Passive Elbow Movement Assistant (PEMA): A portable exoskeleton to compensate angle-dependent tone profile of the elbow joint post-stroke

Abstract

Significant impairments in upper extremity function are commonly observed after neurological injuries such as stroke. While the efficacy of robotic training has been demonstrated, the use of these devices is confined to the laboratory setting due to its complexity and power requirements. In this study, we developed a passive, portable device (Portable Elbow Movement Assistant; PEMA) that can provide assistance during elbow movements of stroke survivors. The geometric properties of the device were designed to allow morphological changes in the elastic components during movements, so that the assistance produced by the elastic component counteract the angle-dependent flexor hypertonia commonly observed in stroke survivors. A mathematical model for the proposed design was first developed to characterize the assistance provided by the device. The capacity of the device was then tested in a pilot testing with four healthy subjects, for whom a custom device to simulate elbow flexor hypertonia (providing an increased resistance for the extended posture) was implemented. The proposed device was found to effectively counteract the angle-dependent flexion moment, produced by the hypertonia simulator, as a significant decrease was observed in the slope of the angle-activation relationship (movement phase) and activation level (hold phase) of the triceps brachii muscle. The assistance did not affect the activation of the antagonist muscle (biceps brachii), indicating an independent modulation of the agonist and antagonist muscles resulted from the assistance.