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.