Recovering Control Parameters in Seated Position for People with Medullar Injury

People living with spinal cord injury (SCI) suffer from paralysis of their back and lower limbs muscles, which negatively impacts the control of their sitting position. Also, instead of using their back and abdominal muscles, which naturally are engaged to stabilize a sitting position, these individuals engage their upper limbs to maintain stability. This paper presents a model-based approach to better understand which strategies contribute to postural control in a sitting position. The proposed model is written in the form of a nonlinear descriptor system. The main difficulty is to be able to reconstruct joint torques which are unmeasurable. An unknown input observer is synthesized in order to estimate these unmeasurable torques. Results issued from simulation and real tests data are presented in order to underline the validity of the approach for estimating postural control parameters which could allow, in future developments, to better qualify the contribution of the upper limbs in rehabilitation exercises.