Estimation and Evaluation of Upper Limb Endpoint Stiffness and Joint Torques for Post-stroke Rehabilitation

This research was aimed to investigate biomechanical properties via estimation of upper limb endpoint stiffness and joint torques during force targeting tasks. Sixteen able-bodied subjects were recruited in the study. A 10-N force task was conducted at right and left force directions for three upper limb postures. Hand endpoint trajectories and the response forces were recorded simultaneously for each trial. The 2x2 endpoint stiffness matrix and corresponding stiffness ellipse were determined by least squares error method. Resultant shoulder and elbow torques were also calculated by inverse kinetics. Mann-Whitney U test and Kruskal-Wallis test was used to analyze the effect of movement directions and postures on endpoint stiffness and joint torques. The results indicated that the force directions and postures have significant effects on endpoint stiffness ellipse of upper limb, the shoulder and elbow joint torques during force production tasks (p<0.05). These results demonstrate the importance of the force directions and posture during performing force targeting tasks. The future work of clinical implementation suggests that upper-limb endpoint stiffness and viscosity can be measured and compared with able-bodied subjects and poststokes.