I. INTRODUCTION
Neurological disorders or brain lesions such as stroke, cerebral palsy, or spinal cord injury may cause partial or complete loss of mobility in limbs. For people suffering any of the aforementioned motor disabilities, the rehabilitation programs, either assisted by a therapist or by a robotic device, aim to recover functionality in the impaired limbs [1]. Rehabilitation programs are based on the intensive and repetitive execution of therapeutic movements of the affected limbs, and aim at regaining and improving muscle strength, motor coordination, and dexterity [2]. Robot-assisted rehabilitation therapies are advantageous because they use information from force and kinematic sensors, or information from the peripheral nervous system (PNS) such as muscle activity (EMG), to drive and control movement-assisted devices. It has been demonstrated that rehabilitation programs may help maintain and promote neural cortical circuits that induce motor re-learning [3].