تاثیر پیچیدگی مدل شبیه سازی در برآورد بارگذاری داخلی در ژیمناستیک

Abstract Evaluating landing technique using a computer simulation model of a gymnast and landing mat could be a useful tool when attempting to assess injury risk. The aims of this study were: (1) to investigate whether a subject-specific torque-driven or a subject-specific muscle-driven model of a gymnast is better at matching experimental ground reaction forces and kinematics during gymnastics landings, (2) to calculate their respective simulation run times and (3) to determine what level of model complexity is required to assess injury risk. A subject-specific planar seven-link wobbling mass model of a gymnast and a multi-layer model of a landing mat were developed for this study. Subject-specific strength parameters were determined which defined the maximum voluntary torque/angle/angular velocity relationship about each joint. This relationship was also used to produce subject-specific ‘lumped’ muscle models for each joint. Kinetic and kinematic data were obtained during landings from backward and forward rotating gymnastics vaults. Both torque-driven and muscle-driven models were capable of producing simulated landings that matched the actual performances (with overall percentage differences between 10.1% and 18.2%). The torque-driven model underestimated the internal loading on joints and bones, resulting in joint reaction forces that were less than 50% of those calculated using the muscle-driven model. Simulation time increased from approximately 3 min (torque driven) to more than 10 min (muscle driven) as model complexity increased. The selection of a simulation model for assessing injury risk must consider the need for determining realistic internal forces as the priority despite increases in simulation run time.

When landing from a dismount in Artistic Gymnastics, the aim is to reduce the velocity of the mass centre to zero while over the base of support using a single placement of the feet. Any steps or unsteadiness during landing can result in a score deduction between 0.1 and 0.3 (F.I.G., 2001). The successful landing from a vault (or other apparatus) poses a problem for a gymnast who must trade off technical difficulty with the probability of a successful landing and with the risk of injury. While minimising injury is a concern, it is not always of paramount importance in competitive environments, such as at the Atlanta 1996 Olympics Games, where an already injured gymnast completed a vault, further exacerbating her injury. The gymnast and coach aim to maximise performance and develop training regimes and technical strategies to achieve this. Similarly, most of the computer simulation research in gymnastics, jumping and landing has been aimed at improving performance (Hiley and Yeadon, 2003; King and Yeadon, 2004) and has not considered the potential injury risks. Using a gymnast to investigate different landing techniques experimentally could lead to injury. On the other hand, a forward dynamics computer simulation model of a gymnast and landing mat could be used to look at the performance enhancement of various landing techniques and gymnastic skills whilst safely assessing the associated injury risk.

The three models were successful in reproducing the kinetics and kinematics during the first 100 ms of the vault landings. Model 3 performed the best during the simulation of both the FR and BR vaults with overall matching scores of 10.1% and 16.2%, respectively. Model 2 performed markedly worse than the other models and may not have faired well due to problems with integrating the torque generator. These problems were due to the different integration procedures, their accuracy and robustness, used in the different processing environments. At certain times there would be a mismatch of the CC torque and the SEC torque leading to an oscillation until they reconverged and this could be solved by working within the same environment for both functions, as in Model 3. All three models matched the FR vault better than the BR vault, due largely to the poor matching of the HGRF in the BR vault. In the experimental data for the BR vault there was a large initial force in the forward direction of travel of the gymnast (Fig. 4) which none of the models were able to reproduce. This peak was unexpected as the kinematic data of the gymnast's feet showed no movement in the direction of travel after the instant of impact. On examination of the high speed video the gymnast could be seen to land with his feet close to the edge of the mat nearest the vault. This caused the mat insert above the force plate to fold under itself, effectively pushing parts of the mat towards the vault whilst the top section remained in the same horizontal location whereas the mat model could not bend and fold. In a full-size landing mat, this folding would not occur and so it is possible that the poor match of the HGRF for the BR vault was an artefact of the experimental set-up used to avoid cross-bridging.