Nonlinear dynamics of human upright postural stability on a balance board using an ankle-hip model
Chumacero-Polanco, Erik Alfredo
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Falls are a leading cause of fatal and nonfatal injury, often requiring expensive hospitalization and rehabilitation. People with balance deficits such as stroke survivors, patients with multiple sclerosis or Parkinson’s disease usually show a higher risk of falls. Hence, it is necessary to find mechanisms to recover balance abilities to reduce their risk of fall. One method for developing such mechanisms is based on balance training on a balance board (BB). BBs provide a simple way to manipulate sensorimotor feedback information to train patients to react to disturbances. However, despite BB’s wide use, the mechanisms responsible for maintaining upright posture on a BB are not yet completely understood. This dissertation aims to investigate the nonlinear dynamics of human upright postural stability on a BB. An anthropomorphic model of the human-BB system is developed by incorporating the hip joint into the human model to form a three degree of freedom inverted pendulum (two for the human body and one more for the BB). Various parameters (such as time-delays, and proprioceptive, visual-vestibular, and BB’s spring stiffness feedback gains) are defined as bifurcation parameters and the effect of these parameters on upright postural stability has been investigated through bifurcation analysis. In addition, the following tasks have been conducted: 1) The effect of misalignment between the ankle joint and the BB’s pivot on the location of the equilibria and the stability properties is addressed, 2) the effect of parametric changes on the size of the basin of attractions (BoAs) and the amplitude of the limit cycle (LC) oscillations is investigated, and 3) PSD functions from simulation results in this study and experimental data from the literature are compared to validate the human-BB model.