Biomechanics / Biomechanical Engineering
Mostafa Haj Lotfalian; Mohammad Hadi Honarvar
Volume 14, Issue 2 , July 2020, , Pages 133-142
Abstract
Margin of stability is a method to assess the dynamic stability in the clinic and laboratory, which is influenced by position and linear velocity of the center of mass (CoM). In this study, the stability factor was calculated by the margin of stability (MoS) method and was used as a cost function to ...
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Margin of stability is a method to assess the dynamic stability in the clinic and laboratory, which is influenced by position and linear velocity of the center of mass (CoM). In this study, the stability factor was calculated by the margin of stability (MoS) method and was used as a cost function to plan movement trajectory of sit to stand. 10 healthy young men were selected in this study and their sit to stand movement were filmed by Optitrack motion capture system. A two-dimensional and four-segment model was defined based on the governing equations of motion to calculate position of CoM, joints torque and using that in optimization process. After calculating the subject’s stability factor by MoS method, the time integral of MoS (C1), the maximum and minimum of MoS (C2) and the time integral of the square of MoS (C3) were defined as the cost functions. genetic algorithm was used to find the optimal model. To determine the quality of predicted trajectories and compare it with the subject’s pattern, root mean square error (RMSE) was used. According to the results of this study, a model which was optimized by C3, predicted the movement trajectory of subjects with 19 and 40 percent less error than C1 and C2 respectively.Nevertheless, none of the models could correctly reconstruct the subjects’ movement trajectory. In a nutshell, using MoS exclusively as a cost function, is not a good choice to predict and plane the trajectory of whole-body movements.
