Michael J. Hiley

The mechanics of the backward giant circle on the high bar

Abstract In Mens Artistic Gymnastics the backward giant circle on the high bar is used to generate the rotation that the gymnast needs to perform the release–regrasp and dismount skills. Bauer presented a point mass model of high bar circling which indicated that ideally a gymnast should flex around the lowest point and extend around the highest point of a giant circle in order to maximise the increase in energy [cf. Bauer, W. L. (1983). In H. Matsui, K. Kobayashi, Biomechanics VIII-B (pp. 801–806). Champaign, IL: Human Kinetics]. In practice gymnasts follow this technique in only a general sense and flex after the lowest point and extend before the highest point. A four segment planar simulation model of a gymnast was developed to investigate these differences in technique. The model comprised arm, torso, thigh and leg segments with a damped linear spring connecting the arm and torso segments. The high bar was also modelled as a damped linear spring. The model was driven using time histories of hip and shoulder angles. It was found that the simplifications introduced into Bauers model by neglecting segmental inertias and the elastic characteristics of the gymnast and the bar were not responsible for the differences between the ideal technique and the typical technique of gymnasts. The technique differences could be accounted for by limitations on the torques that are exerted at the shoulder and hip.

Is skilled technique characterized by high or low variability? An analysis of high bar giant circles.

There is conflicting evidence as to whether skilled performance is associated with lower or higher movement variability. The effect of skill level and task difficulty on movement variability during gymnastics swinging was investigated. Four male gymnasts ranging in skill from university standard through to international medallist performed 10 consecutive regular giant circles and 10 double straight somersault dismounts preceded by accelerated giant circles while kinematic data were recorded. Joint angle time histories of the hip and shoulder were calculated and the turning points between flexion and extension determined during each giant circle. Standard deviations of the time and magnitude of the angles at each turning point were calculated. The more elite gymnasts were found to have less variability in the mechanically important aspects of technique compared to the less elite gymnasts. The variability in the mechanically important aspects of technique was not statistically different between the two types of giant circles, whereas the more elite gymnasts demonstrated more variability in some of the less mechanically important aspects.

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 Mens Artistic Gymnastics. Hiley and Yeadon [2005. Maximal dismounts from high bar. Journal of Biomechanics 38, 2221-2227] 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 30ms the resulting simulation could no longer meet the criteria for sufficient aerial rotation and release window. Since it is to be expected that a gymnasts 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 30ms perturbations, it was found that sufficient linear and angular momentum for a triple piked dismount could be achieved with a realistic release window.

Consistency of performances in the Tkatchev release and re-grasp on high bar

The Tkatchev on the high bar is a release and re-grasp skill in which the gymnast rotates in a direction during flight opposite to that of the preceding swing. Since the release window is defined as the time during which the gymnast has appropriate linear and angular momentum to ensure the bar can be re-grasped, it was speculated that the release windows for this skill would be smaller than for dismounts that are less constrained. One senior male gymnast competing at national standard performed 60 Tkatchev trials. A four-segment planar simulation model of the gymnast and high bar was used to determine the release windows in 10 successful and 10 unsuccessful performances of the Tkatchev recorded using a Vicon motion analysis system. Model parameters were optimized to obtain a close match between simulations and recorded performances in terms of rotation angle (1°), bar displacements (0.01 m), and release velocities (1%). Each matched 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 Tkatchev successfully. The release windows for the successful trials were small compared with those of dismounts. The unsuccessful trials were associated with later release and later timing of the actions at the shoulders and hips.

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.

Achieving consistent performance in a complex whole body movement: the Tkatchev on high bar

If the magnitude of timing and angle variability in whole body coordinated movements were known, this would allow more realistic levels of variability to be included within optimizations of technique. The aim of this study was to determine the technique for improved consistency of performance of the Tkatchev release and regrasp on high bar, while incorporating realistic levels of coordination precision. The effect of gymnast strength and flexibility on consistency of performance was also investigated. Twenty trials (10 successful and 10 unsuccessful) by one national gymnast were recorded using an automatic motion capture system and were analyzed to determine variability in coordination of the giant circle technique prior to release. The standard deviation in the hip and shoulder angles and timings at four key instants in the gymnasts performances were 2.3° and 12 ms. A gymnast-high bar simulation model was used to optimize the technique in the giant circle to maximize the success percentage for which the gymnast could release and regrasp the bar with coordination variability introduced into each simulated technique. When the optimal solution was perturbed randomly in 1000 simulations to the level seen in the gymnast performances 69% produced a successful performance compared with only 17% for the gymnast. An increase in strength (by 25%) and a reduction in variability (by 25%) lead to improved consistency (91% success rate). Flexibility did not appear to play a role as none of the optimizations approached the bounds set by the gymnasts performances.

A comparison of Coulomb and pseudo-Coulomb friction implementations: application to the table contact phase of gymnastics vaulting

In the table contact phase of gymnastics vaulting both dynamic and static friction act. The purpose of this study was to develop a method of simulating Coulomb friction that incorporated both dynamic and static phases and to compare the results with those obtained using a pseudo-Coulomb implementation of friction when applied to the table contact phase of gymnastics vaulting. Kinematic data were obtained from an elite level gymnast performing handspring straight somersault vaults using a Vicon optoelectronic motion capture system. An angle-driven computer model of vaulting that simulated the interaction between a seven segment gymnast and a single segment vaulting table during the table contact phase of the vault was developed. Both dynamic and static friction were incorporated within the model by switching between two implementations of the tangential frictional force. Two vaulting trials were used to determine the model parameters using a genetic algorithm to match simulations to recorded performances. A third independent trial was used to evaluate the model and close agreement was found between the simulation and the recorded performance with an overall difference of 13.5%. The two-state simulation model was found to be capable of replicating performance at take-off and also of replicating key contact phase features such as the normal and tangential motion of the hands. The results of the two-state model were compared to those using a pseudo-Coulomb friction implementation within the simulation model. The two-state model achieved similar overall results to those of the pseudo-Coulomb model but obtained solutions more rapidly.

Investigating optimal technique in the presence of motor system noise: application to the double layout somersault dismount on high bar

Abstract Minimising joint torque is often used as an optimisation criterion when investigating human movement. Alternatively, an aspect of performance may be chosen to be maximised when investigating sporting movements. The aim of the study was to optimise the technique in the backward giant circle prior to a double layout somersault dismount from the high bar using various criteria to determine which best characterised the technique adopted by a gymnast. Ten recorded gymnast trials were used to determine bar release parameters and the level of noise in the gymnast’s movements. A computer simulation model of a gymnast and bar was used to optimise giant circle technique under three criteria: minimising joint torques, maximising the release window and maximising success in the presence of motor system noise. Local and global optimisations of technique were performed using the three criteria starting from the average technique of the 10 recorded trials. All global optimum solutions diverged from the gymnast’s technique. The local optimum for maximising success in the presence of noise had a success rate comparable with the global optimum (98% vs. 100%, respectively). It is concluded that the gymnast’s technique is characterised by maximising success despite operating with motor system noise.

The control of twisting somersaults

In the takeoff and early flight phase of a twisting somersault, joint coordination is based on feed-forward control whereas in the late stages of the flight phase configuration adjustments are made using feedback control to ensure accurate completion of the movement and appropriate landing orientation. The aim of this study was to use a computer simulation model of aerial movement to investigate the extent to which arm and hip movements can control twist and somersault rotation in the flight phase of a twisting somersault. Two mechanisms were considered for the control of twist in simulated target trampoline movements with flight times of 1.4s. In the first case a single symmetrical arm adduction correction was made using delayed feedback control based on the difference between the twist rate in a perturbed simulation and the twist rate in a target movement comprising a forward somersault with 1½ twists. Final corrections were made using symmetrical arm abduction and hip flexion to adjust the twist and somersault angles. In the second case continual asymmetrical arm adduction/abduction adjustments were used to remove the tilt from a perturbed full twisting backward somersault using delayed feedback control based on twist angle and angular velocity. The first method was able to cope with perturbations to a forward somersault with 1½ twists providing the feedback time delay was less than 200 ms. The second method was able to correct a perturbed full twisting backward somersault providing the feedback time delay was less than 125 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.