Feedback signals to adjust and control standing posture

The long-term goal of this study is to provide people with spinal cord injury with the ability to stand and perform reaching tasks with their hands. Functional neuromuscular stimulation (FNS) systems have been used for standing, but functional capabilities are often limited by poor balance control that necessitates use of the hands. Control strategies that use feedback of biomechanical variables may be able to improve the quality of posture control. This work addresses the issue of selecting which variable to use as feedback in a posture control system. An experimental system was developed to provide visual feedback of the instantaneous center of pressure (CoP) or the instantaneous position of the pelvis (PoP) in the transverse plane. Spinal cord injured subjects that use FNS to stand participated in a set of experiments in which they adjusted their posture based on visual feedback of either the CoP or PoP. Results indicate that subjects could adjust posture with either variable as feedback, but that feedback of the PoP provided control that was more intuitive and the strategies used to adjust posture were more appropriate.