Simulation of the Seated Postural Stability of Healthy and Spinal Cord-Injured Subjects Using Optimal Feedback Control Methods.

A two-dimensional, biomechanical computer model was developed, using the software package Working Model(TM), to simulate the postural control of seated individuals. Both able-bodied and spinal cord-injured subjects were represented. The model incorporated active control of the upper body through full-state feedback. Specifically, a linear quadratic regulator scheme was implemented in the model. Nonlinearities were included in the torque computations to mimic physiological constraints and disability. Interactions between the subject and the wheelchair were also included in the model. Simulation results were compared with those obtained from experiments in which the subjects had attempted to remain stable during the application of significant disturbance moments, similar to those experienced during braking in a vehicle. While subjects exhibited more complex control schemes, the model was able to simulate overall stability. Therefore, it is believed that the model could prove beneficial to future research examining the effects of various restraints on stability.