The mechanics of twisting somersaults

Twisting movements are categorised into three mechanical types, named as DIRECT, COUNTER-ROTATION and TILT TWIST. Twisting techniques are studied using mathematical models. A mathematical inertia model is constructed to enable the determination of segmental inertia parameters from anthropometric measurements. A film analysis program is developed so that the angles, which specify the orientation and configuration of the body, may be derived from digitised film data. A computer simulation model, comprising 11 segments and 17 degrees of freedom, is constructed to represent the human body in free fall. The combined use of the three computer programs results in maximum errors of 3% for somersault and 9% for twist in ten filmed movements. The mechanics of twisting techniques are explained using simple mathematical models. An analysis of rigid body motions shows that there are two distinct modes of motion, named as the ROD MODE and the DISC MODE. It is shown that it is possible to change from one mode to the other by varying the angle of pike and this permits the twist to be increased or stopped or even reversed. The capacities of twisting techniques are determined using simulations. For twists from a piked position, delaying the extension from the pike can increase the twist rate although this does depend upon the particular technique used and the initial direction of somersault. The contributions of twisting techniques used in the filmed movements are determined using simulations based upon modifications of the film data. It is found that counter-rotation techniques made small contributions and that aerial techniques, which increased the angle of tilt, were the major contributors, even in movements where the twist was apparent at take off. Using the simulation model it is shown that the build up of twist in the unstable double layout somersault may be controlled by means of small asymmetrical arm movements during flight

The simulation of aerial movement—I. The determination of orientation angles from film data

Quantitative mechanical analyses of human movement require the time histories of the angles which specify body configuration and orientation. When these angles are obtained from a filmed performance they may be used to evaluate the accuracy of a simulation model. This paper presents a method of determining orientation angles and their rates of change from film data. The stages used comprise the synchronisation of data obtained from two camera views, the determination of three-dimensional coordinates of joint centres, the calculation of an angle from a sequence of sine and cosine values and the curve fitting of angles using quintic splines. For each stage, other possible approaches are discussed. Original procedures are presented for obtaining individual error estimates of both the film data and the calculated angles to permit the automatic fitting of quintic splines for interpolation and differentiation and for deriving the time history of an angle as a continuous function from a sequence of sine and cosine values. The method is applied to a forward somersault with 1 1 2 twists and the average error estimate of 17 orientation angles is obtained as 2.1 degrees

OPTIMISATION OF THE BACKWARD GIANT CIRCLE ON ASYMMETRIC BARS

The purpose of this study was to optimise the release window in the backward giant circle performed prior to release for a double layout somersault dismount from the asymmetric bars. An additional aim was to investigate the effect of requiring the optimal technique to be robust to perturbations in timing of the changes in joint angles. A planar computer simulation model was used to maximise the release window (Hiley and Yeadon, 2005) of a female gymnast by manipulating the joint angle time histories during the giant circle prior to release. Optimisations were performed where the timing of the joint actions at the shoulder and hip were perturbed in order to obtain solutions that were robust to such perturbations. Joint angle time histories were limited by muscle data scaled from a male gymnast. Although introducing the requirement for robustness into the optimised giant circle technique reduced the size of the release windows more consistent performances were achieved

INTERACTIVE VIEWING OF SIMULATED AERIAL MOVEMENTS

An 11-segment computer simulation model of aerial movement was used to generate a set of configuration and orientation angles for a double straight somersault with a full twist in the second somersault (back-in full-out). Computer graphics were generated in real-time using OpenInventor from a virtual head-mounted camera and were rendered at 50 Hz to a Trivisio 3scope stereo Head Mounted Display worn by the user to give a trampolinist’s view. Changes in orientation of the user’s head in the real world were detected by a 3D-Bird sensor and were reflected in real-time movements of the head of the virtual trampolinist. The system allowed continuous repetition of the trampoline skill and was tested by several elite gymnasts who learned the correct head movement at a reduced speed before increasing to half actual performance speed

PERFORMANCE SENSITIVITY TO PERTURBATIONS IN ACTIVATION TIMING

This study investigated the sensitivity of optimum jumping performances to perturbations in activation timing. A planar eight-segment computer simulation model was used to simulate the takeoff phase in a high jumping performance. The model was evaluated and subsequently used to produce an optimum performance with a jump height of 2.63 m. The mLJscle activation onset timings at the knee were then varied by ± 5 ms and the effect on the simulated performance was determined. By simply varying the knee activation onset timings the performance did not change in terms of jump height, but the simulations included penalties which indicated that anatomical constraints had been violated. Reoptimisation with a measure of robustness included resulted in an optimum simulated jump of 2.32 m with no penalties which was unaffected by 5 ms perturbations

COORDINATION IN DYNAMIC JUMPING

This study investigated coordination in dynamic jumping using a forward dynamics computer simulation model. A planar eight-segment torque-driven model was used to match the takeoff phase in a recorded running jump for height and recorded jump for distance by varying the torque generator activation timings. Two optimisations were then carried out to maximise height reached and distance travelled for each set of initial conditions used in the matching simulations. Although for each set of initial conditions, the order of activation onset timing was different for the two optimisations, the timing of activation onset in the optimisations for height and distance using the same initial conditions was very similar. This study has shown that the optimal activations are more a function of the initial conditions than the selection of maximal height or maximal distance

OPTIMISATION OF PERFORMANCE IN RUNNING JUMPS FOR HEIGHT

This study investigates the effect of approach conditions and takeoff technique on optimum performance. A planar eight-segment computer simulation model was used to simulate the takeoff phase in high jumping. Optimisations based on performances in the laboratory and at an athletics track were carried out to maximise the height reached by the mass centre in the flight phase. Three pairs of optimisations were performed: (i) optimisation of technique, (ii) optimisation of technique and initial conditions, (iii) optimisation of technique, initial conditions and approach velocity. In the first pair of optimisations the increases in height were 0.12 m and 0.17 m respectively. In the second pair of optimisations the additional increases in height were 0.09 m and 0.19 m and in the third pair further increases of 0.42 m and 0.02 m were obtained

A NEW MODEL OF THE SPRINGBOARD IN DIVING

This paper presents a model which describes the vertical, horizontal and rotational movement of a diving springboard. Model parameters were determined from experimental data. The springboard model was used in conjunction with a diver model to simulate a diving takeoff. Diving performance of an elite female diver was recorded at 200 Hz and was digitised to obtain kinematic data used to drive the simulation. There was good agreement in terms ot linear and angular takeoff conditions between the performance and the simulation. It is concluded that the proposed model is an improved representation of the springboard as a simple mass-spring system. This model will be used in conjunction with a diver model to investigate takeoff techniques and optimise diving performance

CONSTRAINTS AND ROBUSTNESS CONSIDERATIONS IN THE OPTIMISATION OF SPRINGBOARD DIVING TAKEOFF TECHNIQUE: A SIMULATION STUDY

The aim of this study was to investigate the effects of imposing anatomical constraints and robustness requirements on the optimisation of springboard diving takeoff technique. A planar eight-segment model of a diver with torque generators together with a springboard model was used to optimise takeoff techniques for maximum rotational potential in the forward dive group by varying the activation timings of the torque-generators. Optimisation 1 imposed no constraints or robustness requirements. Optimisation 2 imposed anatomical constraints. Optimisation 3 imposed anatomical constraints and a requirement of robustness to perturbations in activation timing. The results showed that imposing both anatomical constraints and robustness requirements have a substantial effect on optimum simulated performance

OPTIMISATION OF TAKEOFF TECHNIQUE FOR MAXIMUM FORWARD ROTATION IN SPRINGBOARD DIVING

The aim of this study was to optimise springboard diving takeoff technique for maximum forward rotation using a computer simulation model. A planar eight-segment model of a diver with torque generators together with a springboard model was developed. The model was evaluated by comparing simulation output with an elite diver's performance. The model was then used to optimise takeoff techniques for maximum rotational potential in the forward dive group by varying the activation timings of the torque-generators. There was a 20% increase in rotational potential in the optimised simulation compared to a performance of a forward two and one-half somersault pike (105 B) dive. The results highlight the importance of technique in springboard diving since by changing only the activation timing alone the diver can generate substantially more forward rotation