Modelling, analysis and feedback control design for upright standing sways

TLDR: The developed musculoskeletal system model is linearized in order to have clear stability analysis using Routh-Hurwitz stability criterion and eigenvalue analysis and reveals how the sway range (sway points) depends on the used anatomical and anthropometry data.

Abstract: Human body upright standing is inherently unstable, and as a bipedal creature, the body can implement several functions such as upright standing, walking and running, with the help of the central nervous system. Understanding the stability control of the human body during upright standing is important for prosthetic design and joint prostheses, walking restoration, diagnosis of nervous system diseases. Also, it is essential to anthropology, clinical research, aerospace science and kinesiology. Therefore, the objective of this work is to model the musculoskeletal system of human upright standing posture for analysis and control design of body sway. An asymmetric Gaussian function is proposed to model the force-length relationship and compared with other existing force-length models. By using least square curve fitting tools with a set of rabbit experimental data, and simulated data that represent sarcomere of the frog. Also, the implicit and explicit ordinary differential equations, are used to model muscle-tendon unit and compare the simulation results in term of singularity. In addition to, the equilibrium analysis is used to determine sway ranges during upright standing, and the equilibrium points can be used to linearize the model for feedback control design and stability analysis of the musculoskeletal system. Furthermore, a switching function is designed to model the intermittent activity of the MG muscle, where the parameters are optimised using the centre of gravity and electromyography data with Genetic Algorithm tool. The musculoskeletal system of the human body is modelled as a single inverted pendulum, which rotates around the ankle joint, in the sagittal plane only. The calf muscles especially the medial gastrocnemius activated intermittently, and soleus activated continuously are included in the model of the musculoskeletal system. The developed musculoskeletal system model is linearized in order to have clear stability analysis using Routh-Hurwitz stability criterion and eigenvalue analysis. The results show that the musculoskeletal system cannot be stabilised at the upright standing without feeding back angular velocity. The equilibrium analysis reveals how the sway range (sway points) depends on the used anatomical and anthropometry data. Finally, the stability analysis shows that during forwarding sway the calf muscles are shortening paradoxically and lengthening during backwards sway, which supports some existing experimental results. The model-based analysis which used in modelling the body upright standing, will help in analysis and understands the dynamics of the body during upright standing. Also, it assists in medical research, in clinical diagnostics and application.