Option selection in whole-body rotation movements in gymnastics / Opções de movimentos na rotação da ginástica

Abstract When a gymnast performs a somersault, the linear and angular momentum along with a particular control of inertia during the flight phase constrain the possibilities for action. Given the complexity and dynamic nature of the human moving system, one could argue that there exist a particular amount of stable coordination states when performing somersaults. The goal of this study was to explore the manifold of movement options and coordination states along with their differentiating parameters for a single somersault in gymnastics based on a simple mathematical model reflecting gymnast’s rotation behavior during the flight phase. Biomechanical parameters determining rotation behavior during a somersault were systematically varied with regard to a particular set of biomechanical constraints defining a successful somersault performance. Batch simulations revealed that from 10229760 simulation cycles only 655346 (approximately 6.41%) led to successful somersault performance. A subsequent analysis of the movement option landscape for the optimum angular momentum revealed ten coordination states for a single somersault that could be clearly distinguished based on the simulation parameters. Taken the results together, it becomes apparent that it may be most advisable to perform a single somersault with a larger moment of inertia when achieving the tucked position, a longer duration to achieve the tucked position, a longer duration of staying tucked, and an intermediate moment of inertia during landing. This strategy comprises the largest amount of movement options associated with an upright landing and thus the highest probability of success when performing a single somersault.

Resumo Quando um ginasta executa um mortal, o momento linear e angular, juntamente com determinado controle de inércia durante a fase de voo, restringem as possibilidades de ação. Devido à complexidade e à natureza dinâmica do sistema do movimento humano, pode-se argumentar que existe determinada quantidade de estados coordenativos estáveis quando se executa mortais. O objetivo deste estudo foi explorar a multiplicidade de opções de movimento e estados coordenativos, juntamente com os seus parâmetros de diferenciação para um único mortal na ginástica, com base em um modelo matemático simples que reflita o comportamento da rotação do ginasta durante a fase de voo. Os parâmetros biomecânicos que determinam o comportamento da rotação durante um mortal variam sistematicamente em relação a determinado conjunto de restrições biomecânicas que definem a execução bem sucedida do mortal. Simulações em série revelaram que, a partir de 10229760 ciclos de simulação, somente 655346 (aproximadamente 6,41%) levaram ao desempenho bem sucedido do mortal. Uma análise subsequente da perspectiva de movimento para o momento angular ótimo revelou 10 estados de coordenação para um único mortal que poderiam ser claramente distinguidos com base nos parâmetros de simulação. Considerados os resultados em conjunto, torna-se evidente que seria mais aconselhável realizar um único mortal com momento de inércia maior quando se atinge a posição grupada, duração mais longa para atingir a posição grupada, duração mais longa da posição grupada, e um momento de inércia intermediário durante a aterrissagem. Essa estratégia compreende a maior quantidade de opções de movimento associados a uma aterrissagem na posição ereta e, assim, a maior probabilidade de sucesso quando se realiza um único mortal.

Effect of rotation bump on removal torque of orthodontic mini-implants

OBJECTIVES: This study is designed to evaluate the mechanical stability of orthodontic mini-implants with vertical grooves in rabbits. MATERIALS AND METHODS: This study was done from March 2011 to February 2012 in Dental Research Institute of Seoul National University. Thirty-two mini-implants in the control group and 32 in the rotation bump (RB) group were inserted in the tibias of 16 rabbits and were removed after two weeks and four weeks, respectively. The maximum insertion torque (MIT), maximum removal torque (MRT), torque ratio (TR) of MRT to MIT and removal angular momentum (RAM) were all measured at the time of removal. RESULTS: There were no significant differences between the two groups in MIT and MRT at two weeks or four weeks. However, TR and RAM at four weeks in the RB group were significantly higher than in the control group (P<0.05). TR of the RB group was significantly increased at four weeks (P<0.05). In both groups, RAM at four weeks was significantly higher than at two weeks (P<0.05). CONCLUSION: These results suggest that RB of the mini-implant could provide resistance to the removal rotation, although it did not increase the MRT.