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Tomoyuki Matsuo, Glenn S. Fleisig, Naiquan Zheng and James R. Andrews

Elbow varus torque is a primary factor in the risk of elbow injury during pitching. To examine the effects of shoulder abduction and lateral trunk tilt angles on elbow varus torque, we conducted simulation and regression analyses on 33 college baseball pitchers. Motion data were used for computer simulations in which two angles— shoulder abduction and lateral trunk tilt—were systematically altered. Forty-two simulated motions were generated for each pitcher, and the peak elbow varus torque for each simulated motion was calculated. A two-way analysis of variance was performed to analyze the effects of shoulder abduction and trunk tilt on elbow varus torque. Regression analyses of a simple regression model, second-order regression model, and multiple regression model were also performed. Although regression analyses did not show any significant relationship, computer simulation indicated that the peak elbow varus torque was affected by both angles, and the interaction of those angles was also significant. As trunk tilt to the contralateral side increased, the shoulder abduction angle producing the minimum peak elbow varus torque decreased. It is suggested that shoulder abduction and lateral trunk tilt may be only two of several determinants of peak elbow varus torque.

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Maurice R. Yeadon and David G. Kerwin

At the 1996 Atlanta Olympic Games, 18 single somersaults with one twist in the women’s compulsory floor exercises were recorded using two video cameras. An 11 segment computer simulation model was used to analyze the twisting techniques used. It was found mat counter-rotation techniques accounted for less than one third of the twist for all gymnasts, indicating that the production of twist was mainly a consequence of the angular momentum and a non-zero tilt angle. Contributions to the tilt angle reached at the mid-twist position were used as measures of the twisting potential of various techniques. Contact techniques accounted for 30% of the tilt produced, the remainder being produced using aerial techniques, which primarily comprised a symmetrical lowering of the arms together with minor contributions from asymmetrical arm and hip movements. There was no evidence of a difference in technique between the highest and lowest scoring competitors.

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Maurice R. Yeadon, Sung-Cheol Lee and David G. Kerwin

At the 1988 Seoul Olympic Games, eight full twisting somersault dismounts from the high bar were filmed using two cameras during the compulsory exercises of the Men’s High Bar competition. Angles describing body configuration and orientation were determined and were input into a computer simulation model of aerial movement. The deviations between simulation and film were less than 2.5° for tilt angles and less than 0.07 revolutions for twist angles. The twisting techniques employed were quantified using the tilt angle as a measure of twisting potential. Contributions to the maximum tilt angle were determined using simulations based on modifications of the film data. Each of the eight competitors obtained most of the tilt using aerial rather than contact techniques. In general, the majority of the aerial contributions arose from asymmetrical arm and hip movements.

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Maurice R. Yeadon

At the 1988 Seoul Olympic Games, four double somersault dismounts with one twist and four double somersault dismounts with two twists were filmed using two 16 mm cameras during the men's horizontal bar competitions. Contributions to tilt angle reached at the midtwist position, determined using computer simulations based on modifications of the data obtained from film, were used as measures of the twisting potential of various techniques. The amount of tilt produced was greater when total twist was greater and when the body was tucked rather than straight. The twisting techniques used varied with the timing of the twist within the two somersaults. Contact contributions were larger when there was more twist in the first somersault. When there was little or no twist in the first somersault, the major contribution came from aerial techniques that comprised mainly arm movements and asymmetrical hip movements in the flight phase.

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Maurice R. Yeadon

At the 1992 Olympic Games six full twisting double somersault dismounts were recorded with two video cameras during the rings individual apparatus finals in the men's Artistic Gymnastics competition. Angles describing body configuration were determined from video data and were input, together with initial orientation angle values and angular momentum components, into a computer simulation model of aerial movement. Mean absolute deviations between simulation and video after the completion of one half twist were 0.01 rev for somersault, 2.8° for tilt, and 0.08 rev for twist. When the estimate of the initial tilt angle was adjusted by up to 1° these deviations fell to 1.6° for tilt and 0.02 rev for twist. All 6 competitors produced the majority of the tilt using aerial techniques that were predominantly asymmetrical movements of the arms. Contributions to the subsequent removal of tilt were determined using reverse simulations, and again arm movements were the main contributors.

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Tim McGarry and Ian M. Franks

The ability to inhibit an earlier intended action in a stop-signal task is commonly assessed using the measures of latency and probability. The usual findings from stop-signal trials of lower response probabilities and shorter reaction latencies at reduced stop-signal delays were reported, as described in previous studies in terms of an independent race between stochastic processes (see Logan & Cowan, 1984). In addition, using the less common measure of amplitude, a continuum of reductions in surface EMG onsets was reported. Weakened motor discharges have yet to be explained in terms of a mechanism of inhibitory control. Using computer simulations of neural functioning, the properties of independence and non-independence were examined for their effects on motor pool output in terms of probability, latency, and EMG onsets. The data provided support to question the requirement of independent processes for a theory of inhibitory control.

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Richard P. Wells, Patrick J. Bishop and Malcolm Stephens

Spinal cord trauma due to head-first collisions is not uncommon in vehicle accidents, shallow water diving, football, or ice hockey. Two approaches to evaluating potential protective devices for ice hockey are described: an evaluative tool based upon an anthropometric test dummy, and a computer simulation of axial head-first collisions. Helmets reduced the peak cervical spine loads during low velocity head-first collisions by up to 8%. It is shown that large thicknesses of appropriate padding are necessary to hold the cervical spine loads to noninjurious levels. A head-first impact of 3.0 m • sec−1 required padding deformations on the order of 94 mm to hold cervical spine loads below 2,000 N.

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Maurice R. Yeadon

At the 1988 Calgary Winter Olympics, six triple somersaults with three twists or four twists were filmed using two cameras. Angles describing body configuration and orientation were determined and were used as input into a computer simulation model of aerial movement. It was found that the twist angle of each simulation deviated from the corresponding angle obtained from film by less than 0.08 revolutions during the first somersault of each movement. Contributions to the tilt angle after one somersault were determined using simulations based on modifications of the film data. It was found that of the six competitors, two initiated the twist during the takeoff phase, two initiated the twist during the aerial phase, and two used a combination of both methods.

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Michael J. Hiley and Maurice R. Yeadon

The release window for a given dismount from the asymmetric bars is the period of time within which release results in a successful dismount. Larger release windows are likely to be associated with more consistent performance because they allow a greater margin for error in timing the release. A computer simulation model was used to investigate optimum technique for maximizing release windows in asymmetric bars dismounts. The model comprised four rigid segments with the elastic properties of the gymnast and bar modeled using damped linear springs. Model parameters were optimized to obtain a close match between simulated and actual performances of three gymnasts in terms of rotation angle (1.5°), bar displacement (0.014 m), and release velocities (<1%). Three optimizations to maximize the release window were carried out for each gymnast involving no perturbations, 10-ms perturbations, and 20-ms perturbations in the timing of the shoulder and hip joint movements preceding release. It was found that the optimizations robust to 20-ms perturbations produced release windows similar to those of the actual performances whereas the windows for the unperturbed optimizations were up to twice as large. It is concluded that robustness considerations must be included in optimization studies in order to obtain realistic results and that elite performances are likely to be robust to timing perturbations of the order of 20 ms.

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Graham E. Caldwell

The effects of relative tendon/fiber proportion and tendon elasticity on the force output of the Hill muscle model (a contractile component [CC] in series with an elastic element [SEC]) were examined through computer simulation. Three versions of the Hill model were constructed. Model 1 examined the effect of relative tendon/fiber proportion on CC kinematics and kinetics during an isometric twitch, while Model 2 compared the effect of changes in tendon compliance. These models revealed force profile differences related to alterations in CC velocity, although the reasons underlying the variation in CC kinematics were different. The relative tendon/fiber proportion and tendon compliance differences were examined in combination in Model 3. Test simulations revealed response differences among the three model versions, and therefore verified Alexander and Ker's (1990) contention that the morphology of muscle is related to design criteria. It is suggested that the implementation of generalized muscle models to represent specific units of the musculoskeletal system should be done carefully and that the implementation process itself warrants further study.