward straight double somersault with arms fully adducted

Mechanics of the giant circle on high bar

In Men's Artistic Gymnastics the accelerated backward giant circle on high bar is used to generate the rotation required for the subsequent skill. When used prior to a dismount at the end of a high bar routine the gymnast performs a number of backward giant circles in order to generate sufficient rotation to perform the dismount. The most common dismounts from high bar require the gymnast to perform two backward somersaults in the layout position. Of all the dismounts performed by elite male gymnasts it is the double layout somersault dismount which requires the most rotation. Observations of elite gymnasts have shown that two different techniques may be adopted in the accelerated giant circle performed before release. Since gymnasts are able to perform the dismount from both types the question arises: What is the best technique for increasing rotation using accelerated backward giant circles? [Continues.

FUNCTIONAL VARIABILITY IN A WHOLE BODY CO-ORDINATED MOVEMENT

Gymnasts flex at the hips in the lower part and extend in the upper part of the giant circle. In order to perform a sequence of circles at even tempo, any variation in angular velocity at the end of the flexion phase needs to be reduced by the end of the extension phase. The aim of this study was to determine the nature and contribution of such adjustments. A computer simulation model of a gymnast on high bar was used to investigate strategies of (a) fixed timing of the extension phase (feedforward control) and (b) stretched timing (feedforward and feedback control). For three elite gymnasts fixed timing reduced the angular velocity variation by 36% and stretched timing by 63%. The mean reduction for the actual gymnast techniques was 61%. It was concluded that both feedforward and feedback control strategies are used by gymnasts for controlling such movements

OPTIMISATION TO IMPROVE CONSISTENCY IN THE TKATCHEV ON HIGH BAR

The purpose of this study was to improve the consistency of performance of the Tkatchev release and re-grasp on high bar. A simulation model (Hiley & Yeadon, 2003) was used to optimise the technique in the giant circle leading up to release in order to maximise the size of the window within which the gymnast could release and successfully re-grasp the bar. The optimal simulation resulted in a release window considerably larger (93 ms) than the gymnast’s actual performances (mean 29 ms). However, when the technique was required to be robust to small errors in timing the size of the release window was smaller. Performing the final hip and shoulder flexion and extension actions earlier and over a larger angle range than in the actual performances lead to the increase in size of release window

OPTIMAL TECHNIQUE, VARIABILITY, CONTROL, AND SKILLED PERFORMANCE

Optimisation is often used in an attempt to explain technique adopted in skilled sport performance. This might take the form of minimising joint torques in an expectation that the optimum simulated technique will resemble the actual performance. If a suitable optimisation criterion can be identified then this may give some insight into the adopted technique. In all human movement there is inherent variation so that no two performances are exactly the same. As a consequence skilled technique needs to be successful in a noisy environment and so optimised technique also needs to be robust to the inherent variation in coordination. In movements in which there is sufficient time for feedback control to operate it is to be expected that there will be greater variation in technique in those phases that adjustments are made. It is also to be expected that there will be little variation in technique for those phases where accurate coordination is crucial to the success of the movement. The aspect that often governs elite technique is that of achieving consistent success rather than some biomechanical measure of movement

Optimal Technique, Variability, Control, and Skilled Performance

Optimisation is often used in an attempt to explain technique adopted in skilled sport performance. This might take the form of minimising joint torques in an expectation that the optimum simulated technique will resemble the actual performance. If a suitable optimisation criterion can be identified then this may give some insight into the adopted technique. In all human movement there is inherent variation so that no two performances are exactly the same. As a consequence skilled technique needs to be successful in a noisy environment and so optimised technique also needs to be robust to the inherent variation in coordination. In movements in which there is sufficient time for feedback control to operate it is to be expected that there will be greater variation in technique in those phases that adjustments are made. It is also to be expected that there will be little variation in technique for those phases where accurate coordination is crucial to the success of the movement. The aspect that often governs elite technique is that of achieving consistent success rather than some biomechanical measure of movement

The margin for error when releasing the asymmetric bars for dismounts

It has previously been shown that male gymnasts using the “scooped” giant circling technique were able to flatten the path followed by their mass centre resulting in a larger margin for error when releasing the high bar (Hiley and Yeadon, 2003a). The circling technique prior to performing double layout somersault dismounts from the asymmetric bars in Women’s Artistic Gymnastics appears to be similar to the “traditional” technique used by some male gymnasts on the high bar. It was speculated that as a result the female gymnasts would have margins for error similar to those of male gymnasts who use the traditional technique. However, it is unclear how the technique of the female gymnasts is affected by the need to avoid the lower bar. A four segment planar simulation model of the gymnast and upper bar was used to determine the margins for error when releasing the bar for nine double layout somersault dismounts at the Sydney 2000 Olympic Games. The elastic properties of the gymnast and bar were modelled using damped linear springs. Model parameters, primarily the inertia and spring parameters, were optimised to obtain a close match between simulated and actual performances in terms of rotation angle (1.2°), bar displacement (0.011 m) and release velocities (< 1%). Each matching simulation was used to determine the time window around the actual point of release for which the model had appropriate release parameters to complete the dismount successfully. The margins for error of the nine female gymnasts (release window 43 - 102 ms) were comparable with those of the three male gymnasts using the traditional technique (release window 79 - 84 ms)

Swinging around the high bar

The motion of a gymnast around the high bar is modelled first as swinging around a rigid rod then more accurately when the rod is considered to be elastic. How the gymnast should best move his hips is also considered

Optimisation of high bar circling technique for consistent performance of a triple piked somersault dismount

The dismount from the high bar is one of the most spectacular skills performed in Men’s Artistic Gymnastics. Hiley and Yeadon (2005) optimised the technique in the backward giant circle prior to release using a computer simulation model to show that a gymnast could generate sufficient linear and angular momentum to perform a triple piked backward somersault dismount with a sufficiently large release window (the period of time during which the gymnast could release the bar and successfully complete the dismount). In the present study it was found that when the timing of the actions at the hip and shoulder joints from the optimum simulation were perturbed by 30 ms the resulting simulation could no longer meet the criteria for sufficient aerial rotation and release window. Since it is to be expected that a gymnast’s technique can cope with small errors in timing for consistent performance, a requirement of robustness to timing perturbations should be included within the optimisation process. When the technique in the backward giant circle was optimised to be robust to 30 ms perturbations it was found that sufficient linear and angular momentum for a triple piked dismount could be achieved with a realistic release window

The margin for error when releasing the high bar for dismounts

In Men's Artistic Gymnastics the current trend in elite high bar dismounts is to perform two somersaults in an extended body shape with a number of twists. Two techniques have been identified in the backward giant circles leading up to release for these dismounts (J. Biomech. 32 (1999) 811). At the Sydney 2000 Olympic Games 95% of gymnasts used the “scooped” backward giant circle technique rather than the “traditional” technique. It was speculated that the advantage gained from the scooped technique was an increased margin for error when releasing the high bar. A four segment planar simulation model of the gymnast and high bar was used to determine the margin for error when releasing the bar in performances at the Sydney 2000 Olympic Games. The eight high bar finalists and the three gymnasts who used the traditional backward giant circle technique were chosen for analysis. Model parameters were optimised to obtain a close match between simulated and actual performances in terms of rotation angle (1.2°), bar displacements (0.014 m) and release velocities (2%). Each matching simulation was used to determine the time window around the actual point of release for which the model had appropriate release parameters to complete the dismount successfully. The scooped backward giant circle technique resulted in a greater margin for error (release window 88–157 ms) when releasing the bar compared to the traditional technique (release window 73–84 ms)