Predictive Simulations for the Design of Assistive Devices During Sit-to-Stand Transfer
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Date
2021-12
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The Ohio State University
Abstract
Lower extremity weakness caused by knee osteoarthritis, stroke, Parkinson's, and other disabilities can affect a person's ability to rise from a chair, clinically known as sit-to-stand (STS) transfer. Standing is crucial for everyday activities, yet it is an increasingly common challenge. Over 60% of nursing home residents struggle to independently stand, and by 2030, 20% of Americans will be over 65. There are three primary clinical interventions to assist with this task: (1) increased muscle strength, (2) raised starting positions, and (3) adding external assistive devices. However, strength training through physical therapy can be time-consuming and ineffective. Raising the starting position modifies the kinematics of the task, but it requires a taller chair or the use of a cushion to boost the effective height. Assistive devices have limitations in accessibility, portability, and cost. Current research does not explain the relative effectiveness of these interventions. The goal of this project is to quantify the relative effects of increased joint strength, chair height, and assistive devices on energetic cost individually and in combination to help inform decision-making strategies for STS transfer. The energetic cost is quantified by the sum of the squares of activation of the torque actuator in the simulation. By using a simplified, one-legged model from the software OpenSim Moco and two-legged models with a stiff or curved back as developed by the Neuromuscular Biomechanics Research Laboratory, I simulated common interventions for STS transfer. I varied strength by increasing the joint torques, starting position by changing the hip and knee angles, and the stiffness of torsional springs to represent virtual assistive devices on the hip, knee, and ankle. Results showed that changes in energetic cost were dependent on which individual joints are weakened and the starting positions evaluated. Overall, increasing the strength of the weakened joint or increasing the chair height led to the most significant reductions in the energetic cost of standing. Additionally, adding an initial motion guess to the simulation's solver and systematically reducing the allowable error with each simulation significantly improved the model's ability to solve. As predicted, increasing the chair height decreased the energetic cost of STS transfer using the stiff back model. The results of simulations from this study and future work can provide insight for clinicians to make personalized decisions to facilitate sit-to stand transfer and improve an individual's independence in everyday activities.
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Keywords
biomechanics, simulations, optimal control, OpenSim Moco, assistive devices, sit-to-stand transfer