Average Threshold Crossing Validation for Functional Electrical Stimulation applied to surface ElectroMyoGraphic signals

Average Threshold Crossing (ATC) technique consists of the generation of an event every time a specific signal exceeds a certain threshold. As far as the surface ElectroMyoGraphic (sEMG) signal is concerned, the ATC parameter is proved to be highly correlated to the muscle contraction force. This project thesis proposes the improvement and the validation of a low power rehabilitation system based on the application of the ATC technique to the sEMG signal. The rehabilitation procedure involved, employs Functional Electrical Stimulation (FES), a therapy consisting of a series of low amplitude current pulses commonly employed to restore motor functions in the affected limbs of spinal chord injury and stroke patients. The system allows the reproduction of a specific movement performed by the therapist from whom the sEMG signal is acquired, in the affected limb of the patient, by means of FES. The system consists of three main parts: an acquisition unit, an elaboration unit and finally an actuation unit. An acquisition board acquires and processes the sEMG and counts the number of TC events generated. Afterwards, the information related to the muscle contraction is sent to the workstation through Bluetooth Low Energy communication, where the FES therapy is elaborated and sent to the stimulator. In order to assess the validation of the overall system, the joint angles of the therapist and patient movements are acquired simultaneously to the acquisition and stimulation processes using two electrogoniometers, in order to verify their degree of similarity. Experimental tests have been conducted on 12 healthy subjects involving four movements: elbow flexion, elbow extension, ankle dorsi-flexion, ankle plantar flexion. The obtained results show that the movement of the subject under control can be mimicked with high fidelity compared to that of the controller.