Gait Analysis
Fatemeh Akbarifar; Mohammad Hadi Honarvar; Mostafa Haj Lotfalian
Volume 15, Issue 1 , May 2021, , Pages 1-11
Abstract
Finding the center of rotation (COR) is needed for defining the anatomical axis of the skeletal system and for the kinematic calculation of joints in biomechanical studies. For this purpose, predictive and functional methods can be used. In the predictive methods, regression equations obtained from anthropometric ...
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Finding the center of rotation (COR) is needed for defining the anatomical axis of the skeletal system and for the kinematic calculation of joints in biomechanical studies. For this purpose, predictive and functional methods can be used. In the predictive methods, regression equations obtained from anthropometric measurements are used, and in the functional methods, the relative motion of the two adjacent segments is used to find COR. The purpose of this study is to formulate the circle fitting algorithm as a functional method with two analytical and optimization solutions. In order to evaluate the algorithm, error analysis was performed by both analytical and numerical methods. Also, effective factors in error estimating of COR position such as standard deviation of measurement system error (σ), rotation angle (α) and the distance between marker and COR (r), was evaluated. The results showed a high correlation (r=0.99) between analytical and numerical solution, which proved the accuracy of the error analysis. In this study, optimization method according to the accuracy of better estimates in low quantities α, less influence on high quantities σ and high speed in problem solving, can be taken into consideration to reconstruct human movements in biomechanical studies. Use of functional methods, eliminates the need for attaching markers to anatomical landmarks and provides a new development in motion data acquisition.
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.
