Shoulder, elbow and wrist stiffness in passive movement and their independent control in voluntary movement post stroke

Functional movements involve coordination of multiple joints. Neurological disorders such as stroke affect multiple joints simultaneously with stereotypical patterns of arm deformity involving shoulder, elbow, wrist and fingers. Some of the symptoms are manifested in passive movement while others in voluntary movement. However, there is a lack of systematic methods to evaluate multi-joint and multi-DOF (degrees of freedom) neuro-mechanical changes during both passive and active movements, especially for complex systems with three or more joints/DOFs involved. The purposes of this study was to develop a systematic method to characterize dynamics and control of the shoulder, elbow and wrist of the human arm individually and simultaneously, including the interactions across the three joints, during both passive and active movements. A new method was developed to decompose the complex system into manageable single-joint level for more reliable characterizations. The method was applied to clinical studies on multi-joint changes associated with hypertonic arm with impaired motor control post stroke during both passive and active movements. In general, the decomposition method can be used for even more complex systems, making intractable system dynamics of three or more joints and DOFs manageable.